Diacria trispinosa (De Blainville, 1821a) forma atlantica Dupont, 1979
Overview
This is a medium sized, pelagic snail with typical colour patterns, 1 cm broad. The slender shell is uncoiled but bilateral symmetrical with a long, sometimes broken off, caudal spine. The rim of the aperture and the middle of the dorsal ribs is brown. It is dark brown anteriorly, the posterior part is light brown, the spines are white. It feeds on small plankton mainly phytoplankton in the epi- and mesopelagic zone of the N-Atlantic Ocean (Diacria t. atlantica swimming).
Taxonomic Description
Relatively large shell, the lateral spines are straight, the caudal spine (Diacria t. atlantica w/ caudal)is proportionally short, the shell aperture is wide. It is dark brown anteriorly, the posterior part is light brown, the spines are white (Diacria t. atlantica, Diacria t. atlantica drawing). The caudal membrane is placed far posteriorly which makes the caudal spine short in relation to the teleoconch.
Shell length up to 9 mm, width up to 10.5 mm.
Juveniles
The juvenile has a long dorso-lateral flattened needle-like shell with lateral sides diverging only anteriorly. The 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 epipelagic in cold water. 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 between 40° and 70°N, see the Diacria t. atlantica map.
Others
This species is frequently found overgrown with hydroids (Diacria t. atlantica w/ hydroid).
Types
Diacria trispinosa forma atlantica Dupont, 1979: 42, fig. 4.
Holotype ZMUC, Paratypes 100 adults ZMUC, 709 adult and 1 young specimen ZMAN.
Type locality: 39°21'N 21°51'W, 300 metres wire, CDAE stat. 1380iv, 19-6-1922.