Planostrea pestigris ( Hanley, 1846 )

Lam, Katherine & Morton, Brian, 2009, Oysters (Bivalvia: Ostreidae And Gryphaeidae) Recorded From Malaysia And Singapore, Raffles Bulletin of Zoology 57 (2), pp. 481-494 : 487

Planostrea pestigris ( Hanley, 1846)

Common name: Flat oyster ( Fig. 4 )

Ostrea pestigris Hanley, 1846: 106–107 .

Ostrea paulucciae Crosse, 1869: 188 .

Ostrea palmipes Sowerby, 1871 , sp. 56, Fig. a–c.

Planostrea pestigris – Harry, 1985: 143, Fig. 22.

Ostrea pestigris – Morris, 1985: 129, Pl. 4A–D; Scott, 1994: 69, Pl. 5B.

Material examined. – Holotype: [ USNM] 666809, ‘‘ Isle of Luzon ; on rocks’’, coll. H. Cumming, no date, dry shell, height, 75 mm.

S y n t y p e o f O s t re a p a l m i p e s: [N H M] 1 9 0 7.1 0.2 8.7 7 & 1907.12.30.10–11, one dry shell no other data.

Description. – Shell of moderate size, up to 50 mm in height,

40 mm in length and 4 mm in width. Outline subquadrate, attenuated dorsally. Shell laterally compressed, generally in one plane. Right valve smaller and closely fitting within the margin of the left valve. Right valve smooth, with the outer shell layer continuous and having few growth increments. Little shell erosion and few encrustations. Exterior cream to yellowish, usually with dark lavender irregular rays. Left valve usually either light or white, with between 6–10 low, widely-spaced ribs which may have obsolete hyote spines at some growth increments. Attachment area small and restricted to near the left umbo. Most specimens are attached to shells of other bivalves and gastropods. Some are unattached. Chomata small, uniform, closely-spaced and in straight lines along the anterior and posterior margins near the hinge. Hinge line straight and short. Marginal commissural shelf on the left valve wide and flat with a well-defined inner edge. Interior of the shell white with a pearly nacre. Chalky deposits prominent on the commissural shelf of the left valve only. Adductor muscle scar white, large and elongate, positioned approximately at the middle of the shell, slightly towards the posterior.

Distribution and habitat. – Indo-West Pacific, the Philippines, Taiwan, Thailand, North Borneo, South and East China Seas, Yellow Sea, Shandong Province, China to Honshu, Japan, Townsville, Queensland, Australia, Mauritius, Intertidal zone to - 10 m on rocks and corals.

Remarks. – Harry (1985) proposed a new genus, Planostrea , exclusively for Ostrea pestigris . This genus is described as of moderate size (to 75 mm), very compressed in one plane, being non-lamellose and with a continuous outer shell layer. Well-developed chomata line up along the dorsal margins near the hinge, with a wide and flat marginal commissural shelf and a lavender outer surface with radial stripes. This species can be distinguished easily from other oysters because of the consistent shape of a smooth, flattened, circular disc. Unlike other oysters, it is usually free from encrustations and the influence of the substratum to which it is attached. This species can be distinguished from Ostrea densellamellosa and Alectryonella plicatula by having a smooth and straight shell margin. The latter two have crenulated shell margins. It is also different from Hyotissa numisma in having a white interior instead of a violet one and in lacking the vesicular microstructure of gryphaeids. This species has been synonymised with Ostrea paulucciae Crosse, 1869 , and Ostrea palmipes Sowerby, 1871 , on the basis of similar shell characters (Tchang & Lou, 1956). Therefore, the O. palmipes from Malaysia as identified by Morris & Purchon (1981) is actually Planostrea pestigris .

Voucher – [ NHM] 20090291, Pelangi Beach, intertidal sand, Pulau Langkawi, Malaysia, coll. B. Morton, 4 Feb.2004, one individual preserved in alcohol .

Figures

Fig. 4. Planostrea pestigris (Hanley, 1846) from Pulau Langkawi, Malaysia (NHM20090291). A, external view of the right shell valve, B, external view of the left shell valve, C, internal view of the right shell valve and D, internal view of the left shellvalve.