The Holothurian Fauna of Cook Strait, New Zealand
Diagnosis: Tubefeet present, tentacles tree-shaped, profusely branched. Retractor muscles usually present. Mesentery of the posterior loop of the intestine in the right or left ventral interradius. Gonads on both sides of the dorsal mesentery. Respiratory trees present. Deposits usually irregular fenestrated plates, sometimes tables.
The Order Dendrochirotida is cosmopolitan, containing predominantly shallow water forms, but a number of species are found in deeper waters, especially in the Arctic region. The numerous species in this order feed selectively on planktonic organisms or detrital material.
There are three families, of which two are represented in Cook Strait. The third family (Psolidae) has two representatives in the New Zealand region, namely Psolus neozelanicus Mortensen which is known from off North Cape, and Pseudopsolus macquariensis (Dendy) recorded from Macquarie Island and Stewart Island.
|1||(4)||Body cylindrical or fusiform, without a well-defined ventral sole.|
|2||(3)||Tentacles 10||Fam. CUCUMARIIDAE|
|3||(2)||Tentacles 15 to 30||Fam. PHYLLOPHORIDAE|
|4||(1)||Body flattened, with a well-defined ventral sole. Mouth and anus dorsal||Fam. PSOLIDAE|
Diagnosis: Tentacles 15–30. usually in two or even three circles, the inner circles having smaller tentacles. Calcareous ring well developed, with or without forked processes.
Heding and Panning (1954) revised the Phyllophoridae and diagnosed five subfamilies. Of these subfamilies, two have representatives in Cook Strait.
|1||(2)||Calcareous ring without posterior processes. The individual pieces of the ring are undivided||Subfamily Thyonidiinae|
|2||(1)||Calcareous ring complex, composed of a mosaic of minute pieces||Subfamily Semperiellinae|
Diagnosis: Calcareous ring without posterior processes. The individual pieces of the ring are undivided.
Heding and Panning (1954) listed 13 genera in this subfamily. A new genus was described from Cook Strait by the writer (Pawson, 1962), thus increasing the number of genera to 14.
Neocucumella Pawson, 1962
Diagnosis: Tentacles 20 (outer ring with five pairs of larger tentacles, interradial; inner ring with five pairs of smaller tentacles, radial). Tubefeet confined to the radii, arranged in double rows. Radial pieces of the calcareous ring each with a deep median anterior notch. Interradials rounded anteriorly. Calcareous deposits numerous two-pillared tables, with symmetrical circular or elliptical bases, 0.05mm in average length, perforated by four large and four small (alternating) holes.
Neocucumella bicolumnata (Dendy and Hindle) Plate III. figs. 1–3
- Pseudocucumis bicolumnatus Dendy and Hindle, 1907, p. 106, Pl. 11, fig. 6, Pl. 12, figs. 13–14; Joshua and Creed, 1915, p. 19; Engel, 1933, p. 36.
- Mensamaria bicolumnata Clark, 1946, p. 406; Dawbin, 1950, p. 38.
- Neocucumella bicolumnata Pawson, 1962, p. 65, figs. 1–2.
- Non: Amphicyclus thomsoni (Hutton).
Material Examined: VUZ 64, off Point Howard Wharf, 5 fathoms, blue mud, 1 specimen.
Diagnosis: Shape fusiform. Colour light brown. Tubefeet dark brown. Tentacles reddish-brown.
Description: The single specimen is 30mm in total length, and the body is attenuated posteriorly to form a more or less distinct "tail" region. The anterior end narrows as an introvert which carries the crown of 20 tentacles. The body wall is quite thin but opaque, and there is some transverse wrinkling near the posterior end.
Colour in alcohol light brown. The tubefeet are dark brown and the tentacles are dark reddish-brown. The tubefeet are confined to the five ambulacra, where they are arranged in double rows. There are no tubefeet on the introvert. Near the extreme posterior end of the body they are more scattered, and the double row arrangement is lost.
Two rings of richly branched tentacles surround the mouth. The outer ring has five pairs of large tentacles 4—5mm in length, lying in an interradial position, while the inner ring has five pairs of small tentacles, 1mm in length, radially placed. The mid-dorsal pair of larger tentacles are smaller than the other outer ring tentacles.
