Clio pyramidata Linnaeus, 1767 forma antarctica Dale, 1908a
This is a shelled, uncoiled, pelagic snail, up to 1.7 cm long. The shell is transparent, cylindrical in shape and round in cross-section. The reddish, dark-brown visceral mass is seen through the shell. Growth lines are prominent beside the strong transverse wavy sculpture on the surface. The lateral sides are rounded in cross section and only developed in the most upper part of the shell. It is a good swimmer that feeds on phytoplankton and protozoa. It lives in the subantarctic of the southern oceans (Clio p. antarctica).
A faint dorsal and a broad ventral rib are found in the most anterior portion of the shell, and the lateral ribs bordering the ventral side are only visible near the shell aperture. In damaged or not fully grown shells these ribs are usually invisible. Transverse striae make the shell resemble that of Hyalocylis striata. The shell is completely straight. The embryonic shell is pointed and separated from the rest of the shell by a depression. When the shell is intact it is quite long in relation to its width. The cross-section near the embryonic shell is round, near the aperture it is nearly round. A fully grown specimen may have a depressed ventral side near the aperture, so the cross-section is more rounded triangular. The border of the dorsal aperture is slightly higher than the ventral one, but in all other formae of the species, this difference in height is greater.
The shell measures up to 17 mm long.
A special description is not available.
The form is protandric hermaphrodite and sometimes strobilation occurs.
The form is a phytophage.
The forma antarctica is found directly south of the area of lanceolata and convexa. This forma is found in the W-Atlantic between 20°S and 55°S, south of the Agulhas Current south of Australia and New Zealand at 50°S, and west of Chile at 50°S. That the forma antarctica occurs so far northward in the W-Atlantic, is comparable with the occurrence of other cold water species such as Limacina helicina subsp. antarctica forma rangi and Limacina retroversa subsp. australis. Normally it lives in Antarctic Intermediate Waters, see the Clio p. antarctica map.
Clio antarctica (nom. nov. pro. australis) d'Orbigny, 1836: 177 (1846): 688, pl. 8, figs. 9-11.
Syntypes: BMNH 18184.108.40.206, 3 fragments (dry collection, originally alcohol collection).
Type locality: 57°10'S 70°W. Coll.: CVAM.