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Diacavolinia triangulata Van der Spoel, Bleeker and Kobayasi, 1993

Overview

This is a large uncoiled thecosomatous pteropod, 0.9 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 large. Shell sculpture consists of growth lines and faint transverse striation. The dorsal lip has a notch, a gutter but no constriction, there is usually no inner hump. Micro-zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in Indo-Malayan and adjacent waters at shallow depths. (Diacavolinia triangulata 2).

Taxonomic Description

The shell is rather triangular, transparent. The large dorsal lip has a notch in the rostrum and a gutter but no constriction; an inner hump is not present in the holotype. In specimens from the Banda Sea a clear hump is developed and the spines are sharp. The thickened ventral lip is moderately sized and shows a weak median depression. The lateral spines do not bend (except for a few specimens in which they are not perfectly pointing laterally) they are not hooked but elongated, ending in a blunt tip; the gutter corners are large. The 17 thin, ventral ribs are line-shaped. The ventral side is swollen, the lower half is flattened in profile, the lateral lines are nearly straight, and the flanks are not developed. The dorsal side is somewhat flattened, with large central rib and moderate latero-dorsal ribs and lock ribs. The lock area is large with large main tubercle and link. The main tubercle and the lunar tubercle are separated by a large flat open area, the minor tubercle is very small. An extremely small second lock system is present. The growth lines are strong and dorsally some ribs are also present. A small outer hump is present but the inner hump is not developed. The protoconch II area does not project. In the holotype the caudal joint is 1.92 mm; the caudal fold, 1.60 mm long, is nearly straight. There are no lip flaps; lip bellies are present and the lip shoulders are small. The aperture is wide, the lip angle is about 148°, the lock angle is 72°, and the side angle is 65°. The centre of the wings is purple and connected to the lips by a yellow patch. The lips are purple (Diacavolinia triangulata). The holotype has a shell length of 9.20 mm and a width of 8.80 mm.
The shell length ranges from 9.20 to 4.88 mm and width from 8.88 to 4.40 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 triangulata occurs in the Indo-Malayan and adjacent areas, see the Diacavolinia triangulata map.

Others

The closest relative is Diacavolinia mcgowani but this species has more blunt lateral spines and no hump, nor lip shoulders. Diacavolinia triangulata and Diacavolinia grayi resemble each other but the latter species is smaller. In specimens with sharp spines, which may be confused with Diacavolinia longirostris, the hump is the discriminating character. Specimens of Diacavolinia pacifica with long spines strongly resemble Diacavolinia triangulata with an inner hump, but in Diacavolinia pacifica the first 1/4 of the lateral lines of the dorsal lip runs parallel to the shell axis, which is never found in the present species.

Types

Diacavolinia triangulata Van der Spoel, Bleeker and Kobayasi, 1993: 148, fig. 26.
Holotype (ZMA. moll. 3.92.026) and 32 paratypes (ZMA. moll. 3.92.027) in ZMAN.
Type locality: Albatross Philippine Expedition. Philippine Sea.
Etymology: The shell makes a perfect triangular impression, hence the name triangulata.

Diacavolinia triangulata