Two New Species of Zygonemertes (Nemertea : Enopla : Monostilifera) from Hokkaido, Japan

Abstract

Two new species of the marine monostiliferous hoplonemertean genus Zygonemertes (Nemertea: Enopla) are fully described and illustrated from specimens collected in Hokkaido, northern Japan. Zygonemertes shintai sp. nov. is characterised by a posteriorly lobed central stylet basis, ten proboscis nerves, and anterior pouches of the intestinal caecum that do not reach the ganglionic lobes of the brain. Zygonemertes jamsteci sp. nov. is distinguished from the most similar species, Z. virescens (Verrill, 1879), by having a proboscis as long as the body and a mixed type of pre-cerebral septum. All stages of oogenesis are present simultaneously in mature females of Z. jamsteci. Their oocytes seem to originate from the ganglionic cells of the lateral nerves. All six sectioned specimens of Z. jamsteci were infected by large numbers of unidentified acephaline eugregarines.