Accepted by C. Mah: 28 Feb. 2018; published: 12 Apr. 2018 ZOOTAXA ISSN 1175-5326 (print edition) ISSN 1175-5334 (online edition) Copyright © 2018 Magnolia Press Zootaxa 4407 (4): 533–542 http://www.mapress.com/j/zt/ Article 533 https://doi.org/10.11646/zootaxa.4407.4.5 http://zoobank.org/urn:lsid:zoobank.org:pub:AD2F0E64-B560-4B21-89E2-AB3DEE3E443F New species of the genera Havelockia and Thyone (Echinodermata: Holothuroidea) and first record of T. crassidisca from the southwestern Atlantic Ocean LUCIANA MARTINS 1,2 & MARCOS TAVARES 1,3 1 Museu de Zoologia, Universidade de São Paulo, São Paulo-SP, 04263-000, Brazil. 2 ORCID: 0000-0002-8107-3265. E-mail: martinsrluciana@gmail.com. 3 ORCID: 0000-0002-7186-5787. E-mail: mdst@usp.br Abstract Two new species in the genera Thyone and Havelockia are described and illustrated based upon specimens collected from off the southeastern Brazilian coast. Thyone florianoi sp. nov . is characterized by having two pillared body wall tables with four-holed discs and introvert with multilocular tables. Thyone crassidisca is recorded herein for the first time from the South Atlantic Ocean (Brazil). Havelockia mansoae sp. nov . is distinctive in having two pillared body wall tables with four-holed discs and introvert with plates. This is the first record of the genus Havelockia from Brazilian waters. Key words: biodiversity, shallow water, sea cucumber, Dendrochirotida, new species, new species record Introduction With over 8000 km of tropical and warm temperate shorelines and a continental shelf surface area of approximately 820 000 km 2 (Lana et al. 1996), Brazil's complex coastal zones include dozens of estuaries and hundreds of kilometers of tidal flats, sand bars, sand and mud beaches, rocky shores and biogenic, sandy, muddy and patchy rocky sublittoral bottoms. Brazil's shore is home to some of the world's most extensive mangroves forests (Spalding & Collins 2010), and also salt marshes, countless coral reefs and sandstone and coralline algae reefs as well as extensive beds of oysters, mussels, sponges, macroalgae, seagrass, rhodoliths and kelp. Hundreds of coastal islands add to the complexity of the Brazilian coast (Ab'Sáber 2001). Current knowledge of Brazil's benthic marine fauna is inadequate and new taxa and new records are constantly being discovered or first recorded. The holothurian fauna is particularly poorly known, accounting only for about 15% of the Brazilian echinoderm fauna (Tiago & Ditadi 2001), whereas Echinoidea and Asteroidea represents about 30% and 18% respectively (Tommasi, 1999). However, several recent publications have made significant contributions to the knowledge of the Brazilian echinoderm fauna (e.g., Martins et al. 2012 a, b, c; Prata et al. 2014 a, b; Martins & Souto 2015; Moura et al. 2015; Martins et al. 2016; Souto et al. 2017; Martins & Tavares 2017). In the present paper three species are added to the Brazilian holothurian fauna, two of which are herein described as new, namely Thyone florianoi sp. nov . and Havelockia mansoae n. sp. Thyone crassidisca Pawson & Miller, 1981, previously known to range from North Carolina to Florida, is recorded for the first time from the southeastern Brazilian coast. Color and scanning electron microscope images are given to all three species in addition to detailed morphological descriptions. Materials and methods Holothuroid morphological techniques and terminology follow Samyn et al. (2006). Ossicles were extracted from different body regions (i.e., introvert, tentacles, body wall and anal regions) using liquid household bleach, washed in five changes of distilled water, and then in five changes of absolute ethanol. A number of ossicle samples were mounted on slides with Entellan Merck® for permanent storage and then examined and measured under an optical