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The Holothurian Fauna of Cook Strait, New Zealand

Family Molpadiidae

Family Molpadiidae

Diagnosis: Tentacles with lateral digits, or claw-shaped. Tentacle ampullae long (reduced in one deep-water species). Spicules derived from triradiate tables with solid three-pillared spire; tail with tables with round to oblong disc, or long fusiform rods. In one species large fusiform plates or rods develop in the skin of the body wall with advancing age. Dark red egg-shaped phosphatic bodies often present. In some species anchors and racquet-shaped plates present in young individuals. Mostly large forms, 6–15cm long (Deichmann, 1960).

The members of this family are unique in that the calcareous deposits of the juvenile may be transformed into phosphatic material with the passage of time. The phosphatic material is deposited as small orange or red concentrically laminated granules. As a consequence of this phenomenon, juveniles, half-grown specimens, and adults of the same species have often been placed in different species, because of the differences in their spiculation. Clark (1907) referred all of the then known species of the family Molpadiidae to the genus Molpadia Risso. Heding (1931) attempted a revision of the family, listing the known species under five genera, one of which (Pseudomolpadia) was a new genus. Later, Heding (1935) erected another new genus (Eumolpadia). Deichmann (1936), pointed out a number of inconsistencies in Heding's reasoning, and suggested a return to Clark's (1907) idea that all of the species be placed under the single generic name Molpadia in the meantime, until the life histories of at least a few typical cases be worked out.

Heding (1931, 1935) used differences in structure and sculpture of the calcareous ring, in certain features of internal anatomy, and (to a lesser extent) in calcareous deposits, as criteria for separation at the generic level. It appears that these criteria may be rather unreliable, and subject to more or less drastic changes with growth. The calcareous deposits of the tail are relatively unaffected by deposition of phosphatic material and these deposits are thus reliable criteria for identification of juvenile and adult specimens alike. The deposits in the body wall should be used only when the life history of the species is fairly well known, and a series of specimens have been examined, or when the body wall deposits page 11are so distinctive as to belong to a certain species. The calcareous ring should supply characters of secondary importance only.

Two genera of Molpadiidae are represented in the Cook Strait collections.

Key to the Cook Strait Genera in Family Molpadiidae
1 (2) Deposits include anchors and three-armed anchor-plates, and spired tables with three perforations Heteromolpadia n.g.
2 (1) Deposits in the form of large fusiform rods and scattered irregular tables Molpadia Risso

Heteromolpadia n.g.

Diagnosis: Molpadids whose calcareous deposits include two-armed anchors associated with single perforated anchor-plates of varying shapes, usually having three marginal projections. No rosettes of racquet-shaped plates; no fusiform rods. Phosphatic bodies present, at least in adult specimens.

Type Species: Ankyroderma marenzelleri Theel.

Also included here: Ankyroderma tridens Sluiter.

Discussion: Heding (1931) in his subdivision of the genus Molpadia proposed a new genus Pseudomolpadia for those species which have the anchors either united with a single fenestrated plate, or supplied with more than two arms. In this genus Heding placed the following species:

1. brevicaudata (Koehler and Vaney) 1905 type species.
2. marenzelleri (Theel) 1886.
3. tridens (Sluiter) 1901.
4. inflata (Augustin) 1914.

Subsequently, Deichmann (1936) pointed out that it is only in tridens and marenzelleri that the anchor-plates are definitely known to be "not united in rosettes". Thus brevicaudata and inflata do not belong with the two other species unless it is proved that they have single anchor-plates. As brevicaudata is the type of Pseudomolpadia, this generic name cannot be used here, and it is necessary to propose a new genus, Heteromolpadia, with H. marenzelleri (Theel) as the type species.

Key to the Species of Heteromolpadia
1 (2) Deposits in the body wall include tables, typically with three perforations H. marenzelleri (Theel)
2 (1) No such tables present H. tridens (Sluiter)
Heteromolpadia marenzelleri (Theel) Plate II
  • Ankyroderma marenzelleri Theel, 1886. p. 41. Pl. 3. fig. 1 a-g.
  • Molpadia marenzelleri Clark, 1907. p. 171. Pl. 10. fig. 23; Benham, 1909, p. 70, Pl. 11, fig. 4, a-d; Deichmann, 1936, p. 464; Dawbin, 1950, p. 39, Pl. 2, fig. 17; Deichmann, 1960.
  • Molpadia dendyi Benham, 1909, p. 71, Pl. 11, figs. 1–3.
  • Pseudomolpadia marenzelleri Heding, 1932, p. 280.

