Mediterranean Rotifers: a very inconspicuous taxon

Abstract

Biogeographia vol. XXIV - 2003 (Printed October, 31 st 2003) Marine biogeography of the Mediterranean Sea: patterns and dynamics of biodiversity Mediterranean Rotifers: a Very inconspicuous taxon CLAUDM RICCI, DIEGO FONTANETO Universziiz Stamle zli Milzmo, Dz'}7zzrtz'mem‘0 dz‘ Biolagia, Via Celoria 26, I—20]33 Milano (Italy) Key words: Rotifera, Mediterranean Sea, marine rotifers. SUMMARY Occurrence of rotifer species in the sea is here reviewed, with emphasis on the Mediterranean Sea. Most of the few investigations dealt with rorifer species in Arctic and Antarctic Seas and along Northern European coasts, while Mediterranean area has received very little attention. Despite the few studies, one hundred five rotifers are reported as strictly marine, of these only 20 are signaled in the Mediterranean Sea. The species number is doubled if the freshwater rotifers that are occasionally found in the sea are added. Reasonably, the short list of rotifers from the Mediterranean is to be ascribed to the very few studies carried out and not to absence of rotifers in the area. ROTIFERS Phylum Rotifera comprises 1800 species of microscopic metazoans (80—2000um in length) divided into three major groups: Monogononta (~1450 species), Bdelloidea (~350) and Seisonidea (2) (Segers, 2002). They are characterized by short life cycle and direct development, most are filter-feeders, some are predators and few live as parasites. The three groups differ because of their reproduction. Seisonids are always amphimictic, with sex ratio 1:1, and monogononts punctuate thelytokous parthenogenesis (producing females) with arrhenotokous parthenogenesis (producing males) and subsequent sexual reproduction. Mating produces a diploid egg with delayed development, called resting egg; however, among most monogonont species only females are known so far. Bdelloids consist of parthenogenetic females only (Mark Welch and Meselson, 2000). Monogononts live in aquatic habitats like rivers, lakes, ponds, temporaiy and permanent pools, lagoons and seas, and very few can live in the water films around soil particles (Nogrady et al., 1993). Bdelloids are commonly part of the meiofauna of any habitat where Water is occasionally present, thus they can be found in rivers, lakes, ponds, but also among soil particles, and in mosses and lichens (Donner,