Characteristics of Isognomon isognomon

Order Pteroimorpha

·         Subclass of Bivalvia

·         Large taxon of epibenthic bivalves

·         Lamellibranch gills

·         Attach to substrates using byssus or cementation

·         Mantle margin not fused

·         One foot is reduced

·         Gills are usually large and assist in feeding

Superfamily Pterioidea

Family Isognomonidae

·         Mesozoic species

·         Tropical and warm temperate environment

·         Typically equivalve or mytiliform in outline

·         Umbones are incurved a little and some are not at all

·         Lack of anterior auricle

·         With or without anterior byssal gape, affecting both valves

·         Commissure or joints are either planar or undulantes

·         Surface ornaments are either smooth or concentrically lamellose. Some are all irregularly undulating

·         Ligament areas are wide, flat with numerous narrow ligament pits

·         Has single large, sub-centrally located adductor muscles

·         Shell structure are relatively thick

Genus Isognomon

·         Structure of the ligament extends along the entire dorsal surface of the shell

·         Massive byssus

·         Nacreous area is relatively large and its margins are less definite

·         No pallial retractor

·         No corresponding ride within distal region of the shell

·         Straight hinge

·         Toothless but has a series of short ligamental pits that resemble tooth-like structure

Species- Isognomon isognomon, Pacific Toothed Oyster

·         Shells are straight or slightly curved (inconsistent)

·         Hinge teeth is about equal to the width of shell

·         Colouration of exterior- Inconsistent mixture of purple, black and brown

·         Short posterior wing

·         Large internal mother-of-pearl area but narrow non-mother-of pearl border

·         Elongated and vertically disposed

·         Can be found in clusters of single on the underside of rocky substrates and crevices

·         Widely spreaded throughout Indo-Pacific region and northern Australia