Material Examined: VUZ 10, Palliser Bay, 200–250 fathoms, green mud, 1 specimen; VUZ 15, Palliser Bay, 100–150 fathoms, mud, 16 specimens; VUZ 21, Palliser Bay, 38 fathoms, mud, 1 specimen; VUZ 87, South of Cape Palisler, 400 fathoms, mud, rock and gravel, 1 specimen; VUZ 96, off Palliser Bay, 380 fathoms, mud, 13 specimens; Cook Strait, 40 fathoms, 2 specimens, collected by F. Abernethy, 14/11/1952; off Foxton, 50 fathoms, 1 specimen.

New Zealand Oceanographic Institute, Wellington: B 11, Hawke Bay, 35 fathoms, mud, 1 specimen; B 44, Hawke Bay, 14 fathoms, sandy mud, 1 specimen; page 12B 49, Hawke Bay, 44 fathoms, fine grey-green mud, 1 specimen; A 435, off Foxton, 64 fathoms, sandy mud, 1 specimen; C 185, off Wanganui, 25 fathoms, mud, 1 specimen; C 186, off Wanganui, 25 fathoms, mud, 1 specimen; C 189, entrance to Tasman Bay, 30 fathoms, soft mud, 1 specimen.

Diagnosis: Deposits in the body wall comprise spired tables with 3 large perforations, and anchors associated with single three-armed perforated anchor-plates up to 0.4mm in length. Tail deposits lozenge-shaped, 0.1–0.16mm in length.

Description: Short-tailed, fat-bodied holothurians which are greyish-white as juveniles, and gradually become red in colour with growth, until the largest specimens are almost uniformly dark red. The calcareous deposits comprise distinctive anchors, anchor-plates and tables. The tables in the tail persist unchanged throughout life, and are always readily usable as a diagnostic character. The deposits in the rest of the body become gradually transformed into phosphatic bodies with age, and thus they range from well-formed anchors, anchor-plates and tables in smaller specimens to simple, small, concentrically laminated ovoidal red phosphatic granules in larger specimens. Large specimens of the species often lack calcareous deposits altogether, except in the tail, and are dark red is colour, due to the presence of great numbers of phosphatic deposits.

Three groups, based mainly on colour of specimens, may be recognised:

1. Small specimens: 15–30mm in total length. The smallest specimen on hand is 15mm in total length, with a tail length of 6mm. The ratio tail: body in this group is about 1: 3. The body is about twice as long as it is broad. These animals are uniformly greyish-white in colour, and the body wall is quite thin, but opaque. The body is often clothed in particles of mud and sand, which are caught on the arms of anchors and the spires of the tables, as they project above the level of the skin. When touched, the skin gives the sensation of carrying a number of short sharp spines. The inadequate development of the gonads indicates that the specimens in this group may not be sexually mature, and they may be regarded as juveniles.

2. Medium Specimens: 30–70mm in total length. The shape is approximately the same as that in the juvenile, but the tail: body ratio has now become 1: 6. These specimens are orange to dark red in colour, with many greyish spots. The tail and circum-oral regions still retain the grey colour of the juvenile. At this stage in growth, many of the calcareous deposits have been transformed into red phosphatic material, and thus there are but small numbers of anchor arms and table spires projecting from the skin.

3. Large Specimens: 70–101mm in total length. The largest specimen is 101mm in total length, with a tail length of 12mm. The tail: body ratio is here 1:8. In these specimens the body is uniformly dark red, while the tail is grey. In these large specimens, virtually all of the calcareous deposits have been transformed into phosphatic bodies. No anchor arms project above the skin, and the skin is quite smooth and leathery to touch.

