(Figs. 10 and 11 S)
Planaria pellucida Mertens, 1833, page 8.
Planaria velellae Lesson, 1830, page 453.
Plananoceros gaimardi (de Blainville) Ehrenberg 1831, page 54. Stylochus pellucidus (Mertens, 1833) Ehrenberg 1836, page 67. Planaria oceanica Darwin, 1844, page 246.
Eurylepta oceanica (Darwin, 1844) Diesing 1850, page 211. Stylochoplana tenera Stimpson, 1857, page 22, 29.
Nautiloplana oceanica (Darwin, 1844) Stimpson 1857, page 20. Carenoceraeus oceanica (Darwin, 1844) Schmarda, 1859, page 14. Stylochus gaimardi (de Blainville) Schmarda, 1859, page 33. Stylochus tener (Stimpson, 1857) Diesing 1862, page 568. Gnesioceros pellucidus (Mertens, 1833) Diesing 1862, page 571. Stylochus pelagicus Moseley, 1877, page 24.
Planocera pelagica (Moseley, 1877) Lang 1884, page 439. Planocera simrothi Graff, 1892, page 190, 200.
Planocera graffi Lang, 1879, page 470.
Stylochus sp. Grube, 1840, page 52.
Material examined. Nine specimens. One exemplar from El Salto, near La Restinga, El Hierro, Canary Archipelago (Fig. 1, H2; Table 1 and 2). 87 slides of sagittal serial sectioned specimen and stained with AZAN; Catalogue number: MNCN 4.01/ 1387-1474.
Type locality. Atlantic Ocean, between Newfoundland and Ireland (Mertens 1832).
Distribution. Pacific Ocean (Graff 1892; Woodworth 1894; Plehn 1896); Cape Verde and Ascension islands (Plehn 1896; Laidlaw 1903); Vietnam (Dawydoff 1952); the North Sea (Prudhoe 1982); Japan (Kato 1938); the Mediterranean Sea (Lang 1879, 1884; Riedl 1959; Marquina et al. 2014); pelagic fauna of the Atlantic Ocean (Graff 1892; Plehn 1896); Canary Archipelago (De Vera et al. 2009).
Occurrence in the Canary Island. Planocera pellucida was observed at depths of up to 10 metres, in spring and summer time.
Description. Body shape oval. Length 1–2.5 cm. Smooth dorsal surface. Pigmentation variable from cream to translucent. Intestinal branches orange or garnet (Fig. 10 A). A pair of small nuchal tentacles (1 mm) with basal eyes (Fig. 10 B). Ruffled pharynx in the anterior third of the body, oriented anteriorly. Oral pore is in the second third of the body and central in the pharynx.
Reproductive organs (Fig. 10 C, D, E and F) male copulatory organ with the characteristic spiny cirrus and female organ with a well-developed bulbous vagina (Bock 1913; Faubel, 1983; Marquina et al. 2014).
Distribution remarks. This is a cosmopolitan species is already known for the Mediterranean Sea (Marquina et al. 2014). Its presence has also been observed in regions with high human activity, such as the natural pools of La Maceta, in El Hierro, or in Punta del Hidalgo, Tenerife; in the latter locality, P. pellucida was the only polyclad recorded. It is evident that P. pellucida has a high adaptive and colonization ability, a high dispersal capacity and therefore a wide distribution (Faubel, 1984).