Conservation of sequence in the internal transcribed spacers and 5.8S ribosomal RNA among geographically separated isolates of parasitic scuticociliates (Ciliophora, Orchitophryidae)

Nucleotide sequence from the internal transcribed spacers (ITS1 and ITS2) a nd the 5.8S gene from the ribosomal RNA gene cluster of isolates of the scu ticociliate Orchitophrya stellarum from 4 asteroid hosts were compared. Sur prisingly, these data (495 bp) were identical for O. stellarum isolated fro m the testes of Asterias amurensis from Japan; Pisaster ochraceus from Brit ish Columbia, Canada; Asterias rubens from The Netherlands; and Asterias vu lgaris from Prince Edward Island, Canada. These sequence data were compared to those from 3 scuticociliates which parasitise crustaceans: Mesanophrys pugettensis, M. chesapeakensis and Anophryoides haemophila. No difference w as found in this region between the nucleotide sequence of M. pugettensis a nd M. chesapeakensis. The sequence of Mesanophrys spp. differed by 9.2% in the ITS1 and 4.7% in the ITS2 from that of O. stellarum. The sequence from the ITS1 (135 bp) and ITS2 (233 bp) of A. haemophila differed by 42.6 and 2 0.5% respectively from those of O. stellarum. Therefore, nucleotide sequenc e of the ITS regions in these scuticociliates is highly conserved.