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Clio pyramidata Linnaeus, 1767 forma sulcata (Pfeffer, 1879)

Overview

This is a shelled pelagic snail, up to 2 cm long, with a transparent uncoiled shell. The shell is triangular in shape. The cross section is triangular and the lateral sides are not gutter-shaped. The reddish dark brown visceral mass is seen vaguely through the relatively thick shell. It is a good swimmer that feeds on phytoplankton and protozoa. It lives in the Antarctic waters in the upper water layers where it can occur in mass blooms (Clio p. sulcata from dorsal).

Taxonomic Description

The shell is transparent, colourless. The cross-section near the apex is round and triangular near the aperture (Clio p. sulcata line). The transverse striation is regular and pronounced growth lines are also visible (Clio p. sulcata). The ventral side has one rib, the dorso-lateral sides together have five large longitudinal ribs and sometimes seven. The nearly straight, lateral ribs of the ventral side diverge, in the caudal part the divergence is less than in the cranial half of the shell. A slight dorsal curvature of the shell is seen and, incidentally, a pronounced curving of the shell top to the left is observed. The triangular cross-section near the aperture has a nearly straight base, due to the fact that the ventral side does not bend inwards as in the forma lanceolata. The embryonic shell is droplet-shaped and pointed, separated from the adult shell by only a faint but evident incision. As in the forma lanceolata some specimens are found with chestnut-brown lips, others have white lips. The radula formula is 1-1-1, and is composed of poorly developed teeth (Clio p. sulcata radula). The cusps of the teeth are blunt and the dentation is absent or represented only by undulation. The number of transverse rows varies between 5 and 11.
Shell measurements: length up to 20 mm, width up to 10 mm.

Juveniles

A special description is not available, the juveniles are of the Clio p. pyramidata type.

Reproduction

The form is a protandric hermaphrodite, and sometimes strobilation occurs (Clio p. sulcata aberrant), see the other forms in this species for explanation of this process.

Ecology

The form is a phytophage.

Distribution

The forma sulcata is found between the range of forma antarctica and the Antarctic Continent. South of Australia, between 180°W-160°W and 140°W-90°W, the forma sulcata is absent- and the forma antarctica is not recorded between 40°W-10°E, 70°E-110°E, 170°E-120°W. Both sulcata and antarctica live in the currents surrounding the Antarctic Continent which will, in all probability, generate a circum-antarctic distribution. The distribution of Clio pyramidata forma sulcata and Limacina helicina subsp. antarctica is continuous around Antarctica and nearly continuous for Limacina retroversa subsp. australis. The forma sulcata is found in the Antarctic surface waters, the forma antarctica is typical for the Intermediate waters between Subantarctic and Antarctic waters, see the Clio p. sulcata map.

Types

Cleodora sulcata Pfeffer, 1879: 240, figs. 11-12.
Syntypes: seven specimens described and figured by Pfeffer (1880) are present in HMNH with the label belonging to the type series of Clio p. forma martensi. The label of the type specimens of Clio p. forma sulcata was found with 2 specimens of Hyalocylis striata.

Clio pyramidata sulcata