Atorcula sp.

Hausmann, Imelda M., Nützel, Alexander, Roden, Vanessa Julie & Reich, Mike, 2021, Palaeoecology of tropical marine invertebrate assemblages from the Late Triassic of Misurina, Dolomites, Italy, Acta Palaeontologica Polonica 66 (1), pp. 143-192 : 160-161

Atorcula sp.

Fig. 16A, B .

Material.—Three teleoconch fragments (PZO 12815, 12816,

12817) from Lago Antorno surface samples, Italy, Carnian, Triassic.

Description.—Shell high-spired; one fragment (apex missing) comprises five whorls, is 13.4 mm high and 7.0 mm wide ( Fig. 16A ); whorls moderately convex; sutures distinct; shell smooth; growth lines parasigmoidal with shallow opisthocyrt sinus below suture and opisthocline on remaining part of whorl face; base moderately convex, smooth with growth lines only; transition from whorl face to base a rounded edge; protoconch unknown; two illustrated specimens ( Fig. 16A, B ) show circular borings: one specimen with two borings, one unsuccessful; other specimen with a single boring.

Remarks.—The high-spired shape, the smooth shell and the parasigmoidal course of the growth lines on the base suggest that the present specimens represent the genus Atorcula . However, Atorcula is also characterized by an axially ribbed larval shell but the protoconch of the present material is unknown. Moreover, Atorcula has spiral furrows on the base whereas the base of the present specimens lacks spiral furrows. Atorcula canalifera also has a less convex, almost straight whorl face. This species was obviously a preferred target for a boring predator. At least some of the specimens that were illustrated by Zardini (1978: pl. 27: 6–13) as Anoptychia canalifera ( Münster, 1841) are probably conspecific with the present specimens. These specimens are mainly from the location Costalaresc. As in the present specimens, several of Zardini’s (1978) specimens have drill holes.

Atorcula canalifera ( Münster, 1841)

Fig. 16C–E .

1998 Atorcula canalifera ( Münster, 1841 sensu Kittl 1894) ; Nützel 1998: 161–162, pl. 26: F(?), G–I. (additional synonymy therein)

Material.— Twelve specimens, 2 from bulk samples, 10 from surface samples; 7 from Lago Antorno ( PZO 12819 , 12888 , 2 figured specimens; PZO 12818 , 5 specimens); 5 from Misurina Landslide ( PZO 12697 , figured specimen; PZO 12696 , 4 specimens); Italy, Carnian , Triassic .

Description.—Shell high-spired slender, acutely conical; teleoconch fragment of 6 whorls 14.9 mm high, 6.3 mm wide; whorl face straight to very slightly convex; whorls smooth or with faint spiral striation; suture distinct; base f latly convex with several spiral furrows. Juvenile specimen ( Fig. 16E ) with relatively large larval shell with distinct axial ribs and a single smooth teleoconch whorl is preserved.

Remarks.—The material at hand is very close to Kittl’s (1894: pl. 4: 45, 46) type material of Atorcula canalifera (see Nützel 1998).

Stratigraphic and geographic range.—Carnian, Upper Triassic; northern Italy (Cassian Formation).

Figures

Fig. 16. Protorculid gastropods from Lago Antorno (A–D) and Misurina Landslide (E), northern Italy, Cassian Formation, Carnian, Upper Triassic. A. Atorcula sp., PZO 12816, in lateral view with drill holes (A1),A2, close up showing incomplete drillhole (right) and complete one (left).B. Atorcula sp., PZO 12817, in lateral view (B1), B2, close up showing drill hole.C. Atorcula canalifera (Münster,1841), PZO 12819, in apertural view.D. Atorcula canalifera (Münster, 1841), PZO 12888, in apertural view.E. Atorcula canalifera (Münster, 1841), PZO 12697, axially ribbed larval shell and first smooth teleoconch whorls, in lateral view.