Diagnosis: Calcareous ring with long processes, composed of a mosaic of minute pieces. Deposits large scales with many perforations, and smaller buttons with few perforations. No cups.

Type Species: Stolus sacellus Selenka.

At the present time, this genus contains less than ten species.

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Stolus huttoni (Dendy) Plate VII

• Cucumaria huttoni Dendy, 1896, p. 32, Pl. 3, figs. 19–20; Ludwig, 1898, p. 39; Farquhar, 1898, p. 324; Perrier, 1905, p. 93; Mortensen, 1925, p. 384, figs. 33–35; Dawbin, 1950, p. 36.
• Stolus huttoni Panning, 1949, p. 463, abb. 58.

Material Examined: VUZ 62, opposite Worser Bay, 4–5 fathoms, green sand, 1 specimen.

Diagnosis: Body large (up to 180mm total length), U-shaped, completely invested by large overlapping scales, which are overlain by small perforated buttons 0.01–0.03mm long. Colour grey to yellow.

Description: The single specimen is U-shaped, with a total length of 125mm. The integument is very hard and thick, due to the presence of great numbers of calcareous deposits. The colour in alcohol is yellowish-white. The tentacles are abundantly speckled with brown spots on a grey background.

Tubefeet are present in all radii and confined to them. They are more numerous in the mid-ventral portion of the body, where they are arranged in distinct double rows. A semi-transparent introvert is surmounted by a crown of ten richly branched tentacles, of which the ventral pair is the smallest.

The calcareous ring is complex, each piece being composed of a number of fragments (Plate VII, fig. 2). The radials each have a pronounced anterior notch and long, narrow posterior processes. The interradials are not notched, but do possess long posterior processes.

The oesophagus is short and muscular (Plate VII, fig. 1), and joins to the thinwalled convoluted intestine. The rectum is long and straight and runs to the terminal anus. Two long and slender Polian vesicles are attached to the ventral side of the water-vascular ring (Plate VII, fig. 1). The stone canal is short, and runs anteriorly in the dorsal mesentery to terminate in a conspicuous madreporite (Plate VII, fig. 2).

The two trunks of the respiratory trees arise from near the anterior end of the rectum as flattened tubes.. At the level of the junction between the intestine and the rectum, each trunk divides and gives rise to a long and a short branch. The two long branches extend anteriorly for a considerable distance and attach to the body wall in the interradii. Each trunk carries many short, sparsely branched respiratory tubules (Plate VII, fig. 8).

There are two bunches of intertwining, unbranched, filamentous genital caeca. The genital duct opens into the introvert in the dorsal interradius (Plate VII, fig. 1).

The radial muscles are narrow, especially near the posterior end of the body. They thicken in the anterior half, and are thickest at the point of origin of the retractors, which is about one-third of the way along the body from the anterior end. Transverse muscles are present as fine fibres. All of the muscles are orange coloured in preserved material.

Calcareous deposits:

1. Large Scales: The body is completely invested in oval to round imbricating scales (Plate VII, fig. 3), with an average diameter of 1.0mm.

2. Perforated Buttons: Great numbers of perforated buttons overlie the scales (Plate VII, fig. 4). These are 0.1–0.3mm long, and have two to twenty perforations. The presence of these buttons gives the integument a granular appearance.

3. Tubefoot Deposits: The endplate in each tubefoot is surrounded by perforated deposits 0.1–0.25mm in length (Plate VII, fig. 6). They are easily distinguishable from the buttons in the skin as they are not nearly as thick, and are more irregular in outline.

4. Tentacle Deposits: Irregular perforated buttons and rods of varying shape and average length 0.2mm are present in the digits of the tentacles (Plate VII, fig. 7). The tentacles are consequently prickly to touch.

5. Introvert Deposits: The thinwalled introvert contains small perforated buttons of a different character from those in the rest of the body wall (Plate VII, fig. 5). They are oval to rectangular in shape and have few (6–12) perforations. Average length of these buttons is 0.05mm.

Distribution: Stolus huttoni has previously been recorded from Oamaru (Dendy, 1896) and Otago Harbour (Mortensen, 1925). The new locality Wellington Harbour, somewhat extends the area of distribution of this species.

Ecology: Specimens of S. huttoni have been taken from sandy or muddy bottoms in sheltered shallow areas.

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Discussion: Dendy (1896) stated that the tubefeet are absent from the dorsal radii, and Ludwig (1898) agreed with him. Perrier (1905) found tubefeet on the lateral regions of the dorsal side, and Mortensen (1925) stated that the dorsal tubefeet are inconspicuous "and form only a single irregular zig-zag series". The present writer noted tubefeet in all radii, the dorsal tubefeet appearing to be confined to the middle 1/3 of the body.

There is some variation in the number of Polian vesicles. Dendy (1896) found two in the type specimen. Ludwig (1898) found one, while Mortensen (1925) noted the presence of five long and slender Polian vesicles. The present specimen has two. Therefore no taxonomic importance can be attached to Polian vesicle numbers in this species.

Dendy (1896) figured the calcareous ring of the holotype, but his figure did not show the anterior notches in the radial pieces, nor the bifurcating posterior ends of the interradials.

S. huttoni has no near relatives, either in New Zealand or overseas.