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The Holothurian Fauna of Cook Strait, New Zealand

Order Apodida

Order Apodida

Diagnosis: Modified vermiform holothurians with smooth, rough or warty surface. Tubefeet totally lacking, except for the tentacles. Anal papillae, tentacle ampullae, and respiratory trees absent. Tentacles 10 to 20 or even more in number, simple, digitate or pinnate. Characteristic deposits anchors and wheels, though some species lack deposits altogether.

The Order Apodida contains three well defined families, of which two have representatives in Cook Strait.

Key to the Families in Order Apodida
1 (2) Deposits in the form of perforated plates accompanied by anchors Fam. SYNAPTIDAE
2 (1) Deposits include wheels.
3 (4) Wheels with six spokes, together with sigmoid or C-shaped rods. Wheels arranged in papillae, or scattered in the body wall Fam. CHIRIDOTIDAE
4 (3) Wheels complex, with eight or more spokes Fam. MYRIOTROCHIDAE

Family Synaptidae

Diagnosis: Tentacles with the stalks cylindrical or terete, not becoming widened distally, either with digits along each side for most of their length (pinnate), or with only one or two digits along each side near the tip (digitate), or without digits at all (simple). Calcareous deposits usually anchors and perforated plates often accompanied by irregular curved rods or minute particles (miliary granules), but any or all of these may be wanting. (Clark, 1907.)

The presence of distinctive anchors and anchor-plates appears to be the most important character for distinguishing this family. However, where calcareous deposits are lacking, the tentacles must be examined. Anchors are also found in the Family Molpadiidae, Order Molpadida, but reference to Plate I, fig. 4 page 4 (Protankyra uncinata) and Plate II, fig. 9 (Heteromolpadia marenzelleri) will show that the two types of anchors are readily distinguishable.

Family Synaptidae contains in excess of 120 species, the majority of which are littoral. There are a few species which live at depths below 250 fathoms. The family is especially well represented in the Indo-Pacific region, where more than half of the known species occur. A single species is at present known from New Zealand waters.

Protankyra Ostergren, 1898

Diagnosis: Tentacles digitate, 10–12, rarely 13 or 14. Digits two on each side. Cartilaginous ring wanting. Polian vesicles 2–10 or rarely only one. Stone canal usually single. Stocks of the anchors more or less branched, but only finely toothed; arms usually serrate; vertex without knobs. Anchor-plates without handles, with numerous perforations, and with a more or less imperfectly developed bow across the outer surface of the posterior end. The anchor-plates and their perforations have either smooth or dentate margins.

Type Species: Protankyra abyssicola (Theel).

The genus Protankyra is a large and perplexing one. Most of the species are distinguishable on the basis of differences in the shape and size of the anchors and anchor-plates and their ornamentation. Heding (1928) stated ". . . . the ciliated funnels are of the greatest value as specific characters in Protankyra". It is felt, however, that the calcareous deposits should be regarded as of primary importance in diagnosing species of this genus, and such variable structures as the ciliated funnels should be used with caution.

The single New Zealand representative of this genus is quite distinct from the other known Protankyra species.

Protankyra uncinata (Hutton) Plate I, figs. 2–10
  • Synapta uncinata Hutton, 1872. p. 16; Theel, 1886. p. 27; Dendy, 1896, p. 25; Farquhar, 1898, p. 325.
  • Synapta inaequalis Hutton, 1872, p. 17.
  • Protankyra uncinata Mortensen, 1925, p. 367, figs. 48–51; Heding, 1928, p. 252; Dawbin, 1950, p. 40.

Material Examined: VUZ 32, off Petone Beach, 8 fathoms, mud, 3 specimens; VUZ 37, off Shelly Bay, 10–11 fathoms, mud, 8 specimens; VUZ 40, off Ward Island 2–4 fathoms, mud, 2 specimens; VUZ 64, off Point Howard Wharf, 5 fathoms, blue mud, 10 specimens.

Diagnosis: Tentacles 12, with sensory cups and four terminal digits. Colour white transparent to reddish brown. Anchors small (0.3–0.5mm long), usually symmetrical, with unbranched finely toothed stocks. Arms with few serrations or none. Anchor-plates oval or rectangular, smooth, with large smooth polygonal perforations of average diameter 0.025mm. Ciliated funnels slipper-shaped, numerous.

Description: The body is smooth, approximately cylindrical in shape, tapering abruptly to the terminal anus. Many of the specimens are completely contracted and carry a number of transverse wrinkles. In extended specimens the skin is semi-transparent. Length of largest extended specimen 100m; diameter at anterior end, 5mm. In alcohol, the colour varies between white transparent and reddish brown.

The skin is prickly to touch, the prickly sensation being caused by the sharp-pointed anchor arms which project above the level of the body wall. These arms can be seen with the naked eye. When completely contracted, the anterior end of the body folds inward and the tentacles disappear from view. If the animal is viewed end on, the five interradial areas between the radial muscle bands appear as soft fleshy lumps. This method of contraction may be a characteristic of the species. (Plate I, fig. 8.)

Twelve elongate, cylindrical tentacles surround the mouth, which lies in a shallow depression. There is a brown pigment spot at the base between each pair of tentacles. Each tentacle carries a terminal claw composed of two pairs of digits, and the stems carry a number of sensory cups on their inner margins (Plate I, fig. 9). The true function of these cups has apparently not been determined.

