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.

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.

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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.

Calcareous deposits:

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.