Karyotype of Pareas iwasakii

The standard female karyotype of Pareas iwasakii, a species endemic to the southern Ryukyus, Japan, is described. This is the first report of the chromosomal arrangement for the subfamily Pareatinae. The present material had 2n=36 chromosomes, consisting of eight pairs of biarmed macrochromosomes and ten pairs of apparently uniarmed microchromosomes. Of these, pair 4 was heteromorphic, and thus is supposed to be the ZW-sex chromosome pair. The remaining pairs appeared homologous. The karyotype of this morphologically highly specialized snake largely fits the broadly prevailing henophidian/caenophidian format, which most likely represents a primitive state of the extant colubrid karyotypes.