OCCURRENCE OF LIMNADIA LENTICULARIS (LINNAEUS, 1761) (CONCHOSTRACA, LIMNADIIDAE) IN EMILIA-ROMAGNA, ITALY

BY

FRANCA SCANABISSI and STEFANO TOMMASINI1) Dipartimento di Biologia Evoluzionistica Sperimentale, Università degli Studi di Bologna, Via Selmi, 3, 1-40126 Bologna, Italy

ABSTRACT

Rice-growing is only a few decades old in Italy's Po River delta. Yet, the new biotope has been colonized by numerous species of Crustacea , including the conchostracan Limnadia lenticularis. This species, which up till now had been found in Italy only in the Piedmont area, is for the first time reported in the Emilia-Romagna region and its geographical range in northern Italy could be confirmed. Selected taxonomical traits observed under SEM and features essential for the identification of the species are reported and discussed.

RÉSUMÉ

La culture du riz a été implantée dans la région du delta du fleuve Po il y a quelques dizaines d'années seulement. Le nouveau biotope a été colonisé par de nombreuses espèces de Crustacés Branchiopodes, y compris le Conchostracé Limnadia lenticularis. Cette espèce qui, en Italie, n'avait été trouvée que dans le Piémont, est signalée pour la première fois de l'Emilie-Romagne, et sa distribution est confirmée dans l'Italie du Nord. Les caractères taxonomiques de détermination de l'espèce ont été observés au MEB, décrits et discutés.

INTRODUCTION

Although Linnaeus first described Monoculus lenticularis as a species in 1761, it was only in 1820 that Brongniart attributed it to a new genus, Limnadia. The anatomy of L. lenticularis (L., 1761) was studied by Nowikoff (1905) and Daday de De6s redescribed this taxon in his monograph on Phyllopoda Conchostraca (1925). The first report of L. lenticularis in Italy was by Fox in 1951, who found it in temporary pools in the Piedmont region (northern Italy), and the species was

1) To whom correspondence should be addressed. 207 collected in the same pools by Zaffagnini in 1967. No other reports are known from Italy. Like other Conchostraca, L. lenticularis lives in temporary pools and needs unpolluted water. The introduction of rice-growing in the Emilia-Romagna region (northern Italy), probably provided the impetus for colonization by this species, as it had done for other Conchostraca as well (Scanabissi Sabelli & Tommasini, 1990). In order to provide a basis for a comprehensive survey of the species range in northern Italy, an adequate characterization of its morphology will be help- ful. Therefore the external morphology of Limnadia lenticularis was examined by scanning electron microscope (SEM) and the diagnostic features needed for species identification are redescribed, although some traits considered by us and others as being too variable were excluded.

MATERIAL AND METHODS

Females of Limnadia lenticularis were collected in May 1993 and 1994 from parthenogenetic populations in rice paddies located in Ferrara Province and kept for several days in the laboratory. The specimens examined were fixed in ethanol (70%), processed through a graded acetone series, critical point dried, fixed on stubs with double-sided adhesive tape, vacuum-coated with gold (2 min at 30 mA) and observed under a JEOL JSM5200 SEM.

RESULTS

Among the branchiopod samples collected were several mixed populations of Conchostraca, including the usual (cf. Scanabissi Sabelli & Tom- masini, 1990) and a species not referable to that family. These were determined as Limnadia lenticularis (Linnaeus, 1761 ) (family Limnadiidae) by morphologi- cal and anatomical data (cf. Nowikoff, 1905; Daday de De6s, 1925; Straskraba, 1965; Cottarelli & Mura, 1983; Nourisson & Thi6ry, 1988; Brendonck, 1989). The populations consisted of females and, hence, were classified as partheno- genetic after Zaffagnini (1967). These females deposit but a few eggs that are held under the valves of the carapace for several days and are then deposited on the bottom of the pool. Like those of most Branchiopoda (: Gilchrist, 1978; : Tommasini et al., 1989; Conchostraca: Tommasini & Scan- abissi Sabelli, 1989; Zaffagni, 1970; : Margaritora, 1983), the eggs have a resistant shell designed to withstand the dry spells common to temporary astatic pools and rice paddies.