The calcareous ring is composed of ten simple pieces. Each radial piece is approximately rectangular in shape and has a wide and deep posterior notch and a pronounced median anterior notch. There are no anterior processes on the radials. Interradials are Y-shaped, with the tail of the "Y" directed anteriorly. This anterior projection is bluntly rounded. Length of each radial piece 2.0mm; length of each interradial piece 1.0mm.
The internal anatomy has been described by Dendy and Hindle (1907).
Calcareous deposits of three types were found:
1. Tables: The skin contains very large numbers of tables, closely aggregated together. In general the table disc is oval in shape, and has eight perforations, four large (approximately 0.013mm diameter) and four small (approximately 0.007mm diameter). Average table length is 0.05mm, breadth 0.03mm (Plate III, fig. 1). Departures from this basic pattern are so rare that only three tables of unusual shape were found (Pl. III, fig. 3). At its centre the disc of each table carries two short pillars, which are joined at the top by a single crossbar. Average height of pillars is 0.02mm.
2. Tentacle deposits: The digits of the tentacles contain large numbers of rod-like deposits (Pl. III, fig. 2). The extremities of the rods are expanded and carry a number of perforations (up to 20 in each rod). Average length of the tentacle rods is 0.06mm. No unperforated rods were found.
3. Tubefoot deposits: The tubefeet carry well developed endplates in their sucking discs.
Distribution: The type specimen was recorded from "off Dunedin" (Dendy and Hindle, 1907). Joshua and Creed (1915) recorded a specimen from Australia, probably collected near Adelaide. The new record, Wellington Harbour, enlarges the distribution area of the species, but N. bicolumnata is still a rare species.
Discussion: Dendy and Hindle (1907) described an S-shaped intestine, feebly developed respiratory trees, a single Polian vesicle, and gonads consisting of two bunches of very long filaments in their specimen of this species..
The systematic historv of N. bicolumnata has already been outlined (Pawson. 1962).
Diagnosis: Calcareous ring tube-shaped with long processes; both radials and interradials are composed of a complex mosaic of small pieces.
Heding and Panning (1954) included five genera in this group, of which two are represented in the Cook Strait region.
|1||(2)||Deposits (when present) small tables, typically with eight perforations, and a short blunt two-pillared spire||Neothyonidium Deichmann|
|2||(1)||Deposits perforated plates, with a long, sharp spire composed of two long rods fused together||Pentadactyla Hutton|
Neothyonidium Deichmann, 1938
Diagnosis: Dendrochirote holothurians with 20 tentacles which are arranged in pairs. Calcareous ring complex. Radials with long posterior processes. Deposits tables with two columns. (Heding and Panning, 1954, in part.)
Type Species: Neothyonidium hawaiiense (Fisher).
A single species, N. dearmatum is known from New Zealand at the present time.
Neothyonidium dearmatum (Dendy and Hindle)
- Phyllophorus dearmatus Dendy and Hindle, 1907, p. 103, Pl. 11, figs. 7–8, Pl. 12, fig. 15, Pl. 13, fig. 20; Joshua, 1914, p. 4; Mortensen, 1925, p. 353, figs. 36–37; Clark, 1938, p. 494.
- Lipotrapeza dearmatus Clark, 1946, p. 411.
- Neothyonidium dearmatum Heding and Panning, 1954, p. 191, fig. 93.
Diagnosis: Calcareous deposits usually absent from the skin, apart from the anal extremity, where they take the form of two-pillared tables (average length 0.07mm), typically with eight perforations, four large alternating with four small.
Discussion: This interesting species has been recorded from Akaroa Harbour (Dendy and Hindle, 1907), and Wellington Harbour (Mortensen, 1925). Joshua (1914) reported the presence of specimens at various points along the south coast of Australia.
Pentadactyla Hutton, 1878
Diagnosis: Medium-sized dendrochirotes with 20 tentacles in two rings. Tubefeet distributed evenly over the body. Deposits in the skin either spired tables of irregular shape with rough tapered spires, or smooth, shiny lattice-plates.
Pentadactyla longidentis (Hutton) Plate V
- Thyone longidentis Hutton, 1872, p. 16; Theel, 1886, p. 141.
- Thyone caudata Hutton, 1872, p. 16.
- Pentadactyla longidentis Hutton, 1878, p. 307; Heding and Panning, 1954, p. 199.
- Thyonidium rugosum Theel, 1886, p. 95, Pl. V, fig. 5.
- Thyonidium caudatum Theel. 1886, p. 147.
- Thyonidium longidentis Dendy, 1896, p. 42, Pl. VI, figs. 62–69; Farquhar, 1898, p. 326.
