Crassostrea gigas ( Thünberg 1793 )

Lam, Katherine & Morton, Brian, 2009, Oysters (Bivalvia: Ostreidae And Gryphaeidae) Recorded From Malaysia And Singapore, Raffles Bulletin of Zoology 57 (2), pp. 481-494 : 485-487

Crassostrea gigas ( Thünberg 1793)

Common name: Giant Pacific oyster ( Fig. 3 )

Ostrea gigas Thünberg 1793: 140–142 , Pl. 6, Figs. 1–3 .

Ostrea gigas – Lischke 1869: 174.

Ostrea laperousii Schrenck 1861: 92–93 , Fig. 6 .

Ostrea laperousii – Schrenck 1867: 475–482, Pl. 19, Figs. 1–6 .

Ostrea (Crassostrea) gigas – Hirase 1930: 45–49, Figs. 61–63.

Ostrea (Crassostrea) lapérousei – Hirase 1930: 49–55.

Crassostrea gigas – Torigoe 1981: 304–305, 325, Pl. 2, Fig. 1 , Pl. 14.

Material examined. – Type not studied. The type material is probably in the University Museum , Uppsala, Sweden .

Voucher: [ NHM]20090290, Johor Strait, Malaysia, coll. K. S. Tan, Nov.2004, dry shells of three individuals .

Description. – Shell height up to ~ 60 mm, outline variable with usually spatulate to oval individuals. Attachment area of left valve depending on substratum type. Both valves concave with left valve more deeply cupped and hence with a deep umbonal cavity. Both valves with dichotomous radial ribs from the umbo; the tops of the ribs well-rounded, and radial ribs with growth squamae recognisable on both valves. Older part of the right valve, i.e., the dorsal surface, usually eroded. Wavy plications along the shell margins reflect the positions and height of the ribs. No chomata. Adductor muscle scar reniform, antero-dorsal border concave and close to the postero-ventral shell margin from the valve centre. External coloration of both valves is variable from white and light purple with deep purple lines radiating from the umbo. Internally, shell white with patches of chalky deposits and hollow chambers. Muscle scar colourless with occasional purple growth lines.

Distribution and habitat. – Distribution of native Crasssotrea gigas includes Japan, Korea, maritime districts of Russia and the Yellow Sea of China. Mariculture stocks occur in British Columbia to California, Hawaii, Guandong Province in China, Tasmania, New Zealand and Brazil (Inaba & Torigoe, 2004).

Remarks. – Morphological variations in shell form occur among individuals occupying different substrata. Growth form of the shell can be cup-shaped with a deep umbonal cavity, transversely flattened with a large attachment area on the left valve or dorso-ventrally elongated in mud grown individuals (Lam, 2003).

Figures

Fig. 3. Crassostrea gigas (Thünberg, 1793) from Johor Strait, Malaysia (NHM20090290). A, external view of the right shell valve, B, external view of the left shell valve. C, internal view of the right shell valve D, internal view of the left shell valve.

Fig. 1. Saccostrea cuccullata (Born, 1778) from Pulau Langkawi, Malaysia, showing external and internal views of the right and left shell valves. A–D, ecotype occurring on mangrove trees (NHM20090286), E–H, ecotype occurring on low intertidal beach rocks (NHM20090287), I–L, ecotype occurring on intertidal rocks (NHM20090288).

Fig. 2. Saccostrea mordax (Gould, 1850) from Pulau Langkawi, Malaysia (NHM20090289). A, external view of the right shell valve, B, internal view of the right shell valve and C, internal view of the left shell valve.

Fig. 6. Hyotissa imbricata (Lamarck, 1819) from Pulau Langkawi, Malaysia (NHM20090293). 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 shell valve.

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.

Fig. 5. Dendostrea folium (Linnaeus, 1758) from Pulau Langkawi, Malaysia (NHM20090292). A, external view of the right shell valve, B, external view of the left shell valve, C, anterior view of an individual, showing the “graspers” developed to hold on to a Modiolus micropterus shell, D, internal view of the right shell valve and E, internal view of the left shell valve.