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


This is a large thecosomatous pteropod, 2 cm long, living at moderate depths. It has a flat dorsal side with moderately developed ribs. There is no keel along the lateral sides. The caudal spine is straight. 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 NW-Atlantic Ocean (Cavolinia t. bermudensis dorsal).

Taxonomic Description

The hyaline or opaque shell shows a slightly vaulted dorsal surface, with moderately or even poorly developed ribs. The dorsal lip is separated from the dorsal surface by a well developed arch-shaped rib. In ventral view the lateral margins of upper lip and shell-body form a smooth regular line without clear incisions at the base of the dorsal lip. The upper aperture lip is rounded. The lateral sides show no keel and the lateral spines do not project caudad. The caudal spine is straight, while the shell margins between the caudal and lateral spines are composed of a concave and a straight section. The ventral side is moderately vaulted (Cavolinia t. bermudensis, Cavolinia t. bermudensis3, Cavolinia t. bermudensis lateral). The aperture has a triangular shape. The shell structure consists of tiny transverse ribs and nearly invisible growth lines (Cavolinia t. bermudensis 1, Cavolinia t. bermudensis 2). The whole shell is yellowish-brown (Cavolinia t. bermudensis photo, Cavolinia t. bermudensis photo2 with expanded balancers).
The shell length varies between 12.0 and 19.5 mm, while the width varies between 9.5 and 13.5 mm, the averages are 15.8 and 10.2 mm respectively.


A special description is not available.


This form is a protandric hermaphrodite.


This form is phytophagous and epipelagic.


This forma is restricted to the North-West Atlantic, see the Cavolinia t. bermudensis map.


Cavolinia tridentata forma bermudensis Van der Spoel, 1974: 105, fig, 4d, 6a.
The holotype (U.S.N.M. 38334) is kept dry in the USNM, together with four (U.S.N.M. 703761, 703762, 703763, 703764) paratypes, one paratype is kept in the ZMAN.
Type locality: Off Martha's Vingard, U.S. Fish. Com. Stat. 876.

Cavolinia tridentata bermudensis