MOLECULAR SYSTEMATICS IN THE ACANTHOCEPHALAN GENUS ECHINORHYNCHUS (SENSU-LATO) IN NORTHERN EUROPE

New biological species and high levels of inter- and intraspecific gen etic divergence were discovered in an allozyme study of some North Eur opean members of the acanthocephalan genus Echinorhynchus (sensu late) , parasites of fish and malacostracan crustaceans. (i) A strong differ entiation between the marine E. gadi and the fresh- and brackish-water E. salmonis (genetic identity I similar or equal to 0) supports a gen eric distinction between these taxa; however, the subdivision would no t entirely concur with the concepts of Echinorhynchus (sensu stricto) and Metechinorhynchus suggested earlier. (ii) Samples of E. gadi from the Baltic, Norwegian and North Seas included three distinct, partiall y sympatric biological species (spp. I-III; I similar or equal to 0.5) . (iii) E. bothniensis, previously only known from the northern Baltic Sea, represents a complex of freshwater taxa with an intermediate hos t relationship to the 'glacial relict'. Mysis spp. and with a distribu tional and host analogy to the North American E. leidyi. A population in a northern lake in the Barents Sea basin is closely related to E. b othniensis of the Baltic area, but is probably specifically distinct; the divergence between these populations (I similar or equal to 0.6) i s similar to that between their Mysis host species. (iv) Considerable intraspecific differentiation (F-ST = 0.25), probably reflecting postg lacial population bottlenecks, was found between Baltic and nearby lac ustrine E. bothniensis, and between Atlantic and Baltic E. gadi sp. I.