- Phyllophorus longidentis Ludwig, 1898, p. 49; Dendy and Hindle, 1907, p. 101, Pl. 13, fig. 18 a-d; Benham, 1909, p. 28; Mortensen, 1925, p. 325; Dawbin, 1950, p. 39, Pl. 2, fig. 15.
- Thyonidium anatinum Perrier, 1903, p. 142.
- Phyllophorus anatinus Perrier, 1905, p. 112, Pl. V, figs. 1–9.
Material Examined: VUZ 15, Palliser Bay, 100–150 fathoms, mud, 1 specimen; VUZ 32, off Petone Beach, 8 fathoms, mud, 2 specimens; VUZ 37, off Shelly Bay, 10–11 fathoms, 1 specimen; VUZ 64, off Point Howard Wharf, 5 fathoms, blue mud, 6 specimens; VUZ 69, Somes Is. to Days Bay, 11 fathoms, mud, 1 specimen; VUZ 87, South of Cape Palliser, 400 fathoms, mud, rock, gravel, 2 specimens.
Diagnosis: Colour dark brown in life and in alcohol. Calcareous deposits in the form of very numerous oval to cruciform spired plates 0.3mm long, together with smooth plates 0.5mm in length. Polian vesicle single, bulbous.
Description: These are stout holothurians, with a total length varying between 20mm and 70mm. The body tapers abruptly posteriorly to form a more or less distinct tail. There is, however, considerable variation in shape, depending on the degree of contraction of specimens. The body carries a number of short (1–3mm long) spinous projections scattered over its surface. These projections render the skin prickly to touch.
The colour is dark brown in life and in alcohol. The anterior and posterior extremities are lighter in colour, and the tentacles are greyish-white, with small brown-red spots.
An introvert, usually retracted, is present, and carries a crown of 20 tentacles which are disposed in two circles. The outer ring has five pairs of large (4mm long) interradial tentacles, while the inner ring has five pairs of small (l-2mm long) radial tentacles. The mouth lies in a shallow depression in the centre of an oral disc. The introvert is thin-walled and transparent, and carries double rows of tubefeet on the radii.page 25
Plate V.—Pentadactyla longidentis (Hutton).—Fig. 1, internal anatomy of adult dissected from the dorsal side (portions of gonad removed); fig. 2, pharynx and calcareous ring of a large specimen; fig. 3, deposits from a tubefoot; fig. 4, bodywall deposits; fig. 5, tentacle rods.
Abbreviations: a.n., anterior notch; an., anus; a.p.r., anterior process of radial; cl., cloaca; c.r., calcareous ring; g.d., genital duct; g.tub., genital tubules; int., intestine; ir.p., interradial piece; mad.d., stone canal; mo., mouth; m.f., muscle fibres; oes., oesophagus; p.p.r., posterior process of the radial; P.v., Polian vesicle; r.l.m., radial longitudinal muscle; r.m., retractor muscle; r.p., radial piece; r.resp., right respiratory tree.
The calcareous ring is large, composed of ten pieces, each piece comprising a complex mosaic of small fragments (Pl. V, fig. 2). This ring has been well described by Dendy (1896) and Dendy and Hindle (1907). The ring from the largest specimen differs from that figured by Dendy in some respects. The notched anterior ends of the radial pieces are more rounded (Pl. V, fig. 2), the splits in the radial pieces are much wider in proportion and better defined, and the anterior projections of the interradial pieces are more irregular in outline. The small fragments which are aggregated to form the radial pieces tend toward a rectangular shape, while those in the interradials are polygonal.
A thinwalled oesophagus runs into a long coiled intestine (Pl. V, fig. 1). The rectum is thinwalled and transparent. The cloaca is attached to the inside of the body wall by numerous muscle strands.
The single Polian vesicle is elongate, transparent and bulbous (Pl. V, fig. 1). The stone canal runs anteriorly in the dorsal mesentery, terminating in a nodular madreporite.
Left and right respiratory trees arise from the ventral side of the anterior end of the cloaca, and both extend to the anterior end of the body cavity, where they are attached to the pharynx.
A large mass of dichotomously branching genital caeca lies at the level of the middle of the body. The genital duct is long, and runs anteriorly in the dorsal mesentery close to the body wall (Plate V, fig. 1), opening to the outside in the dorsal interradius, immediately posterior to the outer ring of tentacles. The genital caeca contain large yolky eggs.
