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

Overview

This is a larger thecosomatous pteropod, 1.5 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 a very faint transverse striation. Micro-zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in the NE-Atlantic Ocean (Cavolinia t. dakarensis ventral).

Taxonomic Description

The shell is hyaline sometimes opaque with a flat dorsal side and moderately developed ribs. The dorsal lip is separated from the dorsal side by a moderately or poorly developed arch-shaped rib between the closing mechanisms. The lateral sides have no lateral keels and the margin of upper lip and shell-body forms an irregular line by the incisions at the base of the lip. The dorsal lip is truncated with a more or less straight upper border, about 4 mm long. (Cavolinia t. dakarensis dorsal, Cavolinia t. dakarensis dorsal2, Cavolinia t. dakarensis lateral, Cavolinia t. dakarensis line drawing). The aperture is irregular and triangular. The caudal spine is straight and relatively long. The lateral spines curve caudally. The margin of the shell between caudal and lateral spines shows a concave and a straight portion. The ventral side is moderately vaulted. The shell structure consists of faint growth lines and quite faint transverse striation. The yellowish-brown hue over the shell is less intense on the dorsal lip and along the lateral sides.
The shell length varies between 14.5 and 21.5 mm, the width varies between 9.5 and 14.5 mm, the averages are 16.9 and 11.4 mm respectively.

Juveniles

A special description is not available.

Reproduction

This form is a protandric hermaphrodite.

Ecology

This form is phytophagous and epipelagic to mesopelagic.

Distribution

This form is restricted to the North-East Atlantic ocean, see the Cavolinia t. dakarensis map.

Types

Cavolinia tridentata forma dakarensis Van der Spoel, 1974: 105, figs. 4b, 6b.
Holotype in ZMUC, Paratypes: 10 specimens ZMUC, 2 specimens ZMAN.
Type locality: 32°55'N 21°51'W CDAE stat 1148vii.

Cavolinia tridentata dakarensis