BASTERIA, 50: 13-24, 1986 On the systematics of some Recent Rissoa (Gastropoda, Prosobranchia) A. Verduin c/o Rijksmuseum van Natuurlijke Historie, P.O. Box 9517, NL 2300 RA Leiden, The Netherlands INTRODUCTION is with satisfaction It some that I present this paper, because I consider it the comple- tion of revisional work the Recent ofthe Rissoa. my on European representatives genus the My previous papers on subject are mentionedin the references. Only a few species have not been discussed, as for instance the northern records from out- (in my opinion, side NW. Europe are probably incorrect) R. albella Loven, 1846, which has been discussed by Fretter & Graham (1978: 200), or the rare R. gemmula P. Fischer, 1871. These about which I have are species nothing new to report. A special part in this revisional work has been played by the apex, of which there exist i.e. the and the smaller shells with dif- proved to two types, larger one one.Often, of ferent types apex are very similar indeed as regards all other morphological characters. Nevertheless, I felt obliged to consider them different biological species. It seems worth-wile to sum up the reasons why. Rehfeldt (1968) has demonstratedthat amongR. labiosa-membranaceathe two types of apex correspond with different types of larval development, at least in the Roskilde- in Denmark. The smaller of correlates with small and fjord type apex numerous eggs a larval The of with fewer and pelagic phase. larger type apex corresponds larger eggs, part of which form "nurse-embryos" which degenerate and are consumed by the other larvae the with the in capsule, and a non-pelagic development. In my experience, range of the form with the smaller type of apex, i.e. R. labiosa (Montagu, 1803), ex- tends all the way down from Norway to Israel, though the form with the larger type of i.e. R. membranacea Adams, seems to have its southern limit in W. apex, (J. 1800), France (Verduin, 1982). It is difficult to understand such differencesin the range if one of for the difference in considers both forms varieties only one species. The same is true the number of ribs whorl between R. labiosa and R. membranacea mixed per among a sample from St. Lunaire, W. France, which obviously had been dredged (Verduin, 1982: Otherwise, both are similar indeed as fig. 2). species very regards morphology and variability. Surprisingly, among this group of species there proved to exist a 1 The Rissoa introduced De Freminvillein Risso but without generic name was by a paper by (1813: 87), description, definition or indication as required by Art. 12 of the I.C.Z.N. All specific epithets which ac- the introduction nomina nuda. The is for the rectified list of in companied are same true species, published the De Freminville same year by d'Omalius d'Halloy (1813: 341). Though the species meant by were in De is described the next year by Desmarest, this cannotalter the fact that Rissoa Freminville, 1813|, not an available name. Type species of Rissoa is R. ventricosa Desmarest, 1814, by subsequent designation (Buc- quoy, Dautzenberg & Dollfus, 1884: 262). In the subgenus Rissoa s.s. I included all species with conical (and in and shells with To these I added R. not fusiform, as Apicularia Goniostoma) punctate spiral sculpture. splen- dida, because of its striking overall similarity to R. ventricosa. 14 BASTERIA, Vol. 50, No. 1-3, 1986 second with the of ofwhich the be limited population larger type apex, range seems to to Tunisia. It may have originated quite recendy in the Golfe de Gabes or the former which well known for their endemic forms. I consider it lagoon of Tunis, are many a distinct species, R. paradoxa (Monterosato, 1884) (see Verduin, 1982). It is remarkable that the Rissoa contains more of less genus many pairs more or consists of similar species which differ as regards the type of apex. Another such pair munda which often be R. radiata Philippi, 1836, and R. (Monterosato, 1884), may only identified their of a mixed from the Golfe de reliably by type apex. Among sample ribs, with Gabes, however, all specimens ofR. radiata possess longitudinal as compared only 11 % of those of R. munda (see Verduin, 1976: 36). Again, the ranges are dif- with the smaller ferent. Both species occur in the entire Mediterranean, but the species of i.e. R. radiata, also occurs the Atlantic coast of to type apex, along Europe, up Bretagne, France, and probably even further north (2 shells in RMNH, dredged S. of Risoy near Bergen, Norway). R. guerinii Recluz, 1843, and R. lia(Monterosato, 1884) also may often only be iden- of lia also be tified reliably by their type of apex. Yet, many shells R. may recognized by other morphological characters, in particular the colour. R. guerinii, which has the smaller type of apex, occurs along the European Atlantic coast up to S. England, and in the western part ofthe Mediterraneanand