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Clio pyramidata Linnaeus, 1767 forma excisa Van der Spoel, 1963

Overview

This is a shelled, uncoiled, pyramidally shaped, pelagic snail, up to 2 cm long. The shell is transparent, broadly triangular in shape and in cross-section. The upper part of the lateral sides run parallel to each other. The reddish, dark brown visceral mass is seen through the shell. Growth lines are prominent, the lateral sides are round in cross section. It is a good swimmer that feeds on phytoplankton and protozoa. It lives in the Subantarctic waters of southern ocean (Clio p. excisa).

Taxonomic Description

The lateral ribs (Clio p. excisa ventral) are concave near the embryonic shell, convex in the medially and finally straight and parallel to the body axis. The caudal part of the shell of the forma martensi resembles the present forma but the ribs of the ventral side in martensi are never parallel to the body axis(Clio p. excisa diagram). The lateral ribs are somewhat more developed than in the other formae and the swelling on the ventral side is more pronounced. The four longitudinal ridges on each latero-dorsal side are also more developed than in most other formae. These characters render the shell broader and stronger than in other formae. The shape of the pallial gland in excisa differs from that in sulcata, which corresponds to differences in the shell shape. The gland is trapezoid in sulcata, whereas in excisa two lobes are attached to the upper corners of the trapezoid gland which projects caudally. The radula formula is 1-1-1, it is composed of about 10 transverse rows and resembles the radula of the forma sulcata.
Shell measurements: up to 20 mm long, up to 11 mm wide.

Juveniles

A special description is not available.

Reproduction

The form is a protandric hermaphrodite, and strobilation may occur.

Ecology

The form is phytophagous.

Distribution

This form is found in Antarctic waters between 20°W-10°E, see the Clio p. excisa map.

Types

Clio pyramidata forma excisa Van der Spoel, 1963: 19, figs. 1-4.
Holotype: RMNH (alcohol collection). Paratypes: RMNH, 26 spec. (alcohol collection).
Type locality: 57°31'S 02°56'W. Coll.: CWNE, Dr. W. Vervoort.

Clio pyramidata excisa