Tuatara
Tuataraaims at stimulating and extending the interest of secondary
school pupils, university students and amateur naturalists in the
natural sciences, and at the same time presenting reviews of value
to scientists showing the present applications and future scope of
biological research. Articles and reviews of a suitable standard are
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Cited’ to the more important references.
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University of Wellington, P.O. Box 196. Wellington, New Zealand.
VolumeIX
Part3
January1962
Tuatara, Vol. 10, Part 1
Tuatara
is the journal of the Biological Society, Victoria University of Wellington, New Zealand, and is published three times a year.
Zoology Department, Victoria University of Wellington
To most people, the word slug conjures up a picture of a rather repulsive, brownish-grey slimy animal, passionately addicted to eating cabbages. There are in New Zealand, however, representatives of two widely differing families of slugs, the introduced European Limacidae, and the native Athoracophoridae which are found only in the Western Pacific area. External differences between the two are easily observed: the Limacidae have two pairs of tentacles, a mantle area covering the anterior aspect of the back, a brown or grey coloration, and carnivorous or herbivorous habits, whereas the Athoracophoridae have only one pair of tentacles, a smaller, much less obvious mantle area, a distinct pattern of dorsal grooves, and a highly developed dorsal tracheate lung of a nature found in no other mollusc. The native slugs may grow up to six inches in length, are often more attractively coloured than their introduced counterparts, and frequently have numerous dorsal papillae.
New Zealand slugs are fairly common in bush and grassland, and are frequently found under logs, in leaf mould, and in the leaf bases
There are in New Zealand four genera of native slugs (one genus newly described — Burton, Trans. Roy. Soc. N.Z. in press) containing twenty-two known species (eleven newly described — Burton, Trans. Roy. Soc. N.Z. in press). There are some wide ranging common species such as Pseudaneitea papillata in the South Island and southern North Island, and Athoracophorus bitentaculatus which is widespread in both islands, but in general the species tend to be restricted in range, for example Pseudaneitea dendyi found as yet only in Mid-Canterbury, and Pseudaneitea schauinslandi, only in the Marlborough Sounds area. Slugs are rare or absent in very dry areas such as Central Otago and in the volcanic central plateau of the North Island, but are otherwise fairly common.
The distribution of the subantarctic Athoracophoridae poses interesting problems. Five species are known from four islands, but none as yet have been found on the mainland. Only one species occurs on more than one island. This species is found on both Campbell and Macquarie Islands, and its mode of dispersal is as yet unknown. Dispersal over a land bridge seems unlikely for two reasons. First, the slugs would have to survive the Pleistocene glaciation subsequent to the loss of the bridge, and secondly, the broad expanse of deep water between Macquarie and Campbell Islands makes a land bridge between the two improbable. Furthermore, oceanic wind drift dispersal of eggs or adults among rafting masses of vegetation does not seem probable, as this envisages the raft either moving against the West Wind Drift or completing a circumpolar journey. However, it is possible that Macquarie Island has been colonised by animals drifting from the coast of Australia, and if this is so the colonisation of Campbell Island would easily follow.
The four species found are contained in two genera, one of which, Pseudaneitea, is common on the mainland. The other genus, however, is only found in the subantarctic islands. If the slugs have been on the islands only since the Pleistocene, this points to a high rate of speciation. Generic differentiation appears to be considerably slower.
The slugs eat only fungi, and usually select encrusting fungi. For example Athoracophorus bitentaculatus is often found at night feeding on Capnocdium moniliforme on the leaves of Pseudowintera axillaris. The jaw is elasmognathic, having a horny plate held vertically in the anterior portion of the buccal mass and protruded through the mouth to scrape up fungus as the slug moves.
As the animal moves successive waves of contraction and relaxation traverse the sole from posterior to anterior. The expanded, relaxed parts of the sole stay fixed with mucous while the contracted zone is in forward motion.
The slug breathes mainly through the skin of the back, which is kept moist by a renal secretion passing along the grooves. The role of the lung in respiration is not yet known, but it is probably not very effective. The eggs (Pl. 3, fig. 3) are round, gelatinous, papillated, and a light translucent yellow. They vary in diameter according to the species, ranging from 3-4 mm. in Athoracophorus bitentaculatus to 7 mm. in Pseudaneitea papillata. They are laid in batches of up to fifty in damp, cool surroundings from the beginning of spring through to late summer, and take up to three months to hatch. The young slug develops in a curled position, with the mouth opposite the posterior tip of the sole. When the slug is due to hatch, it attempts to straighten out, as though exerting pressure opposite the head, which soon breaks through the egg wall. The slug then crawls away.
Specimens deprived of water shrink and soon die. One specimen which escaped at night was found as a small heap of dried-up tissue at the end of a forty-yard slime trail.
It is usually necessary to narcotise the slugs carefully before preserving them, otherwise the buccal mass will be protruded through the mouth and the animal may contract and distort so much that many features will be obscured. The most readily available narcotic is an infusion of tobacco in water. One large pinch of tobacco to a pint of water is sufficient, and after the container is thoroughly shaken the narcotic is ready for use. Specimens should be immersed for at least eight hours, preferably longer if they are large. Other narcotics may be better for large specimens; a dilute solution of Blackleaf 40, which also contains nicotine, is suitable. When properly narcotised the slugs will be relaxed and extended, sometimes with their tentacles protruding. They may be preserved in either 70% alcohol or 4-6% formalin solution. In general formalin is preferable, as the tissues remain softer and colour retention is slightly better.
For injection of the circulatory system, freshly narcotised specimens only can be used, otherwise the arteries become constricted and burst under pressure. A fine capillary tube drawn from glass tubing and fitted with a rubber pipette bulb is best for this purpose. Slugs may be injected with a gelatin solution stained with indian ink, or with coloured latex; injections are usually made into the ventricle or common aorta (Pl. 2, fig. l).
To prepare a whole mount of the radula, remove the entire buccal mass and macerate it in strong caustic soda. The radula should not be left too long after the flesh around it has dissolved, otherwise the basement membrane disintegrates. Wash the radula in water, then transfer to concentrated aniline blue for two minutes. Wash in lactic acid. Unroll and flatten the radula before mounting in polyvinyl alcohol.
A detailed account of one species only (Pseudaneitea papillata) is given. This species is common and anatomically typical.
Pseudaneitea papillata
External Features (Plate 1, fig. 1)
This is a handsome species growing up to 101 mm. long, dark olive green excepting the off-white sole and hyponotum, with black head shield and mantle area and obvious conical, black-tipped papillae up to 2 mm. in diameter near the mid-dorsal line. The body is semicylindrical, the back broadly convex, and the tail tapers to a blunt point. When the animal is at rest, the tentacles are partially retracted, the head shield recessed, the anterior portion of the perinotum protruded on either side, and the body longitudinally compressed to half the length attained while crawling. The sole is smooth, broad anteriorly, tapers to a rounded posterior tip, is divided into one broad median and two narrow lateral muscular zones, and is bordered on either side by a narrow hyponotum. On the ventral
PLATE I : Pseudaneitea papillata (Hutton). Fig. 1: Externals — dorsal aspect. Fig. 2: Buccal mass and associated structures. Fig. 3: Sub-buccal arteries and nerves. Fig. 4: Sub-buccal arte:ies, ganglia removed. Fig. 5 : Radula — central and lateral teeth.
an., anus; ao, anterior branch of aorta; b.a., buccal artery; b.g., buccal ganglion; b.m., buccal mass; c.a.v., cerebral arterial vesicle; c.g., cerebral ganglion; ga.a., ganglionic artery; g.o., genital orifice; h.s., head shield; l.gr., lateral groove; b.a., mantle area; m.gr., median groove; mo., mouth; o.a., oral artery; od., odcntophore; oes., oesophagus; o.n., oral nerve; ov., oviduct; p.a., pulmonary aperture; ped.g., pedal ganglion; ped.gl., pedal mucous gland; ped.n., pedal nerve; pen., penis; ph.a., pharyngeal artery; r.o., renal orifice; sal.d., salivary duct; ten., tentacle; ten.a., tentacular artery; ten.n., tentacular nerve; vag., vagina; v.d., vas deferens; v.g., visceral ganglion; I, II, III, IV, visceral nerves.
