Cytogenetics of pill clam, pisidium mitchelli (Bivalvia: Pisidiidae)

A cytogenetic study was carried out on the chromosomes of pill clam, Pisidium mitchelli (Bivalvia: Veneroida: Pisidiidae) collected from River Chenab fed stream Gho-Manhasan (Jammu, J&K, India). Chromosomes were studied using Giemsa staining and two banding techniques viz. C-banding & Ag-NOR banding. P. mitchelli shows a diploid chromosome number of 2n=62 consisted of seven metacentric, three submetacentric, eighteen subtelocentric and three telocentric chromosomal pairs. The fundamental arm number (FN) was 118. The mean haploid length and total diploid length was 21.58µm and 43.16µm respectively. Preliminary C-band studies revealed the presence of terminal blocks besides the presence of centromeric heterochromatin. The nucleolar organizer region (NOR) was found on one chromosome pair i.e. on the metacentric chromosome pair no. 6. The cytogenetic relationship between P. mitchelli and other species of Veneroida was also discussed.