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

Overview

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

Taxonomic Description

The shell is hyaline or opaque with a flat dorsal surface, having nearly invisible longitudinal ribs. The dorsal lip is separated from the dorsal side by a flat but distinct arch-shaped rib. The lateral sides have no keel, the tops of the lateral spines are directed caudad. The dorsal aperture lip is truncated with a straight upper margin, about 4 mm long. The relatively long caudal spine is straight and the shell margin, between caudal and lateral spines, is concave. The ventral side is moderately vaulted (Cavolinia t. danae, Cavolinia t. danae dorsal 2). The growth lines and transverse ribs are not distinct ventrally. The aperture is trapezoid. The shell colour is irregularly distributed yellowish-brown.
Shell length varies between 12.0 and 16.0 mm and width varies between 8.0 and 10.5 mm, with averages of 14.8 and 9.5 mm respectively.

Juveniles

A special description is not available.

Reproduction

This forms is a protandric hermaphrodite.

Ecology

The form is phytophagous.

Distribution

This forma is restricted to the Indian Ocean north of 25°S, see the Cavolinia t. danae map.

Types

Cavolinia tridentata forma danae Van der Spoel, 1974: 107, fig 5f, 6e.
The holotype is kept in alcohol in the ZMUC, two paratypes are preserved in alcohol in the ZMAN.
Type locality: 14°16'S 41°48' E, CDAE stat. 3951iv.

Cavolinia tridentata danae