Chromosomal heteromorphism in a Japanese population of Pectinatella gelatinosa and karyotypic comparison with some other phylactolaemate bryozoans

Five different karyotypes were present in germinating statoblasts obtained from a sampling of a predominately or exclusively asexually reproducing population of Pectinatella gelatinosa from Lake Tatara-numa, Japan. Karyotypes were consistent in having 18 chromosomes, a unique telocentric, a pair of minute metacentrics, and at least one prominently secondarily constricted element. In a number of cases, a sampling of statoblasts from a single large colony yielded more than one karyotype, perhaps because there had been fusion of smaller colonies with different karyotypes. Some individual statoblasts may have been chimeric, but this was not conclusively demonstrated. The possibility of asexually-maintained permanent chimerism in phylactolacmates involving karyotypically distinct ectodermal and peritoneal cell lines is discussed. Karyotypically, P. gelatinosa is more similar to Lophopodella carteri than to Pectinatella magnifica.