First study of the Polycladida (Rhabditophora, Platyhelminthes) from the Pacific Coast of Costa Rica Author Soutullo, Patricia 0000-0002-9691-0038 Dept. Biodiversidad y Biología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC). José Gutiérrez Abascal 2, Madrid, Spain. Patricia Soutullo: patriciasoutullo @ gmail. com; https: // orcid. org / 0000 - 0002 - 9691 - 0038 patriciasoutullo@gmail.com Author Cuadrado, Daniel 0000-0002-9691-0038 Dept. Biodiversidad y Biología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC). José Gutiérrez Abascal 2, Madrid, Spain. Patricia Soutullo: patriciasoutullo @ gmail. com; https: // orcid. org / 0000 - 0002 - 9691 - 0038 patriciasoutullo@gmail.com Author Noreña, Carolina 0000-0002-9691-0038 Dept. Biodiversidad y Biología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC). José Gutiérrez Abascal 2, Madrid, Spain. Patricia Soutullo: patriciasoutullo @ gmail. com; https: // orcid. org / 0000 - 0002 - 9691 - 0038 patriciasoutullo@gmail.com text Zootaxa 2021 2021-04-22 4964 2 363 381 journal article 7069 10.11646/zootaxa.4964.2.7 c36b481b-c2c3-4f7c-b5b9-614607673bb8 1175-5326 4709585 7E356498-C414-4B75-A3E5-5E9E85291BBB Paraplanocera angeli n. sp. ( Fig. 3 ) Material examined : A specimen from the type locality and designated as holotype . Sagittal sections stained with AZAN . 62 slides: MNCN 4.01 / 2205 to MNCN 4.01 /2266 Type locality: Playa Langosta beach, in Las Baulas National Marine Park of Guanacaste , Costa Rica , 10 ° 17’32.2 “N 85 ° 51’12.7” W ; 24, May, 2018 ( Fig. 3A ) Habitat: Low intertidal, below stones on sand. Etymology: The name of the species, Paraplanocera angeli n.sp. is dedicated to Ángel Delso, for his help and moral support throughout the project. Description: External characteristics ( Fig. 3B, C ): Body shape oval, very delicate and with waved margins. Length 20 mm . Colouration transparent, yellowish intestinal branches due to the intestinal content and brilliant dots produced due to the refraction of light in the ovaries. Nuchal tentacles plumb and located at the first third of the body. Tentacular eyes at the base of tentacles and two groups of cerebral eyes between the tentacular appendix. Ruffled pharynx in the middle of the body. Male and female gonopore separated. Reproductive system ( Fig 3D ): copulatory organs located in the last body third. The male organ comprises a prostatic vesicle with two accessory vesicles, cirrus with bristles and two adenoids, and a short homogenously ciliated atrium. The entire complex is surrounded by a well-developed muscular layer. The prostatic vesicle is covered with a spongy epithelium that forms inside long finger like prolongations. The vasa deferentia form two spermiducal bulbs that empty separately into the distal region of the prostatic vesicle. The cirrus is sinuous and covered with short but fragile bristles. It empties directly into the ciliated male atrium. In the proximal region of the atrium appear two elongated and glandular formations that resemble the teeth of other Paraplanocera , but are not sclerotized, the so-called adenoids ( Faubel 1983 ) ( Fig. 3D ). The female reproductive system shows a short and ciliated atrium that opens in a well-developed vagina bulbosa covered with long, flexible cilia. Frontally appears a ciliated, conical blind sac, the bursa copulatrix, covered with a ciliated epithelium and surrounded by a well-developed musculature. Caudally emerges the Lang´s vesicle. In this region, the female duct is covered with a cuboidal epithelium and an underdeveloped muscle layer ( Fig. 3D ). Remarks: The species captured in Costa Rica belongs to the genus Paraplanocera Laidlaw, 1903 due to the presence of nuchal tentacles, tentacular and cerebral eyes, adenoids and the presence of the bursa copulatrix and Lang’s vesicle within the female copulatory organ. Currently this genus consists of 10 species ( Faubel 1983 ). Paraplanocera aurora Laidlaw, 1903 ; P. discus ( Willey, 1897 ) ; P. fritillata Hyman, 1959 ; P. langi ( Laidlaw, 1902 ) ; P. marginata Meyer, 1922 ; P. misakiensis Yeri & Kaburaki, 1918 ; P. oceanica (Hyman, 1953) ; P. oligoglena ( Schmarda, 1859 ) ; P. rotumanensis Laidlaw, 1903 and P. rubrifasciata Kato, 1937 . All species show sclerotized adenoids, with the exception of Paraplanocera angeli n.sp and P misakiensis . Both species share naked non-sclerotized adenoids, but can be clearly distinguished by the inner epithelium of the bursa copulatrix; folded and naked in P. misakiensis , smooth and ciliated in P. angeli n.sp. Other differences between the two species are the dorsal colouration, olive green in P. misakiensis and translucent in P. angeli n.sp. ; the arrangement of the cerebral eyes, only at the level of the tentacles in P. angeli n.sp. ( Fig. 3B ) and the shape of the female atrium, widened in P. misakiensis and narrow and elongated in P. angeli n.sp. Therefore, the differences found between the two species establish P. angeli n.sp. as a new species of the genus Paraplanocera .