Hyotissa sinensis (Gmelin, 1791)

Lam, Katherine & Morton, Brian, 2004, The Oysters Of Hong Kong (Bivalvia: Ostreidae And Gryphaeidae), Raffles Bulletin of Zoology 52 (1), pp. 11-28 : 26

Hyotissa sinensis (Gmelin, 1791)

Common name: Honeycomb oyster ( Figs. 6 D-F)

Ostrea sinensis Gmelin, 1791: 3335 ; Sowerby 1871, Pl. III, Fig. 5 . Hyotissa sinensis Morris, 1985: p. 120 -123, Pls. 1A, B; Scott, 1994:

70, Pl. 5D.

Material examined. – Type not studied, presumably in the Spengler Collection at the Zoologisk Museum , Copenhagen ( ZMUC), Denmark, or in the Adanson Collection of the Muséum National d’Histoire Naturelle , Paris , France ( MNHN). Voucher – One dry shell, (height 78.2 mm)( NHM 1981130 ), Mirs Bay, Hong Kong, trawl, 10 m, coll. J. D. Taylor, 23 Mar.– 8 Apr.1977 ; one dry shell (height 51.7 mm)( SBMNH 141713 ), southeastern waters of Hong Kong, trawl, 7-55 m, coll. P. H. Scott, 13 Apr.– 1 May.1992 .

Description. – Shell large, up to ~ 150mm in height, rounded to oval in outline. Shell is thick and heavy in large individuals. Surface irregularly folded with radial ribs on both valves. Shell margin with irregular wavy plications corresponding to rib positions. Attachment area on the left valve depends on substratum type. Two colour morphs are identified, i.e. pale yellow and deep purple. Chomata in a vermiculate pattern are restricted to the anterior and posterior hinge margins. Shell interior is white and covered by a layer of vesicular shell microstructure. Commisural shelf is broad and coloured either pale yellow or deep purple. The hinge line is straight and comparatively long. The adductor muscle scar is large, circular and positioned to the posterior side of the centre of the shell. It may be colourless, i.e. white, or cream or purplish brown depending on the individual and the presence of growth lines.

Distribution. – Hyotissa sinensis occurs in the sublittoral zone at Kat O Chau, Mirs Bay, at between 8 and 10 m, in the eulittoral zone of East Ping Chau and subtidal waters of southern Hong Kong. It also aggregates on the walls and ceiling inside the marine cave on Conic Island. This species favours marine salinities rather than estuarine conditions and is restricted to the Western Pacific from southern Japan, the coast of China to the Philippines and probably as far south as northern Queensland, Australia ( Scott, 1994).

Remarks. – Hyotissa sinensis has been considered to be synonymous with Hyotissa hyotis by some authors ( Morris, 1985). This species, however, can be distinguished from the latter by the weak irregular folding of the margins. H. hyotis has a sharp and acute plicate shell margin reflecting the shape and position of the well-defined, regularly-spaced radial ribs on both valves.

Figures

Fig. 6. Hyotissa from Hong Kong showing external and internal views of the right valves and the internal views of left valves. A-C. H. imbricata (SBMNH 345718). D-F. H. sinensis (NHM 20030494). Scale bar = 20 mm.

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.