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Diacavolinia pacifica Van der Spoel, Bleeker and Kobayasi, 1993

Overview

This is a medium sized, uncoiled thecosomatous pteropod, 0.5 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 well developed. Shell sculpture consists of faint growth lines and faint transverse striation. The dorsal lip has a notch and a small gutter, but a constriction is absent, there is a pronounced inner hump. Micro-zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in the Indian and Pacific Oceans at shallow depths (Diacavolinia pacifica 2).

Taxonomic Description

The hyaline shell is slightly triangular; has a brown hue, especially near the the lock and hump and on the dorsal side. The dorsal lip has a notch in the broad rostrum and a small gutter, but no constriction. The inner hump is pronounced but not continuous with the underside of the lip shoulders, as in D. angulosa. In some specimens a flat nose is present. The ventral lip is large and shows a clear median depression. The lateral spines are straight, projecting laterally except for the right spine that bends slightly dorsally in some specimens (Diacavolinia pacifica lip). The spines are sharp and hooked; the gutter corners are large (Diacavolinia pacifica line). The 15 thin ventral ribs are vaguely a comb-shaped; the 5 ribs near the aperture are much stronger (Diacavolinia pacifica). The lateral lines are nearly straight and the flanks are moderately developed. The dorsal side is convex with a weak central, latero-dorsal, and lock ribs. The lock area is moderately sized, like the main tubercle and link. The lunar tubercle is well developed, the minor tubercle is reduced. The same lock mechanism is found in the long-spined form. There is no second lock mechanism. The growth lines are well developed and there are about 10 stronger lines at the top of the dorsal side. A hump is present with a strongly developed inner hump. The protoconch II area moderately projects. In the holotype the caudal joint is 0.96 mm; the caudal fold, 0.96 mm long, is nearly straight. There are no lip flaps; well-developed lip bellies and moderate lip shoulders are present. The aperture is narrow. In the holotype the lip angle is 143°, the lock angle is 76°, and the side angle is 70°. In the centre of the wings an orange area is present, the lower flaps of the wings and posterior footlobe are brown-purple. The holotype has a shell length of 4.40 mm and the width is 4.16 mm.
The length range from 4.76 to 3.92 mm and width from 4.32 to 3.84 mm.

Juveniles

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

Reproduction

This species is a protandric hermaphrodite.

Ecology

This species is phytophagous.

Distribution

Diacavolinia pacifica is an Indo-West Pacific species being found in the W-Indian and NW-Pacific Oceans, see the Diacavolinia pacifica map.

Others

Morphologically Diacavolinia angulosa is the closest relative, but the present species has a more hollow rostrum and the shell is triangular in ventral view rather than Diacavolinia angulosa. As in Diacavolinia angulosa, populations with short-spined shells and with long-spined shells are found. No special taxa for both forms are proposed as growth seems the only factor causing this difference.

Types

Diacavolinia pacifica Van der Spoel, Bleeker and Kobayasi, 1993: 140, fig. 15.
Holotype (ZMA. moll. 3.92.016) and 2 paratypes (ZMA. moll. 3.92.017) in ZMAN.
Type locality: 06°29.9'S 131°09.2'E, 98-280 m depth, Snellius II Exped., Stat. 33 cast 2, 6 August 1984.
Etymology: This species seems to occur mainly in the Pacific Ocean, hence the name pacifica.

Diacavolinia pacifica