Longitudinal muscles are represented as five broad flat straps (Pl. V, fig. 1). Retractor muscles arise from the longitudinal muscles one-third of the way along the body cavity from the anterior end, and they are inserted into the anterior notches of the radial pieces of the calcareous ring (Pl. V, fig. 1). Transverse muscles are visible as fine fibres, but they are not conspicuous.
1. Body wall deposits: The body wall is completely invested in perforated plates, many of which possess a central spire.
The spired plates (Pl. V, fig. 4a) are usually round to oval in adult specimens. In juveniles and some adults the spired deposits tend towards a cruciform shape. Average greatest diameter of the spired plates is 0.3mm. The spire is usually centrally placed on the plate, and is composed of two rods which fuse together near the base. These deposits are so placed in the skin that the spires project above the level of the body wall.
Larger plates which lack spires are also common in the skin. They are elongate (average length 0.5mm), and have larger numbers of perforations than the spired plates (Plate V, fig. 4b).
2. Tubefoot deposits: The tubefeet do not appear to have endplates in the strict sense, but they contain large numbers of deposits, mainly spired plates of varying shape (Plate V, fig. 3).
3. Tentacle deposits: The tentacles contain numerous small rods, some of which are perforated (Plate V, fig. 5). Rod length varies between 0.02mm and 0.1mm.
There are no deposits in the introvert.
Distribution: This species is a prominent member of the holothurian fauna of New Zealand, especially in the Cook Strait region, where it is known to occur in numbers. Specimens have been taken from as far north as Cape Egmont to the west of the North Island, and it is likely that the species is present in the same latitudes to the east. Mortensen (1925) recorded a specimen from Akaroa Harbour in the South Island. Pentadactyla longidentis may yet prove to have a wider distribution than formerly supposed.
Ecology: Preference is shown for a muddy bottom, and specimens have been taken from depths ranging between 3 fathoms and 400 fathoms.
Discussion: The variability of body shape has led to some confusion in the past, some new species having been based on specimens of unusual shape. However this error was rectified by Dendy and Hindle (1907) and Mortensen (1925). The presence of large yolky eggs in the genital caeca leads to the suggestion that this species lacks a pelagic larva and has direct development.
Because of its colour, shape, and the rough texture of the body wall, this species is one of the most easily recognised of the Cook Strait holothurians.
Diagnosis: Tentacles 10, equal, or with a smaller ventral pair. Tubefeet confined to the radii or scattered over the body. The mesentery of the posterior loop of the intestine lies in the left ventral interradius.
About 30% of the known New Zealand holothurian species are placed in this very large family. Panning (1949) revised the group, diagnosing five subfamilies on the basis of calcareous rings and calcareous deposits. Two of these subfamilies have representatives in the Cook Strait region.
|1||(2)||Calcareous rings composed of 10 solid pieces. Calcareous deposits cups and plates||Subfam. Colochirinae|
|2||(1)||Calcareous ring long and slender, the entire ring composed of a complex mosaic of minute pieces||Subfam. Thyoninae|
Diagnosis: Calcareous ring simple, without bifurcated processes, or at the most moderately deep, with short undivided processes. Radials and interradials undivided. In the skin plates and baskets; no tables (After Panning, 1949).
|1||(2)||Body cucumber-shaped, straight. Deposits cups and knobbed plates of two types||Ocnus Forbes|
|2||(1)||Body typically U-shaped. Deposits cups, and large scales of average diameter 1.0mm||Heterothyone Panning|
Ocnus Forbes, 1841
Diagnosis: Calcareous ring simple, without posterior processes. Deposits in the form of knobbed plates and cups. The cups form an investing layer (Panning. 1949, in part). Type Species: Ocnus brunneus (Forbes).
Of the three species of Ocnus known from New Zealand, one, O. calcareus has been recorded from the Cock Strait region.
Ocnus calcareus (Dendy)
- Colochirus calcareus Dendy, 1896, p. 38, Pl. 5, figs. 44–53; Farquhar, 1898, p. 325.
- Colochirus brevidentis Ludwig, 1898, p. 442, taf. 26, figs. 22–29.
- Cucumaria calcarea Mortensen, 1925, p. 335, fig. 26 c-d; Dawbin, 1950, p. 38, Pl. 2, fig. 11.
- Ocnus calcareus Panning, 1949, p. 437.
- Non: Ocnus brevidentis (Hutton).
