| Summary: | A new species of holothuroid, Pseudothyone labradorensis sp. nov. (order Dendrochirotida and family Sclerodactylidae), was discovered off the coast of Labrador (eastern Canada) at a depth of 740–969 m. Two specimens were described based on morphological and genetic parameters. Distinctive characters included pinkish body colour, presence of tube feet on a 'tail', supporting rod-shaped ossicles in the tube feet, and rod-shaped ossicles in the tentacles. To investigate its phylogenetic relationships, partial sequences of COI were obtained for the new species as well as for the type species P. raphanus and another North Atlantic species P. serrifera. According to the phylogenetic analysis, P. labradorensis sp. nov. appeared in a well-supported clade with P. raphanus and P. serrifera . Molecular data also suggest polyphyly of the genus, showing the Northeast Pacific species Pseudothyone belli recovered outside of the clade containing the type species. Pseudothyone labradorensis sp. nov. is the first species of the genus from the Northwest Atlantic. A key to the North Atlantic Pseudothyone is provided.
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