Two new deep-sea myzostomid species (Annelida: Myzostomida) from the Northwest Pacific off Japan

Abstract

Two new deep-sea myzostomid species, Pulvinomyzostomum unicorne sp. nov. and Eenymeenymyzostoma abyssale sp. nov., are described from the Northwest Pacific off Japan. Pulvinomyzostomum unicorne sp. nov. was collected from the crinoid host Pentametrocrinus varians at a depth of 1506 m near Shima Spur, Japan, NW Pacific Ocean, characterized by its distinctive scalloped body margin with 20 equal-sized conical cirri, lack of dorsal ridges or color patterns, a smooth proboscis, and a single cirrus extending from the base of the parapodia. Eenymeenymyzostoma abyssale sp. nov., the deepest record for the genus, was found at 511 m depth on the black coral Leiopathes cf. annosa at the Nishi-Shichito Ridge, Japan, NW Pacific Ocean. This species exhibits an oval, thick body without marginal cirri, transparent and orange coloration internally when alive, and uniquely lacks parapodial cirri. Molecular phylogenetic analyses based on COI, 16S, and 18S sequences strongly supported the placement of these new species within their respective genera.