Three new species of Mesacanthion Filipjev, 1927 (Nematoda: Thoracostomopsidae) from Argentine coasts Author Russo, Virginia Lo A67891F9-E1BD-407D-AA67-E2ED5C722A21 Laboratorio de Meiofauna Marina (LAMEIMA) - Instituto de Diversidad y Evolución Austral (IDEAus-CONICET), Blvd. Alte. Brown 2915, U 9120 ACF Puerto Madryn, Chubut, Argentina. lorusso@cenpat-conicet.gob.ar Author Pastor De Ward, Catalina T. 421DA5CB-6FDD-4219-BC2C-79AE72A2E8F1 Laboratorio de Meiofauna Marina (LAMEIMA) - Instituto de Diversidad y Evolución Austral (IDEAus-CONICET), Blvd. Alte. Brown 2915, U 9120 ACF Puerto Madryn, Chubut, Argentina. pastor@cenpat-conicet.gob.ar text European Journal of Taxonomy 2021 2021-12-28 787 17 31 http://dx.doi.org/10.5852/ejt.2021.787.1611 journal article 2666 10.5852/ejt.2021.787.1611 84081e4a-a912-4d46-aa7d-55684073019a 2118-9773 5817931 F386403A-8DDA-4BC3-9197-A57E7AA05732 Key to species of Mesacanthion with simple spicules shorter than 2 abd and subventral precloacal setae present This key can be taken as an addition of the last entrance (22) in the key to species of Mesacanthion in Jeong et al. (2019) to include two new species. 1. Precloacal supplement organ less than 2 spicule lengths distant to cloaca ...... M. pali Wieser, 1959 – Precloacal supplement organ more than 2 spicule lengths distant to cloaca .................................... 2 2. Gubernaculum without dorsal apophysis ........................................ M. longigubernaculum sp.nov. – Gubernaculum with dorsal apophysis ............................................................................................... 3 3. De Man´s b index greater than 5 .............................................. M. longissimesetosum Wieser, 1953 – De Man´s b index smaller than 5 ............................................................. M. sanantoniensis sp. nov.