Diagnosis: Deposits include cups, and knobbed plates of two types, one type with four perforations and 12 marginal knobs, the other type with many small perforations and numerous central and marginal knobs.
Discussion: Although Ocnus calcareus is not a particularly common species it is known from Auckland, Wellington, Stewart Island, and Juan Fernandez Islands. Mortensen (1925) said of this species "as it is a littoral form, which can be transported on floating algae, the occurrence of this species at Juan Fernandez is not so very surprising. But it is to be expected that it will prove to occur also on the other subantarctic localities".
O. calcareus is similar to O. brevidentis (Hutton) in some respects, but the two species differ markedly in the structure of their calcareous deposits, as pointed out by Dendy (1896) and Mortensen (1925).
Heterothyone Panning, 1949
Diagnosis: Calcareous ring composed of 10 solid pieces; radials each with a more or less well developed posterior notch. Deposits include large scales l-2mm in diameter, which invest the body, and well developed deep cups, usually with four perforations.
Type Species: Heterothyone alba.
Also included here: H. ocnoides (Hutton).
Panning (1949) erected the new genus Heterothyone, with species alba as the type, and he also included under this generic name the species pigra (Koehler and Vaney) and semperi (Bell). This genus was placed in Subfamily Thyoninae Panning, which was diagnosed as follows:
"Calcareous ring slender, with long processes; radials and interradials flat, fused together; the entire calcareous ring composed of a complex mosaic of minute pieces" (Panning, 1949).
Dissection of many specimens of the species alba showed that the ring is in fact composed of 10 solid yet fragile pieces. Consequently this species belongs in Subfamily Colochirinae Panning.
Descriptions of the species semperi (Bell, 1884) and pigra (Koehler and Vaney, 1905) point out that the ring in these species is composed of a mosaic of pieces. Thus semperi and pigra should remain in Subfamily Thyoninae, but a new generic name should be supplied. I propose the name Hemithyone for these species, with Hemithyone semperi as the type species.
The species alba is quite closely allied to another New Zealand species originally described as Colochirus ocnoides (Dendy). This has already been pointed out by other workers, including Dendy (1896) and Mortensen (1925). Panning (1949) resurrected Reiffen's (1901) genus Ludwigia for species ocnoides (Reiffen had designated ocnoides as the type of Ludwigia). However, Ludwigia is preoccupied, and the name cannot be used again. Under this generic name Panning (1949) listed 17 species (including ocnoides). Of the 16 species beside ocnoides, none appear to possess the large imbricating scales investing the body which are so characteristic of the species ocnoides and alba. In this respect, and in others, the two New Zealand species are distinct and I have placed them together in genus Heterothyone, and transferred the genus to Subfamily Colochirinae.
The 16 species included in Ludwigia by Panning (1949) are listed below. These may have to be assigned to new genera in due course. I am not in a position to critically examine these species, but study of the literature shows that they tend to fall into two categories on the basis of their calcareous deposits. It must be pointed out that descriptions of some of these species are inadequate.
Species which have buttons with four holes: spyridophora (Clark); vicaria (Bell); lefevrei (Barrois); tetracentriophora (Heding); punctata (Ludwig); solida (Deichmann); gemmata (Pourtales); pervicax (Theel); suspecta (Ludwig).
Species which have buttons with more than four holes, or none: lactea (Forbes); planci (Brandt); glacialis (Ljungman); hedingi (Panning); lutea (Sluiter); bouvetensis (Heding); ekmani (Heding).
|1||(2)||Small holothurians (up to 30mm long); radials with a poorly defined anterior notch; interradials with long and narrow anterior processes||H alba (Hutton)page 29|
|2||(1)||Larger holothurians (up to 60mm long); radials each with a well defined anterior notch; interradials with short and broad anterior processes||H. ocnoides (Dendy)|
Heterothyone alba (Hutton) Plate VI
- Chiridota alba Hutton, 1872, p. 17.
- Echinocucumis alba Hutton, 1878, p. 307.
- Colochirus alba Dendy, 1896, p. 35, Pl. 4, figs. 21–32; Farquhar, 1898, p. 325.
- Cucumaria alba Ludwig, 1898, p. 29; Perrier, 1905, p. 85; Dendy and Hindle, 1907, p. 98; Mortensen, 1925, p. 346; Dawbin, 1950, p. 36.
