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Diacavolinia aspina Van der Spoel, Bleeker and Kobayasi, 1993

Overview

This is a small 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 when the ventral and dorsal sides grow together. The lateral spines are reduced. Shell sculpture consists of faint growth lines and extremely faint transverse striation. The broad dorsal lip has a notch; constriction, gutter and hump are absent. Micro-zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in the E-Indian Ocean and Indo-Malayan waters at shallow depths (Diacavolinia aspina).

Taxonomic Description

The colourless, hyaline shell is only slightly triangular. The dorsal lip has no notch in the broad rostrum; there is no gutter and no constriction. The ventral lip is normal sized and shows a moderate median depression. The lateral spines are reduced and do not bent dorsally; they are rounded. The dorsal side is flattened, the central rib and latero-dorsal ribs are moderately developed and the lock ribs are small. Among the ventral ribs, the five near the aperture are strongly developed and about eight posterior ribs are only weakly developed; they are all linear. The flanks are slightly developed; the lateral lines are slightly concave. The lock area is visible and the lock mechanism is small. The main tubercle is high and conical, the lunar one is normal and the minor one is strongly reduced. A second lock system is visible but rudimentary. The growth lines are typical except for the anterior part on the dorsal side where they are strongly developed and form about 10 ribs. There is a clear but shallow hump. The protoconch II area moderate project. In the holotype the caudal joint is 1.00 mm; the caudal fold is 1.00 mm and nearly straight, the left and right fold in ventral view form an angle. There are no lip flaps; the lip bellies are weak and the lip shoulders are small. The aperture is well open. In the holotype the lip angle is 158°, the side angle is 75°, and the lock angle is 69°. The aperture rim is sharp.
The shell length ranges from 5.04 to 3.12 mm and width ranges from 3.60 to 2.48 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 aspina is found in the Indo-Malayan and adjacent E-Indian Ocean, in the epipelagic zone, see the Diacavolinia aspina map.

Others

Diacavolinia aspina cannot be a juvenile of Diacavolinia striata though the former is somewhat smaller, since the hump in Diacavolinia aspina is not present in Diacavolinia striata and it cannot disappear during growth.

Types

Diacavolinia aspina Van der Spoel, Bleeker and Kobayasi, 1993: 141, fig. 16.
Holotype (ZMUC. gas 163) and 9 paratypes in ZMUCÊ(ZMUC. gas 163), 12 paratypes (ZMAN. Moll 3.92.018) in ZMN.
Type locality: 2°57'S 99°36'E, 0-400 m depth, CDAE., Stat. 3860 xi-xv, 20 October 1929. Etymology: The shell has no spines, hence the name.

Diacavolinia aspina