ID Keys
*Images in development

Pterioida & Mytiloida

#1
Shell, triangular, mytilform, modioliform or oval
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Shell alate (winged), subcircular-slightly pectiniform or elongated ventrally
Go to #21
  
#2
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Shell triangular, beaks terminal
Atrina fragilis
  
Shell mytiliform, modioliform or oval
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#3
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Shells oval or modilioform with radial sculpture on all or part of shell
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Shell mytiliform or modioliform lacking radial sculpture
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#4
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Oval shells
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Modioliform shells
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#5
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Small shell (to 4mm) with prominent divaricate ribbing
Crenella decussata
  
Minute shell (to 1mm) with radial striations
Crenella pellucida
  
#6
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Sculpture over whole shell of radial riblets and raised commarginal lamellae
Rhomboidella prideauxi
  
Sculpture radial only absent medially
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#7
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Shell tumid, rhomboidal, 15-18 anterior riblets
Musculus subpictus
  
Shell modioliform not inflated, 15 or fewer anterior riblets
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#8
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Rather narrow ,modioliform with less than 40 posterior riblets
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Somewhat wedge shaped, 40-60 posterior riblets, 12-15 anterior riblets
Musculus niger
  
#9
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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
  
#10
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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
  
#11
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Shell robust
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Shell thin almost flexible with commarginal corrugations
Mytilus trossulus
  
#12
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Shell robust, distinctly hooked at the beak ie. anterior ventral margin concave
Mytilus galloprovincialis
  
Shell robust, anterior ventral margin straight
Mytilus edulis
  
#13
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Robust shells, umbos subterminal (shelf). Dyssodont teeth in juveniles under 2mm
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Glassy or thin shells, umbos set back from anterior (mostly deep water). Dyssodont teeth in all
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#14
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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
  
#15
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Periostracal bristles serrated, ligament margin long and straight
Modiolus barbatus
  
Periostracal bristles smooth or absent
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#16
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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
  
#17
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Glassy, outline oblique, dorsal margin steep becoming anterior
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Thin to glassy shells modioliform but beaks set well back from anterior, dorsal and ventral margin subparallel
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#18
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Inner posterior dorsal margin finely denticulate (bathyal)
Dacrydium ockelmanni
  
Inner posterior and anterior dorsal margins denticulate, denticles as rough parallel bars (arctic)
Dacrydium vitreum
  
#19
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Thin glassy shells, anterior and posterior dysodont denticles present, with sparse periostracal hairs (woodfall)
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Thin shell with weak posterior dysodont denticles below ligament, periostracum smooth. (whalefall)
Idas simpsoni
  
#20
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Dorsal and ventral margin subparallel
Idas argenteus
  
Dorsal and ventral margins at a distinct angle to each other
Idas lamellosus
  
#21
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Ligament in multiple grooves along straight dorsal margin
Isognomon bicolor
  
Ligament external, sunken set in long line
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#22
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Circular/quadrangular
Pinctada imbricata
  
Alate/wing shaped
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#23
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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