KARYOTYPES OF FIVE SUBANTARCTIC BIVALVE SPECIES

Abstract

Chromosomes of five subantarctic species were studied from mitotic metaphases using cell suspension techniques. Among the Protobranchia, Malletiagigan-lea has a diploid chromosome number of 2n = 38 with five metacentric, seven submetacentric, five sub-telocentric and one telocentric pairs, and Yoldia (Aequiyoldia) woodwardi also shows 2n = 38 but with ten metacentric, six submetacentric and three sub-telocentric pairs. Among the Lamellibranchia, the pterioidan Limatula pygmaea has 2n = 38 with six metacentric, eleven submetacentric and two sub-telocentric pairs, the veneroidan Cyclocardia astar-toides has 2n = 30 with five metacentric and ten telocentric pairs and the anomalodesmatan Laternula elliptica has 2n = 40 with two metacentric, one submetacentric, two subtelocentric and fifteen telocentric pairs. Our results indicate that in all the Nuculoidea studied so far, a diploid number of 2n = 38 has been found. In addition, the karyotypes show a close overall appearance in relative lengths with a majority of meta-centric-submetacentric chromosomes. The species differ in the proportion of the different morphological types of chromosomes. In the Lamellibranchia, each species corresponds to a particular case within their respective orders (Pterioida, Veneroida, Anomalodesmata).