Ovicides paralithodis (Nemertea, Carcinonemertidae), a new species of symbiotic egg predator of the red king crab Paralithodes camtschaticus (Tilesius, 1815) (Decapoda, Anomura)

Abstract

Ovicides paralithodis sp. n. is described from the egg mass of the red king crab Paralithodes camtschaticus (Tilesius, 1815) from the Sea of Okhotsk, off Hokkaido, Japan, and Alaska, USA. Among four congeners, O. paralithodis can be distinguished from O. julieae Shields, 2001 and O. davidi Shields and Segonzac, 2007 byno eyes; from O. jonesi Shields and Segonzac, 2007 by the presence of basophilic, vacuolated glandular lobes in the precerebral region; and from O. jasoni Shields and Segonzac, 2007 by the arrangement of the acidophilic submuscular glands, which are not arranged in a row. Ovicides paralithodis represents the third described species of egg-predatory nemertean from P. camtschaticus, the second described carcinonemertid species from Japan, and the 21st described species in the family. The intensity of infestations may exceed 24,000 worms per a single egg-bearing pleopod of P. camtschaticus. A preliminary molecular phylogenetic analysis based on sequences of 28S rRNA and cytochrome c oxidase subunit I genes among selected monostiliferous hoplonemertean species supported the monophyly of Carcinonemertidae, suggesting that within the lineage of the family, evolution of the unique vas deferens, Takakura’s duct, preceded loss of accessory stylets and accessory-stylet pouches.