Dupont, 1979

Described form occurring in the area (Van der Spoel et al., 1997): Diacria trispinosa (De Blainville, 1821) forma atlantica Dupont, 1979

Description
A medium sized, pelagic snail with typical colour patterns, shell 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.
Relatively large shell, the lateral spines are straight, the caudal spine [D.t.atlantica-caud] 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 D.t.atlantica-dr]. The caudal membrane is placed far posteriorly which makes the caudal spine short in relation to the teleoconch.
Juveniles have 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.

Size
Shell length up to 9 mm, width up to 10.5 mm.

Ecology
This animals are phytophagous and epipelagic in cold water. It feeds on small plankton mainly phytoplankton in the epi- and mesopelagic zone [D.t.atlantica-sw]. It swims with two wings and sinks with retracted wings. The shell is frequently covered by hydropolyps. [D.t.atlantica-hyd].

Depth range
Epi- to mesopelagic depths.

Distribution in the North Sea
Might be found in the northern North Sea as an occasional guest from the NE Atlantic.

World distribution
This forma is restricted to the N-Atlantic Ocean between 40° and 70°N.

[After Van der Spoel et al., 1997]

Kingdom Animalia
Kingdom Animalia
Phylum Mollusca
Class Gastropoda
Subclass Opistobranchia
Order Thecosomata
Suborder Euthecosomata
Superfamily Limacinacea
Family Cavoliniidae
Subfamily Cavoliniinae
Genus Diacria
Species Diacria trispinosa

Status in World Register of Marine Species

Accepted name: Diacria trispinosa (Lesueur, 1821)

Scientific synonyms and common names

Diacria trispinosa var. minor | n. var. (part) Boas, 1886

Diacria trispinosa forma atlantica n. forma Dupont, 1979

Dupont, L., 1979. Note on variation in Diacria Gray, 1847, with descriptions of a species new to science, Diacria rampali nov. spec., and a forma new to science, Diacria trispinosa forma atlantica nov. forma. Malacologia, 18: 37-52.

Tesch, J.J., 1947. Pteropoda Thecosomata. Fiches d'Identification du Zooplancton, 8 (1947). Conseil International pour l'Exploration de la Mer, Kopenhagen.

van der Spoel, S., L. Newman and K.W. Estep, 1997. Pelagic Molluscs of the World. World Biodiversity Database CD-ROM Series. Version 1.0. ETI, University of Amsterdam, Amsterdam.

Spoel, S. van der, 1972. Pteropoda Thecosomata. Fiches d'Identification du Zooplancton, 140-142 (1972). Conseil International pour l'Exploration de la Mer, Kopenhagen.

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