With scissors make a lateral incision along the left side just dorsal to the perinotum, and continue it over the dorsal aspect of the head. Carefully reflect the skin, except for the region around the mantle area to which the circular lung, bilobed renal organ, shell rudiments, and thin-walled atrium are attached. The lung and renal organ may be reflected with the skin, but the atrium must be carefully detached from the ventral wall of the dorsal blood sinus before the skin can be completely reflected and pinned down. Remove the thin, membranous wall to expose the viscera in the haemocoele.
PLATE II: Pseudaneitea papillata (Hutton). Fig. 1 : Anatomy — in situ. Fig. 2: Alimentary system and associated blood vessels.
alb., albumen gland; at., atrium; b.m., buccal mass; g., ganglionic mass; her., hermaphrodite gland; int., intestine; liv., liver; od., odontophore; oes., oesophagus; p.ao., posterior branch of aorta; ped.gl., pedal mucous gland; ped.n., pedal nerve; pen., penis; ren., renal organ; r.m., retractor muscle; sal.a., salivary artery; sal.d., salivary duct; sal.gl., salivary gland; st., stomach; vag., vagina; vas def., vas deferens; ven., ventricle.
The mouth opens into a buccal chamber in the highly muscular buccal mass (Pl. 2, fig. 1; Pl. 3, fig. 2). A thin-walled oesophagus traverses the dorsal aspect of the buccal mass, passes ventral to the connective between the cerebral ganglia, and expands into an elongate, thin-walled stomach, which extends posteriorly to the liver. Here it recurves to merge into a thicker-walled, narrower intestine, which extends forwards to loop around the common aorta, passes back to the liver, then recurves to extend anteriorly to the rectum. The stomach and the loops of the intestine spiral around each other. The lobulate liver, orange in fresh material, occupies the posterior third of the body cavity. A pair of off-white, lobulate salivary glands flank the anterior wall of the stomach, and give off from their anterior ends each a tubular, convolute salivary duct, passing ventral to the supraoesophageal connective to merge into the anterior aspect of the buccal mass.
The genital orifice, a short, narrow, slightly curved slit in the margin of the head shield lateral to the right tentacle, opens from a broad, short, often thin-walled vagina, to the end of which are attached the broad, long, muscular, slightly sinuous oviduct and the muscular, twisted penis. A thin-walled, rounded receptaculum seminis is attached to the oviduct near its anterior end by a narrow stalk. The convolute glomerate gland, of unknown function, is attached to the oviduct near its posterior end.
Attached at the posterior end of the oviduct are four structures: a rounded bulbose gland of unknown function, a yellow, U-shaped albumen gland, the end of the vas deferens, and the end of the highly convoluted hermaphrodite duct. The other end of the hermaphrodite duct arises from a large, oval, lobed ovotestis, which lies dorsally, posterior to the rectum. From the oviduct the vas deferens runs to the bulbose gland, and then along the course of the oviduct, under the right tentacular nerve, and out to the distal tip of the penis, which is marked by the insertion of a long retractor muscle with its origin in the dorsal midline.
PLATE III : Pseudaneitea papillata (Hutton). Fig. 1 : Reproductiva system. Fig. 2 : Buccal mass — sagittal section. Fig. 3 : Eggs. Fig. 4 : Elasmognathic jaw. Fig. 5 : Head-ventral aspect.
Ib.gl., albumen gland; ant.ao., anterior aortic branch; ant.gen.a., anterior genital artery; a.p., accessory plate; b.c., buccal cavity; bulb.gl., bulbose gland; gen.a., genital artery; glom.gl., glomerate gland; her.d., hermaphrodite duct; her.gl., hermaphrodite gland; j., elasmognathic jaw; m.c., median cusp; mo., mouth; od., odontophore; oes., oesophagus; ov., oviduct; ov.a., oviducal artery; pen., penis; rec.sem., receptaculum seminis; r.m., retractor muscle; vag., vagina; vas def., vas deferens; w., wing.
The accessory glands, that is, the glomerate and bulbose glands, and the albumen gland are subject to an annual cycle, during which they grow to a very large size in May and June, and then diminish in size during the summer. Only when these glands reach their maximum development do the viscera fill the entire body cavity. During summer and autumn, the posterior tip of the liver lies at about two-thirds body length, and the body cavity posterior to this is unoccupied.
The heart, situated dorsally, consists of a thin-walled, transparent atrium which communicates with the smaller, thick-walled, white, muscular ventricle, from the left side of which the common aorta arises. This short vessel divides almost immediately into anterior and posterior aortic branches. The anterior branch gives off a genital artery which supplies the hermaphrodite gland, oviduct, and accessory glands, and then gives off a salivary artery to the salivary glands, before expanding to form a small vesicle between the visceral and pedal ganglia. From the vesicle arise paired tentacular and oral arteries, median buccal and pharyngeal arteries, and the anterior genital artery on the right side. The posterior aorta, before terminating in the liver, gives off numerous branches which ramify to supply the stomach and intestine. Blood collects in the large ventral sinus, which encloses the alimentary and reproductive systems, and in two small dorsal sinuses enclosing the renal organ and the pulmonary diverticula. Blood passes into the pulmonary sinus, and thence to the atrium for recirculation.
The cerebral ganglionic mass is composed of paired cerebral, visceral, and pedal ganglia, just posterior to the buccal mass. The cerebral ganglia are smooth, white, rounded structures, superimposed on the lateral aspects of the paired visceral ganglia. The paired pedal ganglia are posterior and ventral to the visceral ganglia.
The cerebral ganglia give off paired tentacular nerves, paired nerves to the buccal ganglia situated on either side of the dorsal aspect of the buccal mass, and three pairs of nerves, arising in a common root on either side, to the oral region. The visceral ganglia, composed of numerous small ganglia just visible to the naked eye, give off four nerves from the posterior side, numbered I-IV from left to right. N. I runs on the left side of the stomach to enter the muscles of the back close to the renal organ. N. II runs along the anterior branch of the aorta to enter the back posterior to the renal organ. N. III at first follows N. II, but then runs posteriorly, following the coiling of the intestine; it gives branches to the hermaphrodite gland and the intestinal loop. N. IV runs over the dorsal aspect of the rectum into the skin. A major pedal nerve arises from the lateral
Surprisingly, no nerve supplying the penis, vagina, and oviduct has been found.
The pulmonary aperture lies in the centre of the mantle area, and is bordered by a sphincter muscle. Lying immediately below it is an expanded pulmonary chamber, its floor and walls lined with muscle tissue. Several passages through this muscle branch to form numerous thin-walled, fingerlike diverticula which radiate out to form the roof of the pulmonary sinus. The effectiveness of the lung as a respiratory structure is not yet known. Some workers believe that it is primarily secretory in function. Probably the major part of air exchange takes place through the skin, which is kept moist by a secretion from the renal organ. The secretion is pumped from the renal orifice at intervals ranging from 2-20 seconds, and runs over the entire back, aided by contractions of the muscles bordering the grooves.
The radula is saddle-shaped, inrolled dorsally at the sides, and expanded anteriorly to form a broad rasping surface in the buccal chamber. When flattened out on a slide, it forms a broad chevron with 130-150 rows of teeth, each row with up to 150 teeth on either side; these figures are variable. In each row there is only one central tooth; all others are laterals.
Each tooth consists of a broad, flat stem rooted proximally in the transparent basement membrane, and a distal recurved head bearing a number of denticulate reflections. The denticle number in any given specimen is subject to wide variation, and is unsuitable for diagnosing species.
