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

A new species of polychaete worm, <i>Melinnopsis nathanieli</i> <b>sp. nov.</b> (Annelida, Melinnidae), is described from the Porcupine Abyssal Plain in the northeast Atlantic at ~4850 m depth. Forty-two specimens were collected during RRS <i>James Cook</i> cruises JC247 and JC263 in 2023 and 2024 respectively. The new species is morphologically similar to <i>Melinnopsis gardelli</i> and <i>Melinnopsis chadwicki</i>, described from deep Australian waters, but differs from these species in having fewer (~ 16) abdominal uncini in a row compared with 30 in both <i>M. gardelli</i> and <i>M. chadwicki</i>. 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 <i>Melinnopsis</i>, where molecular data is available, and genetically most similar to <i>M. gardelli</i> (pairwise distance 3.5%). Tubes of <i>M. nathanieli</i> <b>sp. nov.</b> were observed to act as a biogenic substrate for Actiniaria and Ascidiacea. Seafloor images of <i>Melinnopsis nathanieli</i> <b>sp. inc.</b> 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 <i>Melinnopsis</i> species is presented. This is the first species of <i>Melinnopsis</i> to be described from the northeast Atlantic.