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