The chromosomes of 16 molluscan species

Abstract Chromosome numbers were determined for two species of Placophora, eleven species of Gastropoda, one species of Pelecypoda and two species of Cephalopoda. No heterotypic or supernumerary chromosome resulted from the analysis of meiotic and, when possible, of mitotic chromosomes. For this reason no positive evidence emerges for the presence of differentiated sex chromosome pairs. Data available seem to indicate that evolution within the Mollusca phylum has been accompanied by a decrease in both chromosome number and DNA content (according to Hinegardner, 1974), if we consider subclasses, orders and families (apart from the subclass Prosobranchia). On the contrary the primitive class …