THE CHROMOSOMES OF PLATYNEREIS-DUMERILII (POLYCHAETA, NEREIDAE)

The chromosomes of Platynereis dumerilii (Audouin & Milne-Edwards) are described here for the first time. A modal chromosome number of 2n=28 was recorded, based on counts conducted on metaphase spreads prepared from 24-h-old larvae. The karyotype comprises seven pairs, each of re latively large median (arm ratio, p/q=1 . 00-0 . 59) and submedian (ar m ratio, 0 . 59-0 . 33) chromosomes. Attempts were also made to band t he chromosomes using C-banding and silver staining methods. C-band-pos itive regions were localized on four chromosome pairs (three median, o ne submedian). A further two chromosome pairs (both median) were obser ved to have terminal nucleolar organizer regions (NORs). To our knowle dge, this is the first time that these banding methods have been succe ssfully applied to any polychaete species. These results are discussed in relation to the karyotypic variation within the class Polychaeta, and the family Nereidae in particular. A stable karyotype consisting o f a moderate number of large and morphologically well-differentiated c hromosomes, coupled with the ease of culture under laboratory conditio ns and short generation time, suggests that P. dumerilii is a potentia lly suitable model for evaluating marine contaminants for genotoxic ac tivity.