[Karyologic study of gill neoplasia in Macoma balthica (Mollusca, Bivalvia)].

This paper reports the first karyological study of a gill neoplasia in the bivalve Macoma balthica from the Bay of Gdansk (Poland). Chromosomes were studied with an air-drying technique from gill tissue. Out of 47 specimens studied, 34 showed normal cells and a variable number of mitotic metaphases with a normal diploid chromosome number of 2n = 38, 6 had hypertrophied nuclei and a high number of mitoses with 70 to 98 chromosomes, and 7 specimens showed intermediate features. The karyotype of normal metaphases included 11 metacentric, 2 submetacentric and 6 subtelocentric chromosome pairs. The karyotype of abnormal metaphases, i.e. with a high number of chromosomes, revealed chromosomal aberrations inferring neoplastic disorders such as: different number of metacentric, submetacentric, subtelocentric and telocentric chromosome pairs than in the normal karyotype, increase of chromosome pairs especially in the small and medium-sized chromosomes, irregular monosomy and occurrence of microchromosomes. According to neoplasias recorded in bivalves species, the prevalence observed in this neoplasia is relatively high. As Macoma balthica inhabits the polluted Bay of Gdansk, the effects of environmental parameters should be elucidated.