Tuatara: Volume 3, Issue 1, May 1950
A Guide to the Holothurians of New Zealand
A Guide to the Holothurians of New Zealand
Holothurians or sea cucumbers form a class whose members are strikingly different from those of the other classes of Echinoderms. They have been distinct for a great length of time, as clearly recognisable holothurians ( Eothuria) are known from the Upper Ordovician of Girvan, Scotland. These very ancient specimens show more features in common with the Echinoidea than are shown by any recent holothurians and in particular have a test of loosely fitting plates, even in the adult. In recent forms there is a reduction of the calcareous test to the form of small bodies of varied shape embedded in the body wall and not imposing the rigidity of structure so characteristic of the other Echinoderms. As a consequence holothurians are soft bodied, many being worm-like and unattractive in appearance and the group is less frequently noted or gathered by collectors than are the other Echinoderms. Only one species, the rather conspicuous, mottled brown Stichopus mollis, found below the low tide level in Cook Strait and Stewart Island is commonly recognised in New Zealand as a sea cucumber and it is just as frequently referred to as a “sea-slug.”
Representatives of the class are, however, known from a variety of habitats on the sea floor, ranging from the intertidal zone to the greatest depths from which dredgings have been obtained. In and a little below the intertidal zone in tropical waters, especially in coral reefs, holothurians are often large, or vividly coloured and comprise a conspicuous part of the fauna. Some of the larger species are important as beche-de-mer or trepang, whose sun dried bodies form an important item of food for a number of Oriental peoples. Most of the abyssal holothurians belong to the order Elasipoda which is not known from shallower water and so cannot strictly be included in the fauna of New Zealand. One small group, the Pelagothuriidae, are the only holothurians in which the adult is adapted for swimming, but so far no Pelagothuria has been taken in New Zealand waters.
Most of the New Zealand species are rather small and inconspicuous or live buried in sand and mud, and can only be found by careful searching, while many are as yet only known from deeper water. Some of the latter have been thrown up on beaches, occasionally in enormous numbers after heavy storms and have become known in this way, while others have only been collected by dredging in deeper water. From all these habitats the total number of holothurians described for New Zealand (including the Auckland and Campbell islands) is twenty-nine, and a distinctive variety of one of these species has also been described. All these species are included in the present key. Other species may possibly be found by careful searching in the intertidal zone, and it is highly probable that systematic dredging round the New Zealand coast would reveal quite a number of holothurians not yet recorded.
Our present knowledge of the New Zealand species began with the description of eight species by Hutton in 1872 and three more in 1878, but he did not describe calcareous deposits in either of these papers. The main foundation for the knowledge of New Zealand holothurians was laid with more detailed accounts by Dendy (1896) and Dendy and Hindle (1907). A number of smaller papers by other authors have appeared and are cited by Mortensen (1925) who made a careful revision of nearly all the previously known species and added ten new ones from the material collected during his stay in New Zealand in 1915. This brought the New Zealand total to its present number.
The identification of holothurians by external features is made difficult by their tendency to contract strongly, and to withdraw tentacles and tube feet on preservation. In this state it is very difficult to gauge accurately the size of the living animal and many species then appear very similar externally, although it is usually possible to determine the main group to which they belong. The difficulty can be partially overcome by narcotising the animal in sea water to which Epsom salts is added. In this they usually extend and when completely narcotised they should be preserved in alcohol. Lengths given in this key are for specimens extended in this way. For the more precise identification of holothurians it is usually necessary to examine the shape and relative numbers of the small calcareous particles in the body wall. This can be done by treating a piece of the body wall with a solution of bleaching powder (sodium hypochlorite) and then examining it under a microscope. By this means it is also possible to see the arrangement of the calcareous particles. If the body wall is thick, the particles can be separated out by gently boiling a small piece in a 5 per cent, solution of caustic potash, until the softer portions are macerated away, leaving only the calcareous particles. These may vary in shape even within a single individual, and changes during the life of the animal are known in some species. In spite of this there is sufficient distinctiveness between the species in the shapes, sizes and arrangements of these particles to make them the most important of the diagnostic characters for identifying holothurians. Identifications arrived at by other means should, if possible, be checked against a detailed account of the spiculation of that species. Excellent descriptions of a number of species and references to papers decribing the remainder are given by Mortensen (1925) Vid. Medd. Dansk. naturh. For., 79, p322 et.seq. Name changes introduced by H. L. Clark since Mortensen's account are Mensamaria bicolumnata (formerly Pseudocucumis bicolumnatus), M. thomsoni (formerly P. thomsoni) and Lipotrapeza dearmatus (formerly Phyllophorus dearmatus).
The locality records given in this key are for points from which the species has definitely been collected and are not meant to imply that the species is confined to those localities. Further collecting will doubtless show that a number of species are considerably more widespread than is known at present.
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Explanation of Plates.
Plate 1.
These figures are not drawn to the same scale; sizes are given in the key. Fig. 1. Anterior end of
Stichopus mollis showing ventral side bearing tube feet, and the tentacles with disc shaped tips (T) surrounding the slit like mouth. Fig. 2.
Psolus neozelanicus, dorsal side showing imbricating scales. Fig. 3.
Psclidiella nigra, latero-ventral view showing distinct light coloured sole bearing tube feet round the edge and a double row along the centre. Fig. 4.
Cucumaria ocnoides, side view showing tube feet restricted to three rows (two showing) in the middle third of the body. Fig. 5.
Paracaudina coriacea. Fig. 6. Profuse branching found in the tentacles of Order
Dendrochirota. In preserved material the branching may appear to be much more crowded than illustrated. Fig. 7. Finger like processes of tentacle typical of many of the Order
Apoda. Fig. 8.
Trochodota dendyi.
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Plate 2.
Fig. 9.
Cucumaria bollonsi, buttons and cups from the skin. Fig. 10.
C. brevidentis, a button. Fig 11.
C. calcarea, a button. Fig. 12.
C. farquhari, A. part of large scale; B. cup. Fig 13.
C. amokurae, A. large scale from side of the body; B. × shaped bodies. Fig. 14.
Mensamaria bicolumnata, tables bearing a double spire. Fig. 15.
Phyllophorus longidentis, plates bearing a double spine. Fig. 16.
Paracaudina coriacea, a rounded plate. Fig. 17.
Molpadia marenzelleri. A. anchor plate; B. anchor; C. perforated plate bearing spine; D. phosphatic concretion. Fig 18. Wheel as found in many of the Order
Apoda. Fig. 19. Hook or sigmoid body as found in
Trochodota. Fig. 20.
Protankyra uncinata, A. anchor; B. tentacle bearing two pairs of finger like processes, and sensory cups on the stalk. Fig. 11.
Chirodota nigra, smooth oval bodies found along the muscle radii. Fig. 22.
Chirodota gigas, thick curved rods from along the radii. (Figs. 2, 9, 12, 13, 20, after Mortensen; figs. 14, 22, after Dendy and Hindle; fig. 17 after Theel.)