" Karyotype and ribosomal gene localization in Oxynoe olivacea (Mollusca, Opisthobranchia, Sacoglossa ). "

Data from literature indicate that Opistobranchs are very little known at a kryological level, because information about karyotype and chromosome banding are lacking. In this paper we study the conventional karyotype of Oxynoe olivacea and map the ribosomal genes with fluorescent in situ hybridization (FISH) using a  Paracentrotus lividus  (Echinodermata) 4.3 kilobase  (Kb)  rDNA probe  (prR14)  consisting of sequences from  the 3' end of 18S rDNA to the 3' end of 26S rDNA.
In late developing embryos the diploid chromosomes number is 2n=30, 15 metacentric and subtelocentric pairs. One small sized metacentric chromosome pair bears ribosomal clusters terminally in one of the two arms. The presence of two large sized metacentric chromosome pairs associated with a decrease of the chromosome number from 34, that is typical in sacoglossan, to 30, suggests that a Robertsonian fusion may have operated during evolution of O. olivacea karyotype.

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