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The Bathyal Holothurians of the New Zealand Region

Ypsilothuria Perrier, 1886

Ypsilothuria Perrier, 1886

Sphaerothuria Ludwig, 1894

Diagnosis: Tentacles eight, lateral tentacles enlarged. Body U-shaped, mouth and anus dorsal. Body invested in large (ca. 1mm diameter) thick scales composed of many layers of calcareous material. Each scale carries a long spire at or near its centre.

Type Species: Y. talismani Perrier.

Ypsilothuria bitentaculata (Ludwig) Text-fig. 1, figs. 2–5

Sphaerothuria bitentaculata Ludwig, 1893, p. 112; Ludwig, 1894, p. 141, P1. 12, figs. 16–17, P1. 14, figs. 5–14; Mitsukuri, 1897, p. 149; Koehler, 1898, p. 384; Sluiter, 1901b, p. 115; Ohshima, 1915, p. 266; Deichmann, 1930, p. 152, P1. 19, figs. 4–5; Ludwig and Heding, 1935, p. 196; Baranova, 1957, p. 242.

Ypsilothuria bitentaculata Koehler and Vaney, 1905, p. 87; Heding, 1942, p. 28; Panning, 1949, p. 455.

Material Examined: Dominion Museum Stn. B.S.201, 2 specimens + fragment of juvenile; B.S.202, 1 specimen + fragment of adult.

Description: Body subglobular, anterior and posterior ends drawn out to form short "siphons" (Text-fig. 1, fig. 3); anterior (oral) siphon wider than posterior siphon. Length measured about greater curvature 32, 25 and 24mm, horizontal diameter 10, 8 and 9mm respectively. Bodywall with numerous projecting spines; prickly to touch; tubefeet rare, restricted to radii, more common on siphons than elsewhere. Colour in alcohol, greyish-white to light brown.

Fragment of juvenile with anal and oral siphons intact; distance between them 2mm.

Tentacles typical, with two lateral tentacles much larger than rest. Internal anatomy is similar to that in Echinocucumis hispida (Barrett) (Text-fig. 2, fig. 1).

Body invested in overlapping spired scales, each scale composed of many layers of calcareous material, which forms a reticulated network. Scales of varying shape (Text-fig. 1, fig. 4), usually oval, of average diameter 1.2mm. An almost solid spiny spire arises from centre, or near centre of each scale; spires have an average height of 0.5mm. In anterior and posterior siphons, scales reduced to form simple perforated plates (Text-fig. 1, fig. 5) of average length 0.7mm which lack spires.

Largest tentacles contain straight or curved narrow plates of average length 0.13mm, with many short and blunt projections along their length, and a few perforations (Text-fig. 1, fig. 2).

Remarks: Ludwig (1894) and Heding (1942) have given descriptions of northern representatives of this species. The New Zealand specimens are typical of the species in most respects.

Ypsilothuria bitentaculata has been recorded from numerous localities in the Pacific Ocean (see Ohshima, 1915), and appears to be circum-Pacific, ranging in depth from about 250–4,000 metres. Ohshima (1915) also notes that while in tropical regions Y. bitentaculata has a considerable bathymetric range, in temperate regions the animal lives in depths not exceeding about 700 metres. Heding (1942) has established that Ypsilothuria (= Sphaerothuria) attenuata page 7
Text-fig. 1.—Echinocucumis hispida (Barrett). Fig. 1: Two complete specimens (outline only). Ypsilothuria bitentaculata (Ludwig): Fig. 2, tentacle deposits; Fig. 3, three complete specimens (outline only); Fig. 4, spired scales from bodywall (outline only); Fig. 5, perforated plates from anterior and posterior siphons. Abbreviations: m., mouth; sp., spire.

Text-fig. 1.—Echinocucumis hispida (Barrett). Fig. 1: Two complete specimens (outline only). Ypsilothuria bitentaculata (Ludwig): Fig. 2, tentacle deposits; Fig. 3, three complete specimens (outline only); Fig. 4, spired scales from bodywall (outline only); Fig. 5, perforated plates from anterior and posterior siphons. Abbreviations: m., mouth; sp., spire.

Perrier is a variety of Y. bitentaculata, and notes that this form is "distributed in the abyssal parts of the Atlantic, from Davis Strait to the type locality off Senegal". In the same paper Heding erects another variety, Y. bitentaculata var. virginiensis, for a specimen collected in the West Indies at a depth of 375 metres.

Clearly, Y. bitentaculata is a cosmopolitan species, capable of some variation in the form of its deposits, but, nevertheless, well defined and readily recognisable.