Prosthiostomum parvicelis

Prosthiostomum cf. parvicelis (fide Ramos-Sánchez, Carrasco-Rodríguez, García-Madrigal & Bastida-Zavala 2021) Prosthiostomum cf. parvicelis – Ramos-Sánchez et al. 2021: 309–315, figs 6a–f, 7a–f, 8a–c (locality: La Tijera and San Agustinillo Beaches, Oaxaca, Mexico). Distribution Tropical Eastern Pacific. Central coast of Oaxaca: La Tijera and San Agustinillo Beaches. Habitat Fouling. This species is found inside and around empty shells of the barnacle Megabalanus peninsularis (Pilsbry, 1916) which encrust the surf zone of the rocky coast. Remarks The distinction between Prosthiostomum cf. parvicelis and the nominal species is difficult, mainly due to the limited information provided in the original description and redescription by Hyman (1939b, 1953b). In the original description and redescription of P. parvicelis, Hyman (1939b, 1953b) characterized only the male reproductive system of her specimens focusing on everted structures and the reproductive system in lateral position. Prosthiostomum cf. parvicelis has a light brown color with dark brown to dark green spots distributed around the body, while the dorsal region lacks pigmentation. It has three longitudinal lines, two of which are conglomerate brown to dark green spots distributed from the anterior to posterior region of the body, separated by a thin line without pigmentation. The vagina is oriented towards the anterior region of the body.