FISH-based karyotyping of (Pallas, 1766), Schulze, 1914, and Itô, 1947 (Cnidaria, Hydrozoa).

An account is given of the karyotypes of Itô, 1947, Schulze, 1914, and (Pallas, 1766) (Cnidaria, Hydrozoa, Hydridae). A number of different techniques were used: conventional karyotype characterization by standard staining, DAPI-banding and C-banding was complemented by the physical mapping of the ribosomal RNA (18S rDNA probe) and H3 histone genes, and the telomeric (TTAGGG) sequence by fluorescence hybridization (FISH). We found that the species studied had 2n = 30; constitutive heterochromatin was present in the centromeric regions of the chromosomes; the "vertebrate" telomeric (TTAGGG) motif was located on both ends of each chromosome and no interstitial sites were detected; 18S rDNA was mapped on the largest chromosome pair in and on one of the largest chromosome pairs in and ; in , the major rRNA and H3 histone multigene families were located on the largest pair of chromosomes, on their long arms and in the centromeric areas respectively. This is the first chromosomal mapping of H3 in hydras.