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The Holothurian Fauna of Cook Strait, New Zealand

Family Chiridotidae

Family Chiridotidae

Diagnosis: Calcareous deposits in the form of six-spoked wheels; sigmoid or C-shaped rods may be present. Tentacles with short stalks, becoming widened distally, where they bear 3–10 digits on each side. The digit-bearing portion forms a disc and the tentacles are therefore peltato-digitate.

Clark (1907) noted that the sexes are separate in many species. Sigmoid rods have each end curved in opposite directions, often in planes at right angles to each other. Rods in which the ends are curved inward towards each other are C-shaped or bracket-shaped.

This family comprises mainly small holothurians. The group is world-wide, and most of the species live in the littoral zone. Three genera and six species of Chiridotidae are known from New Zealand, of which three species are found in the Cook Strait region.

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Key to the Cook Strait Genera in Family Chiridotidae
1 (2) Calcareous deposits absent from the body wall Kolostoneura Becher, 1909
2 (1) Wheels present, scattered or arranged into loose heaps, or sometimes so scattered as to be easily overlooked. Sigmoid rods also present in numbers Trochodota Ludwig, 1892

Kolostoneura Becher, 1909

Diagnosis: Calcareous deposits absent from the body wall. Tentacles ten. General features of anatomy similar to those in Trochodota Ludwig.

Type Species: Kolostoneura novae-zealandiae (Dendy and Hindle).

The genus Kolostoneura is monotypic, and Dendy and Hindle (1907) originally placed the species in genus Rhabdomolgus. Becher (1909) proposed a new genus for the New Zealand species to eliminate any suggestion of a genetic relationship with Rhabdomolgus ruber Keferstein, which is known from deeper waters in the Northern Hemisphere. Clark (1921) fully agreed with Becher's decision, and stated that Kolostoneura was probably derived from Trochodota by loss of (1) wheels and (2) sigmoid hooks. Mortensen's (1925) discovery of sigmoid hooks in some specimens from Plimmerton infected by ectoparasitic snails lends support to Clark's thesis.

Kolostoneura forms a parallel to Anapta Semper, which is described as a Leptosynapta Verrill without deposits in the skin, and Achiridota Clark, which is a Chiridota Eschscholtz without deposits (Clark, 1921).

Kolostoneura novae-zealandiae (Dendy and Hindle)
  • Rhabdomolgus novae-zealandiae Dendy and Hindle, 1907, p. 113. Pl. 11, figs. 1–4; Pl. 13, figs. 16–17; Pl. 14, figs. 22–29.
  • Kolostoneura novae-zealandiae Becher, 1909, p. 35; Clark, 1921, p. 164; Mortensen, 1925, p. 383; Dawbin, 1950, p. 40.

Material Examined: Island Bay, intertidal rock pools, 11 specimens, collected by A. D. Allen and D. L. Pawson. 15/7/1959; Napier, muddy tide pool, 3 specimens, collected by D. L. Pawson, 20/5/1959.

Diagnosis: Colour in life pinkish brown to white transparent. White and transparent in alcohol. Tentacles pinnate, occasionally containing calcareous deposits.

Description: Small holothurians, approximately cylindrical in shape, white transparent in alcohol. The radial longitudinal muscles can be clearly seen through the skin. Total length varies between 15mm and 40mm. Each of the ten tentacles gives rise to five pairs of pinnately arranged digits, which increase in length toward the distal extremities of the tentacles.

Dendy and Hindle (1907) gave a very thorough description of the internal anatomy of this species. Mortensen (1925) added that he almost invariably found calcareous deposits in the tentacles.

Distribution: Dendy and Hindle's (1907) specimens were taken from New Brighton Beach, Kaikoura, and Owenga in the Chatham Islands. Mortensen (1925) found specimens at Akaroa, Plimmerton, Takapuna Beach and Stewart Island. The new locality, Napier, leads to the suggestion that K. novae-zealandiae may prove to be present around the entire New Zealand coast. The species is endemic to the New Zealand region.