The calcareous ring is composed of twelve small, square pieces. The five radial pieces are each perforated for the passage of the radial nerves.

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Plate I.—Trochodota dunedinensis (Parker).—Fig. 1, tentacle rods. Protankyra uncinata (Hutton).—Fig. 2, tentacle digit deposits; fig. 3, portion of an anchor from the posterior end of the body; fig. 4, anchor and anchor-plate; fig. 5, developing anchor-plates; fig. 6, anchor-plate; fig. 7, anterior of the body, dissected from the dorsal side (portions of gonad removed); fig. 8, anterior end of a contracted specimen; fig. 9, tentacle; fig. 10, tentacle stem deposits.

Plate I.—Trochodota dunedinensis (Parker).—Fig. 1, tentacle rods. Protankyra uncinata (Hutton).—Fig. 2, tentacle digit deposits; fig. 3, portion of an anchor from the posterior end of the body; fig. 4, anchor and anchor-plate; fig. 5, developing anchor-plates; fig. 6, anchor-plate; fig. 7, anterior of the body, dissected from the dorsal side (portions of gonad removed); fig. 8, anterior end of a contracted specimen; fig. 9, tentacle; fig. 10, tentacle stem deposits.

Abbreviations: c, sensory cup; di., tentacle digit; g.ap., genital aperture; g.d., genital duct; g.tub., genital tubules; int., intestine; mad.d., stone canal; p.v., Polian vesicle; r.l.m., radial longitudinal muscle; st., tentacle stem; stom., stomach; ten., tentacle; tr.m., transverse muscles.

A short, thin-walled oesophagus leads into a well-defined stomach which has a thick muscular wall (Plate I, fig. 7). The intestine takes a short loop and terminates in an undifferentiated cloaca.

There are 4–5 Polian vesicles, two or three of which may be longer than the rest (Plate I, fig. 7). They are tubular, and their length varies between 3mm and 25mm. The single stone canal leaves the water-vascular ring on the dorsal side, and runs anteriorly in the dorsal mesentery as a short loosely coiled tube 0.2mm in diameter, terminating in a small madreporite of an irregular shape.

The genital tubules are moniliform and sparsely branched, arranged in two bunches, extending for about half of the length of the body cavity in mature specimens. The common page 6genital duct lies in the dorsal mesentery, and opens to the exterior as a minute genital pore in the mid-dorsal interradius, immediately posterior to the ring of tentacles (Plate I, fig. 7). Longitudinal muscles are well developed, and transverse muscles are represented as bunches of fine fibres.

Calcareous deposits of four types were found:

1. Anchors: The anchors are approximately symmetrical, although some asymmetrical examples were found, especially near the posterior extremity of the body (Plate I, fig. 3). The total length of each anchor varies between 0.3mm and 0.5mm. The arms have 3–7 irregular serrations on their upper edges, or none at all, but smooth anchor arms are not common. The stock is unbranched, and carries a number of fine teeth, irregularly arranged (Plate I, fig. 4).

2. Anchor-plates: The anchor-plates lie in association with anchors in the skin. They are rectangular to oval in shape, with an average length of 0.3mm, and have many large and small polygonal to circular perforations (Plate I, fig. 6). The narrower end of the anchor-plate is reflected to form a bridge for the support of the anchor stock. The anchor is supported in such a way that the arms can project above the level of the skin. Anchors develop before anchor-plates, and stages in the development of anchor-plates (Plate I, fig. 5) are commonly found near the extreme posterior end of the body.

3. Tentacle Deposits: Curved and dumbbell shaped rods are present in great numbers in the tentacles. The curved rods are C- or bracket-shaped, 0.03–0.06mm long, and they are confined to the tentacle digits, where they form an investing layer (Plate I, fig. 2). Dumbbell shaped rods invest the tentacle stems. Thy are 0.02–0.05mm in length (Plate I, fig. 10).

Distribution: Protankyra uncinata is now known from Auckland, Colville Channel (Mortensen, 1925), and Wellington Harbour, and may yet prove to have a wider distribution pattern. This species is restricted to the New Zealand region.

Ecology: Mortensen's (1925) specimens were taken from muddy or sandy bottoms at depths ranging between 5 and 35 fathoms. The present collection contains specimens taken from a muddy bottom at depths ranging between 2 and 11 fathoms. This species is then a member of our sub-littoral fauna, and may eventually come to be known from other sheltered muddy localities.

Discussion: Mortensen (1925) figured small irregular perforated buttons which he found ". . . . in the anterior end . . . more or less sparsely". These were not found in the specimens on hand. He also commented on the small size of the eggs in this species (approximately 0.1mm in diameter), and suggested that Protankyra uncinata may possess a typical auricularia larva.

Hutton (1872) gave a very inadequate description of his two new species Synapta uncinata and Synapta inaequalis. As a consequence Clark (1907) declared that the two species were absolutely unrecognisable on the basis of Hutton's descriptions. Mortensen (1925) established the validity of P. uncinata and reduced P. inaequalis to synonymy with that species. P. inaequalis was based on a fragment of skin containing asymmetrical anchors, but Mortensen (1925) suggested that this was probably an individual variant of P. uncinata.

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.