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 |