The calcareous ring is made up of 10 sculptured pieces, 5 radials and 5 interradials, which are joined to form a solid ring (Plate II, fig. 8). Each radial piece has two rounded anterior projections and a slightly bifurcated posterior projection. There are no perforations for the passage of the radial nerves. The radial pieces each carry a groove for attachment of the radial muscle. Each interradial has a single anterior process, carries a sharp ridge, and has no posterior process. The ring has 15 grooves for tentacle ampullae. Sculpture of the ring varies considerably in this species. The calcareous ring in the juvenile has long and slender posterior projections.

A short thin-walled oesophagus leads into the intestine, which takes a very large loop and runs to the cloaca, which is undifferentiated, save for the numerous very fine muscle strands attaching it to the body wall. These strands also fill the cavity in the tail.

A single Polian vesicle leaves the water vascular ring in the left ventral interradius. It consists of a short narrow tube which carries a dark brown bulbous extremity (Plate II, fig. 1). The stone canal lies in the mid-dorsal interradius, runs anteriorly and dorsally into page 13
Plate II.—Heteromolpadia marenzelleri (Theel).—Fig. 1, Internal anatomy of adult, dissected from the dorsal side (portions of the gonad removed); fig. 2, tail deposits; fig. 3, anchor-plates; fig. 4, deposits from the extreme anterior end of the body; fig. 5, phosphatic deposits; fig. 6, mid-body tables; fig. 7, stages in development of a mid-body table; fig. 8, calcareous ring of an adult specimen; fig. 9, anchors; fig. 10, mid-body tables showing phosphatic material.

Plate II.—Heteromolpadia marenzelleri (Theel).—Fig. 1, Internal anatomy of adult, dissected from the dorsal side (portions of the gonad removed); fig. 2, tail deposits; fig. 3, anchor-plates; fig. 4, deposits from the extreme anterior end of the body; fig. 5, phosphatic deposits; fig. 6, mid-body tables; fig. 7, stages in development of a mid-body table; fig. 8, calcareous ring of an adult specimen; fig. 9, anchors; fig. 10, mid-body tables showing phosphatic material.

Abbreviations: amp.g., groove for passage of tentacle ampulla; c.r., calcareous ring; g.ap., genital aperture; g.d., genital duct; g.tub., genital tubules; int., intestine; ir.p., interradial piece; m.a., attchmeant area for radial muscles; mad., madreporite; m.f., muscle fibres; oes., oesophagus; ph.mat., phosphatic material; p.v., Polian vesicle; r.l.m., radial longitudinal muscle; r.p., radial piece; r.resp., right respiratory tree; tr.m., tranverse muscles.

page 14 the centre of a spherical madreporite. The madreporite is joined to a pore-canal which opens to the exterior near the anterior end of the body, posterior to the gonopore.

Two respiratory trees arise from the cloaca. Each consists of a single flattened tube which gives rise to a number of short side branches (Plate II, fig. 1). The left tree extends about one third of the way along the body cavity. The right is considerably longer, and runs to the anterior end of the body, attaching to the dorsal pieces of the calcareous ring (Plate II, fig. 1).

The gonads are represented in the mature specimens as extensively branched vesicular caeca, which are arranged in two bunches, lying one to each side of the dorsal mesentery. The caeca are loosely intertwined around and over the intestine and the right respiratory tree. The common genital duct runs anteriorly in the dorsal mesentery to open to the exterior as a well-defined genital aperture in the mid-dorsal interradius, immediately posterior to the ring of tentacles.

The longitudinal muscles are five broad strap-like double bands (Plate II, fig. 1). No "retractor muscles" were seen. Transverse muscles are visible as fine white fibres against the dark coloured background of the body wall (Plate II, fig. 1).

Four types of calcareous deposits are known in this species:

1. Tail Deposits (Plate II, fig. 2): The tail contains a large number of very closely aggregated tables which have elongate discs (0.1–0.16mm long), and carry short three-pillared spires. The discs each have 7–12 perforations. The three pillars of the spire are joined by one or sometimes two crossbars, and the pillars at their distal extremities give rise to a few short spines. Some tables were seen to lack spires and they merely took the form of flat perforated plates. The tail deposits in the juvenile differ little from those in adult specimens. The anus is surrounded by a small number of irregular and distorted tables.

