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Diacria trispinosa (De Blainville, 1821a) atlantica dark form Hilgersom and Van der Spoel, 1987

Overview

This is a medium sized, pelagic snail with typical colour patterns, 1.2 cm broad. The slender shell is uncoiled but bilaterally symmetrical with a long, sometimes broken off, caudal spine. It is almost completely chestnut brown ventrally with the same colour (except for a white spot on the anterior dorsal side) dorsally on the ribs and between the ribs. The lateral and caudal spine are colourless. It feeds on small plankton, mainly phytoplankton, in the epi- and mesopelagic zone of the Atlantic Ocean upwelling areas (Diacria t. trispinosa dark form).

Taxonomic Description

It is almost completely chestnut brown ventrally with the same colour (except for a white spot on the anterior dorsal side) dorsally on the ribs and between the ribs (Diacria t. atlantica (DF)). The lateral and caudal spine are colourless (Diacria t. atlantica w/ caudal spine). The relative large shell is dorso-ventrally flattened and has three spines. Its overall colour is dark brown. The aperture is slit-like and runs between the lateral spines.
Shell length is 9.5 mm, width is 12 mm, ratio upper lip-spine tip/spine tip-membrane is 1.15, spine mark width is 1.05 mm, aperture height is 0.75 mm.

Juveniles

The juvenile has a long, dorso-lateral flattened needle-like shell with lateral sides diverging anteriorly only. Protoconch I is globular. There is no sculpture on protoconch I or II. The lateral sides of protoconch II are thickened.

Reproduction

This form is a protandric hermaphrodite.

Ecology

This animals are phytophagous and coldwater epipelagic. The shell is frequently covered by hydropolyps. It swims with two wings and sinks with retracted wings.

Distribution

This forma is restricted to the N-Atlantic Ocean in the upwelling waters off NW-Africa, see the Diacria t. atlantica DF map.

Types

Diacria trispinosa forma atlantica dark form Hilgersom and Van der Spoel, 1987: 99, fig. 4. Types were not indicated.
Type locality: 21°45'N 18°05'W, Nectar exp. III stat 2, 10-3-1982.

Diacria trispinosa atlantica dark form