Stage One (fig. 3A, B, H), total length 4.0mm (4.25mm)

The first larval stage (fig. 3A) is described by Gurney (1924: 150–151, fig. 60). The protopod of the 2nd antenna has only one ventral spine. The second spine which Gurney attributes to all larval stages does not appear until stage two. The telson (fig. 3H) is deeply cleft, and comprises two narrow and tapering rami each bearing plumose setae posteriorly. The posterior border of the telson is fringed with fine hairs medially and between each of the inner five pairs of long plumose setae.

The first (outer) seta is smooth and does not articulate with the telson. Gurney (1924) records the second telson seta present as a fine, smooth hair, springing from the base of the third seta—a condition normal among anomuran and thalassinid larvae. This is commonly known as the "thalassinid hair". In the Wellington larvae this seta is conspicuous and fringed with fine hairs along its entire length (fig. 3B). This reduced seta was not seen in the larvae of the Sydney species (Dakin and Colefax, 1940: 180–181, fig. 269a) though specifically looked for by those authors, but is present in the Samoan species (Gurney, 1938), and in J. nocturna (Gurney, 1942, fig. 101b) though missed by Caroli (1924) and by Tattersall (1938).

In J. novaezealandiae the third, fourth and shorter seventh telson setae are each fringed with fine hairs and minute spines along their entire length, but the fourth seta may have two or three large basal spines (fig. 3B). The fifth seta has a row of about ten large, basal spines along both inner and outer margins, but is without fine hairs in this region. Minute spines and fine hairs decreasing in size distally, occur for the remainder of its length. The sixth seta is similar, but large spines without supplementary hairs fringe its outer margin for approximately half its length (fig. 3B).

The armature of these posterior telson setae is of specific significance and must therefore be placed on record. With the lateral cornu of the telson considered as a modified first seta (Gurney, 1924) the telson formula is 7 + 7 setae as is normal in stage one larvae of Anomura and Thalassinidea.

Chromatophore Pattern

Chromatophores of the stage one larva have been illustrated in a previous publication (Wear, 1965; text-fig. 5D). All chromatophores are orange, small, numerous and very diffuse. Concentrations of pigment are found below the eyes, above the mandibles and maxillae, in the basipods and exopods of the 1st and 2nd maxillipeds, in the last four abdominal segments and in the telson. In later larval stages chromatophores appear above the 3rd maxillipeds and the pereiopods.

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Stage Two (fig. 31), total length 4.9mm to 5.3mm (5.15mm to 5.55mm)

The second larval stage has also been described by Gurney. The protopod of the 2nd antenna now has a second spine ventrally. The 1st and 2nd maxillipeds have natatory exopods each with six long plumose setae, and the exopod of the 3rd maxilliped bears four such setae. The telson (fig. 31) is rather more triangular than in stage one and usually bears 10 + 10, 10 + 11 or occasionally 11 + 11 posterior setae. These setae, with the exception of the lateral cornu and the thalassinid hair, usually possess a few marginal basal spines.

Stage Three (fig. 3C, D, E, J), total length 7.4mm to 7.7mm (7.6mm to 7.9mm)

The third larval stage was not present in Gurney's material and has therefore not been described.

The peduncle of the 1st antenna is two-segmented, with eight plumose setae along its inner margin (fig. 3C). The unarmed inner ramus exceeds the length of the outer ramus.

The 2nd antenna possesses a two-segmented protopod, with two ventral spines arising from the anterior margin of the distal segment (fig. 3D). The endopod is three-quarters the length of the exopod (squama) and is without terminal plumose setae, but has a small, ventral subterminal hair. The exopod has 13 or 14 marginal plumose setae (fig. 3D).

The 3rd maxilliped has a natatory exopod with six terminal setae as in stage two, but the endopod is somewhat longer and more robust.