2. Mid-body Tables (Plate II, fig. 6): These tables are small (about 0.15mm across), and they typically have three large perforations. A three-pillared spire with a spinous distal extremity arises from the centre of each table and the pillars are joined to each other by 3–7 crossbars. The tables lie so that the spires project through the skin. Developing tables are common in small specimens (Plate II, fig. 7). In juveniles, the tables are present in large numbers, closely aggregated together, but their numbers decrease with growth of the animals as they become transformed into phosphatic deposits. Medium-sized specimens have scattered tables, while large specimens have very few tables or none.

3. Tables from the extreme anterior end of the body (Plate II, fig. 4): These are elongate tables which often tend towards a fusiform shape, and have 3–7 perforations. The disc is surmounted by a three-pillared spire with crossbars.

4. Anchors and Anchor-plates (Plate II, figs. 3, 9): Anchors with anchor-plates are present in numbers in juveniles, while in large specimens they are absent, due to their dissolution into phosphatic bodies. Medium-sized specimens may still possess anchors and anchor-plates, but when present, they are commonly in the process of dissolution.

The anchors are of varying sizes, lengths ranging between 0.2mm and 0.3mm. The attaching portion of the anchor is saucer-shaped and has 3 perforations. The shaft is straight and cylindrical. The arms are short and curved, and each has two to five small serrations (Plate II, fig. 9).

The very characteristic anchor-plates are not all the same shape, but the basic form is an irregular plate having three (sometimes two) elongate marginal projections. The plate is freely perforated, while the projections each have one or two perforations or none at all (Plate II, fig. 3). Each anchor-plate supports one anchor in such a manner that part of its shaft and arms lie outside the skin. The method of support is simple (Plate II, fig. 3a), so that the anchors are easily detached from their plates. Some anchors were found on their own, holding to the surface of the body by the ends of their arms or by their serrations.

Anchor-plates from medium-sized specimens show various stages in their transformation into phosphatic material (Plate II, figs. 3a, 3b), while juvenile anchor-plates show no trace of phosphatic material (Plate II, fig. 3c). One anchor-plate was found to possess a spire composed of three rods joined by crossbars (Plate II, fig. 3b). This plate had two large perforations and 12 smaller ones. A mid-body table from a juvenile specimen carried a marginal process which showed some resemblance to part of the shaft and arms of an anchor (Plate II, fig. 6a).

Phosphatic Deposits: Apart from the tail deposits which remain unaffected, the anchors, anchor-plates and tables in turn become transformed into phosphatic spherules with advancing age. It is therefore possible to encounter specimens which lack anchors, anchors and anchor-plates, or anchors anchor-plates and tables. Transformation into phosphatic material is a gradual process and one often sees deposits which are in the process of dissolution (Plate II. figs. 3a, 3b, 10).

page 15

The resulting phosphatic bodies are amber or red, ovoid to spherical, and they superficially resemble starch grains (Plate II, fig. 5).

Knowledge of the changes in deposits with growth serves to explain clearly the differences in colour between small, medium and large individuals of this species. The greyish-white juveniles have very few phosphatic bodies and many calcareous deposits. The medium-sized specimens, dark red with greyish spots, have clusters of phosphatic bodies, and the greyish patches represent areas where calcareous deposits still remain. The uniformly dark red large individuals have great numbers of phosphatic bodies and very few calcareous deposits.

Distribution: Theel (1886) described the type specimen from east of East Cape in 700 fathoms. Benham (1909) recorded specimens of H. marenzelleri from 38 fathoms in Hawke Bay, and Molpadia dendyi from deeper water off the coast of the North Island. The new localities recorded here indicate that H. marenzelleri is a common species about the deeper waters of the southern half of the North Island. As the species is eurybathic, it probably has a wider distribution.

Ecology: This species lives on a muddy or sandy bottom.

Discussion: The status of this species has been in doubt for some time, owing to insufficient knowledge of the juvenile and its deposits. The present findings indicate that H. marenzelleri is a valid species, characterised by the peculiar anchor-plates.

Molpadia Risso, 1826

Diagnosis: Molpadids whose calcareous deposits include tables, anchors, and rosettes of racquet-shaped plates and large fusiform rods in various combinations. Tail deposits fusiform.

Type Species: Molpadia musculus Risso.

