CHROMOSOME-NUMBER AND KARYOTYPE OF DONAX-TRUNCULUS L (MOLLUSCA, BIVALVIA, TELLINACEA)

A chromosome study of Donax trunculus was made with specimens collected from a population of the French Atlantic coast. The karyotype, not previously described, consists of 19 pairs of chromosomes (2n = 38) as in the majority of the speices so far investigated in the Veneroida. There was no evidence of morphologically identifiable heterosomes. The karyotype is characterized by (1) a high total chromosome length which reaches 228.56-mu-m, (2) a great heterogeneity of the chromosome length, and (3) a high number meta- and submetacentrics, 9 and 7 pairs respectively vs. 3 pairs of subtelocentrics, giving a fundamental number of 70. Comparison with two other closely related families having reported karyological data - Scrobiculariidae and Semelidae - suggests that, although chromosome numbers are identical, the karyotype is clearly different from one family to the other.