Ostrea denselamellosa Lischke, 1869

Lam, Katherine & Morton, Brian, 2004, The Oysters Of Hong Kong (Bivalvia: Ostreidae And Gryphaeidae), Raffles Bulletin of Zoology 52 (1), pp. 11-28 : 24

Ostrea denselamellosa Lischke, 1869

Common name: Densely lamellated oyster ( Figs. 5 G-I)

Ostrea denselamellosa Lischke, 1869: 177 , Pl. 13, Figs. a, b, Pl. 14, Fig. l; Torigoe, 1981: 333, Pl. 22.

Ostrea auriculata Sowerby, 1871 , Pl. 25, Figs. 60a-c.

Ostraea multicostata Sowerby, 1871 , Pl. 25, Fig. 61.

Material examined. – Type not studied. Probably in the Naturhistorisches Museum, Vienna, ‘‘prop Jedo et Nagasaki’’(near Tokyo and Nagasaki) .

Description. – Shells are ~ 70mm in dorso-ventral height, and subtriangular to oval. Attachment of the left valve is restricted to a small area ventrally. The right valve is nearly flat and covered by dense layers of brown, overlapping, thin and brittle lamellae, or scales, arising from growth lines. The left valve is either white or purple, slightly cupped with radiating ribs ending in a densely plicate margin. Chomata are inconspicious along the anterior and posterior margins near the hinge. The hinge line is straight and short. Ligament area short. The interior of the shell is white with yellow patches and has a pearly nacre. Small patches of white chalky deposits are prominent on the interiors of both the left and right valves. The adductor muscle scar is colourless, half moon-shaped with lightly coloured growth lines. It is positioned dorsoventrally and slightly towards the posterior end of the shell.

Distribution. – Ostrea denselamellosa is a rarely-encountered species which occurs on the continental shelf (~ 20m) in the southern waters of Hong Kong, e.g. Cheung Chau, Po Toi Island. In a trawl survey of Hong Kong’s waters in 2002, only empty left valves were found. The only two existing complete specimens from Hong Kong have been deposited in the Australian Museum, Sydney (Registration number: c.108985). These were collected by fisherman at Cheung Chau in 1973. This species is common among the islands of Japan, Korea and along the northern coast of China ( Torigoe, 1981; Lee et al., 2000). It is a palatable oyster but difficult to obtain and only by dredging. Attempted culture in Japan has been unsuccessful (Cahn, 1950).

Remarks. – Some authors considered Ostrea futamiensis Seki, 1929 to be an ecomorph of O. denselamellosa . The two species have, however, been separated in terms of egg diameter, larval colour, differences in adult shell characters and by differences in the electrophoretic analysis of adductor muscle proteins ( Torigoe, 1981).

FAMILY GRYPHAEIDAE

SUBFAMILY PYCNODONTEINAE

Figures

Fig. 5. Dendostrea and Ostrea from Hong Kong showing external and internal views of the right valves and the internal views of left valves. A-C. D. folium (SBMNH 345717). D-F. D. crenulifera (NHM 20030493). G-I. O. denselamellosa (AM 108985). Scale bar = 20 mm.