The 1st pereiopod comprises a long rod-like endopod and a natatory, two-segmented exopod with six terminal plumose setae (fig. 3E). The 2nd, 3rd and 4th pereiopods are biramous. The exopod of the 2nd pereiopod is a slender unsegmented rod without setae, and those of the 3rd and 4th pereiopods are undeveloped buds (fig. 3E).

The telson is now separate from the 6th abdominal segment which has ventral procurved hooks similar to those of the first five segments (fig. 3J). There is no sign of pleopods. Uropods are present but the endopod and exopod have not separated from the protopod. The exopod has about 12 marginal setae but no lateral tooth, and the much smaller endopod has about four marginal setae (fig. 3J). The telson is broadly triangular, with the concave posterior margin having 11 or 12 pairs of setae including those of the slender posterolateral cornua. The third visible pair of setae (probably the original 4th setae) is now smooth, has lost articulation with the telson and migrated towards the cornua giving the posterolateral angles a more or less bifurcate appearance. Within this bifurcation of the lateral process (1st seta) and the third visible pair of setae, the second seta is reduced to a small spine. This spine is probably the third seta of stage two, as the thalassinid hair is now absent. The inner eight (or nine) pairs of setae which articulate with the telson, each have a few marginal basal spines.

It is in the third and subsequent larval stages of J. novaezealandiae in which the telson bifurcates at the posterolateral angles, that specific distinction from the later stage larvae of J. nocturna, the Sydney species and Kurian's Adriatic species becomes really apparent. In these latter three species the posterolateral cornu of the telson remains as a single process.

Stage Four (fig. 3K), total length 9.3mm to 10.0mm (9.45mm to 10.15mm)

The stage four larvae of Jaxea novaezealandiae agree in essential detail with the larva Gurney describes as stage three. However the following additional points have been noted.

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The endopod of the 2nd antenna does not exceed the length of the exopod as in Gurney's larva, but the two rami are subequal. The 2nd pereiopod has a natatory exopod with four or six terminal plumose setae. Pleopod buds are not usually visible, but in occasional larvae tiny pleopod rudiments may be seen on segments two to five. The telson is more usually of the form shown in fig. 3K rather than that drawn by Gurney (1924: 152, fig. 61g). The "serrations" present on the lateral distal third of the telson are in fact stout spines, each having a definite articulation with the telson (fig. 3K). These spines vary in number between four and seven, but larvae are rarely found with an equal number of these spines on each side of the telson. Telson spines of this type are rare among thalassinid larvae, and certainly unique in the Laomediidae.

Stage Five (fig. 3L, M), total length 11.6mm to 12.5mm (11.75mm to 12.65mm)

This stage agrees with Gurney's stage four. The third (unarmed) telson setae only rarely extend beyond the tips of the outermost pair (fig. 3M). However, this trend become more obvious in the sixth larval stage (fig. 3N).

Stage Six (fig. 3N), total length 13.8mm to 15.2mm (14.1mm to 15.5mm)

This stage agrees with Gurney's stage five. The third telson setae now extend well beyond the outermost pair. This sixth stage is abundant in the plankton, and is probably the final trachelifer stage in the life history, as the first post-larval stage was obtained from these in the laboratory. There are also six stages in J. nocturna (Caroli, 1924) and in the Sydney species (Dakin and Colefax, 1940). Although post-larvae were not obtained by Dakin and Colefax, their sixth larval stage (15mm in total length) is at a similar stage of development to J. novaezealandiae stage six, and it is not expected that further trachelifer stages would follow in the Sydney species.

Stage Six A (fig. 3F, G), total length 15.5mm to 17.0mm (15.9mm to 17.4mm)

Stage six a was not seen by Gurney. This larva differs from stage six in the following characters.

The endopod of the 2nd antenna extends beyond the 1st antenna, and the segments of the endopod are visible beneath the cuticle (fig. 3G). The pereiopods have increased in size and are visibly segmented beneath the cuticle. The abdominal pleopods are now long biramous rods without setae (fig. 3F) and are longer than half the length of the abdominal segments. The telson is similar to that of stage six, but the third telson setae are more strongly developed than the first setae which are now relatively reduced and subterminal.