in Sicily. In the Adriait is replaced by R. decorata (Philippi, 1846). R. lia occurs in the entire Mediterranean. ventricosa and R. variabilis Miihlfeld, Though R. Desmarest, 1814, (Von 1824) may be similar indeed 1980: 130, even considered them very (Piani, conspecific), they may authors have them not be considered sibling species, because most recognized as distinct the basis of characters other than the of species on shell-morphological type apex. Both may, however, also be separated by theirapex, thatof R. variabilis being the in the entire R. ventricosa is larger type. That species seems to occur Mediterranean; replaced by R. splendida Eichwald, 1830, in the eastern Mediterranean. with different of R. Other pairs of sibling species types apex are pulchella Philippi, 18362 and R. marginata Michaud, 1832, R. monodonta Philippi, 1836, and R. auriformis , Pallary, 1904, R. auriscalpium (L., 1758) and R. rodhensis Verduin, 1985, and R. similis R. 1983 and 1985 Scacchi, 1836, and scurra (Monterosato, 1917) (see Verduin, 1976, respectively). These, however, do not add much new information. MATERIAL EXAMINED AND ACKNOWLEDGEMENTS As far as not mentionedotherwise, this study is based on samples in my private col- ashore. Material from other collectionsis indicated KBIN lection (Vrd), all washed as (Koninklijk Belgisch Instituut voor Natuurwetenschappen, Brussels), RMNH (Rijks- museum van Natuurlijke Historie, Leiden), ZMK (Universitetets Zoologiske Museum Kobenhavn), Aar (private collection of Dr J.J. van Aartsen, Dieren) and Mnk (do. of Ir. H.P.M.G. Menkhorst, Krimpen a/d IJssel). I am obliged to these persons and in- stitutions for making their material available. I also thank Dr. Ph. Bouchet, Paris, Prof. Dr L.B. Holthuis, Leiden, and Prof. Dr. E. Gittenberger, Leiden, for advice in nomenclatorial matters, and in addition Mr. J.G. de Bruijn, Teyler's Stichting, Haarlem, and Mr. A.W. Janssen, Leiden, for providing literature. 2 This name is preoccupied by Risso, 1826. Van Aartsen et al. (1984: 22) suggested the replacement diversa but I hesitate that name as no has been name Nordsieck, 1972, to use as long lectotype designated. Verduin: Systematics of some Recent Rissoa 15 1-5. Rissoa 1. Figs. species. Rissoa ventricosa, Biograd, Jugoslavia (Vrd 0006). 2. Rissoa splendida, Biograd, Jugoslavia (Vrd 0049). 3-5. Rissoa variabilis, 3: Getarès, S. Spain (Vrd 0017); 4: Port Le Niel, S. France 5: forma (Vrd 0117); spongicula, Sfax, Tunisia (Aar 9176). Magnification 12.5 x . 16 BASTERIA, Vol. 50, No. 1-3, 1986 SYSTEMATIC PART Rissoa (Rissoa) splendida Eichwald, 1830 (fig. 2) Rissoa splendida Eichwald, 1830: 219 (Crimea); 1853: 266, pi. 10 fig. 8 Types. — No information available. — has the smaller of It is similar to R. Description. R. splendida type apex. very ventricosa, but be the less slender habitus, the may distinguished by by spiral sculpture the base of the and the which is degenerated into a few weak spiral striae at shell, by of dark which is somewhat than in pattern of spiral rows tiny spots, more conspicuous R. ventricosa, giving the shell a slightly darker appearance. common. Distribution. — Adriatic Sea, eastern Mediterranean, Black Sea; Discussion. — doubt whether the is sufficient to Though one may original diagnosis recognize the species with certainty, the type locality and the figure published by define the in The Eichwald (1853: pi. 10 fig. 8) species a very satisfactory way. species I is washed ashore in great numbers at many localities in its range. Therefore, was sur- Schwartz Mohrenstern did it from where prised that von (1863: 46) not report Rhodes, in it is rare. my experience not different from R. There can be little doubt that R. splendida is a good species, ven- Both rather in their entire and both at tricosa. are constant range, occur together many localities in the Adriatic Sea, where they do not seem to hybridize. Rissoa (Rissoa) variabilis (Megerle von Mühlfeld, 1824) (figs. 3-5) Rissoa costata Desmarest, 1814: 7, pi. 1 fig. 1 (no precise locality mentioned). 7 Turbo variabilis Megerlevon Miihlfeld, 1824: 212, pi. fig. 9ab ("das osterreichische Littorale",i.e. NE, Adriatic Sea). Rissoa spongicula Dautzenberg, 1883: 311 (Golfe de Gabes) — of be Types. Dr. Ph. Bouchet, Paris, wrote to me that the types Desmarest must considered lost. About those of Von Miihlfeldand of Dautzenberg I have no informa- tion. — variabilis has the of With R. ventricosa it shares Description. R. larger type apex. the punctate spiral striae, and with R. splendida the conspicuous colour pattern, which in R. variabilis into continuous colour lines. The ribs may even develop are remarkably tapered and knobby. The slenderness of R. variabilis is subject to considerable spatial variation. — is Distribution. Entire Mediterranean; common. The very slender form spongicula restricted to the Golfe de Gabes, Tunisia.