Variation of karyotype composition and genome size in some muricid gastropods from the Northern Hemisphere

Members of the Muricidae in the Northern Hemisphere show striking variation in chromosome number. The majority of the species examined to date have chromosome numbers in the range 2n &equals 60-70, while the Atlantic dog-whelk, Nucella lapillus is unique in having a Robertsonian polymorphism with 2n values in the range 26–36, and Ocinebrina aciculata; is newly recorded here as 2n = 86. The karyotype composition and genome size of eight muricid species from the N Atlantic and NE Pacific are described and compared. These results are discussed with reference to the evolution and biogeography of the family, and differences in the proportions of heterochromatin and packing ratios of the metaphase chromosomes. Evolution in N. lapillus, the derived form within the group, appears to have involved a reduction in chromosome number and haploid chromosome length, but an increase in both genome size and packing ratio.