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Diacavolinia constricta Van der Spoel, Bleeker and Kobayasi, 1993

Overview

This is a medium sized, uncoiled thecosomatous pteropod, 0.6 cm long. It has a flat dorsal side with moderately developed ribs. The ventral side is vaulted. The caudal spine is absent and a caudal spine mark is not left as the ventral and dorsal sides grow together. The lateral spines are small. Shell sculpture consists of faint growth lines and faint transverse striation. The dorsal lip has a notch, a constriction and a gutter. Micro-zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in the Atlantic Ocean at shallow depths (Diacavolinia constricta).

Taxonomic Description

The hyaline shell is not triangular; it has a brown hue over the entire surface.
The strongly bent dorsal lip has a notch in the relatively broad rostrum, a constriction, and a gutter. The ventral lip is large and shows a weak median depression. The lateral spines are not bent, they are placed relatively far anterior, and hooked but are not very sharp at the tip. The gutter corners are small. The 19 clear ventral ribs are comb-shaped. The lateral lines are slightly convex and the flanks are clearly present. The dorsal side is flattened, with moderately developed central and latero-dorsal ribs; the lock ribs are moderate. The lock area is large with a large main tubercle, large link, large lunar and a small minor tubercle. A second lock system is present. The growth lines are typical and sculpture ribs are found on the dorsal side. A hump is absent. The protoconch II area does not project; it has a moderate caudal joint. In the holotype it is 1.28 mm; the moderately developed moon-shaped caudal fold is 1.36 mm long. There are no lip flaps; large lip bellies and strong lip shoulders are present. The aperture is extremely narrow, the lip angle is about 124°, the lock angle is 71°, and the side angle is 74°.
The shell length range is 5.60-4.08 mm and the width range is 5.28-3.44 mm.

Juveniles

A special description for this form is not available, see Diacavolinia longirostris.

Reproduction

This species is a protandric hermaphrodite.

Ecology

This species is phytophagous.

Distribution

Diacavolinia constricta is found in the central N-Atlantic Ocean, see the Diacavolinia constricta map. One record in the central Indian Ocean indicates a wider distribution.

Others

This is a rare species, closely related to Diacavolinia strangulata. It is considered a separate species on the basis of the difference in the rostrum and its allopatry with D. strangulata.

Types

Diacavolinia constricta Van der Spoel, Bleeker and Kobayasi, 1993: 145, fig. 22.
Holotype: (ZMA. moll. 3.92.025) in ZMAN.
Type locality: 28°27.5'N 29°51.2"W, 0-47 m depth, AMNAPE Exped., Stat. 88 trawl 4, 1 June 1983.
Etymology: The name is based on the very strong constriction of the rostrum.

Diacavolinia constricta