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Cavolinia globulosa (ms. Rang) (Gray, 1850)

Overview

This is a small globular shelled pteropod, about 0.6 cm long. The transparent shell is brownish. The lateral spines are small, the caudal spine is curved and also small. The dorsal and ventral sides are strongly vaulted (Cavolinia globulosa). It lives in the surface layers of the Indo-Pacific Ocean and is a phytophagous mucus feeder.

Taxonomic Description

The shell is hyaline and extremely globular. The ventral side is heavily vaulted so that the shell length and shell thickness are equal. Especially the anterior part is strongly rounded, so that the surface directly ventrally to the shell aperture runs in a caudal direction (Cavolinia globulosa SEM), this part is brownish. The ventral lip is slightly curled outwards. In the upper part of the ventral side, strong transverse ribs are present. Curving of the ventral side is in some specimens so abrupt and strong that an edge, also found in Cavolinia gibbosa, occurs. The caudal spine (Cavolinia globulosa caudal tip) is shorter and more strongly curved dorsally than in Cavolinia uncinata. The embryonic shell is usually absent and a closing membrane is then found at the place of the rupture. On the top of the caudal spine near the membrane, the lateral ribs continue. Parallel to these ribs four other ribs occur giving the posterior end a hexagonal shape. The lateral spines, without dents, are small, the distance between their tops is smaller than the largest shell diameter, in the middle (Cavolinia globulosa lateral). The shell, in dorsal view, is completely round except at its base. The dorsal side shows a small vaulting. The dorsal lip is so strongly bent ventrally that it forms a hood over the aperture, perpendicular to the shell axis. The smooth, dorsal side has only five longitudinal ribs. The upper ventral shell side is reddish, as are the other thicker shell parts. Details of the shell sculpture are given in the photographs of dorsal and ventral ribs: Cavolinia globulosa ribs, and of the primary sculpture ribs with the secondary growth ribs: Cavolinia globulosa ribs 2. The wings around the lips, the neck and the upper part of the ventral side of the body are reddish/brown. The lips are reddish brown. The Cavolinia globulosa radula (formula 1-1-1) is composed of about 9 transverse rows of teeth: Cavolinia globulosa radula2.
Shell measurements: up to 6 mm long, 4.5 mm broad.

Juveniles

The juvenile is composed of a blunt rounded protoconch I, with fine striation and a small protoconch II from which the juvenile shell develops as two nearly flat circular valves. The Cavolinia globulosa protoconch II with caudal opening after loss of protoconch I, and a Cavolinia globulosa juvenile are shown. The Cavolinia globulosa juvenile2 shows the growth lines. Irregular calcareous ridges are formed as shown in: Cavolinia globulosa details1, Cavolinia globulosa details2, Cavolinia globulosa details3, Cavolinia globulosa protoc.-II. During development the minute stage occurs where the body is much smaller than the shell: Cavolinia globulosa minute, the body is small but complete: Cavolinia globulosa minute body)

Reproduction

This species is a protandric hermaphrodite.

Ecology

This species is phytophagous.

Distribution

The distribution of this species differs from most other Cavoliniidae patterns as it is restricted to the Indo-Pacific Oceans and Red Sea, where it occurs in all warm waters, see the Cavolinia globulosa map. Specimens are incidentally transported by the Agulhas current into the Atlantic Ocean so that only a few scattered records are known from the S-Atlantic and even one from the N-Atlantic Ocean.

Types

Cavolina (Hyalaea) globulosa Gray, 1850: 19
Lectotype: MHNP (dry collection) Paralectotypes: MHNP, 4 spec. (dry collection).
Type locality: "Nouvelle Hollande" (= Australia). Coll.: RANG.

Cavolinia globulosa