Baseodiscus Diesing, 1850

Gibson, Ray & Sundberg, Per, 2002, Some heteronemerteans (Nemertea) from the Solomon Islands, Journal of Natural History 36 (15), pp. 1785-1804 : 1790

Genus Baseodiscus Diesing, 1850

Diagnosis

Based on accounts of several species of Baseodiscus given by Gibson (1974, 1979, 1985b), the genus may be diagnosed as: Heteronemertea without horizontal lateral cephalic slits, some species with shallow oblique grooves; proboscis with two (outer longitudinal, inner circular) muscle layers and no muscle crosses; rhynchocoel short, rarely more than one-third of the body length; rhynchocoel wall circular musculature not interwoven with adjacent body wall muscles; dorsal brous core of cerebral ganglia forked only at rear into upper and lower branches; nervous system with neither neurochords nor neurochord cells; foregut with distinct subepithelial gland cell layer, usually at least in part separated from the epithelium by delicate longitudinal, circular and/or oblique muscle strands; dermis well developed, with separate outer glandular and inner connective tissue zones; caudal cirrus absent; cephalic glands extensively developed, extending post-orally among the outer body wall longitudinal muscle bres; single apical organ present; excretory system mostly with external nephridiopores, but some species with eVerent ducts discharging into lumen of foregut; eyes present, small and numerous; sexes separate.

Baseodiscus quinquelineatus (Quoy and Gaimard, 1833) (gure 3)

Material examined

One specimen, from a coral reef at at Rove, close to the White River , just west of Honiara .

External features

The striking colour pattern of Baseodiscus quinquelineatus , typically comprising ve longitudinal, slender black or dark brown stripes (three dorsal, two ventral) on a white or cream background, is diagnostic for the species and is shown in gure 3. Reported variations in the typical colour pattern include ve dorsal and two ventral stripes, and examples in which the stripes are irregularly interrupted (see Gibson, 1979: 155–156, gure 7C, D). The specimen from Rove was about 100 cm long and 10 mm in maximum width; lengths of over 6 m and widths of more than 15 mm have been reported for this species ( Gibson, 1979).

Internal anatomy

Baseodiscus quinquelineatus was redescribed by Gibson (1979: 153–157, gure 7C–F, 8); the morphology of the present material is very similar and no signi cant diVerences could be distinguished.

Geographic distribution

Baseodiscus quinquelineatus has been recorded, under various synonyms (see Gibson, 1995) from the eastern coast of Australia, including the Great Barrier Reef Province, the Torres Straits, Japan, Singapore, Java, Ambon, Timor, New Guinea, the Loyalty Islands and the Solomon Islands.