Diagnosis: Midventral radius with a double row of pedicels. Dorsal surface lacking any large appendages.

Type Species: Benthodytes typica Theel.

Remarks: Benthodytes embraces approximately 20 species, of which one, B. typica, has a cosmopolitan distribution, while B. sanguinolenta appears to be confined to the Pacific Ocean. The species are most commonly found at depths of approximately 3,000 metres, and have been taken from depths in excess of 5,000 metres.

Benthodytes hystrix Sluiter Text-fig. 7

Benthodytes hystrix Sluiter, 1901b, p. 59, Pl. IV, fig. 4, Pl. IX, fig. 10; Heding, 1940, p. 367.

Material Examined: In the collection of the Department of Zoology, Victoria University of Wellington, VUZ 109, off Palliser Bay, 600 fathoms, mud, 2 specimens.

Description: Both specimens extensively damaged externally; some features of external anatomy impossible to determine. One specimen approximately 130mm long, while another approximately 155mm long. Body more or less cylindrical, four to five times as long as broad. Tentacles destroyed in both specimens. Mouth appears to lie on ventral surface of body, a short distance behind anterior end. Anus subdorsal, a large aperture. Bodywall thick, soft, but parts of dorsal side invested in a thin rough layer comprising calcareous deposits. (This layer of calcareous material may have been continuous in living specimens). Layer finely papillate; each papilla contains a calcareous deposit.

Colour in life, "uniformly dark purple". In alcohol, specimens grey ventrally, mottled dark purple dorsally.

The two specimens are a male and a female of same species. In both, oesophagus thin-walled and intestine describes a large S-shaped loop (Text-fig. 7, figs. 1, 2). Cloaca enlarged, attached to bodywall by fine muscle fibres. Entire alimentary canal purplish-black. Longitudinal muscles broad straps, dark brown in male, violet in female. Transverse muscles inconspicuous.

Male damaged anteriorly, lacking water-vascular ring and some related structures, but in female, there is a single cylindrical Polian vesicle 45mm long, which arises from ventral side of water-vascular ring. Dorsally, stone canal emerges from ring vessel, terminating in a small bulbous madreporite, which opens to exterior in dorsal interradius, about 20mm from anterior end of body.

Gonad well developed in both specimens. In male, there are two genital ducts, each about 45mm in length, which subtend short branching tufts of genital caeca. Female has two genital ducts, one being about 30mm long, the other almost twice that length. Genital caeca composed of a small number of conspicuous bifurcate sacs, containing large eggs 0.9–1.1mm in diameter. In male and female, the two genital ducts unite to form a single canal which opens to exterior immediately adjacent to madreporite (Text-fig. 7, figs. 1, 2).

Calcareous deposits present in bodywall, gonad, stone canal and madreporite.

Bodywall with large numbers of four-armed spicules, arms radiating from a central point, which also carries two smaller processes; arms 0.4–0.6mm in length, page 29

Text-fig. 7.—Benthodytes hystrix Sluiter: Fig. 1, internal anatomy of female, left ventral view; Fig. 2, internal anatomy of male, right ventral view; Fig. 3, calcareous meshwork from madreporite; Fig. 4, four armed deposits of male; Fig. 5, unusual deposit from male specimen; Fig. 6, deposits from male genital duct; Fig. 7, rods from stone canal; Fig. 8, four armed deposits of female; Fig. 9, developing genital duct deposit; Fig. 10, deposits from female genital duct. Abbreviations: an., anus; cl., cloaca; g.d., genital duct; gon., gonad; int., intestine; mad., madreporite; mad.d., stone canal; m.f., muscle fibres; oes., oesophagus; p.v., polian vesicle; r.l.m., radial longitudinal muscle; r.v., ring vessel.

page 30 spinous, curved; inner faces of central processes densely spinous (Text-fig. 7, figs. 4; 8). Spicules of male (Text-fig. 7, fig. 4) differ little from those of female (Text-fig. 7, fig. 8), although in former they bear fewer spines. Deposits orientated in body wall in such a way that curved arms are directed inwards, and the central processes project above level of the bodywall. A single spicule of unusual shape was found in bodywall of male specimen (Text-fig. 7, fig. 5).

Walls of genital ducts and caeca carry three- to five-armed deposits. Those of female (Text-fig. 7, fig. 10) more robust than those of male (Text-fig. 7, fig. 6). Ends of arms smooth or weakly spinous. Developmental stages of these deposits also common (Text-fig. 7, fig. 9).

Madreporite invested in complex meshwork of calcareous material (Text-fig. 7, fig. 3), which also contains four-armed spicules of type found in gonad and genital caeca. Stone canal contains straight rods of average length 0.3mm with spinous extremities (Text-fig. 7, fig. 7), as well as widely scattered four-armed deposits.

Remarks: The specific identity of these specimens is not clear, for external features cannot here be used as a guide in determining the species. The calcareous deposits of the skin and gonads resemble those described by Sluiter (1901) for Benthodytes hystrix, a single specimen collected in the East Indies at a depth of 2,798 metres. Some differences in spiculation, especially in regard to the size of the spicules and certain features of their shape, between the present material and Sluiter's may not be significant, when the unique character of the spicules themselves is considered. Ohshima (1915) notes that B. gotoi has some spicules of exactly the same type as those in B. hystrix, but also has others with an anchor-shaped spire, similar to those in B. anchora Herouard. Theel (1882) illustrates the gonads of male and female of B. abyssicola Theel, and his figures show that the gonads in that species closely resemble those of B. hystrix. It is apparent that sexual dimorphism of this nature is not uncommon throughout the elasipods. The slight differences between the calcareous deposits of male and female in the present material are not important, but it is of considerable importance to have some indication of the range of variation of these deposits.

Distribution: B. hystrix was previously known only from the East Indian region in depths ranging from 768 to 2,798 metres (Sluiter, 1901b, Heding, 1940).