Anostraca,Conchostraca, Cladocera and Copepoda from Tunisia

In samples from 62 localities in Tunisia and La Calla area in N.E. Algeria, 56 species of Entomostraca were found. More than half of these are widespread and give little insight into the origin of the regional fauna. A few are endemic to the area and three groups are of relictual nature. The first one consists of northern species, some of which are known to have reached the central Sahara. It is argued that their populations have an estimated age of about 5–6000 yrs. At first sight, the second and more numerous group of species, the Ethiopian relicts, should be older. However, until historical times pathways around the Sahara may have functioned. One was along the Atlantic coast; a second and older one was via the Nile. The second possibility is almost a certainty, since a third group of relicts, the Oriental one, has migrated into the central Sahara as far as (and therefore probably together with) the northern relicts. This group must have come via the Nile Delta and the Libyan desert. If that pathway has also been used by Ethiopian species, all three groups of relicts are of the same age. In our Tunisian collection, only one Oriental element is represented.From a taxonomical point of view, morphological differences between the Chydorids Alona rectangula Sars and Alona elegans Kurz are sorted out and illustrated. Alona rectangula is best regarded as a superspecies. Hybridisation with A. elegans appears possible.Contribution n° 23 from project Limnology of the Sahara, under Contract n° 2.0009/75 with the Fonds voor Kollektief Fundamenteel Onderzoek, Belgium