EROSARIA NEBRITES FORM LABROSPINOSA
by E. L. Heiman*)

Abstract: Distinguishing shell characters of Erosaria nebrites labrospinosa from the Pleistocene of Hurghada, Egypt are found also in the living populations of Erosaria nebrites from East Sinai, hence the former is treated below as a form of Erosaria nebrites. A conclusion is also drawn that E. nebrites is a monotypic species.

Key words: Mollusca, Gastropoda, Erosaria nebrites, Pleistocene, Erosaria labrospinosa, variability, Red Sea.

Erosaria nebrites (Melvill, 1888) is a common and very variable species living in the entire Red Sea, the Gulf of Aden and the Arabian Sea (Oman). Fifteen forms (varieties) of E. nebrites are currently known (Heiman, 2002).

Some shells belonging to one of these forms: f. dilatata, are so unusual that they are mentioned by Heiman & Mienis (1999) as a possible link between the living populations of E. nebrites and their forerunner, the Pleistocene E. nebrites labrospinosa Lorenz, 1992- Plate 1, Figs. 3, 6.

It should be mentioned that the Pleistocene events in history of the Earth began about 2,500,000 years ago and ended about 10,000 years ago; this period is sometimes named the Ice Age.

It turned out after additional study, that the distinguishing shell characters of Erosaria nebrites labrospinosa from the Pleistocene of Hurghada, Egypt can be found also in the living populations of Erosaria nebrites from East Sinai.

Lorenz (1992) studied the Pleistocene Cypraeacea from the vicinity of Hurghada, Egypt. Fossilized shells of Erosaria nebrites (Melvill, 1888) found near Hurghada were separated into two groups. In one group were shells similar or identical to those of the living E. nebrites and in the second group were shells differing to some extent from typical nebrites shells. A shell from the Pleistocene of Hurghada, Egypt, can be seen on Plate1, Figs. 10-11.
In the first group a phenomenon of the displaced dorso-marginal blotches was observed-Plate 1, Figs 1-2.

"In many specimens the marginal blotches (which are supposed not to reach the base or the edges of the shell in E. nebrites) are split into two smaller blotches, of which one is situated below the marginal edge, and the other above. In the related E. erosa from the Indo-Pacific the same marginal blotches occur, however situated directly on the marginal edge, or below, so that they are visible ventrally as well. It is suspected that E. nebrites has directly and continuously developed from E. erosa (which has still existed in the Red Sea in the Pleistocene of Port Sudan). The position of the marginal blotches in living specimens of E. nebrites and E. erosa represent a constant and reliable feature for distinction".

Although the entire question of distinguishing E. erosa from E. nebrites is out of the scope of this article, it should be noted that the position of the dorso-marginal blotches varies in shells of both species (erosa and nebrites) and this shell character can hardly be used for distinguishing between erosa and nebrites. Examples of the variability of this shell character in shells of E. nebrites from East Sinai can be seen on Plate 1, Figs. 4-5 and 7-9.

Shells of the second group of the Pleistocene E. nebrites are described as a subspecies Erosaria nebrites labrospinosa Lorenz, 1992-Plate 1, Fig. 3, 6. "This new subspecies is characterized by processes of the labral teeth reaching the marginal edge, forming spines and tubercles. In well preserved specimens even on columellar side such tubercles and ridges can be seen."

This diagnostic shell characters of E. nebrites labrospinosa can be observed also in shells of the abovementioned f. dilatata of E. nebrites living in the waters bordering East Sinai in the Gulf of Aqaba as illustrated on Plate 1 Figs. 12-14.

Hence shells of the living populations of E. nebrites from East Sinai and shells of E. nebrites found in the Pleistocene of Egypt can not be distinguished conchologically and E. nebrites labrospinosa should be considered synonym of E. nebrites.

Unusual shells of E. nebrites with the prominent spines and tubercles on the base and margins, which are found from time to time together with typical shells of this species, can be treated for convenience as a form: E. nebrites, form labrospinosa.

Schilder & Schilder (1938) studied 294 nebrites shells and recognized (rather intuitively) two new subspecies: E. nebrites ceylonica and E. nebrites mozambicana, which practically do not differ conchologically from the nominate subspecies E. nebrites nebrites. The name of each of these subspecies explains the geographical area of their distribution, but the Schilders added that these two new subspecies need further study for clarifying their taxonomic identity. Schilder & Schilder (1971) listed E. nebrites as a subspecies of Erosaria erosa (Linnaeus, 1758) and two abovementioned taxa as synonyms of E. nebrites. 65 years after the Prodrome was published, there is no scientific evidence that populations of E. nebrites are living in the waters bordering Ceylon and Mozambique and these two taxa can be considered indeed synonyms of E. nebrites.

In addition, the conclusion can be drawn that E. nebrites is a monotypic species.

Plate 1 Shells of Erosaria nebrites
1.	2.	3.
1-2. Shells of E. nebrites with displaced dorsomarginal blotches; Pleistocene; Hurghada; Egypt; from a work by Lorenz (1992)from a work by Lorenz (1992)		3. E. nebrites labrospinosa,from a work by Lorenz (1992)
4.	5.	6.
4-5. Shells of E. nebrites with displaced dorsomarginal blotches; East Sinai		6. E. nebrites f. typical, E. Sinai
7.	8.	9.
7-9. Shells of E. nebrites with displaced or absent dorsomarginal blotches; East Sinai
10.	11.	12.
10-11. E. nebrites f. labrospinosa, Pleistocene, Hurghada, Egypt		12. E. nebrites f. labrospinosa East Sinai
13.	14.
13-14. E. nebrites f. labrospinosa, East Sinai

References

References
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