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Creseis virgula (Rang, 1828b) forma constricta Chen and Bé, 1964b

Overview

This is a shelled pelagic snail, up to 0.4 cm long, with a transparent, uncoiled shell. The cross-section is round. The surface is smooth. The shell is short and narrow, tube-shaped and slightly curved. The visceral mass is seen through the shell. It is a clumsy swimmer that feeds on phytoplankton and protozoa. It lives in the upper warm waters layers of the Atlantic Ocean (Creseis v. constricta).

Taxonomic Description

The shell is smooth except for some growth lines. The cross section of the shell is circular. It is conical and straight or slightly curved. A well defined constriction separates the protoconch from the adult portion of the shell; the protoconch has a distinct bulge. there is a gentle size increase towards the anterior part of the adult shell. The posterior end is round and brown.
The holotype is 3.5 mm long, 0.38 mm wide. The protoconch is 0.54 mm long and 0.12 mm wide.

Juveniles

The Creseis v. constricta protoconch is narrow but blunt at its tip. First it grows narrow then bulges outwards so that the anterior part of protoconch I is wide. Before the protoconch II and teleoconch are formed, a narrow constriction occurs.

Reproduction

This form is a protandric hermaphrodite.

Ecology

This form is phytophagous.

Distribution

This form is found in the N-Atlantic Ocean but probably has a wider distribution, see the Creseis v. constricta map.

Geological Record

This form is found in the Pleistocene of the Mediterranean.

Types

Creseis virgula conica Chen and Bé, 1964: 194, fig. 4d.
Types not officially indicated but probably present in Lamont Geological Observatory, USA.
Type locality: 44°00'N 41°00'W.

Creseis virgula constricta