Tooth formation takes place at the root of the odontophores, located at the posterior end of the radula; teeth here are rudimentary, with very long denticles in proportion to stem length. They remain clear when the radula is stained in aniline blue, presumably because they are still surrounded by non-staining basement membrane.
References
Department of Botany, Victoria University of Wellington
Visiting botanists from the north temperate zone are usually greatly impressed and not a little puzzled by the apparently tropical form of many of the plants in our lowland, podocarp-dicotylous forests.* Most New Zealand botanists regard these forests as subtropical in nature and origin following the original suggestion by Cockayne (1926), but visitors and authors of books on plant geography usually find this designation difficult to accept. Thus Polunin (1960) says ‘The rain forest in New Zealand is almost entirely temperate in nature, in spite of the prevalence of large tree ferns’ and Chapman (1958) feels that it is time that Cockayne's subtropical concept ‘ceased to colour the New Zealand botanist's interpretation of lowland forests’ and further states ‘It would seem then that Cockayne's and Schimper's view of the New Zealand lowland forest (except kauri forest) as subtropical cannot be substantiated.’ The basic objection seems to be that New Zealand is not thought to have a subtropical climate, nor to be situated within the subtropical zone. With the exception of the Auckland peninsula the first point is probably valid, the second point also, although it should be noted that unlike the tropical zone the subtropical zone is not geographically defined. Most people, however, would agree that New Zealand is rather too far from the equator to be included in such a zone, defined or not. A further objection, based on floristics, is put forward by Chapman (1958) who points out that ‘the lianes and epiphytes (of the New Zealand lowland forests), regarded as a subtropical feature, belong mostly to families other than those found as lianes and epiphytes in the tropics.’ Before attributing too much weight to these objections based on latitude, climate and floristics, we should remember that world vegetation types are primarily defined in terms of their structure and the life forms of the plants composing them. Admittedly a particular vegetation type usually develops in relation to a particular climate, but it should never be assumed that the two must always occur together. Vegetation change usually lags behind climatic change, so it is not unusual to find
* The term ‘lowland forest’ in the remainder of the text refers to this type alone and does not include lowland Nothofagus forest.
There is also no necessary correlation between latitude and vegetation. Because of the temperature decrease from the equator to the poles world climates, and hence vegetation types, tend to follow a latitudinal sequence. The correlation between vegetation and the broad, geographically defined, latitudinal zones — tropical, temperate and polar — is reasonably good, but even here there may be some transgression of boundaries, e.g. where tropical rain forest extends a little beyond the Tropic of Capricorn in South America, south-east Asia and Australia (Richards, 1952).
With regard to the matter of floristics it should be emphasised that two areas of vegetation can be accepted as belonging to the same type without there being any floristic relationship between them. Thus what is known as Mediterranean scrub vegetation has developed independently in five widely separated areas in the world in relation to a particular climate, but the plants of any one area are largely unrelated to those of the other four. Similar cases of parallelism in plant form occur in the desert areas. Water-storing plants in the deserts of North America and South Africa, for example, are remarkably similar in appearance, but are in fact quite unrelated taxonomically. Plants of this form in North America belong to the Cactaceae and in South Africa mostly to the Euphorbiaceae. More pertinent to Chapman's argument are the tropical rain forests themselves. Tropical rain forest occurs in three widely separated areas: in south and central America; in south-east Asia and adjacent Pacific areas; and in central Africa. In his book on the tropical rain forest Richards says in reference to these areas, ‘In each of these formations almost all the species and many of the genera and families are peculiar and not shared with the other two.’ So the questionable contention that the epiphytes and climbers of New Zealand's lowland forests are largely unrelated to similar forms in the tropics would appear to have no bearing on the problem of whether or not the forests in question should be termed subtropical.
Chapman's second argument is also based on floristics. He questions Cockayne's belief that the affinities of the New Zealand lowland forest are with Malaya and suggests that the relationships are more with such islands as Samoa, Tonga, Fiji and New Caledonia. This may be so, but as these islands and Malaya both support tropical forest the question of the status of the New Zealand lowland forest is not affected.
Floristic relationships may lend support to the idea that two similar stands of vegetation can be classified as the same type, but the absence of such affinities cannot be taken as opposing such an idea.
From the foregoing it would seem that, ideally, the names of world vegetation types should be based on structure and life form and not on latitude, climate or floristics. However, it is not easy to devise
I think the second part of this paper will show quite clearly, that in terms of structure and life form the New Zealand lowland forest has a great deal in common with tropical rain forest in general, and floristically much in common with the adjacent tropics in particular. If a relationship with tropical rain forest is accepted, we must then decide whether the local forest should be placed in a world category next to tropical forest or next-but-one. Authors who have called the New Zealand forests temperate or warm-temperate have mostly recognised an intermediate category which they have termed subtropical. Schimper (1903) recognised these three types with the subtropical type rather vaguely defined as ‘impoverished tropical rain forest’. He states further, ‘It is difficult to draw the line between these forests and the much more peculiar temperate rain forests.’ He placed all the New Zealand forests under the latter heading.
More recently Dansereau (1957) has recognised the same types and again the differences are difficult to appreciate. Under subtropical forests Dansereau states ‘The fall in temperature reduces the number of flowering species’ and gives as an example of the type the forests of Hawaii. However, oceanic islands in general tend to be low in species in proportion to their areas, so isolation rather than temperature may be the explanation in this case. Under temperate rain forest Dansereau states that vascular epiphytes are few, but in New Zealand lowland forest, which he includes here, vascular epiphytes are quite abundant. The example given is northern New Zealand kauri (Agathis) forest, but the photograph illustrating the type is of Nothofagus forest.
In another recent plant geography text (Polunin 1960) the three forest types again appear. On page 350 Polunin mentions tropical, subtropical and warm-temperate rain forests, but I cannot find any further reference to the subtropical type elsewhere in his book.
In developing the schemes outlined above I think the authors have been led astray by their failure to distinguish between the New Zealand lowland forests (Agathis-dicotylous and podocarp-dicotylous) and the Nothofagus forests, which in general replace the latter at higher elevations and on poorer sites in the lowlands. In my view the Nothofagus forests are more akin to the temperate deciduous forests of the northern hemisphere than to the lowland forests in New Zealand. The fact that, in some places, there may be a wide transition zone where the forests intermingle, is no argument against separating them. Even the markedly different broadleaf-deciduous and coniferous forests in the northern hemisphere exhibit such transitions. Richards (1952) when referring
Eucalyptus and subantarctic rain forest dominated by Nothofagus — is everywhere extremely sharp.'
In a later edition of Schimper's work, van Faber (1935) followed Cockayne in differentiating between the two forest types, terming the lowland forests subtropical and the Nothofagus forests temperate.
Dansereau has also revised his scheme recently (Dansereau 1958), but it is still not clear whether or not he accepts two forest types for New Zealand. In this version only tropical and temperate rain forests are recognised. The examples given for temperate rain forest are New Zealand Nothofagus forest and the laurel forests of the Canary Islands.
It certainly seems that, on a world scale, an intermediate category between the New Zealand lowland forest and tropical rain forest cannot be maintained. The view that the New Zealand lowland forest comes into a category adjacent to that of tropical rain forest is supported by a comparison of the former with the montane tropical, or subtropical, forests of New Guinea. Robbins (1961), who has studied forests in both New Zealand and New Guinea, describes the mixed podocarp-broadleaf forest in montane New Guinea and observes ‘It is in such forest of the inland mountain regions that affinities with the New Zealand rain forests are so striking.’ Robbins also notes that there are many more species in this New Guinea forest than in its New Zealand counterpart, and that in most cases the genera are not known in New Zealand. He provides a list of the genera that are shared with New Zealand, and of these one is a moss, eight are ferns, three are gymnosperms and twenty-five angiosperms. These floristic affinities lend support, but are not necessary to the belief that these mixed montane forests in New Guinea belong to the same vegetation type as the lowland forests of New Zealand.