- Cucumaria filholi Perrier, 1903, p. 144; Perrier, 1905, p. 88, Pl. V, figs. 10–12.
- Heterothyone alba Panning, 1949, p. 464, abb. 59, figs. a-i.
Material Examined: VUZ 15, Palliser Bay, 100–150 fathoms, mud, 1 specimen; VUZ 30, off Somes Island, 5–10 fathoms, mud, 13 specimens; VUZ 69, Somes Island to Days Bay, 11 fathoms, mud, 1 specimen; Kau Bay, 20 fathoms, mud, 1 specimen.
Diagnosis: Small, U-shaped, colour white in life. Radials with a poorly defined anterior notch; interradials with long and narrow (almostneedle-like) anterior processes. Deposits scales and deep cups. The cup rims carry many small projections.
Description: These are pure white to grey holothurians, almost invariably U-shaped, with the ventral surface occupying the greater curvature. The total length varies between 10mm and 25mm. The tentacles are retracted in all specimens, and the anterior end of the body is bluntly rounded. Toward the posterior end, the body tapers gently to form a slender tail. The body wall is thick and firm, due to the investing layer of imbricating scales.
There are ten tentacles, the ventral pair being the smallest. They are grey, covered with dark brown spots. The crown of tentacles is carried on a short, thinwalled introvert.
Tubefeet are numerous, confined to the radii anteriorly and posteriorly, but scattered in radii and interradii on the ventral surface of the middle of the body, in greater numbers than elsewhere. These tubefeet are stiff, and not completely retractile, their walls containing large numbers of perforated rods.
The calcareous ring is composed of ten pieces, five radials and five interradials (Plate VI, fig. 4). The radials each have a well developed anterior process with an attachment area for the radial muscle and a poorly defined median split. The posterior process of the radial is long and broad, with a shallow but distinct V-shaped posterior notch. Each inter-radial piece is Y-shaped, with the tail of the "Y" directed anteriorly.
A short thinwalled oesophagus leads into the thinwalled intestine, which is extensively coiled near the middle of the body (Pl. VI, fig. 1). The rectum runs direct to the terminal anus and the cloaca is undifferentiated. Both intestine and rectum are dark brown in colour.
The water-vascular system surrounds the oesophagus immediately posterior to the calcareous ring (Plate VI, fig. 1), and gives rise to a single bulbous Polian vesicle from its ventral side (Plate VI, fig. 1). The stone canal is a short coiled white tube, terminating in a minute nodular madreporite which is attached to the dorsal mesentery.
The right respiratory tree is considerably longer than the left, and extends to the extreme anterior end of the body. In some specimens the right tree carries a short subsidiary branch. The left tree is about half as long as the right. Respiratory tubules are long and narrow, branching copiously.
The gonad consists of two small bunches of unbranched genital caeca (Plate VI, fig. 1), which lie half way along the body cavity. As a consequence the genital duct is a long and narrow tube, which runs anteriorly on the dorsal mesentery, opening to the exterior in the introvert, in the dorsal interradius. In some specimens the genital caeca are packed with small eggs (Plate VI, fig. 8), which vary considerably in size (0.05—0.3mm diameter).
Radial longitudinal muscles, retractor muscles and transverse muscles are poorly developed, the radial muscles being represented as thin white straps.
Plate VI.—Heterothyone alba (Hutton).—Fig. 1, internal anatomy of adults; fig. 2, buttons; fig. 3, tentacle deposits; fig. 4, pharynx and calcareous ring; fig. 5, scales from the skin (in outline only); fig. 6, cups; fig. 7, surface features of a scale; fig. 8, genital tubule packed with eggs.
Abbreviations: an., anus; a.p.r., anterior process of radial; c.r., calcareous ring; g.d., genital duct; g.tub., genital tubule; int., intestine; ir.p., interradial piece; l.resp., left respiratory tree; mad., madreporite; mad.d., stone canal; m.f., muscle fibres; oes., oesophagus; ped., pedicel; ph., pharynx; p.p.r., posterior process of radial; P.v., Polian vesicle; re., rectum; r.m., retractor muscle; r.resp., right respiratory tree; r.v., ring vessel; v.t.f., ventral tubefoot.
2. Gups (Plate VI, fig. 6): Deep perforated cups overlie the plates in large numbers. The basin of each cup has four perforations, while the cup rim carries a number of irregular projections. Average diameter of the cups is 0.03mm, and the cups are approximately as deep as they are wide.
