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Diacavolinia flexipes (Van der Spoel, 1971a)

Overview

This is a medium sized, uncoiled thecosomatous pteropod, 0.8 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 and strongly curved dorsally. The shell sculpture consists of faint growth lines and a very faint transverse striation. The broad dorsal lip has a notch and no constriction, but a gutter is present. Micro-zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in the Red Sea and NW-Indian Ocean at shallow depths (Diacavolinia flexipes 2).

Taxonomic Description

The slightly triangular hyaline shell is colourless except for a brown strip medially on the dorsal side. The centre of the wings is dark purple-brown, the same colour as lips and visceral mass. The dorsal lip has no notch in the broad rostrum and no constriction, but it is gutter-shaped. The ventral side is strongly swollen. The ventral lip is medium sized and has no, or only a small median depression. The lateral spines curve strongly dorsally (Diacavolinia flexipes 3), over 40° to 90°; they are hooked and sharp; the gutter corners are well developed. The spine surface bears a strong characteristic groove from gutter corners to spine tips. The ventral ribs are composed of about 4-8 strong ribs near the aperture, and about 8 very small ribs; they are linear (Diacavolinia flexipes, Diacavolinia flexipes ventral ribs). The lateral lines are straight and the flanks are weak. The dorsal side is clearly convex, with a strong central rib and small latero-dorsal ribs; the lock ribs are more faint. The lock area is just visible, the main tubercle and link are moderately sized. The lunar tubercle is large, the minor tubercle is normal sized. A second lock system is present with a large dorsal tubercle. The growth lines are well developed on both shell sides. Only a slight indication of a hump may be present in some specimens but there is no inner hump. The protoconch II area does not project. In the holotype the caudal joint is about 2.00 mm, it is shifted far to the dorsal side; the caudal fold, 1.92 mm long, is slightly moon-shaped. There are no lip flaps; clear lip bellies and small or no lip shoulders are present. The aperture is wide. In the holotype the lip angle is 155°, the lock angle is 63°, and the side angle is 80°.
The shell length ranges from 8.00 to 4.50 mm the width from 6.60 to 3.60 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 flexipes mainly occurs in the Red Sea and the N-Indian Ocean. It seems endemic to the N-Indian Ocean and Red Sea, see the Diacavolinia flexipes map.

Geological Record

This species was known from the Holocene of the Red Sea but probably already occurred in the Riss Glacial.

Others

This species is characterised by the extremely strong curve of the lateral spines. Specimens from the Oman coast differ in general shape from Red Sea specimens by having a more tongue-shaped dorsal lip and a more slender shell. In some of the Oman specimens a shallow notch developed. Also typical of the Oman population is the brown colour of the dorsal lip.

Types

Cavolinia longirostris forma flexipes Van der Spoel, 1971; 16, figs. 15-16, 19, 21.
Holotype and 17 paratypes in Department of Zoology University of Tel Aviv, three paratypes in ZMAN.
Type locality: David Bay Entedeber, Red Sea; Coll. E 62/317, Dr. L. Fishelson leg.
Etymology: The spines are bent dorsally like feet, hence the name flexipes.

Diacavolinia flexipes