Nothofagus forests also occur in the montane areas of New Guinea and according to Robbins ‘beech forests exist side by side, as in New Zealand, with a mixed broadleaf-podocarp forest with usually a sharp boundary between the two’. On the basis of fossil pollen evidence, Couper (1960) has shown that Nothofagus and the podocarps are fairly recent immigrants into New Guinea from the south. They established themselves in New Guinea during the Pliocene cooling that led to the Pleistocene ice ages.
If it is granted that the New Zealand lowland forests come into a type next to that of tropical rain forest, it does not necessarily follow that they should be termed subtropical. Warm temperate rain forest might be considered more appropriate by many people, although personally I favour the term subtropical, as I feel that it best expresses the fairly close relationship with tropical rain forest. Richards also uses the term subtropical in this context and, referring
As there is often a gradual transition from subtropical to tropical rain forest, the former is not easy to define. In general subtropical rain forest appears to differ from tropical rain forest in the following respects — fewer species; tendency towards local dominance of tree species (although this also occurs in some tropical rain forests according to Richards); an admixture of species of a more temperate nature (in New Zealand these are gymnosperms — podocarps or Agathis); smaller leaf size on the average; a greater abundance of tree ferns and bryophytes; denser undergrowth; a deeper humus layer in the soil; a greater accumulation of rotting logs due to the slower decay rate with lower temperatures; fewer tree species exhibiting buttressing and cauliflory; and sometimes a greater profusion of epiphytes.
Chapman feels that there might be a case for regarding the Agathis dominated forests in New Zealand as subtropical, but not the podocarp-dicotylous forests. These forest types can be classified as distinct within New Zealand, but I don't think they can be assigned to different vegetation types on a world scale.
It is interesting to note that both Cockayne (1921) and Robbins (1958) believe that the dicotylous element in the New Zealand subtropical forest is tending to replace the podocarp element at the present time. Robbins refers to ‘the general decline of the podocarp element in New Zealand mixed forests’ and ‘the trend towards a replacement of podocarp forest by broadleaf forests at present evident in the New Zealand vegetation pattern’. If this is so then presumably these New Zealand forests are tending to become less different from tropical rain forest in this respect.
Elsewhere in the world subtropical rain forest occurs, or formerly occurred, in southern Queensland and New South Wales, in limited montane and coastal areas in eastern South Africa, in south-east Brazil, in a limited area in south Chile, in southern Florida, south Japan, south and south-east China and possibly in the Canary Islands. In the last case the forest is known as laurel forest and occurs in moist gullies on the mountain sides. Schimper describes it as ‘a sclerophyllous forest transformed into a temperate rain forest, or a stage intermediate between them with a closer approximation to the sclerophyllous forest’. Christ (1885) mentions ‘a poor development of lianes and the absence of true epiphytes’ and also ‘Several of the woody species were partly identical with or partly related to Mediterranean sclerophyllous plants.’ It seems doubtful whether such forest can be regarded as being in the same category as subtropical forest, or even Nothofagus forest as Dansereau has suggested.
Subtropical and tropical rain forests are fairly restricted in their distribution at the present time, but fossil evidence indicates that they were very much more widespread in the early Tertiary prior to the ice-age. At this time world climates were much more uniform than now and were, in general, warm and moist. Under these conditions tropical and subtropical rain forests extended from the equator to about 50° north and south to include such places as the south of England and Oregon. General cooling and progressive desiccation in some areas in the later Tertiary, culminating in the ice-ages, caused the extinction of most of the rain forest outside the geographical tropics. The surviving areas, listed earlier, of subtropical rain forest in temperate regions, are mostly near the tropics, but in several places in the southern hemisphere they extend to middle latitudes. The great preponderance of ocean in the southern hemisphere may have sufficiently reduced the severity of the climatic minimum in the middle latitudes to allow these forests to persist. In New Zealand, during the last glaciation, it has been suggested that forests were largely, if not entirely, restricted to areas north of about 39° (Harris pers. comm.). With the improved climate since that time forests have re-established themselves throughout the country.
Before giving some account of the structure and life forms of the New Zealand lowland forest I should like to discuss briefly the term ‘subantarctic rain forest’ as applied by Cockayne to the Nothofagus forests in New Zealand. Cockayne based the name on the Nothofagus forests extending into subantarctic South America and it could be inferred from this name that the subantarctic regions provide the optimum climate for this type of forest. If ‘subantarctic rain forest’ was regarded by Cockayne as a distinct world vegetation type, then I think his interpretation is open to question. As I have mentioned earlier, Nothofagus forest is structurally similar to the temperate deciduous forests of the northern hemisphere, the chief difference being that not all species of Nothofagus are deciduous. In South America there is a mixture of deciduous and evergreen species, in New Zealand only evergreen species, in Tasmania one evergreen and one deciduous species, in Australia and New Guinea only evergreen species. However Russel (1936) points out that some of the New Zealand species might well be described as near deciduous, as it is usually not long after the new season's leaves appear, that the previous season's leaves are shed. In my opinion the Nothofagus forests should be regarded as coming close to the category of temperate deciduous forests. Certainly Cockayne's ‘subantarctic’ forest appears to have very little in common with the subarctic or coniferous forest in the northern hemisphere.
The accompanying map shows the approximate distribution of lowland forest in pre-European times. Forests in which Nothofagus is present are not shown. It is clear now that the lowland forests must have been even more extensive in pre-Maori times, as it is believed that many of the shrubland areas, particularly in the North Island, resulted from forest fires begun by Maoris. This belief is supported by the frequent appearance in Cook's log of the phrase ‘Fires inland’. The most extensive areas of lowland forest were in the North Island, but the type was also quite well represented in disjunct areas throughout the South Island and in Stewart Island. In the southern half of the country particularly, species become fewer with increasing latitude. An outpost of the forest is to be found in the Auckland Islands which, at 50° south latitude, are about the same distance from the equator as London. The low coastal forests here consist of Metrosideros umbellata (bearing many aerial roots) with a tree fern, Cyathea smithii, in the gullies, more occasional Neopanax simplex, several under-shrubs and several ferns, including six filmy ferns (Hymenophyllum).
Much of the New Zealand lowland forest was destroyed following European settlement, but in most of the original areas stands still remain in national parks, in other reserves, and under management by the Forest Service. In some places also, abandoned land is now reverting to forest.
The composition of the lowland forest is variable. Mostly there is a mixture of podocarps and angiosperms, but in places podocarps may form almost pure stands, or elsewhere, particularly coastally, podocarps may be absent. North of 39° S. the very large trees of the kauri (Agathis australis) play an important role.
In the podocarp-dicotylous forest six layers may be recognised: three canopy layers, a small tree layer, a shrub layer, and a layer of ground plants. The uppermost, usually discontinuous, canopy layer comprises emergent trees, mostly podocarps and Metrosideros robusta, and the two lower canopy layers are mostly dicotyledonous. The small tree layer comprises dicotyledons and tree ferns, the shrub layer mostly dicotyledons, and the ground layer mostly ferns. This stratification is similar to that of tropical rain forest, although in the latter the uppermost canopy layer is formed by dicotyledons only. The usual discontinuity of the uppermost stratum gives a characteristically uneven surface to both types of forest. (Fig. 3.)
In addition to what can be termed self-upholding plants there is usually an abundance of lianes and both herbaceous and shrubby epiphytes. These also are features in common with tropical rain forest.
Fig. 1 : Distribution of lowland forest in New Zealand in pre-European times. Based on vegetation map in the New Zealand Pictorial Atlas.
Life Forms and Geographic Affinities
In New Zealand the following genera occur in the lowland forests.
