Marine Fish Parasite Argulus caecus (Crustacea: Branchiura: Argulidae) Accidentally Collected from a Fixed Net Caught Squid in Northern Japan

Abstract

An ovigerous female of a fish ectoparasite Argulus caecus C. B. Wilson, 1922 was collected from a squid, probably Todarodes pacificus (Steenstrup, 1880), from a fixed net installed in Otsuchi Bay, an inlet of the northwestern Pacific Ocean, Iwate Prefecture, northen Japan. Since the original description of A. caecus was insufficient, this paper reports on the morphology of the species based on a detailed examination of the female. In particular, the first and second antennae, the first and second maxillae, and four pairs of legs, whose features were poorly known, are reported in detail. The specimen of A. caecus is inferred to have detached itself and moved from a fish host, perhaps a coastal puffer, to the squid while these two animals were trapped in the net or when they were removed from the net. Following Argulus scutiformis Thiele, 1900, A. caecus is the second species of Argulus found from northern Japan located in the northern temperate or subarctic region, and its occurrence in this region is likely to be affected by the Tsushima Warm Current and its branch, the Tsugaru Warm Current, both of which flow off the coast of the region.