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Diacavolinia limbata (d'Orbigny, 1836) forma limbata (d'Orbigny, 1836)

Overview

This is a large uncoiled thecosomatous pteropod, 1.2 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 broad dorsal lip has a small notch and gutter but no constriction. Micro-zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in Atlantic Ocean at shallow depths (Diacavolinia l. limbata).

Taxonomic Description

The triangular hyaline shell has a brown purple hue. The very long dorsal lip has a small notch in the broad rostrum, and a gutter but no constriction. The ventral lip is moderately sized and has a well-developed median depression. The ventral side is convex and does not show the flattened area as found in the forma africana. The lateral spines are slightly bent, sharp, and hooked; the gutter corners are large. The 25 ventral ribs are line-shaped; there are two groups, an anterior group of 15 strong ribs and a posterior group of weak ribs (Diacavolinia l. limbata ribs, Diacavolinia l. limbata ribs). The lateral lines are slightly convex. The flanks are not pronounced. The dorsal side is slightly convex, with well-developed central ribs, lateral ribs and lock ribs. The lock area is well developed and visible with a large main tubercle and link. There are no separate lunar or minor tubercles. In some specimens a double main tubercle is found. A second lock mechanism is found at the upper level of the attachment of the spines to the lateral side. The growth lines are typical. A hump is absent. The protoconch II area does not project far, the relatively small caudal joint is about 1.36 mm (Diacavolinia l. limbata closing fold); the caudal fold, about 1.68 mm long, is moon-shaped. There are no lip flaps; low and strong lip bellies and small lip shoulders are present. The aperture is wide, the lip angle is about 140°, the lock angle is 74° the side angle is 74° (Diacavolinia l. limbata).
The shell length ranges from 12.75 to 8.33 mm and width from 10.37 to 6.12 mm.

Juveniles

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

Reproduction

This forma is a protandric hermaphrodite.

Ecology

This forma is phytophagous.

Distribution

Diacavolinia limbata forma limbata is found in the upwelling area off NW-Africa and the tropic W-Atlantic, see the Diacavolinia l. limbata map.

Types

Hyalaea limbata d'Orbigny, 1836: 101, (1846) pl. 6, figs. 11-15.
Lectotype and two paralectotypes are preserved in the Laboratoire de Malacologie, Muséum d'Histoire Naturelle, Paris.
Type locality: Between 24°-22°N and 30°-33°W, Expedition to the Meridional Atlantic, 1826-1833.

Diacavolinia limbata limbata