ID Keys

Yoldiellinae

#1

Shell large (to 15mm), robust; posterior subrostrate (c1) to pointed (c2) . Posterior area weakly carinate (keeled)(c3). Lunule and escutcheon variously developed; Reslifer forms a well developed chondrophore projecting below the beaks (c4). = Portlandia

Shell small (to 7mm), fragile. Subovate [c5] to deeply oval [c6]. Lunule and escutcheon absent. Resilifer not expanded into a projecting chondrophore [c7][c8]. = Yoldiella

#2

Posterior dorsal margin almost horizontal, dorsal margins sunken close to umbos. Rostrum acute, slightly flexuose. Surface with slight commarginal sculpture (Arctic shelf).

Portlandia arctica

Posterior dorsal margin almost horizontal. Rostrum blunt, truncated not flexuose. Surface glossy and lacking any sculpture.

Portlandia intermedia

#3

Umbo posterior to the midline of the shell, directed posteriorly; shell distinctively 'bean' shaped and yellow in colour.

Yoldiella fabula

Umbo at the midline or anterior to the midline of the shell.

#4

Hind-gut extends across the both valves.

Hind-gut contained within the right valve only.

#5

Hind-gut configuration - Right valve: parallel or relatively close, tapering anteriorly. Left valve: single loop. Shell sculpture absent.

Hind-gut configuration - Right & left valve: complex multicoiled loop position high in the shell towards the umbos. Shell with fine, regular commarginal striations.

Yoldiella insculpta

#6

Hind-gut configuration - Right valve: parallel, very close together (touching); ventral margin deeply rounded ; posterior margin slightly pointed, anterior margin narrowly rounded; umbo small relative to the size of shell.

Yoldiella curta

Hind-gut configuration - Right valve: close together, not parallel, tapering anteriorly; ventral margin shallowly rounded, occasionally straight; posterior margin truncated; umbo large relative to the size of shell; Shells rarely beyond 2.5mm in length.

Yoldiella annenkovae

#7

Hind-gut forms complex series of coils.

Hind-gut forms a simple, single loop or reverse 'figure of 8' loop.

#8

Shell tumid (inflated), and moderately inequilateral; posterior, anterior and ventral margins all broadly rounded.

Yoldiella jeffreysi

Shell less tumid, only slightly inequilateral; posterior and ventral margins broadly rounded. Anterior margin narrowly rounded. Dorsal margin slightly convex with obvious raised 'humps' at either side of the umbo.

#9

Hind-gut forms a simple single loop. Shell may be inequilateral or equilateral.

Hind-gut forms a reverse 'figure of 8' loop; Shell inequilateral, Ventral margin broadly rounded, lowest extremity posterior or midline. Posterior margin broadly rounded.

Yoldiella valorousae

#10

Shell inequilateral, umbo anterior to the midline of the shell

Shell equilateral, umbo at the midline of the shell.

#11

Umbo small relative to shell size. Posterior extremity at, or above, the horizontal midline.

Umbo broad and prominent relative to shell size. Posterior margin narrowly rounded. Posterior extremity at, or below, the horizontal midline.

#12

Posterior, anterior and ventral margin all broadly rounded. Posterior extremity at the horizontal midline of the shell; Distinct notch at the junction of the posterior dorsal margin and umbo; Shell very compressed laterally relative to size.

Yoldiella biscayensis

Posterior margin obliquely truncated. Posterior extremity well above the horizontal midline of the shell, becoming slighlty rostrate in large specimens.

#13

Dorsal margin gently sloping, slightly convex and crimped. Shell elongate, narrow in height. Ventral margin shallowly rounded.

Yoldiella lucida

Dorsal margin steeply sloping, straight to slightly concave Ventral margin deeply rounded.

Yoldiella incala

#14

Dorsal margin steeply sloping, slightly concave. Posterior margin narrowly rounded. Shell outline almost trigonal in shape. (Shallow depths <500m).

Yoldiella philippiana

Dorsal margin gently sloping sloping, slighlty convex. Posterior margin narrowly rounded, may have slight flex or truncation. Shell elongate oval. Umbo prominent, projecting above the dorsal region.

#15

Shell tumid, strongly inflated. Umbo very large and prominent relative to shell size. Posterior margin narrowly rounded.

Yoldiella lenticula

Shell moderately tumid. Posterior margin narrowly rounded, often with a slight flex or trucation to lower posterior margin. Umbo moderatly broad relative to shell size.

Yoldiella propinqua

#16

Shell moderately compressed to very compressed laterally. Shell fragile, not solid and robust in proportion to size. Hinge with obtuse internal angle (>90°).

Shell tumid, strongly inflated. Shell very solid in proportion to size. Umbo distinctly large in proportion to size. Hinge very broad, with acute internal angle (< or = 90°). Teeth robust.

Yoldiella solidula

#17

Shell outline deeply oval, height of shell 75-80% of length. Umbo distinctly small in proportion to shell size. Posterior margin weakly rostrate and flexuose in larger specimens. Dorsal margins gently sloping.

Yoldiella frigida

Shell outline ovate; Dorsal margin almost horizontal.

#18

Hinge distinctly weak relative to shell size, with internal angle almost 180º. Teeth weakly formed. Ventral margin lowest point posterior of the midline. (Deep water 1000-5000m).

Yoldiella thaerella

Hinge moderate relative to shell size. Ventral margin shallowly rounded, lowest point at the midline of shell. (Bathyal, rarely beyond 1000m).