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The Holothurian Fauna of Cook Strait, New Zealand

Subfamily Colochirinae

Subfamily Colochirinae

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).

Key to the Cook Strait Genera in Subfamily Colochirinae
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).

page 28
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.

"Ludwigia"

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).

Key to the Species in Genus Heterothyone Panning
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.

Calcareous deposits:

1. Large Scales (Plate VI, figs. 5, 7): The body is completely invested in calcareous scales which are approximately oval in shape. The average greatest length of these scales page 30
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.

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.

page 31 is 1.0mm, but there is some considerable size variation. The surfaces of the scales are reticulate, and carry small knobs (Plate VI, fig. 7). In general, the free edges of these overlapping scales face the posterior end in the posterior half of the body, and the anterior end in the anterior half of the body.

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.