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The Bathyal Holothurians of the New Zealand Region

Family Synallactidae Ludwig, 1894

Family Synallactidae Ludwig, 1894

Diagnosis : Tentacle ampullae lacking. Respiratory trees usually not connected with a rete mirabile. Stone canal usually in connection with the bodywall, sometimes opening outwards through the bodywall. No Cuvierian organs. Deposits tables; C-shaped bodies may be present and, very rarely, buttons. (After Mortensen, 1927.)

Remarks: This family is cosmopolitan, comprising mainly deepsea forms. Approximately fifteen genera are recognised at the present time, of which two, Bathyplotes Östergren and Mesothuria Ludwig, are known from the New Zealand region. The genera may be readily distinguished as follows:

1 (2) Gonad composed of a single tuft; deposits tables with approximately circular discs bearing large perforations Mesothuria (p. 18)
2 (1) Gonad composed of two tufts; deposits tables with cross-shaped discs Bathyplotes (p. 15)

Bathyplotes Ostergren, 1896

Diagnosis: Tentacles 15–20, mouth ventrally turned, anus subdorsal. Ventrolateral radii with feet in one or more rows. Midventral radius naked, or with a small number of feet. Dorsal surface with small papillae more or less distinctly in rows. Genital organs in two tufts. Radial muscles undivided. Deposits tables with cross-shaped disc and spire built up of four rods, usually with several cross beams.

page 16

Type Species: Holothuria natans M. Sars.

Remarks: According to Deichmann (1930) this genus is very closely related to Synallactes Ludwig. Bathyplotes is a cosmopolitan genus, containing in excess of twenty species. Known bathymetric range is from 60 metres (B. rubicundus Sluiter) to about 3,000 metres (B. profundens Koehler and Vaney).

Bathyplotes natans (Sars) Text-fig. 4

Holothuria natans M. Sars, 1868, p. 20.

Stichopus tizardi Theel, 1886a, p. 193.

Bathyplotes tizardi: Östergren, 1896, p. 354, Pl. 13, figs. 36–43; Ludwig, 1901, p. 138, Pl. 12, figs. 3–4, Pl. 18, figs. 1–9; Mitsukuri, 1912, p. 35, Text-fig. 8; Ohshima, 1915, p. 224.

Bathyplotes fallax Ostergren, 1896, p. 355.

Bathyplotes natans: Ludwig, 1901, p. 137 (complete list of references); Greig, 1921, p. 7; Mortensen, 1924, p. 220, figs. 105, 106; Mortensen, 1927, p. 384, figs. 228, 229; Deichmann, 1930, p. 100, Pl. 9, figs. 1, 2, 8; Heding, 1942, p. 11, Text-figs. 11, 12 (1–2).

Bathyplotes reptans Perrier, 1902, p. 352, Pl. 12, figs. 3–4, Pl. 18, figs. 1–9.

Material Examined: Marine Dept. Stn. 24, 2 specimens; Stn. 25, 1 specimen; Stn. 27, 4 specimens; Stn. 27, 4 specimens; Stn. 31, 4 specimens; Lower Chalky Sound, 160 fathoms, fragment.

Description : Total length varies between 100mm and 230mm, most specimens over 150mm in length. Body approximately five times as long as broad, flattened ventrally. All specimens with outer layer of bodywall lacking, or partly torn away. Single specimen in fair condition with naked midventral radius; lateral ventral radii each with two rows of irregularly scattered short papillae approximately 2mm in diameter. Papillae soft, lacking calcareous deposits, or at most with a small number of spinous rods. Dorsal surface of body bears small papillae in radii, but arrangement cannot be determined. Tentacles 16–19, surrounding a ventrally turned mouth.

In alcohol, dorsal surface of body with light brown spots of varying size, up to 1.5mm diameter. Ventral surface similar laterally, but at centre bodywall light violet, with brown spots in general approximately half size of those on dorsal side. Tentacles uniformly light to dark brown.

Calcareous ring firm, pieces fused together. Radials notched anteriorly, interradials bluntly pointed (Text-fig. 4, fig. 2). Radial pieces rather larger than interradials, with small anterior projections, one to each side of anterior notch. Both radials and interradials notched posteriorly.

A single bulbous Polian vesicle (Text-fig. 4, fig. 1) arises from ventral side of water-vascular ring. Madreporite small, attached to bodywall, but not deeply embedded. Stone canal a simple, short tube, not coiled. Gonad two bunches of weakly branching caeca (Text-fig. 4, figs. 1, 3), one bunch to each side of dorsal mesentery. Common genital duct 20mm in length, opening to exterior near madreporite. Respiratory trees long (approximately ⅔ length of body), unbranched, slightly flattened tubes, carrying numerous simple respiratory sacs (Text-fig. 4, figs. 1, 7). Trunks arise from a single root; they contain small brown pigment (?) spots along their entire length (Text-fig. 4, fig. 7).

Intestine thin-walled, light to dark brown, describing an S-shaped loop in posterior half of body. Radial longitudinal muscles broad, flat, undivided, dark brown straps. Dorsal radial muscles lie very close together for most of their length (Text-fig. 4, fig. 1); area of mid-dorsal interradius greatly reduced.

