Abstract
We analyzed chromosomes of four species of East Asian dobsonflies (Megaloptera: Corydalidae): Protohermesgrandis (Thunberg, 1781), P.immaculatus Kuwayama, 1964, P.disjunctus Liu, Hayashi et Yang, 2007 and P.costalis (Walker, 1853). The chromosome number in all species was 2n = 24, consisting of 11 pairs of autosomes plus the XX chromosomes in females and the Xy(p) in males. The karyotype of P.immaculatus which occurs in near the central part of the Ryukyu Islands, and is a vicarious species of P.grandis, was similar to the karyotype of P.grandis. On the other hand, the karyotype of P.disjunctus, which is from the Sakishima Islands, and is a vicarious species of P.costalis, resembled that of P.costalis. The X chromosomes are submetacentric, while the Y is the smallest, dot-like chromosome of the set. The sex chromosomes of the first meiotic metaphase (MI) spermatocytes in all species invariably appear as a bivalent-like structure known as parachut bivalents Xy(p), suggesting that the species in this genus share a common sex-bivalent mechanism.