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Cavolinia inflexa (Lesueur, 1813) forma labiata (d'Orbigny, 1836)

Overview

This is a large shelled thecosomatous pteropod, 0.8 cm long, living in the upper water layers. It has a flat dorsal and ventral side. The caudal spine is long and straight. The lateral spines are well developed below the middle of the shell. Shell sculpture consists of faint growth lines. Micro-zooplankton and phytoplankton are its food, it is a mucus feeder. It lives in the mainly in the Indo-Pacific but also in the Atlantic Ocean (Cavolinia i. labiata 2).

Taxonomic Description

The shell is broader than in the other formae, its diameter is 80% of its length. The lateral spines are well developed and distinctly bent caudally (Cavolinia i. labiata lateral spine). The upper lip is continuous with the dorsal side of the shell, rather long and distinctly pointed. The part of the shell caudal to the lateral spines is smaller than in the other formae (Cavolinia i. labiata, Cavolinia i. labiata shell). The lateral spines have a dent which is more pronounced than in Cavolinia uncinata. The closing apparatus, in the shell aperture, is marked by a small swelling of the dorsal side. The colour and transparency of the shell, the lack of longitudinal ribs and transverse ribs on the ventral side, the dentation of the upper lip and curving of the shell in a dorsal direction are the same in all formae. The dorsal side in the median line is reddish as are the thicker parts of the shell.
Shell measurements: up to 8 mm long, 5.5 mm wide of which about 36% is occupied only by the caudal shell part, while this is 50% in the forma inflexa and about 40% in the forma imitans.

Juveniles

A special description for this forma is not available, see Cavolinia i. inflexa for a general discussion on the juveniles.

Reproduction

This form is a protandric hermaphrodite.

Ecology

This form is phytophagous and epipelagic.

Distribution

The species as a whole, shows a warm water distribution, while the forma labiata shows a tendency for a bisubtropical distribution, see the Cavolinia i. labiata map. The forma labiata is more abundant in the South Atlantic, South Indian and Pacific Oceans. The N-S range is the same in all formae. The forma labiata is found also in the Mediterranean. In the Indian Ocean, a population of labiata is found between 0°N and 40°S, and a smaller population of the species is also found in the central and south Arabian Sea. The south Indian and Atlantic populations are connected by the population in the Agulhas Current, composed of a mixture of the formae inflexa and labiata. The forma labiata is in the West Pacific only found in the equatorial area, but this does not prove that it is not bisubtropically distributed as records of true bisubtropical species are also found in this area.
Diurnal vertical migration occurs between a mean day level at 88 m and a mean night level at 98 m. A completely different vertical migration and distribution is found for the formae in the Mediterranean.

Geological Record

It penetrated the Adriatic already in the Pre-Boreal.

Types

Hyalaea labiata d'Orbigny, 1836: 104 (1846), pl. 6, figs. 21-25.
Lectotype: BMNH 1854.12.4.18 (dry collection, originally alcohol). Paralectotypes: BMNH 1854.12.4.18., 7 spec. (dry collection, originally alcohol).
Type locality: Atlantic Ocean 24°-34°S 28°-38°E. Coll.: CVAM.

Cavolinia inflexa labiata