Stylochus neapolitanus

Stylochus neapolitanus (Delle Chiaje, 1841 –1844) Lang, 1884

Figure 5

Material examined. Two specimens from "Puerto Deportivo de Ribeira" (21/12/2012). 42°33.776'N; 008°59.339'W. One specimen from "Couso" (02/05/2014). 42º31.248'N; 09º2.570'W. Both locations in Ría de Arousa, Galicia, Spain.

Description. Fixed worms 10–12 mm long and 3–5 mm wide. Body shape elongated with a slightly pointed anterior end and rounded posterior end, with straight margins sometimes with a few undulated waves. Dorsal surface marbled with whitish and dark reddish brown pigmentation, with an orange (or orange and white) pigmented band along the body margins. (Fig. 5 A, B). Ventral surface smooth and whitish (Fig. 5 C). With welldeveloped conical nuchal tentacles, characterised by an orange medial band. Tentacular eyes at the base and inside the tentacles (Fig. 5 D). Cerebral eyes between both tentacles. Marginal eyes at the anterior end. Frontal eyes absent. Brain just anterior to the tentacles, apparent and positioned slightly ventral. Oral pore ventral, near the first third of the body; pharynx with deep folds. Male and female genital pores separate, but close to each other, opening at the last third of the body. Ovaries ventral and well developed. Testes not observed.

Reproductive system (Fig. 5 D, E). Located at the posterior end (Fig. 5 D). Male copulatory organ consists of a muscular seminal vesicle, a free pear-shaped prostatic vesicle and a small penis papilla. Vasa deferentia open separately in the latero-proximal region of the elongated seminal vesicle. The ejaculatory duct joins the prostatic vesicle drain duct, and they converge together in the short penis papilla. The free prostatic vesicle is lined with tubular septa, arising from its distal inner wall, that lie parallel to each other. Extravesicular prostatic glands with long necks piercing the proximal region of the prostatic vesicle. Short penis papilla housed in a small male atrium.

The female system is simple and composed of an ascending vagina externa, where the shell glands open, and a backwards-directed vagina interna that ends with the opening of the oviducts. Male and female pores are separate from each other, but close together, apparently sometimes be housed in a common cavity. Ovaries ventral.

Biology. Stylochus neapolitanus is typically found on the bottom surface of barges, in crevices of compound ascidians or in empty lamellibranch shells (Laidlaw, 1903). In Galicia, S. neapolitanus was mostly found in shallow water, from 1 to 6 metres deep. Worms, when live, reached 15 mm in length.

Distribution (Fig. 1, blue dots): Cape Verde Archipelago (Laidlaw, 1903); Naples, Italy (Lang, 1884); Rufisque, Senegal (Palombi, 1939); Catalonia, Spain (Novell, 2003); Mar Menor, Murcia, Spain (Marquina et al, 2014b).

This is the first record of Stylochus neapolitanus for the European Atlantic coast, and likely the first accurate record for the Atlantic Ocean, as the species identification by Palombi (1939) was based on damaged material and thus, is doubtful.