Prostheceraeus moseleyi Lang 1884

Elongated worms 1–1.5 cm long and 0.5–0.7 mm wide (Figure 5A, B, C). Body shape elongated, wider at the posterior end, with light undulating margins and rounded anterior and posterior ends. Marginal tentacles with characteristic purple pigment. Dorsal surface smooth. Dorsal colouration whitish or yellowish, with dark, rounded spots and a yellow band along the body margin; at times background pigmentation faintly orange or pinkish (Figure 5A, B). Ventral side smooth and pale. Sucker approximately in middle of body. Tentacular eyes scarce and scattered over tentacles; cerebral eyes inconspicuous, in two elongated rows. Plicate cylindrical or tubular pharynx near anterior end, oriented frontally; oral pore behind brain. Male and female genital pores clearly separated and behind pharynx (Figure 5H). Male copulatory apparatus perpendicular to male pore (Figure 5D, G, H). Male system consists of a short penis papilla, armed with a small conical stylet, a true prostatic vesicle with a smooth glandular epithelium, and a seminal vesicle with a thick muscle layer. Vasa deferentia, sometimes very dilated, join an expanded vas deferens (possibly an external seminal vesicle; Figure 5F, G) before opening directly into true seminal vesicle. Prostatic vesicle opens at tip of penis papilla and seminal vesicle opens through a duct into distal end of prostatic vesicle. Female system (Figure 5D, E) lies posterior to male pore and is characterized by a short, rounded female atrium, a cement duct or pouch, followed by a second dilatation of atrium and a posteriorly-orientated vagina. Cement and shell glands empty into cement duct.

Specimens of Prostheceraeus moseleyi were collected from the bottom of the pier at the Yacht Club Ribeira (Ria de Arosa, Galicia, Spain) at a depth of 5 to 10 metres (42°33.7410N, 008°59.3380W). This species was recorded from Italy (Gulf of Naples, Lang 1884) and Spain (in several localities of the coast of Catalonia, Novell 2003). Our sample represents the first record for the Atlantic coast and outside from the Mediterranean Sea.