Richards describes a number of morphological features which are characteristic of some or most tropical forest trees, e.g. slender trunks with thin, smooth bark; small, little-branched crowns; plank buttresses and stilt roots; pneumatophores; leaves mostly about cherry laurel size, simple, smooth margined, with pulvini and narrow prolongations known as drip tips; coppice shoots from bases of trunks common; cauliflory and ramiflory fairly common; insect pollination thought to be the rule.
Although complete information is not available, trees in the New Zealand lowland forests exhibit many of these features. Cockayne describes the majority of New Zealand trees as having slender, thin-barked trunks and small, dense crowns. Most podocarps, Agathis, the Nothofagus species, Metrosideros, Elaeocarpus and Gymnelaea, are numbered among the exceptions. Plank buttresses are rare, the best example being Laurelia novae-zelandiae (Fig. 7). The species of Nothofagus often have buttresses but these are usually fairly thick, although at times they have been referred to as plank-like. Stilt roots in the true sense are probably not present, although the species of Metrosideros produce aerial roots very readily and in M. excelsa particularly they may become quite massive. Pneumatophores are formed by Eugenia, Laurelia and Avicennia. The average leaf size is probably less than that of the tropical rain forest and, although the leaves are predominantly smooth-margined and undivided, there is a significant proportion of leaves with serrated margins and of compound leaves. Drip tips appear to be entirely wanting and pulvini are developed in Dysoxylum spectabile and possibly some others. Many of the trees produce coppice shoots very readily, e.g. Melicytus ramiflorus, Hedycarya arborea, Elaeocarpus dentatus, Weinmannia racemosa. A good example of cauliflory (production of flowers on the trunk) is found in Dysoxylum spectabile and ramiflory (production of flowers on older parts of branches) occurs in Melicytus, Hymenanthera and Myrsine. The conifers and Nothofagus are wind pollinated, but, with the exception of Coprosma, the other trees and shrubs are probably insect pollinated.
A rather variable deciduous habit is exhibited by the fuchsias, two of the hoherias, Plagianthus betulinus, Muehlenbeckia, Sophora and Aristotelia serrata, but this is not necessarily a temperate feature as the deciduous condition, usually of brief duration, is not at all uncommon in tropical rain forests.
Richards's comment on the juvenile forms of some tropical forest trees is very interesting. ‘A number of large rain-forest trees, which later have normally branched crowns, remain unbranched with their leaves crowded on to the last few centimetres of the stem until they are 6-7 m. or more high.’ This is exactly the situation in several New Zealand species of Pseudopanax, a phenomenon which has puzzled New Zealand botanists for some time. Other New Zealand examples are Elaeocarpus dentatus and Knightia excelsa.
The genera marked * are woody, the remainder are herbaceous. Concerning epiphytes Richards writes, ‘The abundance and variety of epiphytes is one of the most striking differences between the Tropical Rain forest and temperate forests. As well as algae, fungi and bryophytes, the epiphytic flora of the Rain forest includes a wealth of pteridophytes and flowering plants. It is the presence of these vascular epiphytes which especially distinguishes the Tropical Rain forest from temperate plant communities.’ ‘In the Montane and Subtropical Rain forest, the two plant formations most nearly resembling the Tropical Rain forest, the epiphytic vegetation, though less rich in species, reaches a degree of luxuriance seldom approached in the lowland tropical forest.’
Metrosideros robusta in particular and possibly also Neopanax arboreum, Weinmannia racemosa, Coprosma australis and Dracophyllum
come into the class of epiphytes known as ‘stranglers’. These are trees which begin life as epiphytes on other trees, but eventually send roots to the ground. The latter surround the host trunk and, on death of the host, form an independent pseudo-trunk. Fig. 2 : Forest interior. Kie-kie (
Freycinetia banksii) on right. Tree fern is Cyathea medullaris. Gollan's Valley, near Wellington.
Photo: Metrosideros robusta establishes itself on a variety of hosts (Fig. 6), the other four chiefly on tree ferns, Neopanax
Fig. 3 : Exterior view of lowland forest. Emergent trees along skyline are rimu (
Dacrydium cupressinum). Nearer trees are mostly kamahi (Weinmannia racemosta).
racemosa).
Akatarawa, near Wellington. Photo:
(Fig. 5) assuming this mode of life more frequently than the other genera. Griselinia lucida usually sends a root to the ground, but does not become independent.
All of the epiphytes listed above can occur as ground plants. Conversely many plants not listed can occasionally occur as epiphytes, particularly on tree fern trunks.
Of the above Fuchsia and Rubus are scramblers, Clematis and Tetrapathaea are tendril climbers, Lygodium, Muehlenbeckia,
and Fig. 4 : Epiphytic Collospermum hastatum and Blechnum filiforme. Leaves of Nikau (Rhopalostylis sapida) appearing at left. Gollan's Valley, near Wellington.
Photo: Ripogonum (Fig. 8) are twiners, and the remainder are root climbers. Some of the ferns may also be epiphytes.
The first four genera are epiphytic and belong to the Loranthaceae, the last two root parasites. Richards mentions that all epiphytic parasites of the tropical rain forest belong to the Loranthaceae. ‘Their brilliant colours often make them conspicuous when in flower, A tree laden with Loranthaceae is one of the most beautiful sights of the Malayan Rain forest.’ Several of the New Zealand species of the family an colourful.
Ferns are by far the most common ground herbs and their abundance is a distinctive feature of the New Zealand forests. Angiosperms are generally less abundant except in forest openings or margins.
Summary of Geographic Affinities
The number of genera here regarded as belonging to the lowland forest is 148. In some cases it is difficult to decide whether a genus should be included or not, e.g. where the species concerned are found at forest margins or are pioneers following clearing, so the number stated could be varied a little either way. Within New Zealand these genera comprise 399 lowland forest species and 864 species over all.
Fig. 5 : Neopanax arboreum (Five-finger) epiphytic on a tree fern. Root-stem junction is near top of photograph. Tree fern trunk appears between descending roots of epiphyte. Plateau bush, upper Hutt Valley, near Wellington.
Fig. 6 : Descending rata (
Metrosideros robusta) roots on pigeonwood (Hedycarya arborea). Silverstream, near Wellington.
Photos:
In the first category 60 genera are largely restricted in their distribution outside New Zealand to the Asian-Polynesian tropics. The remainder are widely distributed in tropical regions, and temperate regions as well in some cases.
Of the third category 2 genera exhibit features generally regarded as tropical. Several species of Griselinia commonly occur as shrubby ground-rooted epiphytes and Laurelia novae-zelandiae has plank buttresses and pneumatophores.
In view of the facts set out above I feel that the conclusion that New Zealand lowland forest is closely related to tropical rain forest is inescapable. I also feel that the use of the term ‘subtropical’ for this forest is justifiable, even though geographic and climatic objections still remain. As mentioned earlier the ideal classification is one based on the nature of the vegetation itself, and it is to be hoped that some botanist with a knowledge of all types of world vegetation will devise such a classification. He would be doing a great service to plant geography.
References
Fig. 7 : Pukatea (Laurelia novae-zelandiae) showing plank buttresses. Tawa, near Wellington.
Fig. 8 : Entanglement of supplejack (Ripogonum scandens). Silverstream, near Wellington. Photos:
63 Penrose Street, Lower Hutt
The lugwormAbarenicola assimilis is the creature responsible for many of the large worm casts seen at low tide on many of New Zealand's sandy beaches in both the North and South Island. The animal is chiefly restricted to sand with a high content of organic matter, and thus the animals are often found in great numbers in areas near the outflow from abattoirs, freezing works, or rubbish tips. The worms range in size from 10 to 35 cm. in length and their soft fleshy bodies are extremely attractive to predatory animals and fish. Most fish will strike at a bait of lugworm in preference to anything else — a fact discovered by the Maoris many years ago. Lugworm bait is eagerly taken by snapper, moki, and tarakihi. Petone Beach, Wellington, in the early spring and summer mornings, is the venue where many a keen surf-fisherman can be seen digging vigorously for these quick-burrowing worms.
