Isognomon ephippium (Linnaeus, 1758)
saddle tree oyster
Isognomon ephippium
photo by FAO

Family:  Isognomonidae (tree oysters)
Max. size:  14 cm SL (male/unsexed)
Environment:  benthic; brackish; marine
Distribution:  Indo-West Pacific: from East Africa, to Melanesia; north to Japan and south to Indonesia.
Diagnosis:  Shell variable, irregularly rounded in outline, with height about equal to length. Dorsal margin straight and relatively short, not expanded posteriorly in a wing-like ear. Anterior margin sharply sinuous dorsally, ventrally strongly convex and extending well forward of umbones. Posterior margin slightly concave, forming an obsolete angulation with the rounded ventral margin. Umbones small, pointing at anterior end of dorsal margin. Outer surface covered with concentric lamellar processes, with very low radial ridge ending at posteroventral angulation. Ligamental area with a dozen transverse grooves. Nacreous area of the inner side of shell surrounded by a broad, non-nacreous margin. Colour: outside of shell horny to purplish brown. Interior nacreous, with a broad dark brown margin.
Biology:  Attached to rocks and other hard substrates, in marine and brackish water areas. Common in muddy estuaries and mangrove where it attaches to prop roots. Littoral and shallow subtidal levels (Ref. 348). Members of the class Bivalvia are mostly gonochoric, some are protandric hermaphrodites. Life cycle: Embryos develop into free-swimming trocophore larvae, succeeded by the bivalve veliger, resembling a miniature clam (Ref. 833).
IUCN Red List Status: Not Evaluated (N.E.) Ref. (123251)
Threat to humans:  harmless
Country info:   

Entered by: Sorongon-Yap, Patricia - 22.02.06

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