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Cavolinia tridentata (Niebuhr, 1775) forma atlantica Van der Spoel, 1974

Overview

This is a large shelled pteropod, 1.6 cm long. It has a flat dorsal side with moderately developed ribs. There are no keels along the lateral sides. The caudal spine is short and straight. The ventral side is moderately vaulted. The shell sculpture consists of faint growth lines and a very faint transverse striation. Micro-zooplankton and phytoplankton are its food, it is a mucus feeder. It lives at moderate depths in the S-Atlantic Ocean (Cavolinia t. atlantica dorsal, Cavolinia t. atlantica lateral).

Taxonomic Description

The hyaline shell has a moderately vaulted dorsal surface (Cavolinia t. atlantica outline). The central rib, on the dorsal side, is well developed, the lateral ribs are less developed. A well developed arch-shaped rib is found at the base of the dorsal lip. The lateral sides do not have keels. The lateral spine points are directed slightly caudally, the caudal spine is short and straight. The shell margin, between caudal and lateral spines, is concave with a more or less straight horizontal portion. The ventral side is moderately vaulted (Cavolinia t. atlantica early adult). The aperture is triangular (Cavolinia t. atlantica). The dorsal aperture lip is rounded or it may have a small additional part with a short straight section, about 3 mm long. The growth lines on the shell are faint and the transverse striation is poorly developed. A light-brown hue nearly covers the whole shell.
The shell length varies between 11.5 and 16.0 mm, the width varies between 8.0 and 10.5 mm, with averages of 15.2 and 9.9 mm respectively.

Juveniles

A special description is not available.

Reproduction

Cavolinia tridentata forma atlantica is a protandric hermaphrodite.

Ecology

Cavolinia tridentata forma atlantica is phytophagous and epipelagic.

Distribution

Cavolinia tridentata forma atlantica occurs in the S-Atlantic between 5°N and 40°S, see the Cavolinia t. atlantica map.

Types

Cavolinia tridentata forma atlantica Van der Spoel, 1974: 106, fig. 4c, 6.
The holotype (U.S.N.M. 123920) (fig. 4c) and one paratype (U.S.N.M. 703765) is stored dry in the USNM, one paratype is stored dry in the ZMAN.
Type locality: St. Helena, coll. Turton.

Cavolinia tridentata atlantica