Description
Shell medium size (up to 3.5 mm in diam¬eter), broad trochiform, broader than high. Protoconch of 3/4 to 1 whorl, 176-196 µm in diameter, with reticulate sculpture; apertural varix not connected to embryonic cap; apertural margin convex. Teleoconch I of one whorl, with 22-27 axial ribs; spiral cord in position of selenizone forming strong angulation. Teleoconch II with up to 2 1/2 whorls; shoulder with 37-39 axial ribs on first whorl, 38-47 cords on second whorl. Base with spirals somewhat stronger than on shoulder, but weaker than axial ribs. Selenizone at periphery of shell, with elevated keels; slit open, with parallel margins. Umbilicus open.

Head-Foot: Whitish, uniform. Cephalic tentacles long, circular, and papillate. Eyes, eye-stalks absent. Neck wide, with two smooth tentacles on each side. Three pairs of long, sparsely micropapillate epipodial tentacles, present; first epipodial tentacle bifurcated at base with one additional short posterior pteriform appendix (epipodial sense organ?); second and third tentacles simple. Papillae tubular, about 27 to 33 pm in length, spirally arranged, with distal cillia. Pallial cavity with two large bipectinate ctenidia, left one of about 10% larger. A relatively long, papillate, conical tentacle extending anteriorly, starting in posterior part of mantle sinus. Hindgut forming inclined "S".

Radula (See picture): Rachidian tooth trapezoidal at base, with nearly straight cups, showing main central denticle, 5 narrower denticles on each side. Five pairs of lateral teeth; laterals 13 similar in outline, overlap¬ping at their bases; cusps elongate, tonguelike, with one prominent main denticle, 4-6 denticles on outer margin, 3-4 narrower denticles on inner margin; fourth lateral tooth narrower than laterals 1-3, with more delicate serration at cusp; lateral tooth fifth wide at base, with prominent main denticle and strongly serrated margins in cusp. Marginal teeth long, narrow, main denticle straight sharp, numerous serrations on both sides.

Anatoma amoena is very similar to euglypta (Pelseneer) but differs in the much coarser axial sculpture, the spire being less depressed, with the ridges bordering the slit much wider apart, giving the last whorl a biangulate outline rather than the single angulation of euglypta.

Because Thieleella amoena is the type species of the genus Thieleella (now synonymous of Anatoma), we select here one of the three syntypes as lectotype with the express taxonomic purpose to fix the species concept.
The most similar species to Thieleella amoena is Anatoma conica. They share the overall globose shell, sculptured with strong axial ribs. However, T amoena has fewer and comparatively narrower axial ribs, a wider selenizone, and an inclined protoconch in apertural view, with flocculant sculpture. In addition, T amoena lacks the flared lower portion of the apertural lip. Furthermore, the two species seem to be allopatric: A. conica occurrs in the Magellan Region, whereas T amoena occurs in Antarctic waters.
Thieleella (= Anatoma) gunteri (Cotton & Godfrey, 1933) from eastern Australia has noticeably stronger sculpture on the shoulder compared to the base, more numerous and fainter spirals, and lacks the flared aperture.
Anatoma shiraseae from Antarctica has a distinct keel on the shoulder, a distinct constriction below the selenizone, and a protoconch with flocculant sculpture. The other Antarctic an atom id species, Anatoma euglypta, has a biconical shell that is not turreted, a hardly sunken suture, an extremely fine and dense axial and even finer spiral sculpture, and a protoconch with flocculant sculpture.

Known only from 89°E on the antarctic continent and from the Ross Sea in 342-870 m.

Circumantarctic. 161-1584 m (living specimens: 280-1584 m)

The original description of was in german. Please click german flag.