The status of this six a trachelifer stage is uncertain, but it is not regarded as an essential stage in the larval life history of J. novaezealandiae. Stage six a was obtained by moult in the laboratory but is extremely rare in the plankton, and it seems probable that the majority of larvae bypass this stage and moult directly from stage six to the first post-larval stage. Stage six larvae showed no sign of a further trachelifer stage beneath the cuticle. However, larvae at a stage of development intermediate between stages five and six were found rarely in the plankton. These showed a further trachelifer moult beneath the cuticle, and although the casts of larvae from which the original stage six a larvae were obtained in the laboratory were unfortunately destroyed, it is likely that stage six a follows this intermediate stage between five and six. This alternative route to the first post-larval stage appears to be taken only rarely.

Dakin and Colefax (1940) have recognised at least three distinct Indo-Pacific species of Jaxea, viz., a New Zealand species (Jaxea novaezealandiae) of which the adult and larval stages are now fully described, a "Sydney" species from New South Wales of which only the trachelifer larval stages are known, and Jaxea sp. from Samoa, which is known only from its first larval stage. Two species are known from the northern hemisphere. These are J. nocturna from the Mediterranean and North Atlantic with both the adult and larvae described and a distinct species from the Adriatic Sea known only from a single sixth stage larva.

The larvae of all five "species" appear to be distinct though closely interrelated. Characters by which these larvae may be separated in the first zoeal stage are given in the key below. The separation of stage one larvae of the five species attributed to the genus Jaxea is difficult, as published descriptions show the first stage larvae to be closely similar. However, specific differences become more apparent in later larval stages. For example, in the unnamed Australian species and the New Zealand species, J. novaezealandiae, stage one larvae are almost identical, but the later stage larvae of these two species are quite distinct, especially in the form and armature of the telson.

The significance of observations on the presence or absence of the reduced second telson seta (thalassinid hair) is not clear. Though not recorded by Dakin and Colefax (1940) for the Sydney larvae, it is known to occur in J. novaezealandiae, the Samoan species (Gurney, 1938) and in J. nocturna (Gurney, 1942). The armature of the telson in stage six of the Adriatic species (Kurian, 1956) suggests that it may also occur in the early larval stages of that species.

In J. novaezealandiae it is, however, important to discuss the derivation of the posterior telson process which loses its articulation with the telson in stage three, and enlarges greatly in subsequent larval stages forming the inner ramus of the bifurcated posterior telson cornu. This seta can be seen beneath the cuticle of second stage larvae about to moult, and appears to be the fourth seta. In stage three larvae the third seta is reduced to a small stout spine within the bifurcated cornu. The thalassinid hair of stage two is apparently lost in the third and subsequent larval stages. Enlargement of the fourth seta occurs in the Euphausiacea, Penaeidea, later stage Thalassinidea (Upogebia, Callianassa etc., see fig. 4) and Anomura, but is most pronounced in the Brachyura in which it forms the greater part of the fork of the telson (Gurney, 1942). This character has therefore been paralleled in Jaxea novaezealandiae.

However, among the Laomediidae of which later stage larvae are known (with the exception of J. novaezealandiae) no such enlargement of the fourth seta is immediately obvious (fig. 4 I-N), as the lateral cornua of the telson are of one process as in the Brachyura. The lateral cornua of the laomediid telson are considered by many authors to be modified first setae (Caroli, 1924; Gurney, 1942; Kurian, 1956; Dakin and Colefax, 1940), and the two or three small spines usually found on the posterolateral margins in late stage laomediid larvae (fig. 4 H-N) are thought to be accessory developments. These spines are admittedly accessory developments in J. novaezealandiae (fig. 4H), and also in J. nocturna (fig. 4K) where they are medial to the lateral cornu. However, in other laomediid larvae (fig. 4I, J, L-N) these posterolateral spines may be the first, second and third telson setae in a more advanced stage of reduction than that shown by the Callianassidae and Axiidae in which the fourth seta enlarges, and the first, second and third setae are reduced to conspicuous lateral sub-terminal telson spines in later larval stages (fig. 4 A-G).

