Karyotype, location of the nucleolar organizer regions (NORs) and heterochromatin presence and composition were studied in the Antarctic whelk Neobuccinum eatoni. The karyotype exhibits 2n = 68 chromosomes with 10 pairs of metacentrics, 14 pairs of meta‐submetacentrics, six pairs of submeta‐subtelocentrics, and one pair of subtelo‐telocentrics. Silver and CMA3/methyl green staining and rDNA FISH evidenced telomeric NORs on the long arm of a pair of medium‐sized submetacentrics. Staining with AT‐specific fluorochromes evidenced telomeric bands on nearly all chromosomes and interstitial Q bands on two pairs of presumably subtelocentric chromosomes. The karyological evolution of N. eatoni seems to be characterized by a generalized neogastropod karyotype associated with a genome size increase following the accumulation of heterochromatin containing AT‐rich repetitive DNA; according to some authors the latter could be related to the modulation of morphological and functional parameters of ecological significance.