New Species of Macellicephala McIntosh, 1885 (Annelida, Polynoidae), Associated with the Reef Stage of a Whale Fall

Decomposing whale carcasses on the seabed (whale falls) are known to support distinct communities, with many taxa new to science. This paper describes a new polynoid species, Macellicephala irisae sp. nov., from a natural whale fall at 1240 m depth in Santa Catalina Basin off California, USA. The new species was associated with a cladorhizid sponge growing on a bone, transitioning from the sulphophilic to reef stage. We also highlight the biodiversity of exclusively deep-sea Macellicephalinae subfamily and its most species-rich genus Macellicephala. Morphological and molecular data support the description of the new species, which is also placed within a phylogenetic context using COI, 16S and 18S markers. The new species possesses distinctive filamentous notochaetae not previously reported in Macellicephala, and with the future increase in taxon coverage, an erection of new genus may be warranted.