VARIABILITY OF COWRY POPULATIONS

20. PALMADUSTA LENTIGINOSA (GRAY, 1825)

by E. L. Heiman*)

Abstract: Variability of Palmadusta lentiginosa is studied in 112 shells. The average shell length, relative width and normalized tooth count are calculated for different populations throughout the distribution range of the species from the Mediterranean Sea and across the Indian Ocean from Red Sea to the eastern part of southern India. The number of dorsal bands and the degree to which the columellar teeth extends on the base in shells of different populations are compared. No consistent difference in shell characters of the studied populations and no clear diagnostic characters are found, which would confirm a subspecific status of these populations, hence P. lentiginosa is recognized here as a monotypic species.

Key words: Mollusca, Gastropoda, Cypraeidae, Palmadusta lentiginosa, variability, distribution.

Palmadusta lentiginosa (Gray, 1825) is an uncommon species inhabiting the Red Sea and the waters bordering the Arabian Peninsula, the Persian Gulf, Pakistan and India up to a region southward of Madras. Currently, it has successfully established itself in a new region: the Eastern Mediterranean (Figs. 1-2).

Variability of P. lentiginosa is discussed below in order to learn more about the possible origin of the new population in the Mediterranean Sea.

Jonklaas & Nicolay (1977) distinguished three zones of distribution of the species. Correspondingly they recognized three subspecies of P. lentiginosa and described the following difference between them:

P. lentiginosa lentiginosa, the nominate subspecies, from the Persian Gulf to 200 miles south of Bombay.

P. lentiginosa dancalica from the southern Red Sea (Massawa and the Dahlak Is.), which are smaller, slender, almost cylindrical and differs from the Indian shells by a single central dorsal band (instead of three transvers bands in lentiginosa lentiginosa), the white base and much rarer “freckles” on the sides.

P. lentiginosa buhariensis from the extreme south of India which is more elongated, the basic color is light blue, the central dorsal band (of three transvers dark bands on the dorsum) is brightest and most distinct; there is a little dark blotch on the apex and two other little blotches on the anterior tip. The base is cream, the teeth are strong, as in the type.

Shell characteristics of 112 specimens from different populations of P. lentiginosa were studied and 101 of them are compared in the following Table 1.

It should be mentioned that the base color in cowry shells is not always a good diagnostic character because it may fade with time. In shells of P. lentiginosa it varies from practically white to light beige depending on freshness of a shell and on a kind of lighting of a specimen inder study. In all studied shells it is whitish to light beige and it is difficult to decide whether it is white or very light beige or cream. This shell character was excluded from the statistical study.

There are three dorsal bands in shells of P. lentiginosa. The central band is the brightest and most distinct and it is usually broad. Other two dorsal bands are less visible and sometimes there is an impression that one of them (or both) is absent. However, it was possible to trace of at least part of these transvers bands in all studied shells.

The formula for 26 shells from Bombay and Karachi (together) turned out to be 24.62.16.14; for 31 shells from southern India (Kilakarai and Madras together) the formula is 26.61.16.14; these formulae are very close to the formula for the population from the Mediterranean Sea.

Small dark spots cover the margins, posterior extremity and part of the base in all shells of P. lentiginosa; sometimes these spots cover also the spire and it is difficult to decide whether there is a separate spire blotch or there are several confluent marginal spots. Anyway, the spire blotch can be distinguished in the majority of shells of all studied populations.

Dark blotches at the anterior extremities are present in the majority of shells of all studied populations.

The columellar teeth of the majority of shells extend onto the base and even up to the middle of the base.

11additional shells not listed in Table 1 include 6 specimens from Trivandrum (western part of S. India), 2 shells from Pamban (eastern part of S. India), 2 shells from Seychelles and 1 shell from Das Id., Persian Gulf. All these shell are also not separable from the studied shells from above localities.

Subspecies are geographically isolated populations of a species. It is expected that the majority of the shells of a subspecies share most diagnostic shell characters of a species but differ from the shells of other subspecies of the same species by at least one diagnostic characteristic. For example Mauritia arabica immanis Schilder & Schilder, 1938 differs from the nominate subspecies Mauritia arabica arabica (Linnaeus, 1758) by the considerably larger average shell length. M. arabica grayana Schilder, 1930 differs from the latter by the usually humped subpyriform shell whereas shells of the nominate subspecies are flat and elliptical to oval. In other words, at least two conditions must exist for distinguishing subspecies—geographical isolation and the difference in shell characteristics confirmed to the majority of individuals of a population.

A formal description of the subspecies P. lentiginosa dancalica and P. lentiginosa buhariensis is not given by Jonklaas & Nicolay (1977) but these names are sometimes used as subspecific in the malacological literature. Populations of P. lentiginosa lentiginosa, P. lentiginosa dancalica and P. lentiginosa buhariensis are geographically isolated so the first of the above mentioned conditions is provided. But, as follows from Table 1, the second condition is absent: there is no practical difference in the shell characteristics of the studied populations.

The number of studied shells is small for a convincing representation of the populations but an impression can be formed that P. lentiginosa is a monotypic species and shell collectors will not be able to distinguish between its different populations due to the absence of a proper diagnostic shell character.

Further study is needed in order to learn the true taxonomic status of different populations of the species (especially populations of the Red Sea and the Persian Gulf). Meanwhile P. lentiginosa should be treated as a monotypic species.

The origin of the new population of P. lentiginosa in the Mediterranean Sea remains uncertain.

Acknowledgements

Many thanks to members of the Israel Malacological Society, to Henk K. Mienis (National Mollusc Collections at the Dept. Evolution, Systematics & Ecology, Hebrew University of Jerusalem and Zoological Museum, Tel Aviv University, Israel) and to Jean and Janine Demartini (Marseille, France) for supplying background information for this article.

References.

Jonklaas, R.S.L. & Nicolay, K. 1977. Cypraea lentiginosa Gray, 1825 (considerations on its range and variability). La Conchiglia (95-96):16.

Lycette, D. 2000. Cowry observations. Triton 2:29-30.

*) P.O.Box 664 Rehovot 76100 Israel E-mail: heimel@netvision.net.il