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Cuvierina columnella (Rang, 1827a) forma columnella (Rang, 1827a)

Overview

This is a shelled pelagic snail, up to 1 cm long, with a completely transparent, bottle-shaped shell. The greatest shell width is found at less than 1/3 of the shell length from posterior. The surface has very faint growth lines. The juvenile shell has a protoconch that points as a needle below the bottle-shaped adult shell, closed by a septum. The visceral mass is seen through the shell. It is a good swimmer that feeds on phytoplankton and protozoa. It lives in the warm upper waters of the Indian and Pacific Oceans, where it can occur in mass blooms (Cuvierina c. columnella).

Taxonomic Description

The hyaline, glassy shell is bottle-shaped and composed of two sections. Usually it is incomplete, the elongated caudal section being lost as it is thrown off in an early developmental stage. A convex septum closes the permanent shell a small distance above the place of rupture. The embryonic shell with the caudal section is probability identical with "Creseis caliciformis". Around the closing septum the circular mark of the caudal shell part is visible. In lateral as well as in frontal view, the mainly cylindrical shell shows a bulge in its caudal half above the septum, this bulge is less expressed dorsally and the greatest shell diameter is found. Just below the aperture the shell is constricted so the diameter is smaller than the aperture diameter. The aperture in apical view is bean-shaped caused by a small depression of the ventral side. The dorsal aperture lip is somewhat higher than the ventral one. The Cuvierina c. columnella sculpture is not very prominent so the shell appears to be smooth. A crossing pattern of transverse and longitudinal lines is seen with magnification. The radula formula is 1-1-1, it is characterised by the typical plates with square basal plate.
The shell measurements are: up to 10 mm long and up to 3 mm wide.

Juveniles

The juveniles are similar to those in the forma atlantica.

Reproduction

This species is a protandric hermaphrodite and has an accessory copulatory organ (cervical organ). The organ is composed of two diverging branches rising from a common root. It originates from a muscular base some distance beneath the posterior footlobe. The receptaculum seminis is attached to the accessory copulatory organ. This organ serves to convey allosperm to the receptaculum. The receiving specimen still has penis but it is changing from a male to a female stage. The receptaculum seminis is a membraneous fold situated at the base of the accessory copulatory organ. Thus it differs from the normal receptaculum which is not membraneous. The place where it is found may seem more aberrant from the normal cavoliniid type since the accessory sexual gland is also found, at the same location where splits off the receptaculum. After copulation the accessory copulatory organ becomes detached and is thrown off just as the penis is by the rupture at a preformed location. This species is protandric with sperm formed first; spermatogenesis stops in stage III or IV. Ripe autosperm are stored in the gonoduct and bursa seminis which develop as swollen parts of the gonoduct during sperm ripening. After sperm formation the eggs develop and fill the complete gonad. There is only one sexual cycle. Eggs and sperm pass through the accessory sexual gland in two separate ways. The penis is thrown off when autosperm are delivered. Before the penis becomes active it is found in the penial sac and a large number of specimens had the receptaculum filled with allosperm while the penis was still in its sac. This showed that copulation was normally not reciprocal and that first sperm are accepted and later sperm are delivered. This phenomenon is not restricted to the present species but was also observed in other Cavoliniidae.

Ecology

This form is phytophagous and epipelagic. The temperature range is 17.9° and 26.2° C.

Distribution

The forma columnella is found in the Indo-Pacific sympatric with the forma urceolaris, see the Cuvierina c. columnella map. The distribution of this warm-water species shows that it is a pantropical species. In the deposit of the Gulf of Aden some rare specimens in pteropod ooze proves that this species may penetrate more north; in the Red Sea it was, however, never found neither alive nor in the pteropod ooze.

Other

The protoconch described for Cuvieria columnella by Grecchi and Bertolotii (1988) does not belong to this species.

Types

Cuvieria columnella Rang, 1827: 323, pl. 45, fig. B1-8.
The type was preserved in the MHNP but is lost.
Type locality: Indian Ocean Coll.: Rang.

Cuvierina columnella columnella