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Taxonomische classification
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Cavolinia tridentata (Forsskal, 1775) forma tridentata (Forsskal, 1775)
(see the Cavolinia t. tridentata.mov movie of this species)

Overview

This is one of the larger uncoiled thecosomatous pteropods, 1 cm long. It has a flat dorsal side with moderately developed ribs. There is no keel along the lateral sides, though the shell is very broad in relation to its length. The caudal spine is straight and relatively long. The ventral side is moderately vaulted. 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 is endemic to the Mediterranean at moderate depths (Cavolinia t. tridentata dorsal).

Taxonomic Description

The of hyaline or opaque shell is triangular in ventral view, showing a relatively flat, dorsal surface with moderately developed dorsal ribs. The dorsal lip is separated from the dorsal surface by a prominent arch-shaped rib between the aperture closing mechanisms. The dorsal lip is rounded and sometimes pointed, so that the aperture is triangular in shape. Lateral sides have no keel. The lateral spines are directed slightly caudad. The shell margin, between caudal and lateral spines is regularly concave. The ventral surface is vaulted (Cavolinia t. tridentata, Cavolinia t. tridentata drawing, Cavolinia t. tridentata dorsal2, Cavolinia t. tridentata lateral). The shell structures consists of clearly developed transverse ribs and faint growth lines. The shell is chestnut brown over its entire surface. The Cavolinia t. tridentata radula formula is 1-1-1.
The shell length varies between 10.0 and 18.0 mm, its width varies between 7.5 and 11.5 mm, the average being 11.2 and 8.5 mm respectively.

Juveniles

A special description is not available.

Reproduction

This species is a protandric hermaphrodite. Gametogenesis studied by Vitagliano (1950) proves to be correlated with RNA production of the follicle cells. There is a spatial relationship between the kind of germ cells produced and the place which they occupy. Oocytes lie close to cells which contain little RNA, sperm lie closer to the follicle cells with large RNA quantities, the former cells are found in the centre of the gonad, the latter in the periphery. The germ cells of both sexes originate from the centre of the gonad, it is still possible that the RNA quantities in the follicle cells do influence the development as oogonium cells are probably restricted to the gonad centre. The difference between male and female gonads was not described by Vitagliano, thus her findings only explained the situation among hermaphrodites.
Zarnik (1911) found 24 chromosomes in the diploid stage.

Ecology

This forma is phytophagous.

Distribution

This forma is restricted to the Mediterranea, see the Cavolinia t. tridentata map.

Geological Record

This forma was found in the Pleistocene of the Mediterranean. It was also found in the Early Pliocene of Italy.

Others

Neurosecretion is described for this species.

Types

Anomia tridentata (ms. Forskal) Niebuhr, 1775: 124, pl. 40, fig B, b1, b2.
The type material was not preserved.
Type locality: the species, and this forma was originally described from the Mediterranean.

Cavolinia tridentata tridentata