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Cavolinia gibbosa (d'Orbigny, 1836) forma gibbosa (d'Orbigny, 1836)

Overview

This is a globular shelled pteropod, about 1 cm long. The transparent shell is reddish (Cavolinia g. gibbosa lateral 2, Cavolinia g. gibbosa ventral 2). The lateral spines are small, the caudal spine is pronounced, as is the upper shell lip. The ventral side is strongly vaulted, the width is >70% of the length. It lives in the surface layers of the Indo-Pacific Ocean. It is a phytophagous mucus feeder (Cavolinia g. gibbosa).

Taxonomic Description

The shell is relatively wide (about 68 % of the length), the ventral vault is extremely high (about 71% of the length (Cavolinia g. gibbosa drawing). In Cavolinia g. gibbosa lateral view this is also clearly seen. The regularly convex ventral vault does not show the 'forma flava-like' edge with sharp top. The cranial part of the ventral side does not run dorso-posteriorly but perpendicularly to the shell axis, it may even be slightly elevated. The dorsal aperture lip is smaller than in the forma flava and the transverse striation (Cavolinia g. gibbosa ribs)on the ventral side is less developed.
The measurements and proportions of the shell are the best means to differentiate the present forma and flava, see the following table after Pfeffer (1880):

flava gibbosa difference
Max. length in mm...................... 10.7 8.0 -2.7
Max. width in % of length.............. 66.0 71.7 +5.7
Max. thickness in % of length.......... 61.0 75.4 +14.4
Min. length in mm...................... 8.8 6.0 -2.8
Min. width in % of length.............. 55.9 62.5 +6.6
Min. thickness in % of length.......... 50.5 68.5 +18.0
Average length in mm................... 9.7 7.2 -2.5
Average width in % of length........... 60.7 68.3 +7.6
Average thickness in % of length....... 56.7 71.2 +14.5

Juveniles

The juvenile shell starts development as a blunt oval protoconch I with fine transverse striations. Only an irregularity in growth separates protoconch I and II, and in the latter the transverse striae are slightly more spaced (Cavolinia g. gibbosa striation, Cavolinia g. gibbosa shell details).

Reproduction

This species is a protandric hermaphrodite.

Ecology

This species is phytophagous.

Distribution

This species is sub-divided into three formae; as its complicated synonymy has led to much confusion, it is impossible to accurately treat their distributions separately, see the Cavolinia g. gibbosa map. The species, as a whole, is usually considered as having a pantropical distribution. The forma flava is found in the Atlantic, the formae plana and gibbosa in the Indo-Pacific. A bisubtropical distribution is not evident in the Atlantic, but the number of records between 10°N and 15°S is significantly smaller than in the other parts of the area. In the Indian Ocean, the bisubtropical distribution is evident. In the Pacific Ocean, a complete separation of the northern and southern population occurs, only the northern population is connected with the east Indonesian Archipelago population. Clio pyramidata forma lanceolata and the present species are the only two species penetrating from time to time, into the Black Sea through the Bosporus.

Geological Record

During the Atlanticum and in recent times this form was found in the Adriatic Sea.

Types

Hyalaea gibbosa d'Orbigny, 1836: 95 (1846), pl. 5, figs. 16-20.
Lectotype: MHNP (dry collection), Paralectotypes: MHNP, 3 spec. (dry collection)
Type locality: Atlantic Ocean Coll.: d'Orbigny.

Cavolinia gibbosa gibbosa