The unionids of Tunisia: Taxonomy and phylogenetic relationships, with redescription of Unio ravoisieri Deshayes, 1847 and U. durieui Deshayes, 1847

Abstract

Using an approach based on molecular, reproductive and morphological characters, four independent evolutionary lineages represented by the following species were identified in Tunisia: Unio ravoisieri Deshayes, U. gibbus Spengler, U. durieui Deshayes and Potomida littoralis (Cuvier). The species U. ravoisieri and U. durieui are redescribed, including details of their distribution, biology and glochidium morphology. The puzzling distribution of the former (Algeria, Tunisia and two localities in Northeast Spain) could reflect introduction or natural dispersal. In Tunisia, the release of the glochidia of U. ravoisieri starts in March, but in Spain this is delayed until August or September. The entire interlamellar space of the outer demibranchs acts as a marsupium (ectobranchy). Glochidia are rounded-triangular, globose, and either hooked or hookless. Unio durieui is distributed across Algeria and Tunisia, where it releases glochidia in December and in March. Glochidia are always hooked, but the elaboration of the hook is variable. The molecular phylogenetic analysis supports two clusters within Unio, each including both European and North African species. Strong bootstrap support was obtained for the two clades within U. ravoisieri, of which one includes specimens from the Iberian Peninsula as well as Tunisia. Unio durieui appeared as the sister species of U. gibbus. The Tunisian populations of P. littoralis were not segregated from those in Europe, and U. fellmanni should be considered a synonym. © The Author 2011.