Calcareous deposits of bodywall four-armed tables, extremities of arms branching dichotomously, forming terminal perforations. Arm length varies from 0.04mm to 0.08mm. A spire comprising four pillars united by several crossbars arises from centre of each table, at point of union of arms. Spire long, with several crossbars, but sometimes (Text-fig. 4, fig. 4) short, with but one or two crossbars. Average page 17
Text-fig. 4.—Bathyplotes natans (Sars): Fig. 1, internal anatomy, right ventral view; Fig. 2, portion of calcareous ring; Fig. 3, portion of gonad; Fig. 4, four-armed tables; Fig. 5, prickly rods from tentacles; Fig. 6, curved rods from tentacles; Fig. 7, portion of respiratory tree. Abbreviations: a.n., anterior notch; c.r., calcareous ring; dors.r.l.m., dorsal radial longitudinal muscle; g.d., genital duct; g.tub., genital tubules (caeca); int., intestine; ir.p., interradial piece; p.v., polian vesicle; r.p., radial piece: resp.t., reipiratory tree; s.c., stone canal; tent., tentacles.

Text-fig. 4.—Bathyplotes natans (Sars): Fig. 1, internal anatomy, right ventral view; Fig. 2, portion of calcareous ring; Fig. 3, portion of gonad; Fig. 4, four-armed tables; Fig. 5, prickly rods from tentacles; Fig. 6, curved rods from tentacles; Fig. 7, portion of respiratory tree. Abbreviations: a.n., anterior notch; c.r., calcareous ring; dors.r.l.m., dorsal radial longitudinal muscle; g.d., genital duct; g.tub., genital tubules (caeca); int., intestine; ir.p., interradial piece; p.v., polian vesicle; r.p., radial piece: resp.t., reipiratory tree; s.c., stone canal; tent., tentacles.

page 18 diameter of tables 0.13mm. No other deposits were found elsewhere in bodywall, apart from some rods with one or two spines in ventrolateral papillae.

Tentacles with rods of two types. Large thick prickly rods of average length 0.35mm (Text-fig. 4, fig. 5), sometimes curved or Y-shaped, often with a small number of perforations at extremities, lie in tentacle stems and terminal discs. Smaller curved rods present in tentacle discs (Text-fig. 4, fig. 6) ; these usually bear small spines on greater curvature; lesser curvature smooth. Average length of smaller rods 0.15mm.

Remarks : In features of internal anatomy and calcareous deposits, these specimens most closely resemble the type species of Bathyplotes, to which they have been assigned. The tables with short spines and with large perforations, while not especially typical of B. natans, appear to fall within the range of variation for that species.

Bathyplotes natans is a species with a wide distribution. Ludwig (1901) noted that it ranges from 60° to 69° N. latitude along the coast of Norway, at a depth of 183–1,229 metres. Mortensen (1927) describes the distribution as "Faroe Channel and off the Irish west coast ... elsewhere distributed from Lofoten to the Cape Verdes; also recorded from the West Indies and off Japan". Deichmann (1954) noted that the Japanese record needed reinvestigation. This apparently has not been done, but the occurrence of the species in New Zealand waters establishes the species in the Pacific Ocean, and the Japanese record is probably correct. The bathymetric range of this essentially cosmopolitan species is approximately 200–1,600 metres.

Mesothuria Ludwig, 1894

Atlantis Herouard, 1902, Zygothuria Perrier, 1898.

Diagnosis : Gonad comprising only a single tuft. Ventral surface flattened. Tubefeet all over body, or in single or double rows on paired radii. Deposits tables with approximately circular disc bearing large perforations, and a spire composed of three processes united by crossbars.

Type Species: Mesothuria multipes Ludwig.

Remarks: This is a large genus, containing in excess of 25 species, of which several are cosmopolitan in distribution. Deichmann (1930, 1954) is in favour of retaining Zygothuria Perrier (type species Zygothuria lactea (Theel)) as a distinct genus to accommodate the "almost footless" species Z. lactea. Heding (1942) reduced Zygothuria to the status of a subgenus of Mesothuria. It does not now seem necessary to retain Zygothuria, even as a subgeneric name.

Mesothuria lactea (Theel)

Holothuria lactea Theel, 1886a, p. 183; 1886b, p. 6.

Holothuria aspera Bell, 1892, p. 50.

Zygothuria lactea Perrier, 1902, p. 322, Pl. XVII, figs. 1–10; Deichmann, 1930, p. 108, Pl. 8, figs. 8–9; Deichmann, 1954, p. 386.

Zygothuria lactea var. oxysclera Perrier, 1902, p. 323.

Mesothuria lactea Herouard, p. 21, Pl. 1, figs. 17–19; Sluiter, 1910, p. 332; Herouard, 1923, p. 13, Pl. 4, figs. 1–3; Mortensen, 1927, p. 382, fig. 227.

Mesothuria (Zygothuria) lactea lactea Heding, 1940, p. 340, Text-fig. 7 (3); Heding, 1942, p. 9, Text-fig. 9.

Material Examined: None.

Remarks: This species was originally described from specimens collected near New Zealand ("Challenger" Station 169) and near the Azores (Stn. 78), in depths of 1,260 metres and 1,800 metres respectively (Theel, 1886a). Subsequently the species was collected from many localities in the Pacific and Atlantic Oceans, and in the Arctic region. Mesothuria lactea is cosmopolitan, in depths ranging from approximately 700 metres to 5,100 metres.