ID Keys
*Images in development


Shell subovate expanded anteriorly, beaks behind the midline (L>H).
Go to #2
Shell outline subircular (H=or >L) to ovate-polygonal (H>L)
Go to #9
Shell subovate, posterior weakly angulate, all but smallest entirely coated with a rust coloured ferruginous deposit
Mendicula ferruginosa
Posterior distinctly more angulate than anterior, lacking deposits or only partially covered with ferruginous or black deposits
Go to #3
Anterior and posterior dorsal margins sloping steeply, posterior blunt, gill with 2 demibranchs
Go to #4
Anterior dorsal margin indistinct not sloping steeply, posterior subacute, gill with 1 demibranch
Go to #5
Anterior dorsal margin straight, posterior obliquely truncated
Thyasira tortuosa
Anterior dorsal margin curved, posterior blunt
Thyasira subovata
Internal dorsal margins either side of beaks minutely denticulate
Go to #6
Internal dorsal margins smooth
Go to #7
Posterior profile roundly angulate, no radial micro-sculpture
Adontorhina similis
Posterior profile bi-angulate, lower part of posterior margin somewhat truncated, radial micro-striations present
Adontorhina keegani
Prominent cardinal tubercle in left valve (abyssal Norwegian Sea)
Mendicula ockelmanni
Taxon under review  
Hinge plate below beak slightly thickened but not with a prominent tubercle (upper bathyal)
Go to #8
Posterior subacute (Atlantic Margin) black deposit over dorsal areas
Mendicula sp#1
Taxon under review  
Posterior ventral margin somewhat truncated (Norwegian Margin), some entirely encrusted with black deposit
Mendicula sp#2
[Taxon under review]  
Shell with dense radial rows of minute granules
Go to #10
Shell with commarginal sculpture or incremental lines only
Go to #11
Outline subcircular
Parathyasira subcircularis
Adductor scars thickened and raised, often showing white through the thinner shell
Genaxinus eumyarius
Adductor scars not thickened
Go to #12
Outline quadrate, ventral margin almost straight, posterior sulcus weak, auricle absent
Axinus grandis
Outline ovate to polygonal, ventral margin rounded
Go to #13
Submarginal sulcus present, auricle absent, posterior sulcus weak
Go to #14
Submarginal sulcus with auricle or submarginal sulcus absent
Go to #16
Outline rhomboidal distinctly higher than long, ventral margin narrowly rounded, posterior area distinct flat to shallowly excavated
Go to #15
Outline rhomboidal but scarcely higher than long, ventral margin broadly curved, posterior area indistinct
Thyasira cf. rotunda
[Taxon under review]  
Subarctic samples, larval shell smooth (The distinction between these species requires further confirmation as well as comparison with high arctic examples of T. dunbari that are pyriform in outline.)
Thyasira dunbari
Atlantic/Norwegian samples, larval shells with radial striations
Thyasira equalis
Ventral extremity in front of midline, posterior outline bi-angulate
Go to #17
Ventral extremity in line with midline, posterior bi-sinuate to evenly curved
Go to #19
Anterior hinge plate heavily thickened into elongate pseudo tooth and socket, submarginal sulcus and lunule deeply excavated. Gill of a single demibranch
Leptaxinus incrassatus
Hinge plate not greatly thickened, lunule and SMS not deep. Gill of 2 demibranchs
Go to #18
Outline pyriform, prominent auricle making posterior outline distinctly biangulate, hinge with small tubercular tooth, lunule flattened
Thyasira succisa
Outline ovate to pyriform, auricle low making posterior outline weakly biangulate, hinge lacking tooth. Lunule slightly elevated
Thyasira obsoleta
Posterior sulcus weak to absent
Go to #20
Posterior sulcus prominent
Go to #23
Hinge with a cardinal peg in RV
Go to #28
Hinge lacking teeth
Go to #21
Anterior dorsal (lunule) margin very short, horizontal. Gill of a single demibranch
Axinulus croulinensis
Anterior dorsal (lunule) margin long, sloping
Go to #22
Outline ventrally narrowed, sculpture of incremental lines only. Gill of a single demibranch
Axinulus brevis
Outline broadly curved ventrally, microscopically radially striated. Gill with both demibranchs
Thyasira sp. #1
[Taxon under review]  
Anterior extended and narrowly rounded (beaked), anterior dorsal margin long sloping gently
Thyasira sp. #2
Taxon under review  
Anterior no more extended than posterior, anterior dorsal margin sloping steeply or indistinct
Go to #24
Auricle and posterior sulcus prominent, posterior outline bi- or tri-sinuate
Go to #25
Auricle low and posterior sulcus shallow, posterior outline weakly sinuous
Go to #27
Posterior sinuose and submarginal sinus both deeply excavated with acute edges, outline trisinuate
Thyasira biplicata
Posterior sulcus and submarginal sulcus with rounded edges, posterior bisinuate
Go to #26
Larval shell large greater than 200μm, periostracum silky, (northern)
Thyasira gouldi
Larval shell smaller than 180 μm, periostracum obscure
Thyasira flexuosa
Shell height becoming greater than length, ligament proportionately longer than in T. scotiae. A shelf species
Thyasira sarsi
Shell height and length equal, ligament proportionately shorter than in T. sarsii. Only known from a bathyal chemosynthetic setting
Thyasira scotiae
Tumid shells, periostracum thin, yellowish
Axinopsida orbiculata
Not inflated, periostracum silky
Thyasira sarsi