Pectinoidea | ID Keys | Marine Bivalve Shells of the British Isles

#1

Robust shells with distinct, external, radial sculpture of riblets, ribs or plications, ctenolium present

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Thin to fragile glassy shells if radial sculpture present then ctenolium absent (mostly deep water)

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#2

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Valves equally convex

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One valve flat, the other convex

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#3

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14-17 well developed ribs

Pecten maximus

18-20 low weakly developed ribs (alien on stranded marine litter)

Euvola ziczac

#4

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Radial sculpture weak or very fine

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Radial sculpture of distinct ribs or undulations

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#5

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Shell with commarginal undulations and very fine radial striations (bathyal/abyssal)

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Shell lacking commarginal undulations

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#6

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Radial sculpture distinct, riblets present of the right valve ear (Atlantic Margin)

Hyalopecten pudicus

Radial sculpture weak, ears smooth (Arctic)

Hyalopecten frigidus

#7

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Sculpture the same on both valves, up to 50 smooth riblets, some shells becoming undulated.

Palliolum tigerinum

Sculpture on left valve stronger, up to 70 fine riblets bearing raised scales

Palliolum striatum

#8

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Radial sculpture plicate (undulations) with or without underlying radial riblets

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Radial sculpture of ribs or riblets only

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#9

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Ears almost equal in size, with or without underlying radial riblets

Pseudamussium peslutrae

Anterior ears much longer than posterior

Palliolum tigerinum

#10

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Sculpture of primary ribs and radial striations

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Sculpture of primary ribs and secondary smaller riblets

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#11

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Sculpture of 19-22 ribs, ears subequal

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Sculpture of 25-35 narrow ribs bearing flattened spines, easrs very unequal

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#12

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Ribs with radial striations

Aequipecten opercularis

Each rib bordered by a row of fine spines (alien on stranded litter)

Aequipecten heliacus

#13

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27-35 ribs, multi-coloured

Mimachlamys varia

41-48, white

Mimachlamys varia nivea

#14

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Disc elongate with up to 50 ribs of uneven size, becoming distorted and cemented after 10-20mm

Talochlamys pusio

Disc subcircular shell not distorted or cemented

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#15

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Shell with distinct primary (c.15) and secondary ribs and riblets (to 45) shelf edge/ bathyal

Karnekampia sulcata

Primary and secondary ribles of similar size, to 140 in large shells (boreal/arctic)

Chlamys islandica

#16

Ctenolium present

Ctenolium absent

#17

Thin often brightly coloured with antimarginal microsculpure only (shelf)

Palliolum incomparabile

Glassy shells with antimarginal sculpture and commarginal rows of small vesicles (shelf edge/bathyal)

Delectopecten vitreus

#18

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With internal riblets

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Lacking internal riblets

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#19

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Exterior of left valve with narrow radial riblets

Parvamussium permirum

Exterior of left valve with commarginal lines only

Propeamussium lucidum

#20

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Radial rows of vesicles present on left valve

Cyclopecten hoskynsi

No radial macrosculpture

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#21

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Commarginal ridges or undulations present

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No commarginal sculpture

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#22

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Commarginal ridges over whole valve

Cyclopecten ambiannulatus

Shell smooth except for few marginal undulations

Catillopecten eucymatus

#23

No antimarginal microsculpture

Similipecten similis

Antimarginal sculpture present on at least part of a valve

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#24

Antimarginal sculpture over whole of left valve

Similipecten greenlandicus

Sparse antimarginal sculpture restricted to umbo of left valve

Similipecten oskarssoni