SUPERNUMERARY CHROMOSOMES IN NEPHROPS-NORVEGICUS L (CRUSTACEA, DECAPODA)

Supernumerary chromosomes have been identified in the chromosome compl ement of Nephrops norvegicus L. by C-banding and restriction endonucle ase-induced banding. These chromosomes showed peculiar features of typ ical B chromosomes in terms of heterochromatin content, asynapsis and distorted segregation. The presence of these chromosomes can, at least partially, account for the numerical variability already observed in this species; 2n and n values determined by counting these chromosomes separately gave a less variable number of chromosomes in the compleme nt. Q-banding was useful to characterize some large B chromosomes with intercalary and subtelomeric bands as well as entirely positive short arms in some small submetacentric chromosomes. Nucleolar organizer re gions have been identified in four pairs of chromosomes by silver stai ning.