*Images in development
Thyasiroidea
Shell subovate expanded anteriorly, beaks behind the midline (L>H).
Shell outline subircular (H=or >L) to ovate-polygonal (H>L)
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
Anterior and posterior dorsal margins sloping steeply, posterior blunt, gill with 2 demibranchs
Anterior dorsal margin indistinct not sloping steeply, posterior subacute, gill with 1 demibranch
Internal dorsal margins either side of beaks minutely denticulate
Internal dorsal margins smooth
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)
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
Shell with commarginal sculpture or incremental lines only
Adductor scars thickened and raised, often showing white through the thinner shell
Genaxinus eumyarius
Adductor scars not thickened
Outline quadrate, ventral margin almost straight, posterior sulcus weak, auricle absent
Axinus grandis
Outline ovate to polygonal, ventral margin rounded
Submarginal sulcus present, auricle absent, posterior sulcus weak
Submarginal sulcus with auricle or submarginal sulcus absent
Outline rhomboidal distinctly higher than long, ventral margin narrowly rounded, posterior area distinct flat to shallowly excavated
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
Ventral extremity in line with midline, posterior bi-sinuate to evenly curved
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
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
Posterior sulcus prominent
Hinge with a cardinal peg in RV
Anterior dorsal (lunule) margin very short, horizontal. Gill of a single demibranch
Axinulus croulinensis
Anterior dorsal (lunule) margin long, sloping
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
Auricle and posterior sulcus prominent, posterior outline bi- or tri-sinuate
Auricle low and posterior sulcus shallow, posterior outline weakly sinuous
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
Larval shell large greater than 200μm, periostracum silky, (northern)
Thyasira gouldi
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
