Diagnosis

Shell large, trochoid-biconical, laterally ex-panded, sculptured with fine, low, and densely cancellate threads on teleoconch II.

Description
Shell large (up to 11 mm in diameter), trochoid, biconical, wider than high, particularly in early juveniles . Protoconch of one whorl, 241-270 µm in diameter, with flocculent sculpture; apertural margin slightly sinusoid, without varix. Teleoconch I of 1/2 to 5/8 whorls, sculptured with 15-25 fine axial lines; interstices with fine, low growth lines; axials often increasing in strength with growth . Teleoconch II of up to least three whorls.Base slightly convex, with approximately 50 fine axial lines in specimens of 1 mm, approximately 150 in specimens of 5.6 mm, crossed by approximately 15 finer spiral threads at 1 mm and 50 spiral threads at 5.6 mm. Selenizone at periphery, with distinct axial lamellae, keels low, thin, fragile. Slit open, with margins parallel in small specimens, converging to almost touching at apertural margin in fully grown specimens. Umbilicus open, continuously sloping with base, wide in juveniles, progressively narrowing with growth. Funiculus present in specimens up to approximate 1.5 mm, not evident in larger ones. Aperture rounded. Operculum multispiral, with central nucleus, yellowish in color.
Head-Foot: Color pale cream, uniform. Cephalic tentacles long, circular, densely papillate; papillae tubular, somewhat enlarged at base, about 25-32 pm in length, arranged in verticiles. Eyestalks short, fused at base of cephalic tentacles; eyes black, with lens. Head separated from foot by wide neck, with one pair of smooth tentacles on each side; anterior neck tentacle folliaceous, posterior neck tentacle cylindrical, sometimes bifurcated. Three pairs of conical, denselly papillate, epipodial tentacles, all with one postero-basal foliated expansion (epipodial sense organ?); first epipodial tentacle divided basally forming two tentacles. Papillae as in cephalic tentacles. Foot long, narrow, with central longitudinal grove; anterior pedal mucus gland located in longitudinal groove at anterior region of foot. Columellar muscle thick, trapezoidal in outline.
Radula: Rhipidoglossate. Rachidian tooth trapezoidal at base, cusp with denticles parallel to radula rows; central denticle largest, six narrower pointed denticles on each side. Five pairs of lateral teeth; laterals 1-3 similar in outline, overlapping at their widely expanded bases; cusps elongate, tongue-like, with a sharp main denticle, narrower, slightly curved denticles at both sizes: 6-7 on outer side, 4-5 on inner side; fourth lateral tooth narrower than laterals 1-3, with one sharp main denticle, 3-5 additional tiny denticles on outer side; lateral tooth 5 claw-shaped, well separated at base from other laterals, with one main terminal denticle, several smaller denticles on both sides. Marginal teeth numerous (~ 30), long, narrow, becoming more delicate towards edge of radula; first marginal tooth enlarged laterally at base; shaft, cusp similar to that of remaining marginal teeth.

Anatoma euglypta is the largest of all anatomid species with up to 11 mm shell size. The Antarctic Anatoma shiraseae Numanami & Okutani, 1990, differs from A. euglypta in having a keel on the shoulder, a distinctive constriction below the selenizone, and coarser sculpture. Thieleella amoena (Thiele, 1912) has a more globose shell, which is as wide as high, a reticulate protoconch, and fewer and more prominent axial lines than A. euglypta. Anatoma conica has a globose shell outline, the shell sculpture is much stronger and less dense and the suture is deeper. Anatoma euglypta resembles in general anatomy to Anatoma yaroni Herbert, 1986, Thieleella reticulata Bandel, 1998 (identified by Sasaki, 1998 as Anatoma sp.), and Anatoma sp. of Strasoldo (1991). Anatoma euglypta differs from A. yaroni in having the posterobasal expansion of tentacles (epipodial sense organ?) in the three epipodial tentacles instead only in the two latter as in A. yaroni, and in having three pallial tentacles instead of only one, as reported for A. yaroni by Herbert (1986). Five pairs of epipodial tentacles were reported for Thieleella reticulata, whereas only three pairs are present in A. euglypta. Strasoldo (1991) noted an anterior threefold tentacle, with an epipodial sense organ; a second threefold group is situated further posterior, and additionally a single tentacle on the left side is encountered.

Anatoma euglypta almost certainly has a circumantarctic distribution, having been recorded from 49°E to the Ross Sea, from the Bellingshausen and Weddell seas, the Antarctic Peninsula, South Shetlands, South Orkneys, South Georgia, the Burdwood Bank, Kerguelen and the Crozets in 18-870 m (122-870 m in the Ross Sea).

Circumantarctic, extending northwards up to off Argentina, the Scotia Arc Islands, and the Sub-Antarctic islands Kerguelen and Crozet, associated to Antarctic and Sub-Antarctic waters. 22-4420 m (living specimens: 94-4420 m)