Ecology: This species has only been taken from the intertidal zone, where it lies concealed under rocks in mud or sand.

Discussion: Examination of the tentacles of all the specimens on hand showed that only two were found to possess calcareous deposits in the tentacles.

K. novae-zealandiae appears to have no near relatives in New Zealand or overseas.

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Trochodota Ludwig, 1892

Diagnosis: Tentacles 10. Digits 2–6 on each side. Polian vesicle single. Calcareous ring of 10 pieces, the radial not perforated. Calcareous deposits sigmoid hooks, scattered, or arranged into groups, and wheels, scattered, never grouped into papillae (Clark, 1907).

Type Species: Trochodota purpurea (Lesson).

This well-defined genus contains in excess of 15 species at the present time. The species are separated on the basis of differences in average wheel size, in the size and arrangement of sigmoid rods, and the size and shape of the tentacle deposits. Some of the known species are closely related to each other and may yet prove to be synonyms.

The greatest concentration of species lies in the Indo-West Pacific region. Two species are known from New Zealand, and both are members of the Cook Strait Holothurian fauna.

Key to the New Zealand Species of Trochodota Ludwig
1 (2) Skin smooth, not papillate, with numerous scattered sigmata and wheels T. dunedinensis (Parker)
2 (1) Skin distinctly papillate. Sigmata arranged into groups in the papillae. Wheels numerous or scarce T. dendyi Mortensen
Trochodota dunedinensis (Parker) Plate I, fig. 1
  • Chiridota dunedinensis Parker, 1881, p. 418; Theel, 1886, p. 34; Dendy, 1896. p. 26. Pl. 3, figs. 1–8; Farquhar, 1898, p. 323.
  • Trochodota dunedinensis Ludwig, 1898, p. 87; Perrier, 1905, p. 123; Clark. 1907, p. 124; Clark. 1921, p. 166; Mortensen, 1925, p. 376, figs. 59b, 60b. 61; John, 1939, p. 315; Dawbin. 1950, p. 40, fig. 19.
  • Chiridota geminifera Dendy and Hindle, 1907, p. 112, Pl. 14, fig. 30.
  • Chiridota benhami Dendy, 1909, p. 151, Pl. 16, fig. 3a-1.
  • Trochodota benhami Clark, 1921. p. 166.
  • Non. Trochodota dunedinensis Allan, 1911, p. 325 (= Trochodota alleni Joshua); Ohshima, 1914, p. 478 (= Trochodota diasema Clark).
  • Chiridota australiana Theel, 1886, p. 16.

Material Examined: Island Bay. intertidal rock pool, 1 specimen, collected by G. W. Gibbs, 11/7/1960.

Diagnosis: Colour in life reddish-brown, darker near the posterior and anterior extremities of the body. Body elongate, cylindrical, smooth, without papillae. Deposits wheels and sigmoid hooks, scattered in the skin. Radials and interradials irregular in shape, notched anteriorly and posteriorly.

Description: These are small holothurians, rarely more than 50mm in length when fully extended. The single specimen in the collection is 35mm in total length; the diameter at the anterior end is 3mm. Colour in life reddish-brown, deepening to a dark brown at the anterior and posterior extremities of the body; the tentacles are transparent, with numerous dark brown spots. Colour in alcohol, yellowish-white and semi-transparent.

The calcareous ring is composed of 12 unsymmetrical pieces. Each piece is narrow, about 1mm in length, with an anterior and a posterior notch. The radials are not perforated and are virtually indistinguishable from the interradials.

The oesophagus is short and thinwalled and enters the intestine which describes an S-shaped loop and runs to the anus. The single Polian vesicle arises from the ventral side of the water-vascular ring. The stone canal is very small and convuluted, lying in the dorsal mesentery, terminating in a minute nodular madreporite.

Gonads consist of a few long and slender tubes which extend almost to the posterior end of the body cavity.

