Chromosome Numbers In Two Species Of Pseudaneitea
A Chromosome count of n=44 has been recorded for both Pseudaneitea papillata and P. aspera.
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.
Materials and Methods
A large specimen of Pseudaneitea papillata, collected from Karori, Wellington, was narcotised in an infusion of tobacco in water. The gonad was removed after four hours, and fixed in two changes of Newcomer's fluid (Newcomer, 1953). Chromosome squashes were stained with aceto-orcein.
The same technique was used for a specimen of P. aspera, collected from the Orongorongo Valley.
Cells undergoing male diakinesis in the ovotestis of P. papillata had 44 bivalents (Fig. 1). Therefore, this species has the same chromosome number as Aneitea sp. of the New Hebrides and Triboniophorus Graeffei of Australia. A similar chromosome number was recorded from P. aspera (Fig. 2).
It is clear that the New Zealand Athoracophoridae have been separated from their relatives in Australia and the New Hebrides for a very long time, and the sharing of a common chromosome number shows that the group displays the same cytological conservativeness seen in most other snail groups. It is still not possible to determine whether the high chromosome number found in the Athoracophoridae has resulted from polyploidy.
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Burch, J. M. and Patterson, C. M. , 1969. The Systematic position of the Athoracophoridae (Gastropoda: Euthyneura). Malacologia 9: 259-260.
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