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In the Laomediidae, therefore, the uniramous telson cornua of the third and subsequent larval stages may in fact be the true fourth setae, in which case the persistence of comparatively well-developed telson setae lateral to the fourth in Jaxea novaezealandiae (fig. 4H) is a rather more primitive condition.

In possessing at least six and occasionally a seventh stage (six a) in the larval life history, Jaxea novaezealandiae passes through a much longer series of ecdyses than do the majority of the Reptantia where the usual number of larval stages is three, rarely four or five. Gurney (1924) comments on this fact, but was unable to establish whether or not the entire series was passed through by a single larva. From laboratory rearing this now appears likely, at least for the first six stages.

Key to First Stage Larvae of the Genus Jaxea

Stage one larvae of four species are known, but a fifth species from the Adriatic Sea is known only from a stage six larva (Kurian, 1956). I have therefore deduced key stage one characters of this species from Kurian's description (see footnote p. 21) in order that the five known larval species may be separated in the first zoeal stage. A complete series of larval stages has been described for the Australian species (Dakin and Colefax, 1940), for Jaxea nocturna Nardo (Claus, 1884; Brook, 1889; Cano, 1891; Bouvier, 1914; Caroli, 1924; Tattersall, 1938; Gurney, 1942; Kurian, 1956) and for J. novaezealandiae, but the Samoan species is known only from a stage one larva (Gurney, 1938).

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1 (8)	Total length greater than 3.0mm.
2 (5)	Lateral pleural process of 1st abdominal somite absent or present as a small blunt structure.
3 (4)	Rostrum present, small, not extending beyond anterior margin of eye; basis of 2nd antenna with two ventral spines; 3rd maxilliped a long uniramous rod; lateral pleural process of 1st abdominal somite absent; 7th telson seta (5th long seta) having outer margin with fine hairs along its proximal half, and small spines along its distal half	Jaxea nocturna Nardo (Caroli, 1924, etc.)
4 (3)	Rostrum absent; basis of 2nd antenna with one ventral spine; 3rd maxilliped a bud-like rudiment; lateral pleural process of 1st abdominal somite present, but small and blunt; 7th telson seta having outer margin without fine hairs, but with small spines along entire length	Jaxea sp.—Samoa (Gurney, 1938: 333–334, fig. 35)
5 (2)	Lateral pleural process of 1st abdominal somite well developed, sharp and procurved.
6 (7)	Rostrum short, extending to anterior margin of eye or just beyond; thalassinid hair absent; all 5 inner pairs of posterior telson setae having spines along both inner and outer margins of basal third, but with fine hairs distally; posterior border of telson with fine hairs medially, and between 2nd and 3rd long plumose setae only	Jaxea sp.—Sydney Harbour, Australia (Dakin and Colefax, 1940: 179–182, figs. 268, 269)
7 (6)	Rostrum longer, extending beyond eye by about half length of eye; thalassinid hair present, conspicuous and plumose; 6th, 5th and occasionally 4th telson setae having large basal spines along inner and outer margins extending along outer proximal half of 6th seta; no hairs occurring together with large spines; otherwise minute spines and fine hairs decreasing in size distally along entire inner and outer margins of 7th, 6th, 5th, 4th and 3rd telson setae; posterior border of telson with fine hairs medially and between all five pairs of long plumose setae	Jaxea novaezealandiae (fig. 3A, B, H)
8 (1)	Total length probably less than 3.0mm*	Jaxea sp.—Adriatic Sea (Kurian, 1956: 75, figs. 144–146)