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Zoology Publications from Victoria University of Wellington—Nos. 68, 69 and 70

Introduction

Introduction

Chromosome numbers in molluscs are generally very conservative, and the haploid number seldom varies by more than one or two between the species of a particular family (Burch, 1965; Patterson, 1969). This is not always the case, however; the family Succineidae of the stylommatophoran suborder Heterurethra has species with chromosome numbers varying from n=5 to n=25 (Patterson 1969, 1970). The only other heterurethran family for which chromosome numbers have been recorded is the family Athoracophoridae, which is found on the New Hebrides, New Britain, the Admiralty Islands, the east coast of Australia, New Zealand, and the subantarctic islands. Aneitea sp. from the New Hebrides has 44 pairs of chromosomes (Patterson, 1969), and Triboniophorus graeffei from New South Wales also has 44 pairs of chromosomes (Burch and Patterson, 1971). These are by far the highest chromosome numbers known for any stylommatophoran land snail, the next highest number reported being n=34 for two slugs of the genus Milax (Beeson, 1960).

It has been suggested that the high chromosome numbers found in the Athoracophoridae could be the result of polyploidy (Burch and Patterson, 1971). Clearly cytological studies on the New Zealand species of the family are necessary.