3. Buttons (Plate VI, fig. 2): Oval to rectangular smooth buttons, with 5–20 perforations are scattered sparingly among the cups in the body wall. The greatest length of the buttons varies between 0.05 and 0.1mm.
4. Tentacle Deposits (Plate VI, fig. 3): The stems and digits of the tentacles contain large numbers of perforated plates and rods, which show considerable variation in shape and size. The perforated plates reach a length of 0.24mm.
Distribution: Heterothyone alba is one of our best known dendrochirote holothurians. It is restricted to the New Zealand region, where it has been taken in numbers from many points along the east coast of the North and South Islands. The species has not been recorded from any of the outlying islands.
Ecology: This species prefers a sandy to muddy bottom in comparatively sheltered localities. A degree of eurybathy is displayed, specimens having been taken from lowtide level to depths of 150 fathoms.
Discussion: Mortensen (1925) suggested that the small size of the eggs in this species may indicate indirect development, with the presence of a true pelagic larva.
H. alba has but one close relative, H. ocnoides (Dendy), which also has a restricted distribution. The two species differ in size, and in certain features of their calcareous rings and calcareous deposits.
Heterothyone ocnoides (Dendy)
- Colochirus ocnoides Dendy, 1896, p. 36, Pl. 4, figs. 33–43: Farquhar, 1898, p. 325.
- Cucumaria ocnoides Ludwig, 1898, p. 30; Perrier, 1905, p. 96, Pl. 1, figs. 9–13, Pl. V, fig. 13; Dendy and Hindle. 1907, p. 100; Mortensen, 1925. p. 347; Dawbin, 1950, p. 36.
- Ludwigia ocnoides Reiffen, 1901, p. 598, taf. 15; Panning, 1949, p. 435, abb. 30, 31.
Diagnosis: Large (up to 50mm long), U-shaped, colour orange in life. Radials each with a well-defined anterior notch; interradials with short, broad and blunt anterior processes. Deposits scales and deep cups. The cup rims have less than ten projections.
Discussion: This species is known in the Cook Strait region from a single specimen taken in Wellington Harbour at a depth of 5–10 fathoms by Mortensen (1925). Other localities include New Brighton (Dendy, 1896, 1898), Dendy and Hindle (1907), and Cloudy Bay and Akaroa (Mortensen, 1925). Mortensen (1925) suggested that H. ocnoides will prove to have a much wider distribution in New Zealand seas.
Diagnosis: Calcareous ring slender, long, with long processes; radials and interradials flat, the entire ring composed of a complex mosaic of minute pieces (Panning, 1949, in part).
The subfamily Thyoninae is represented in Cook Strait by a single species of the genus Stolus Selenka.
Stolus Selenka, 1867
Diagnosis: Calcareous ring with long processes, composed of a mosaic of minute pieces. Deposits large scales with many perforations, and smaller buttons with few perforations. No cups.
Type Species: Stolus sacellus Selenka.
At the present time, this genus contains less than ten species.
Stolus huttoni (Dendy) Plate VII
- Cucumaria huttoni Dendy, 1896, p. 32, Pl. 3, figs. 19–20; Ludwig, 1898, p. 39; Farquhar, 1898, p. 324; Perrier, 1905, p. 93; Mortensen, 1925, p. 384, figs. 33–35; Dawbin, 1950, p. 36.
- Stolus huttoni Panning, 1949, p. 463, abb. 58.
Material Examined: VUZ 62, opposite Worser Bay, 4–5 fathoms, green sand, 1 specimen.
Diagnosis: Body large (up to 180mm total length), U-shaped, completely invested by large overlapping scales, which are overlain by small perforated buttons 0.01–0.03mm long. Colour grey to yellow.
Description: The single specimen is U-shaped, with a total length of 125mm. The integument is very hard and thick, due to the presence of great numbers of calcareous deposits. The colour in alcohol is yellowish-white. The tentacles are abundantly speckled with brown spots on a grey background.
Tubefeet are present in all radii and confined to them. They are more numerous in the mid-ventral portion of the body, where they are arranged in distinct double rows. A semi-transparent introvert is surmounted by a crown of ten richly branched tentacles, of which the ventral pair is the smallest.
The calcareous ring is complex, each piece being composed of a number of fragments (Plate VII, fig. 2). The radials each have a pronounced anterior notch and long, narrow posterior processes. The interradials are not notched, but do possess long posterior processes.
