A new species of holothuroid from the Labrador Sea (eastern Canada): Pseudothyonelabradorensis sp. nov. (Echinodermata, Holothuroidea, Dendrochirotida, Sclerodactylidae).

A new species of holothuroid, Pseudothyonelabradorensis 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 Pseudothyonebelli recovered outside of the clade containing the type species. Pseudothyonelabradorensis sp. nov. is the first species of the genus from the Northwest Atlantic. A key to the North Atlantic Pseudothyone is provided.

Aborjinia corallicola sp. n., a new nematode species (Nematoda: Marimermithidae) associated with the bamboo coral Acanella arbuscula (Johnson).

A new species of Aborjinia Özdikmen, 2010 is described from the tissues of the cold-water bamboo coral Acanella arbuscula (Johnson) from the northwest Atlantic. Aborjinia corallicola sp. n. is characterized by 18.4-33.2 mm long body in adults; outer labial and cephalic sensilla papilliform and located 14-21 µm from anterior end, amphideal aperture located 22-41 µm from anterior end, excretory pore indistinct, rectum and anal opening functional, convex-conoid tail with broadly rounded terminus, spinneret subventral. It is placed in the genus Aborjinia based on the combination of the following characters: outer labial and cephalic sensilla papilliform in shape and located in one circle, contrary to Marimermis Rutsov & Platonova, 1974 (outer labial and cephalic sensilla setiform) and Ananus Rubtsov, 1977 and Thalassonema Ward, 1933 (outer labial and cephalic sensilla in separate circles, if known). From Aborjinia eulagiscae Tchesunov & Spiridonov, 1985 the new species differs in much shorter body, much shorter tail, presence of caudal glands and spinneret in adults, different host species. Our finding represents the first report of a nematode in a parasitic relationship with a cold-water octocoral. Phylogenetic relationships between Aborjinia and other nematodes are analyzed based on 18S rDNA sequences. Summary of all presently known species and genera of the family Marimermithidae is also given.