ID Keys
*Images in development


Shells markedy inequivalve, one flat one concave
Go to #2
Shells equivalve or slightly inequivalve but one valve is never flat
Go to #3
Posterior dorsal margin concave
Pandora inaequivalvis
Posterior dorsal margin straight
Pandora pinna
Ligament set on a on a deeply sunken resilifer, visible externally but may be very small
Go to #4
Ligament set on an internal chondrophore or wholly internal resilifer, not visible externally
Go to #14
Shell nacreous, subovate to trigonal wedge-shaped with weak radial ridges and/or minute pustules or prickles arranged in radial rows
Go to #5
Shell chalky, subovate to oblong, lacking radial ridges, surface may be granular, but not arranged into radial rows
Go to #8
Shell wedge shaped, very broad anteriorly with weak radial ribs and microscopic prickles arranged in rows
Panacca loveni
Shell ovate to subspherical, lacking radial ribs but with microscopic radially arranged pustules
Go to #6
Shell subspherical, strongly umbonate, posterior rounded
Cetomya tornata
Shell subovate, posterior subtruncate
Go to #7
Internal ligament in a brooad shallow chondrophore, external ligament small, cardinal tooth in RV, pustules easily visible
Poromya granulata
Ligament wholly external, set in a shallow sunken resilifer, lacking teeth, pustules microscopic best seen at margins
Cetoconcha bulla
Beaks in front of midline, oval to oblong often mis-shapen
Thracia distorta
Beaks at or behind the midline
Go to #9
Outline subovate to subtrigonal (H≈L)
Go to #10
Outline oblong (L>H)
Go to #11
Outline subtrigonal, umbonate, narrowed posterior set off by a weak ridge, shell smooth
Thracia convexa
Outline subovate, posterior dorsal margin concave, shell with granular micro-sculpture
Thracia myopsis
Pallial sinus shallow, wide extending to only half way to point under resilifer
Thracia pubescens
Pallial sinus deep, rounded extending to point beneath the resilifer
Go to #12
Posterior area set off by a distinct angulation, posterior margin truncate, posterior area more coarsely granular than remainder
Go to #13
Posterior area weakly defined, posterior margin rounded subtruncate coarse granulation over whole of shell
Thracia villosiuscula
Posterior granulation coarse
Thracia gracilis
Posterior granulation fine
Thracia phaseolina
Chondrophore tooth-like extending into umbonal cavity, umbos with a small stress fracture
Go to #15
Chondrophore shallow or absent then ligament supported by lithodesma only
Go to #16
Oblong shell, beaks behind midline, posterior narrowed, with granular microsculpture
Cochlodesma praetenue
Subovate-trigonal, fragile, hyaline (lower slope, abyssal)
Cochlodesma tenerum
Elongate oval to oblong shells, beaks at midline
Go to #17
Subcircular to quadrate shells with beaks at midline or subquadrate shells with beaks in front of midline
Go to #18
Elongate ovate, posterior truncate, overall with fine radial raised lines and with agglutinated sediment grains especially on the posterior area
Lyonsia norwegica
Oblong, posterior obliquely truncate, posterior area set off by an oblique ridge, posterior area with radial riblets, anterior area with weak oblique ridges, overall with microscopic spines in radial rows
Allogramma formosa
Subcircular shell with coiled beaks and 13-16 acute carinate radial ribs
Spinosipella acuticostata
Subovate to quadrate shells lacking prominent radial ribs
Go to #19
Quadrate-polygonal solid shell with a median oblique carina and a lower carina on either side dividing shell into 4 regions
Halicardia flexuosa
Shell not massive or divided into regions by carinae
Go to #20
Shell triangular to subquadrate overall with microscopic pustules
Go to #21
Shells quadrate with fine radial raised lines
Go to #23
Shell triangular, beaks at midline, pustules arranged in rows
Verticordia triangularis
Shell obliquely oval or subquadrate
Go to #22
Shell subquadrate, posterior truncate, weak radial lines present
Lyonsiella abyssicola
Shell subovate, posterior rounded, radial lines absent, pustules large
Lyonsiella subquadrata
Posterior dorsal margin sloping creating a broadly rounded anterior margin and somewhat extended ventrally, radial line dense up to 50 in largest
Policordia densicostata
Posterior dorsal margin straight creating a narrowly rounded anterior profile. Similar shells from the subarctic and arctic are referred to Policordia jeffreysi. Policordia atlantica has a sculpture of sunken grooves rather than raised threads and is not recorded from the NE Atlantic.
Policordia gemma