Freshwater Gammarus species from Europe, North Africa and adjacent regions of Asia (Crustacea-Amphipoda). Part III. Gammarus balcanicus-group and related species

1) This third part of the revision of the freshwater Gammarus species deals with the G. balcanicus-group. Members of this artificial group are characterized by poorly setose pereiopods 3 and 4 and uropod 3 and by the absence of dorsal carinae (processes) on the metasome segments. 2) The morphological characters used in this work are identical to those used in the first part, the revision of the Gammarus pulex-group (Karaman & Pinkster, 1977a). 3) The type material or topotypic material of all studied taxa was reexamined and compared with many (several hundreds) of newly collected samples and material from many European museums. 4) Complete descriptions and many illustrations are given of the males of all species from Europe and Asia Minor. The variability of the various characters is discussed and a key is given of the species of the Gammarus balcanicus-group If necessary, the characters of the females, in case they are different, are likewise figured. 5) It is established that many taxa described from the Balkans must be considered synonyms of G. balcanicus. 6) In numerous localities, members of the G. balcanicusgroup have been found together with members of the G. pulexand/or G. roeseli-group and/or with members of the genus Echinogammarus. 7) Two new taxa are described, G. longipedis n. sp. and G. pseudanatoliensis n. sp., both from Asia Minor. 8) Three taxa of this group are limited to cave-streams: G. halilicae, G. albimanus, and G. longipedis n. sp. Seven species are limited to Lake Ohrid between Yugoslavia and Albany: G. ochridensis, G. stankokaramani, G. parechiniformis, G. macedonicus, G. solidus, G. lychnidensis and G. salemaai. 9) The species from Lake Ohrid not only differ from the other species within this group in morphology but likewise in karyology. All common freshwater gammarids have a haploid chromosome number of 26. In the species from Lake Ohrid this number varies from 12 in G. salemaai to 34 in G. lychnidensis. From these chromosomal numbers we assume that polyploidy is the evolutionary mechanism of speciation within this lake, and that G. salemaai is the ancestral form. 10) From zoogeographical data it can be concluded that this group originates from southeastern Europe and Asia Minor. The only species of this group that invaded a more extended area is G. balcanicus. 11) In G. balcanicus isolated populations are found which are more or less distinct in morphology. Since these populations are interfertile and since a geographical isolation mechanism does not exist, these populations should be considered as mere variations. 12) For all species complete lists of all studied material are given (except for G. balcanicus, for graphical space economy)