Prosthiostomum utarum Marcus 1952

Prosthiostomum utarum Marcus, 1952 Fig. 5 A Material examined. Quintana Roo coast, Mexico • 1; Mahahual; 18.6°N, 87.7°W; 13.4 m; 18 Mar. 2018; A. Hernández leg.; CRPPY -0041. Distribution. This species was described from Sao Sebastiao Island, Brazil (type locality; Marcus 1952) and the Praia das Conchas, Cabo Frío, Brazil (Bahia et al. 2014; Bahia and Schrödl 2018), as well as on the Atlantic coast of Florida. It has also been recorded in the Caribbean Sea, Colombia (Quiroga et al. 2004 a, 2004 b). The discovery of Prosthiostomum utarum on the coast of Quintana Roo presents a new record for this species in the Mexican Caribbean Sea. Description. Body shape elongated, 3 cm in length and 0.7 cm in width with a rounded anterior end and a pointed posterior end (Fig. 5 A). Predominantly white tonalities and distinctive brown pigmentation along the midline and the anterior region. Cerebral eyes organised in two elongated clusters. Marginal eyes along the anterior region. Remarks. Prosthiostomum utarum, originally described as Lurymare utarum (Marcus, 1952), was recently reassigned to the genus Prosthiostomum based on the work of Litvaitis et al. (2019) based on the 28 S gene. The morphology of Gulf of Mexico specimens corresponds to the original description by Marcus (1952). A comprehensive investigation, including both morphological and molecular aspects, is necessary for accurate delimitation of the genera Lurymare and Prosthiostomum.