Stylochus marimarensis sp. nov. (MNCN 4.01/2820 to 3058). Histological sections are postero-anteriorly oriented: A. Dorsal view of a living specimen; B. Ventral view; C. Detail of the tentacles and cerebral eyes; D. Histological section of the male copulatory apparatus; E. Histological section of the female copulatory organs; F. Sagittal reconstruction of the reproductive system. Abbreviations: c, cilia; cg, cement glands; eg, extravesicular glands; ev, external vagina; fa, female atrium; fp, female pore; i, intestine; iv, internal vagina; ma, male atrium; mp, male pore; ov, oviduct; pp, penis papilla; pv, prostatic vesicle; sb, spermiducal bulbs; sv, seminal vesicle.