ID Keys
*Images in development

Pterioida & Mytiloida

Shell, triangular, mytilform, modioliform or oval
Go to #2
Shell alate (winged), subcircular-slightly pectiniform or elongated ventrally
Go to #21
Shell triangular, beaks terminal
Atrina fragilis
Shell mytiliform, modioliform or oval
Go to #3
Shells oval or modilioform with radial sculpture on all or part of shell
Go to #4
Shell mytiliform or modioliform lacking radial sculpture
Go to #10
Modioliform shells
Go to #6
Small shell (to 4mm) with prominent divaricate ribbing
Crenella decussata
Minute shell (to 1mm) with radial striations
Crenella pellucida
Sculpture over whole shell of radial riblets and raised commarginal lamellae
Rhomboidella prideauxi
Sculpture radial only absent medially
Go to #7
Shell tumid, rhomboidal, 15-18 anterior riblets
Musculus subpictus
Shell modioliform not inflated, 15 or fewer anterior riblets
Go to #8
Rather narrow ,modioliform with less than 40 posterior riblets
Go to #9
Somewhat wedge shaped, 40-60 posterior riblets, 12-15 anterior riblets
Musculus niger
Riblets prominent, 20-30 posterior, 8-10 anterior, vivid green and darker spotted colouration
Musculus costulatus
Riblets low relief, 30-40 posterior, 9-12 anterior, olive green to brown
Musculus discors
Beaks terminal, mytiliform. The 3 species of Mytilus present in British waters interbreed and produce hybrids. Separation on morphology is not always possible
Go to #11
Beaks subterminal, modioliform
Go to #13
Shell robust
Go to #12
Shell thin almost flexible with commarginal corrugations
Mytilus trossulus
Shell robust, distinctly hooked at the beak ie. anterior ventral margin concave
Mytilus galloprovincialis
Shell robust, anterior ventral margin straight
Mytilus edulis
Robust shells, umbos subterminal (shelf). Dyssodont teeth in juveniles under 2mm
Go to #14
Glassy or thin shells, umbos set back from anterior (mostly deep water). Dyssodont teeth in all
Go to #17
Periostracum of long simple bristles, internal anterior adductor buttress present, hinge crenulated below beaks
Modiolula phaseolina
Periostracal bristles if present serrated or smooth, interior anterior adductor buttress absent, hinge lacking crenulae
Go to #15
Periostracal bristles serrated, ligament margin long and straight
Modiolus barbatus
Periostracal bristles smooth or absent
Go to #16
Periostracal bristles absent, shell smooth, typically shaded amber with reddish rays
Gibbomodiola adriatica
Periostracal bristles present in juveniles, scars persisting in adults, shells uniformly brown becoming black
Modiolus modiolus
Glassy, outline oblique, dorsal margin steep becoming anterior
Go to #18
Thin to glassy shells modioliform but beaks set well back from anterior, dorsal and ventral margin subparallel
Go to #19
Inner posterior dorsal margin finely denticulate (bathyal)
Dacrydium ockelmanni
Inner posterior and anterior dorsal margins denticulate, denticles as rough parallel bars (arctic)
Dacrydium vitreum
Thin glassy shells, anterior and posterior dysodont denticles present, with sparse periostracal hairs (woodfall)
Go to #20
Thin shell with weak posterior dysodont denticles below ligament, periostracum smooth. (whalefall)
Idas simpsoni
Dorsal and ventral margin subparallel
Idas argenteus
Dorsal and ventral margins at a distinct angle to each other
Idas lamellosus
Ligament in multiple grooves along straight dorsal margin
Isognomon bicolor
Ligament external, sunken set in long line
Go to #22
Pinctada imbricata
Alate/wing shaped
Go to #23
Umbo small but prominent, pointed, posterior margin extends past posterior dorsal wing
Pteria hirundo
Umbo small, broad, posterior margin does not extend anywhere near to posterior dorsal wing
Pteria colymbus