The Bathyal Holothurians of the New Zealand Region

Order Dactylochirotida Pawson and Fell, 1965

Order Dactylochirotida Pawson and Fell, 1965

Diagnosis: Tentacles 8–30 in number, not branched but digitiform or digitate, the digits sometimes bifurcate. Retractor muscles, tubefeet and respiratory trees present. Calcareous ring simple, lacking complex posterior processes. Body U-shaped, enclosed in a test comprising imbricate plates.

Remarks: Of the three families (Ypsilothuriidae, Rhopalodinidae and Vaneyellidae) included in this order (Pawson and Fell, 1965, p. 2) only the Ypsilothuriidae is well represented in bathyal depths.

Family Ypsilothuriidae Heding, 1942

Diagnosis: Spherical to U-shaped holothurians, with eight to ten tentacles, of which two are much larger than the others. Calcareous deposits large plates each with a spiny spire. Tube feet slightly developed, usually placed along the radii. (Partly after Heding, 1942).

Remarks: Heding (1942) proposed this family to include the genera Ypsilothuria Parrier and Echinocucumis Sars, both of which are distinguished from the Cucumariidae in possessing the unique scales in the bodywall together with simple finger-shaped tentacles, of which two are usually larger than the rest.

Panning (1949) reduced the family to the status of a subfamily (Ypsilothuriinae), and included five other genera, namely Ekmocucumis Heding, Abyssocucumis Heding, Psolicucumis Heding, Staurocucumis Ekman and Ypsilocucumis Panning. Ypsilocucumis was proposed (Panning, 1949) to accommodate the species Echinocucumis asperrima Theel. Deichman (1930) was of the opinion that this species is Sphaerothuria, while Heding (1942) regards the species as "a good Echinocucumis". In his diagnosis of the genus, Panning (1949) notes that the species E. asperrima has ten tentacles, and that in the bodywall there are large plates composed of many layers. Ypsilothuria (= Sphaerothuria) has eight tentacles according to Heding (1942) and eight to ten in the opinion of Deichman (1930). Deichmann notes that the two ventral tentacles may tend to become aborted. However, in view of Heding's emphatic statement that Ypsilothuria has "always ... eight tentacles", it is probably desirable to maintain the genus Ypsilocucumis Panning.

The remainder of the genera included in this group by Panning (1949) do not have the remarkable combination of characters found in Ypsilothuria, Echinocucumis and Ypsilocucumis, and I feel that they should be separated from the Ypsilothuriidae and replaced in the Dendrochirotida; they may constitute a family in themselves. As the status of some of these genera is in doubt ( vide Clark and Deichmann, 1936; Heding, 1942), I am unwilling at present to propose a new taxon to accommodate these genera, and prefer to consider them as incertae sedis. A comparative study of these rather unusual holothurians is urgently required.

Key to the Genera of the Ypsilothuriidae
1 (4) Tentacles eight or ten, bodywall with large spired plates composed of many layers of calcareous material.
2 (3) Tentacles ten [ Ypsilocucumis]
3 (2) Tentacles eight Ypsilothuria (p. 6)
4 (1) Tentacles ten, spired plates of bodywall composed of a single layer of calcareous material Echinocucumis (p. 7)

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.

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

Echinocucumis Sars, 1859

Echinocucumis hispida (Barrett) (Text-fig. 1, fig. 1; Text-fig. 2)

Eupyrgus hispidus Barrett, 1856, 46, Pl. 4, figs. 1 a-b.

Echinocucumis typica Sars, 1861, p. 102, Pl. 10, figs. 11–20, Pl. 11, figs. 1–17; Pourtales, 1869, p. 359; Theel, 1886a, p. 118; Theel, 1886b, p. 9, fig. 3; Herouard, 1923, p. 118.

Cucumaria typica Ludwig, 1901, p. 149.

Echinocucumis hispida: Mortensen, 1927, p. 404, figs. 242 (1), 243; Deichmann, 1930, p. 150; Ludwig and Heding, 1935, p. 167; Heding, 1942, p. 29, figs. 31, 32; Panning, 1949, p. 454.

Material Examined: N.Z.O.I. Stn. G.603, 2 specimens.

Description: Both specimens U-shaped (Text-fig. 1, fig. 1), total length (measured about greater curvature of body) 50mm in one specimen, 40mm in the other. Oral extremity in both specimens 2.5mm in diameter. Bodywall hard and brittle but thin, with numerous elongate spinous projections. Tubefeet present in small numbers confined to radii, more common ventrally, difficult to distinguish from spinous projections. Colour in alcohol greyish-white, darker at extremities. Tentacles fingerlike, conical.

Calcareous ring fragile, each piece with a shallow posterior notch. Intestine long, light yellow, coiled at the middle (Text-fig. 2, fig. 1); rectum transparent, large, supported in "tail" by fine muscle fibres. Respiratory trees three, of which one extends to anterior end of body cavity. Remaining two trunks short, about half length of body cavity. Respiratory caeca simple sacs, sparsely scattered on trunks (Text-fig. 2, fig. 1). At base of one short trunk is a small clump of respiratory caeca. Two elongate, tubular Polian vesicles.

A tuft of short unbranched genital caeca filled with large eggs lies at middle of body (Text-fig. 2, fig. 1). Long genital duct opens to exterior in mid-dorsal interradius, immediately posterior to tentacles.

Intestine, gonad, and (to a lesser extent) respiratory trees held close against lesser curvature of body by a short, fragile dorsal mesentery; thus large portions of body cavity virtually empty. Radial muscles thin strands, retractors well developed.

Calcareous deposits in bodywall exclusively single-layered, oval to rectangular plates (Text-fig. 2, fig. 3), with many perforations and an average length of 1.0mm. Most plates bear a single tall excentric spire, which lies near edge; spire spinous (Text-fig. 2, fig. 2), up to 0.7mm in length, derived from three vertical pillars joined by several crossbars. Smaller perforated plates, lacking spires, also common, especially near anterior and posterior ends of body. Tubefeet pass between plates, not through them. Tentacles contain large numbers of curved rods, of average length 0.3mm, perforated mainly at extremities, and with short blunt projections (Text-fig. 2, fig. 4).

Echinocucumis hispida is known from the north-eastern part of the Atlantic Ocean, from the West Indies (as Echinocucumis hispida forma atypica Deichmann) and from east of New Zealand. The species is presumably cosmopolitan, and has a known bathymetric range of about 50 metres to 1,400 metres.