ID Keys

Protobranchia

#1

Shell height greater than length, subcircular to triangular [c1, c2, c3], ligament internal in an anteriorly directed (opisthodetic) chondrophore = Nuculoidea & Pristiglomoidea

Shell longer than high, frequently subrostrate or rostrate [c4, c5, c6], ligament internal in a shallow resilifer or external = Nuculanoidea

#2

Shell subcircular or obliquely oval, hinge with few teeth subparallel to hinge plate [c7] = Pristiglomoidea

Shell triangular to subovate, hinge with numerous, prominent erect teeth [c8] = Nuculoidea

#3

Shell obliquely oval [c9]

Pristigloma alba

Shell subcircular [c10]

Pristigloma nitens

#4

Internal margin denticulate [c11]

Internal margin smooth [c12]

#5

Shell triangular or subtriangular [c13]

Shell subovate [c14], prominent larval shell, cancellate sculpture (abyssal)

Nucula atacellana

#6

Triangular, distinctly higher than long, marked decussate sculpture, commarginal ridges becoming stronger towards margin. (bathyal)

Nucula tumidula

Subtriangular, anterior slope much longer and more gentle than posterior. (shelf)

#7

Sculpture distinctly decussate, lunule with transverse corrugations, periostracum netted

Sculpture fine, lunule smooth, periostracum smooth

#8

Periostracum shiny

Nucula nitidosa

Periostracum matt

#9

Shell height 85% of length, periostracum uniformly coloured shades of olive

Shell height 80% of length, periostracum often with coloured rays

#10

Shells distinctly higher than long, triangular or rhomboidal

Shells longer than high subtriangular or subovate

#11

Shell triangular anterior and posterior equally inclined (abyssal)

Brevinucula verrilli

Shell rhomboidal, umbos inflated (upper slope, northern)

Ennucula corticata

#12

Shell subovate, posterior truncated, surface microscopically granular (bathyal)

Ennucula granulosa

Shell subtriangular or subovate, posterior acute

#13

Shell subtriangular, anterior slope long, almost straight (shelf)

Ennucula tenuis

Shell subovate, anterior slope curving (bathyal)

Ennucula corbuloides

#14

Hinge teeth few, elongate, subparallel with hinge plate

Hinge teeth pointed erect

#15

Shell elliptical

Lametila abyssorum

Shell cylindrical

Silicula fragilis

#16

Shells subrostrate with a posterior ventral sinus

Shells rostrate or subovate to oval

#17

Shells with a sharply pointed dorsally situated posterior beak, ligament both interior and exterior, gut loop multi-coiled

Shells with a pointed, medially or downwardly angled posterior beak, ligament interior, gut loop simple or multi-coiled

#18

Posterior much deeper than anterior, posterior below rostrum bulging

Bathyspinula subexcisa

Posterior a little deeper than anterior, sulcus below rostrum weak

Bathyspinula filatovae

#19

Rostrum blunt

Rostrum acute

#20

Shell thick becoming tumid, sculpture of fine co-marginal ridges

Shells normal thickness, sculpture of weak radial and co-marginal ridges, periostracum pustulose

Ledella pustulosa

#21

Posterior dorsal margin sloping (bathyal)

Ledella messanensis

Posterior dorsal margin almost horizontal, dorsal margins sunken close to umbos. (Arctic shelf)

Portlandia arctica

#22

Minute (<1.5mm), rounded tumid shells

Shells ovate to rostrate

#23

Outline elliptical

Outline subcircular (southern, bathyal)

Microgloma tumidula

#24

Shell smooth, teeth obscure

Microgloma guilonardi

Shell with commarginal ridges at margins, teeth prominent

Microgloma pusilla

#25

External ligament visible close to beaks

Ligament internal not visible in joined valves

#26

Shell oblong, posterior broad, roundly truncated

Malletia johnsoni

Shell subovate to elliptical, posterior pointed

#27

Subovate, robust shells with commarginal ridges

Neilonella latior

Elliptical, fragile smooth shells

Katadesmia cuneata

#28

Robust narrowly rostrate shells with prominent commarginal sculpture

Thin shells with weak sculpture, subovate to oblong

#29

Elongate shells, rostrum blunt

Oval shell, rostrum acutely pointed

Saccella commutata

#30

Commarginal ridges strong across whole shell

Nuculana minuta

Commarginal ridges weak posteriorly, strongest on anterior

Nuculana pernula

#31

Large, subelliptical shell (arctic/subarctic outer shelf)

Yoldia hyperborea

Shells rarely exceeding 10mm, subovate to oblong