Karyotypic analysis of the hermaphroditic viviparous polychaete, Hediste limnicola (Polychaeta: Nereididae): possibility of sex chromosome degeneration

Karyotypes of the hermaphroditic polychaete Hediste limnicola were examined using an air-drying method and genetic material prepared from regenerating tail and newborn juveniles. Materials were obtained from a lineage of cultured worms originating from Watsonville Slough (California, USA) and maintained for six years in the laboratory. Giemsa-stained preparations were analysed by a computer-assisted image-analysing system for the identification of each chromosome pair. A diploid chromosome number of 26 was obtained from well-spread metaphase chromosomes of mitotic cells, consisting of metacentric (N = 11), submetacentric (N = 1) and telocentric (N= 1) chromosomes. It is possible that hermaphroditism in this species evolved through loss of a pair of sex chromosomes, which are present in closely related congeneric species.