Four new species of Antarctic sea cucumbers are described, three with author O Loughlin: Crucella susannae, Euthyonidiella huwi, Laevocnus katrinae; and Laevocnus leachmani with authors Davey and O Loughlin. Pseudocnus Panning is reviewed, and Antarctic species separated into new genus Laevocnus O Loughlin. We raise the three subspecies of Pseudocnus dubiosus, viz. dubiosus (Semper), koellikeri (Semper) and leoninus (Semper), to species status. We refer Cucumaria croceoida Vaney to the synonymy of Cladodactyla crocea (Lesson). We synonymize Dendrelasia O Loughlin with Cladodactyla Brandt, and re-describe the reassigned Cladodactyla sicinski (O Loughlin). This species broods in a dorsal marsupium. The diagnoses of genus Parathyonidium Heding and species Parathyonidum incertum Heding are reviewed. The type specimens for Parathyonidium incertum are listed. Parathyonidium incertum Heding is the only known Antarctic holothuroid that is a coelomic brooder. The Paracucumidae Pawson and Fell is reviewed. Phylogenetic trees are given for species in the genera Cladodactyla, Heterocucumis, Staurocucumis, Laevocnus, Crucella and Paracucumis. Tables are provided for the species of Cladodactyla and Pseudocnus. Keys are included for the species of genus Laevocnus and family Paracucumidae.