A new species of Melinnopsis (Annelida, Melinnidae) from the Porcupine Abyssal Plain, northeast Atlantic

A new species of polychaete worm, Melinnopsis nathanieli sp. nov. (Annelida, Melinnidae), is described from the Porcupine Abyssal Plain in the northeast Atlantic at ~4850 m depth. Forty-two specimens were collected during RRS James Cook cruises JC247 and JC263 in 2023 and 2024 respectively. The new species is morphologically similar to Melinnopsis gardelli and Melinnopsis chadwicki , described from deep Australian waters, but differs from these species in having fewer (~ 16) abdominal uncini in a row compared with 30 in both M. gardelli and M. chadwicki . Phylogenetic relationships among the new species and other species in the family Melinnidae were assessed using the nuclear 18S, and the mitochondrial 16S and cytochrome oxidase subunit I (COI) gene fragments. The new species is genetically distinct from all other species of Melinnopsis , where molecular data is available, and genetically most similar to M. gardelli (pairwise distance 3.5%). Tubes of M. nathanieli sp. nov. were observed to act as a biogenic substrate for Actiniaria and Ascidiacea. Seafloor images of Melinnopsis nathanieli sp. inc. at the Porcupine Abyssal Plain show the worm’s tube positioned perpendicular to the sediment surface, and the long buccal tentacle protruding from the tube. A table containing key characters of all known Melinnopsis species is presented. This is the first species of Melinnopsis to be described from the northeast Atlantic.