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Diacria erythra Van der Spoel, 1971a forma erythra Van der Spoel, 1971a


This is a small, uncoiled, shelled thecosomatous pteropod, 0.3 cm long. 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 9 dorsal striae. Micro- zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in the Red Sea and adjacent Indian Ocean (Diacria e. eryhthra).

Taxonomic Description

The rather globular shell is light 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 well developed, transverse striae on dorsal and ventral surfaces are well developed, the ventral side thicker than in the other formae, but not as thick as in the forma crassa. Lateral spines, as in the forma danae, are directed slightly anteriorly, there are up to 9 imbricate dorsal striae. The lips around the mouth are thin and red. The upper wing parts are yellow and in the centre of the lower parts round yellow to brown spots are present.
Shell length 2.5-3.2 mm, shell width 2.0-2.48, diameter of caudal spine mark 0.90-0.96 mm.


A special description is not available, see for a comparable juveniles D. costata.


This species is a protandric hermaphrodite.


This species is phytophagous and epipelagic.


This form is found only in the S-Red Sea, and probably also in the W-Indian Ocean, see the Diacria e. erythra map.

Geological Record

This species was known from the Late Quaternary of the Red Sea and probably this forma was found during Riss and Wurm glacial in this basin.


Diacria quadridentata erythra forma erythra Van der Spoel, 1971: 5, fig. 6.
Holotype: DZTU (dry collection). Paratype: DZTU 2 spec, and ZMAN 1 spec. (dry collection).
Type locality : Dahlak Archipellago, 15°32'30''N 40°23'E Coll.: ISRSE 65-3592, Dr. Ch. Fishelsohn.

Diacria erythra erythra