Diacria erythra Van der Spoel, 1971a forma crassa Van der Spoel, 1971a
Overview
This is a small, uncoiled, shelled thecosomatous pteropod, 0.4 cm long. It is a large form for the group. It is globular with rounded ventral and dorsal sides and strongly developed ribs. The lateral spines are small. The caudal spine is absent as, in juveniles, the protoconch is broken off, leaving only a mark. Shell sculpture consists of faint growth lines and 6 dorsal striae. Micro- zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in the N-Red Sea (Diacria e. crassa drawing).
Taxonomic Description
The rather globular shell is red-brown and semi-transparent. The dorsal lip is arch-shaped and borders a very narrow shell aperture. The ventral and dorsal sides are both heavily vaulted, and have striae near the aperture lips. The caudal spine mark is oval. Between the small lateral spines and the corners of the spine mark the curved lateral sides are thickened. Usually a faint median depression is present in the ventral side and lip. The aperture lips are thickened. A pair of closing mechanisms, less developed than in Cavolinia, are found in the aperture. The radula formula is 1-1-1. The dorsal ribs are strongly developed, transverse striation on the ventral and dorsal surface is well developed, the ventral surface is strongly vaulted so that shell thickness is equal to shell width, and the ventral side is clearly seen in dorsal view. Lateral spines are faint and situated far posteriorly. About 6 dorsal striae are imbricate (Diacria e. crassa).
Shell length 3.12-4.00 mm, width 2.60-3.32, diameter of caudal spine mark 1.04-1.36 mm. Six dorsal striae
Juveniles
A special description is not available, see for a comparison juvenile Diacria costata.
Reproduction
This species is protandric hermaphrodite.
Ecology
This species is phytophagous and epipelagic.
Distribution
This forma is found only in the N-Red Sea, and N-Indian Ocean, see the Diacria e. crassa map.
Types
Diacria quadridentata erythra forma crassa Van der Spoel, 1971a: 7, fig. 7.
Holotype: DZTU (dry collection). Paratype: DZTU 12 spec. and ZMAN 4 spec.
Type locality: Near Elath Israel. Col. NS. 5995, Dr. Ch. Fishelsohn.