Two species of Nemertopsis (Nemertea: Hoplonemertea: Monostilifera) living in association with Capitulum mitella (Crustacea: Cirripedia: Thoracica: Lepadomorpha)

Two species of the monostiliferous hoplonemerteans, Nemertopsis quadripunctata (Quoy & Gaimard, 1833) and Nemertopsis mitellicola sp. nov., are reported from Shirahama, Wakayama, Japan, based on material obtained among the goose-neck barnacle, Capitulum mitella (Linnaeus, 1767). Redescription of Nemertopsis quadripunctata provides some anatomical features not reported in previous literature; these include: the rhynchodaeum opening to the dorsal portion of the oesophagus in front of the brain, and the oesophagus leading farther anteriorly to open subterminally to the exterior as a mouth; mid-dorsal vessel entering the rhynchocoel to form a single vascular plug; and the epidermis possessing a small pit in cross section, the pit being antero-posteriorly continuous, forming a complete sagittal furrow in the post-cerebral region of the body for at least 1 cm in length. Nemertopsis mitellicola sp. nov differs from all the congeners in having a spirally sculptured central stylet, lateral diverticula on the intestinal caecum, and a cephalic patch, from which two longitudinal dorsal stripes extend backward.