Abarenicola assimilis is fairly common in the sand at Petone Beach and the description of the species here is from specimens taken from that locality. No other colonies were found in the Wellington area during the course of this study.
Wells (1959) established the genus In In Abarenicola, and included in it the New Zealand species previously called Arenicola assimilis Ehlers. Abarenicola assimilis shows a general similarity to the common Northern Hemisphere Arenicola marina (Linnaeus, 1758)
Abarenicola from Arenicola:
Arenicola possesses a single pair of oesophageal caecae, whereas Abarenicola possesses more than two caeca situated in a longitudinal row on each side of the oesophagus. Fig. 3, oes. caec.).Arenicola, the gular membrane is muscular and is the primary agent in the process of proboscis extrusion. Moreover the gular membrane has a pair of septal pouches. In Abarenicola, the gular membrane is extremely thin and non-muscular and probably has no part in the process of proboscis extrusion. (Fig. 3, mm.p.ret.). Septal pouches are absent.Arenicola has a small prostomium which is completely retractable into the nuchal pouch. The prostomium of Abarenicola is broad in front (Fig. 1, D, Pros.) and cannot be retracted into the nuchal pouch.Arenicola the neuropodia of the branchiate segments extend ventrally nearly to the ventral mid-line, but in Abarenicola the ventral ends of the neuropodia are separated from the ventral mid-line by a distance roughly equal to the length of the neuropodium (Fig. 1, G, Neurop.).
The lugworms of the Petone colony showed clearly all those features described by Wells (1959) as diagnostic of the genus Abarenicola, and Abarenicola assimilis is now known to be the common lugworm inhabiting the colder waters of the Southern Hemisphere (Wells, 1961).
The first specimens were dug on April 1, 1961, and subsequently at weekly or fortnightly intervals. The greatest concentration of worms is found at the western end of Petone Beach (Fig. 1, A), and the colony extends eastwards to within a few chains of Petone Wharf. In the zone of heaviest concentration, specimens number three or four per square yard of beach and the concentration diminishes east and west of this zone to about six casts per square chain on the fringes of the colony. Specimens taken at random within the colony all appeared to be of a fairly constant size and at a similar stage of sexual development.
The sand containing the greatest concentration of both mature and immature worms is heavy and black, full of decaying organic matter, such as freezing works offal and seaweeds. The seawater is correspondingly polluted with such matter, and there seems to be a direct relationship between the amount of decaying organic matter in the sand and seawater and the number of animals present.
Specimens were taken from the sand by means of a spade, but only about one worm in every twenty was obtained entire as it was
The burrow of a lugworm is U shaped and is usually about 30 cm. deep. The presence of a worm on the beach is indicated by a coiled casting about 2 mm., in diameter at the anal end, and a countersunk hole at the anterior or head end. The distance between the head and the anal ends of the burrow varies from 10 cm. to 25 cm. (Fig. 1, B). The burrows remain semi-permanent in nature, as the walls of the burrow are lined with mucus secreted by epidermal cells, which binds the wet sand, and prevents the burrow from caving in. When a worm is dug and the burrow exposed, a clear imprint of the worm is left in the sand. When the burrow is covered by water, the worm is in the resting position (Fig. 1, B, A-B). At low water the worm is more usually found in the defaecating position (Fig. 1, B, A1-B1). This position is assumed also at high water, but only temporarily while the worm defaecates.
In the laboratory, a glass U tube was partially filled with sand, topped up with seawater, and set up on a stand. A living Abarenicola assimilis was placed in the tube, and as the worm burrowed, its digging mechanism was observed.
FIGURE 1
(A) Location Map.
(B) Nature of Burrow and Response to Tidal Variation. A — B, resting position; A1 — B1, defaecating position.
(C) External Features. An. — Anus, Br1 - Br13 — Branched gills, Chaet. annl-Chaet. ann19 — Chaetigerous annuli, Mth. — Mouth, Neph P1 - Neph P6 — Nephridiopores, Neurop — Neuropodium, Noto — Notopodium, No. chaet — Notopodial chaeta, Pros. — Proboscis, Se IV Segment IV (a1-a5 — annuli), Tail Seg. — Tail segment, V.M.L. — Ventral midline, A - A - T.S. — Fig. 2A, B - B - T.S. — Fig. 2C.
(D) External Features of Proboscis and Anterior Segments. Chaet. ann2 — Chaetigerous annulus II, Mth. — Mouth, No. chaet. — Notopodial chaetae, Nuch. p. — Nuchal pore, Pap. — Papillae, Pros. — Proboscis.
(E) Mature Ovum. Cyt. — Cytoplasm, Memb. — Outer Membrane, Nuc. — Nucleus.
(F) (1) Side View of Mature Sperm Plate. (2) Top View of Mature Sperm Plate. Sp. tails — Sperm tails.
(G) Transverse section through a parapodium. Br. fil — Gill filament. Circ. mm. — Circular muscles, Coel. — Coelom, Int. — Intestine, Long. mm. — Longitudinal muscles. Neurop. — Neuropodium, No. chaet. — Notopodial chaetae, No. chaet. sac. — Chaetigerous sac., Noto. — Notopodium, V.M.L. — Ventral midline.
The proboscis is extruded by delivery of coelomic fluid under pressure, and is pressed into the sand, displacing it laterally. The anterior segments also become quite turgid and help to enlarge the burrow laterally. Then a wave of contraction passes posteriorly along the length of the animal and by means of the longitudinal muscles and the gripping action of the notopodial chaetae, it draws itself into the sand. The proboscis is again everted, and at the same time a wave of relaxation passes along the length of the body. As the worm attains a greater length, the cross-section is diminished and water moves rapidly down the burrow, bathing the gills and breaking up the tightly packed sand grains in the path of the worm. A further extension of the proboscis and subsequent wave of contraction draws the worm deeper.
Periodically a vertical channel is made to the surface, by a jet of water from the mouth. This, together with the waves of relaxation passing from the anus to the prostomium while the animal is resting, further irrigates the gills.
Observations showed that large local changes in body diameter employed in active burrowing were brought about by the combined action of the somatic longitudinal and circular muscle layers, and fluctuations in coelomic fluid pressure.
The proboscis was observed to have two distinct and independent functions: (a) feeding — a pumping action which actively admits water and sand; (b) digging — sand is laterally displaced, and none appears to enter the mouth.
FIGURE 2
(A) Transverse section of tail on A — A of Fig. 1, C. Circ. mm. — Circular muscles, Coel. — Coelom, Conn. t. — Connective tissue, Dig. epi. — Glandular epithelium, Dors. B.V. — Dorsal blood vessel, Epid. — Epidermis, Ga, V. — Gastric vessel, Int. lu. — Lumen of intestine, Long. mm. — Longitudinal muscles, N.C. — Ventral nerve cord, Nev. B.V. — Neural blood vessel, Obl. mm. — Oblique muscle, Perit. — Peritoneum, Vent. B.V. — Ventral blood vessel.
(B) Vertical longitudinal section of proboscis, 0.5 mm. to left of midline. Bra. — Brain, B.V. — Blood vessels, Com. — Circum - oesophageal commissure, Dphm.1 — First septum, H. Coel. — Head coelom, Mth. — Mouth, Nuch. P. — Nuchal pore, Oes. — Oesophagus, mm. P. ret. — Retractor muscle of proboscis (gular membrane). Other abbreviations as for Figure (A).
(C) Transverse section of branchial region on B — B of Fig. 1, C. Br.8 — Gill VIII, Chloro. tiss. — Chlorogogenous tissue, Eff. aff. br. a. — Efferent and Afferent branchial arteries, Lat. B.V. — Lateral blood vessel, Noto.14 — Notopodium XIV, No. chaet. — Notopodial chaeta, Ooc. — Oocyte, St. lu. — Lumen of stomach. Other abbreviations as for Figure (A).