Calcareous deposits of three kinds were found:

1. Wheels: The dorsal side of the body contains numerous six-spoked wheels in the skin, whose diameters range between 0.06mm and 0.16mm, the average diameter being 0.1mm.

2. Sigmoid Hooks: Sigmoid hooks, with an average length of 0.1mm are scattered among the wheels on the dorsal surface of the body. They lie transverse to the longitudinal axis of the body.

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3. Tentacle Rods: The tentacles contain large numbers of small rods 0.02–0.06mm in length. They are irregular in shape and frequently have enlarged extremities (Plate I fig. 1). The rods are scattered in the stems of the tentacles, but in the digits they are arranged in narrow double rows.

Behaviour of a Living Specimen: A living specimen of T. dunedinensis was placed in a dish of seawater, the bottom of which was partly covered by a thick layer of sandy mud. The general behaviour of the specimen was observed for some time.

1. Feeding: The tentacles were pushed into the mud and sand in turn. Small particles of the substrate adhered to the outer surfaces of the tentacles which apparently were covered by a sticky secretion. No particles of sand adhered to the inner surfaces of the tentacles. The tentacles were then rapidly wiped across the mouth one at a time, or pushed into the mouth, and the adhering particles were removed and ingested. While feeding the specimen was fully extended, and waves of contraction passed along the body from time to time. The feeding process took place almost continuously during the time of observation.

2. Defaecation: The anal aperture of the body was completely closed, and the posterior half of the body contracted. Then the anus opened suddenly and egesta emerged in small lumps. No vermiform "casts" were seen. Defaecation took place at irregular intervals.

3. Locomotion: The specimen pulled itself around the walls of its dish by means of its sticky tentacles. There was no tendency to burrow away from strong light, although the animal was photosensitive.

Distribution: Parker (1881) described the type specimen from Otago Harbour. Since that time specimens of this species have been found in many parts of the South Island of New Zealand, the Cook Strait region, Stewart Island, and the Auckland and Campbell Islands (Mortensen, 1925).

Ecology: T. dunedinensis appears to favour comparatively sheltered sandy to muddy localities where it conceals itself under stones or by burrowing.

Discussion: Mortensen (1925) stated that the oral disc is "distinctly oblique in dorso-ventral section" and "the calcareous ring is . . . parallel to the oral disc". The calcareous ring is no doubt asymmetrical owing to its oblique position.

There appears to be some variation in the course of the intestine in this species. Dendy's T. benhami possessed an S-shaped intestine. However Mortensen (1925) noted that in some of the specimens at his disposal the intestine ran straight to the anus, while in others it looped twice, or described an S-shaped path to the anus. He also showed that the other characters for T. benhami given by Dendy (1909) fell within the range of variation of T. dunedinensis.

Dendy (1896) noted that the sexes are separate in this species, and John (1939) observed that the females are viviparous.

Trochodota dunedinensis has certain characters in common with other species of the same genus. Clark (1921) pointed out that it is almost impossible to make an accurate key to the species of the genus without re-examining many of the species. To the writer's knowledge, this has not been done as yet.

Trochodota dendyi Mortensen

Trochodota dendyi Mortensen, 1925, p. 381, figs. 62–63a; Dawbin, 1950, p. 40.

Diagnosis: Colour white or faint purple. Skin papillate, each papilla containing 3–6 sigmoid hooks. Wheels numerous or absent. Tentacle deposits with bifurcating ends.

Distribution: The type specimen was from Plimmerton. The species is also known from Waikeke (Auckland Harbour), and Paterson Inlet (Stewart Island) (Mortensen, 1925). Restricted to the New Zealand region.

Ecology: Known only from the intertidal zone.

Discussion: Mortensen examined nine specimens of this interesting species and after giving a very careful description, he stated that the species is nearly related to Trochodota japonica (v. Marenzeller) but differs in colour, number of sigmoid hooks in each papilla, and in the shape of the tentacle deposits.