The single Cook Strait representative of this perplexing genus is Molpadia violacea (Studer), which is probably related to the type species of the genus, but the relationship is not absolutely clear, as M. violacea seems to lack the characteristic rosettes of racquet-shaped plates and anchors which are found in M. musculus.

Molpadia violacea (Studer) Plate III, figs. 4–8
  • Trochostoma violaceum Studer, 1876; Theel, 1886, p. 42, Pl. II, fig. 4; Pl. XI. fig. 1.
  • Molpadia musculus H. L. Clark, 1907, p. 165, Pl. XI.
  • Haplodactyla violacea Heding, 1931, p. 280.
  • Molpadia violacea Deichmann, 1960.

Material Examined: VUZ 87, South of Cape Palliser, 400 fathoms, mud, 1 specimen; VUZ 101, off Palliser Bay, 550 fathoms, mud, 6 specimens.

Diagnosis: Deposits in the form of large fusiform rods with two to three arms, up to 1.1mm in length. No anchors or anchor-plates. No rosettes of racquet-shaped plates. Tail deposits two-armed fusiform rods up to 0.8mm in length. One anterior process on each radial piece of the calcareous ring perforated for the passage of the radial nerve.

Description: The smallest specimen has a total length of 47mm; the largest is 78mm in length. The specimens are approximately cylindrical in shape, elongate, with the posterior end attenuated to form a distinct caudal appendage which occupies up to 20% of the total body length.

Colour in alcohol ranges from a light-brownish red to a dark brick-red. The anterior extremity of the body and the tail are greyish-white. The skin is quite thin and coarse to touch.

The calcareous ring is composed of 10 pieces, five radials and five interradials, joined to form a solid ring. Anteriorly, the radials each have two short and blunt processes, one of which carries a small perforation for the passage of the radial nerve. The interradials each have one anterior process and no perforation. The radials have a forked posterior process, while the interradials have none. The ring is sculptured on its outer surface, and the sculpture varies within the species.

The internal anatomy is similar to that in Heteromolpadia marenzelleri,

page 16

Two types of calcareous deposits are present in the skin:

1. Fusiform Rods: These are found everywhere in the body wall, especially in the tail, where they occur in great numbers, closely aggregated together, lying transverse to the longitudinal axis of the body. The rods vary in length up to a maximum of 1.1mm, and they have an expanded central portion which carries a small number of perforations.

(a) Rods from the tail (Plate III, fig. 6): The tail rods are in general smaller (average length 0.7mm) than those from other areas, and have fewer perforations. The ends of the rods tend to project above the level of the skin, and they can be seen with the naked eye.

(b) Rods from the posterior third of the body, near the tail (Plate III, fig. 8): These are massive deposits, with an average length of 1.0mm. Many of the rods have three arms, while others have two, and there are four to eight central perforations. The rods are grouped into small clusters.

(c) Rods from the middle of the body (Plate III, fig. 7): Mid-body deposits closely resemble those from the posterior third of the body in general features, but even more variability in shape is displayed.

(d) Rods from the extreme anterior end of the body (Plate III, fig. 4): These are similar to those from the tail, and are of a comparable size.

2. Perforated tables (Plate III, fig. 7a): Tables (length 0.3–0.6mm) with short central spires and 3–6 perforations are scattered sparsely in the skin. The spire is composed of a single column, and in many cases it is absent. Developmental stages are occasionally seen (Plate III, fig. 5).

Red phosphatic deposits are present, grouped together in small clumps. They are similar to those in Heteromolpadia marenzelleri (Theel).

Distribution: Theel (1886) described specimens taken from the vicinity of Kerguelen Island at depths between 20 and 120 fathoms, and from about 50 miles east of East Cape, New Zealand in 700 fathoms. The two new localities recorded here, Palliser Bay, 550 fathoms, and south of Cape Palliser, 400 fathoms, indicate that this species may be relatively common in deeper waters about New Zealand, and probably elsewhere, achieving its distribution by spreading across the seafloor in deep water.

Discussion: The specimens described here are similar in most respects to those described and figured by Theel (1886). There appears to be a complete lack of anchors and rosettes, even in smaller specimens. Thus the species is sharply distinguished from M. musculus (Risso). Deichmann (1960) believes that M. violacea is an extreme form of M. musculus with narrow rods and lacking the anchor and racquet stage completely.