The oesophagus is short and muscular (Plate VII, fig. 1), and joins to the thinwalled convoluted intestine. The rectum is long and straight and runs to the terminal anus. Two long and slender Polian vesicles are attached to the ventral side of the water-vascular ring (Plate VII, fig. 1). The stone canal is short, and runs anteriorly in the dorsal mesentery to terminate in a conspicuous madreporite (Plate VII, fig. 2).
The two trunks of the respiratory trees arise from near the anterior end of the rectum as flattened tubes.. At the level of the junction between the intestine and the rectum, each trunk divides and gives rise to a long and a short branch. The two long branches extend anteriorly for a considerable distance and attach to the body wall in the interradii. Each trunk carries many short, sparsely branched respiratory tubules (Plate VII, fig. 8).
There are two bunches of intertwining, unbranched, filamentous genital caeca. The genital duct opens into the introvert in the dorsal interradius (Plate VII, fig. 1).
The radial muscles are narrow, especially near the posterior end of the body. They thicken in the anterior half, and are thickest at the point of origin of the retractors, which is about one-third of the way along the body from the anterior end. Transverse muscles are present as fine fibres. All of the muscles are orange coloured in preserved material.
1. Large Scales: The body is completely invested in oval to round imbricating scales (Plate VII, fig. 3), with an average diameter of 1.0mm.
2. Perforated Buttons: Great numbers of perforated buttons overlie the scales (Plate VII, fig. 4). These are 0.1–0.3mm long, and have two to twenty perforations. The presence of these buttons gives the integument a granular appearance.
3. Tubefoot Deposits: The endplate in each tubefoot is surrounded by perforated deposits 0.1–0.25mm in length (Plate VII, fig. 6). They are easily distinguishable from the buttons in the skin as they are not nearly as thick, and are more irregular in outline.
4. Tentacle Deposits: Irregular perforated buttons and rods of varying shape and average length 0.2mm are present in the digits of the tentacles (Plate VII, fig. 7). The tentacles are consequently prickly to touch.
5. Introvert Deposits: The thinwalled introvert contains small perforated buttons of a different character from those in the rest of the body wall (Plate VII, fig. 5). They are oval to rectangular in shape and have few (6–12) perforations. Average length of these buttons is 0.05mm.
Distribution: Stolus huttoni has previously been recorded from Oamaru (Dendy, 1896) and Otago Harbour (Mortensen, 1925). The new locality Wellington Harbour, somewhat extends the area of distribution of this species.
Ecology: Specimens of S. huttoni have been taken from sandy or muddy bottoms in sheltered shallow areas.page 33
Plate VII.—Stolus huttoni (Dendy).—Fig. 1, internal anatomy of adult dissected from the dorsal side; fig. 2, pharynx and calcareous ring; fig. 3, scales from the skin (in outline only); fig. 4, buttons; fig. 5, introvert deposits; fig. 6, tubefoot deposits; fig. 7, tentacle deposits; fig. 8. portion of a respiratory tree.
Abbreviations: a.n., anterior notch; an., anus; cl., cloaca; c.r., calcareous ring; g.d., genital duct; g.tub., genital tubules; int., intestine; ir.p., interradial piece; mad., madreporite; mad.d., stone canal; m.f., muscle fibres; oes., oesophagus; P.v., Polian vesicle; r.l.m., radial longitudinal muscle; r.m., retractor muscle; r.p., radial piece; r.resp., right respiratory tree; r.tub., respiratory tubule; tr.m., transverse muscles.
Discussion: Dendy (1896) stated that the tubefeet are absent from the dorsal radii, and Ludwig (1898) agreed with him. Perrier (1905) found tubefeet on the lateral regions of the dorsal side, and Mortensen (1925) stated that the dorsal tubefeet are inconspicuous "and form only a single irregular zig-zag series". The present writer noted tubefeet in all radii, the dorsal tubefeet appearing to be confined to the middle 1/3 of the body.
There is some variation in the number of Polian vesicles. Dendy (1896) found two in the type specimen. Ludwig (1898) found one, while Mortensen (1925) noted the presence of five long and slender Polian vesicles. The present specimen has two. Therefore no taxonomic importance can be attached to Polian vesicle numbers in this species.
Dendy (1896) figured the calcareous ring of the holotype, but his figure did not show the anterior notches in the radial pieces, nor the bifurcating posterior ends of the interradials.
S. huttoni has no near relatives, either in New Zealand or overseas.