Specimens in seawater were anaesthetised by slowly adding 70% alcohol, and preserved in 5% formaldehyde solution. Serial sections were cut at 10μ on the microtome and stained with Heidenhain's haematoxylin and eosin. Observations of the external features and general behaviour were made on living specimens both in the field and in the laboratory.
The body is divided into an anterior chaetigerous region including the prostomium, a middle branchial region, and a posterior caudal region (Fig. 1, C).
The anterior region is made up of the prostomium or proboscis (Fig. 1. C, D — Pros.), and six chaetigerous segments — each segment consisting of the chaetigerous annulus (Fig. 1, C, D — Chaet. ann.) together with three preceding annuli, and one following annulus. Evidence for this is based on the position of the diaphragm (Fig. 3 —Dphm. 2 and Dphm. 3).
The proboscis is top-shaped when fully extended and covered by short papillae which extend into the oral zone (Fig. 1, D; Fig. 2, B — Pap.). The proboscis cannot be completely withdrawn as in the genus Arenicola.
The specimen sketched (Fig. 1, C) shows that proboscis in a fairly advanced stage of contraction, while in Fig. 1, D, the proboscis is fully extended. A large nuchal pore (Fig. 1, D — Nuch. p.) is located on the mid-dorsal line just behind the proboscis, and opens into a cavity lined with glandular cells (Fig. 2, B — Nuch. p.). The chaetigerous section possesses six neuropodia (Fig. 1, C, G — Neurop.), appearing as transverse slits extending from beneath the notopodia to within about 2 mm. of the ventral mid-line. Each notopodium bears a double row of notopodial chaetae (Fig. 1G, No. chaet.). These are stiff, bristle-like structures which may be articulated in an anterior-posterior direction so as to aid in movement of the animal. A small hooded nephridiopore (Fig. 1, C — Neph. p.) is located just below the fourth to the ninth notopodium on each side. The epidermis of both the anterior chaetigerous and the branchial regions consists of raised polygonal areas of mucus-secreting columnar cells separated by shallow grooves (Fig. 2, C —Epid.).
The brancial region, in addition to neuropodia. notopodia, and setae, is distinguished by the presence of thirteen pairs of contractile gills (Fig. 1, C— Brl -Brl3), which are attached just behind each notopodium. The front pair of gills is always smaller than the rest but still has the same well-developed feathery structure. Both the
The neuropodia in this region are separated from the strongly marked ventral mid-line (Fig. 1, C — v.m.l.) by a distance roughly equal to the length of the neuropodia themselves (Fig. 1, G).
The caudal region is typified by the absence of any specialised external structures (Fig. 1, C — Tail). The tail is very variable in length. Living specimens were found with twenty to thirty tail segiters, while others had as few as two or three. It is probable that specimens with very short tails have at some time been damaged by predators.
The worm brings its anus to the surface of the sand in order to defaecate, and consequently the tip falls easy prey to flounders, or other bottom feeding fish and to the hundreds of herring gulls patrolling the beach at low water. Many gulls were observed to pounce on defaecating worms and plunge their beaks into the burrow. In general, the tail segments are longest in the region of the anus.
Dissection was performed on a freshly-killed specimen which had been previously relaxed in alcohol so that the pressure of the coelmic fluid would not force the internal organs through the primary incision in the body wall. The body cavity was opened by a mid-dorsal longitudinal incision from the proboscis to a short distance down the tail, and the flaps of the body wall were pinned back (Fig. 3). The gut was slightly displaced to the left and pinned.
The coelom is very spacious, and extends from one end of the body to the other. Anteriorly the coelom is partially transversely divided by the retractor muscles of the proboscis (Fig. 3 — mm. p. ret.) and more completely so by three septa (Fig. 3 — dphm. 1), which arise from the groove behind the first annulus posterior to each of the first three chaetigerous annuli. The septa are perforated to allow passage of the coelomic fluid so, in effect, the continuity of flow of the coelomic fluid is not appreciably interrupted. Dorsal and ventral mesenteries support the oesophagus and anterior portion of the gut from the first to the third septum.
From the third septum to the base of the tail, the body cavity is undivided. No mesenteries support the gut which is slightly larger than the portion of coelom in which it lies, and it tends to swing freely with movements of the body. Segmental blood vessels, however, give some elastic support to the mid-gut. Arrangement of repeating organs such as nephridial funnels (Fig. 3 — Neph. f.) and somatic segmental afferent and efferent blood vessels, indicate the segments in this body region.
From the base of the ‘tail’ region to the anus, transverse septa (Fig. 3 — T. dphm.) divide the body cavity into clearly recognisable segments.
The musculature of the body wall is arranged in an outer circular band (Fig. 2, C — Circ. mm.) and a thick inner longitudinal muscle sheath (Fig. 2, C — Long. mm.) which is divided into one dorsal and two ventrolateral sections by the left and right oblique muscle layers (Fig. 2, C — Obl. mm.). The oblique muscles, which divide the coelom longitudinally into three compartments, commence behind the third septum and lose their identity after the first few ‘tail’ segments.
The retractor muscle of the proboscis (Fig. 2, B — mm. P. ret.) is a very thin, weakly developed modification from the longitudinal muscle layer. The retractor muscles of the parapodia (Fig. 3 — mm. Para. ret.) are also derived from the longitudinal muscle, and they extend almost to the mid-ventral line. The parapodial proctractor muscles (Fig. 3 — mm. Para. prot.) are usually eight in number — four each side of the chaetigerous sac, and these muscles move the parapodium in an antero-posterior direction.
The alimentary system consists of:
The proboscis lined with vascular papillae (Fig. 1, D, and Fig. 2, B — Pap.) which trap sand grains and draw them into the mouth when the proboscis is withdrawn. An oesophagus interiorly lined with glandular epithelium and possessing up to twenty-one oesophagael sacs (Fig. 3 — Oes. caec.) opening into the oesophagus by wide ducts.
These caeca or sacs are arranged in two longitudinal rows, one on each side of the oesophagus, and in fresh specimens are red in colour owing to their large blood supply. The anterior pair of caeca are always much larger and longer than the following caeca. The most posterior pairs are in general the smallest of all. One specimen was found to have only eleven pairs of oesophageal caeca and the largest number noted was twenty-one. Figure 3 illustrates a specimen with nineteen pairs of caeca.
FIGURE 3
Abarenicola dissected to show major features of internal anatomy. Ant. oes. caec. — Anterior oesophageal caecum, Br. aff. — Afferent branchial vessel, Br. eff. — Efferent branchial vessel, Br. Nn. — Annulus branch nerve, Chloro. tiss. — Chlorogogenous tissue, Dors. B.V. — Dorsal blood vessel, Dphm. — first 2 anterior septa, Long. mm. — Longitudinal muscle, mm. Para. prof.— Parapodial protractor muscles, mm. Para. ret. — Parapodial retractor muscles, Mth. — Mouth, Neph. f. — Nephridial funnel, (Nephrostome) Neph. sac — Nephridial sac, N.C. — Ventral nerve cord, New. B.V. — Neural blood vessel, Oes caec. — Oesophageal caeca, Para 1 -Para XIX — Parapodia, Phar. — Pharynx, Seg. eff. B.V.— Segmental efferent blood vessel, T. dphm. — Tail septum, Vas. gut. ret. — Vascular reticulum of gut, Vent. B.V. — Ventral blood vessel.
The stomach region (Fig. 3 — Stom.) extends from the level of the heart to the base of the tail where it merges into the intestine. As previously discussed, the stomach has no attachments to the body wall other than the afferent and efferent blood vessels in each segment. The stomach is lined with glandular epithelium and the exterior is a striking mustard/yellow colour from cholorgogenous cells arranged in broad patches, the latter, however, becoming smaller towards the tail. The stomach is richly supplied by blood vessels forming a reticulum (Fig. 3). The intestine is brownish in colour with a poorly developed blood supply in comparison to the stomach. It is supported by numerous septa (Fig. 3 — T. Dphm.) as well as a ventral and dorsal mesentery. It opens at the terminal anus.
