Faunistics and zoogeographical overview of the Mediterranean and Black Sea marine Gastrotricha.

The paper provides an updated overview of the knowledge regarding the marine gastrotrich fauna of 10 Mediterranean and 2 Black Sea countries. Taxonomic account and species distribution come from published records, including electronically disseminated information, as well as original data from 18 localities (16 western and 2 levantine), investigated by the authors between 1990 and 2002. Since the description of the first marine Mediterranean gastrotrich, Emydasys agaso Claparede, 1867, discovered in the Gulf of Naples (Italy), 273 additional species, from 417 locations have been recorded in the basin so far. Of the gastrotrichs found, 143 species, in 24 genera and 6 families, belong to the order Macrodasyida and 131 species, in 11 genera and 3 families, belong to the order Chaetonotida; these statistics include several species as of yet not described. The number of species per location is variable, ranging from 1-37, with a global mean of 8.04  6.69 spp/location. Egypt and Israel show mean values well above the average, with 12.8 and 10.8 spp/loc. respectively, whereas mean values for Algeria, Tunisia, Bulgaria, Croatia, and France are below average (1- 5.43 spp /location); data for Cyprus, Greece, Romania and Italy are within the average value. Acanthodasys aculeatus, recorded in 28% of the investigated location is the most frequently found macrodasyidan; Halichaetonotus aculifer, also recorded in 28% of the investigated localities, is the most common chaetonotidan whereas. Data analysis indicated substantial differences among countries, regarding sampling effort and, consequently, faunistic knowledge. In comparison with the generally good information concerning the Italian fauna (177 species from 246 localities), gastrotrichs from other Mediterranean nations are much less known; along with Italy, only few other Nations have been investigated to a sufficient extent (i.e., Greece: 44 sampled localities, 77 recorded species; France: 37 L, 70 spp; Egypt: 28 L, 81 spp; Israel: 15 L, 55 spp; Cyprus: 9 L, 41 spp), whereas investigation carried out in several other countries can be considered, to a variable degree, incomplete (i.e., Algeria: 16 investigated localities and 11 species found; Romania: 7 L, 30 spp; Tunisia: 5 L, 2 spp; Bulgaria: 3 L, 11 spp; Croatia: 1 L, 12 spp, Spain: 1 L, 3 sp, Malta; 2L, 2 spp.), or nil (e.g., Morocco, Libya, Turkey, Albania). All marine gastrotrich families and most marine genera have representatives in the Mediterranean fauna, notable absences regard the genera Desmodasys, Dinodasys, Planodasys, Prostobuccantia and perhaps Pseudoturbanella; on the other hand representatives of two genera, Emydasys and Dendropodola, are unknown elsewhere in the world except the western Mediterranean. At species level, about 140 taxa have so far been found only in the Mediterranean area, whereas the remainder have some north-Atlantic connections, including several considered as regional cosmopolitans (i.e., reported from at least two Oceans). Within the Mediterranean, the species geographic distribution does not appear to be homogeneous, with several taxa restricted to either the western or to the levantine basin; yet, Italy, Egypt and Israel show the highest numbers of endemic species, 70, 24 and 14 respectively, whereas only one species seems restricted to the Black Sea. A cluster analysis using the Bray-Curtis presence-absence similarity value to examine the relationship between 11 geographic areas, shows a clear separation between the Black Sea and the Mediterranean regions and within this, the Algerian-Tunisian region is separated from and the remaining 9 areas. The latter appear arranged in two main clusters, one including the southern Levantine regions (i.e., Egypt, Israel and Cyprus), the other containing regions of the north-western basin, the Adriatic sea and the two Greek sub-regions. In this cluster, the region comprising coastal France and Formentera (Spain) appears separated from the one containing, arranged into two distinct subsets, the Italian and the Greek areas. However, due to the paucity of information, data from key-areas is urged to confirm or disprove our current perception about numbers and distribution of gastrotrich taxa within the Mediterranean and the Black Sea.