The general features only of the blood system of Abarenicola assimilis are noted here.
There are two chief vessels — one above and one below the alimentary tract, running from one end of the body to the other (Fig. 3). The gut is served by a reticulate system of capillaries in turn which are connected via a pair of red bulbous hearts (Fig. 3 — H.) to a ventral vessel. The dorsal vessel originates near the anus and gives off a pair of segmental vessels (Fig. 3 — Seg. B.V.) at the beginning of each caudal segment. This blood is collected by the ventral vessel. In the gastric region, the blood from the last seven pairs of gills returns by way of afferent vessels to the dorsal vessel, but anteriorly from the level of the sixth gill the dorsal vessel receives numerous branches from the gastric reticulum, but no efferent branchial or nephridial vessels. These are returned via the gastric reticulum. In front of the heart the dorsal vessel receives branches from the oesophagus and each oesophageal caecum, and after many branches are received from the brain it finally disappears in the tiny capillaries of the proboscis.
The ventral vessel is large and covered by chlorogogenous tissue (Fig. 2, C — Chloro. tiss.) and sends efferent branches to the brain, oesophageal caeca, each of the gills, and the caudal septa. It does not appear to have any direct connection with the ventral part of the gut other than through the heart. Other vessels present are lateral vessels supplying the body wall (Fig. 2, C — Lat. B.V.), neural vessels lying each side of the nerve cord along the length of the body (Fig. 2, C; Fig. 3 — Neu. B.V.), and efferent and afferent branchial vessels shown in the section of the gills (Fig. 2, C). The blood flow is: The heart draws blood from the gastric vessels into the highly elastic ventral vessel, from whence it circulates through the body.
The nervous system consists of the brain (Fig. 2, B — Bra.), the circum-oesophageal commissures (Fig. 2, B — Com.) and the ventral
In close apposition to the brain is the nuchal sense organ (Fig. 1, D; 2, B — Nuch. P.). Dorsally it appears as a dark pit divided by a single median papilla (Fig. 1, D) and in longitudinal section the cells are large and distinct (Fig. 2, B). The parapodia and gills are extremely sensitive to light and touch.
There are six pairs of nephridia in all (Fig. 3 — Neph.) located in the fourth to the ninth chaetigerous segment. They are quite large and readily seen. Each nephridium consists of a funnel opening into the body cavity, an elongate central portion, and a small end sac, which opens to the exterior through the nephridiopore situated just below the notopodium. Each nephridium is supplied with an efferent and afferent blood vessel.
Gonads are present in conjunction with each of the six pairs of nephridia in the breeding season. The oocytes and spermatoblasts break free to complete their development in the coelomic cavity. On April 1, 1961, a few worms had liberated their gonadial contents into the coelom, and by August 1, 1961. the breeding season was in full swing. Spermatozoa are aggregated in plates up to 0.75 mm. in diameter until fully mature (Fig. 1, F, 1, 2). When fully mature, the individual spermatazoa break free. Each measures about 1/200 in. in length. When spawning, ripe ova surrounded by a thin membrane, or spermatazoa, are drawn by the action of the ciliated nephrostomes into the nephridia. and liberated through the nephridiopores into the seawater, where fertilisation takes place.
At fertilisation (which was achieved in the laboratory) the diameter of a mature ovum was found to be approximately 0.25 mm. (Fig. 1, E). The nucleus of the ovum is conspicuous and spherical and the cytoplasm is very granular.
After fertilisation the zygote shrinks within the fertilisation membrane and then undergoes a spiral system of cleavage to form a morula.
A. ecaudata(J) and
A. branchialis(A.E.) at Plymouth.'
Jour. Mar. Biol. Assn. U.K., Vol. 37, pp. 267-86.
Arenicola marina.' Quart Jour. Microscop. Sci., Vol. 41, Part I, pp. 1-42.
Proc. Zool. Soc. London. Vol. 133, Part II, pp. 315-35.
Proc. Zool. Soc. London, Vol. 133, Part II, pp. 301-14.
How Lugworms Move, The Cell and the Organism, Cambridge University Press, pp. 209-33.
Polack's (1838) reference to the presence of ‘toads and frogs’ in New Zealand ‘with their barometrical croak! croak! abound in the swamps’, is somewhat mystifying and difficult of interpretation in view of the fact that the indigenous species, belonging to the genus Leiopelma, were not reported till 1853 (Thomson). But, as some of Polack's observations, at first regarded as fanciful, have since been proved correct, this statement cannot be dismissed too lightly. As the indigenous species, Leiopelma, are believed to be silent, they could not have called forth Polack's comment. Accordingly, we must look beyond New Zealand for the authors of the croaks. Some foreign species may have been accidentally or deliberately introduced at a very early date. In a country with few natural enemies the frogs may have increased for a time and then for some unknown reason vanished, for no other observers refer to the croaking of frogs. This suggestion is almost as weak as Polack's statement. Alternatively, Polack may have heard the croaking of frogs or toads in some other land of his travels and when compiling his work forgetfully ascribed them to New Zealand.
As neither agriculture nor university students were flourishing during Polack's sojourn in New Zealand it is obvious that frogs would not have been willfully introduced as subjects for dissection! Alternatively, frogs may have been introduced as a source of
Rana esculenta or R. temporaria, or perhaps some Australian species and liberated them with a joyful vive la grenouille! in much the same way as Captain Cook transported and liberated pigs in the hope that they would increase and multiply to provide food for future visits — the effects of the latter liberations we know well!
The earliest authentic record of an attempt to introduce the European Brown Frog, Rana temporaria, was made in 1864 (Thomson, p. 182). Thirty specimens were brought to Canterbury from Great Britain, but none appear to have survived. Their disappearance was attributed to a swan! Attempts to introduce the Common Toad were made in 1867, but evidently this was also unsuccessful.
Polack's statement must remain a mystery.
Since the article 'Notes on the German Wasp Vespula germanica' appeared in Tuatara Volume IX: No. 1, Dr.
Dr.
Mr. R. Mander, Department of Agriculture, Wellington, supplied the information that Vespula germanica has been found nesting on the following islands: Mokohinau, north of Great Barrier Island;
Mr. G. Fox, caretaker of Kapiti Island, has seen the wasps several times on the island, but thinks they are only occasional visitors from the mainland, since no nests have been located. Surprisingly the wasp has not yet been found on Somes Island in Wellington Harbour, although a prolonged search has been made by the writer.
It is clear, therefore, that Vespula germanica has, since its establishment in Hamilton in 1945, become widespread in New Zealand, and that its position will no doubt strengthen with time.
I am grateful to all the persons mentioned above for supplying such information as they had.
R. A. Fordham
Mr. R. E. Barwick's intimate account of the common skink, Leiolopisma zelandica (Trans. Roy. Soc. N.Z., 84 (3 and 4), describes (p. 377) that these small lizards have a home range in the order of some fifteen square yards which may overlap, but defensive territorial behaviour, known in some skinks, is not exhibited. The following observation of combat between two adults is unique in my experience of casual observation over the past twenty years.
At nine o'clock on the bright sunny morning of January 8 two lizards, closely locked head to head and belly to belly, rolled over and over on to a pathway. The lizards separated, commenced circling about six inches apart, each making an occasional quick dart across the circle at the other, apparently attempting to seize the body with the mouth just before the hind legs. When successful, the lizard caught would extend its body to full length and roll away so breaking from the captor. Both were successful in attack and defence on a total together of five attacks in a period of nearly two and a half minutes. The combat was marked by a high sustained speed of action and terminated with the one lizard running into grass followed by the other. Both were gravid females. This incident may have in it some element of the aggressiveness and readiness to attack characteristic of the gravid female of the otherwise docile north American garter snake. Thamnopis sirtalis.
L. R. Richardson