An interim synopsis of the Bradfordian families with a description of Thoxancalanus spinatus (Copepoda: Calanoida), a new diaixid genus and species from the deep Atlantic Ocean

Abstract

Thoxancalanus spinatus gen. nov., sp. nov. is described from female specimens collected at abyssal depths above the sea bed in the Atlantic Ocean. The new genus belongs among the “Bradfordian” families of the superfamily Clausocalanoidea, characterised by the presence of sensory setae on maxilla and maxilliped and is currently placed in the family Diaixidae of the ancestral group of “Bradfordians” based on setal armament of the maxilliped. Among the Diaixidae the new species is characterised by an oblique row of flat spines on the posterior surfaces of exopod segments 2 in P2–P3, the ornamentation of the basis and exopod of leg 5 with scale-like spinules and by the primitive type of setation of oral parts. Many undescribed benthopelagic “Bradfordian” taxa have been obtained at great depths by the German expeditions DIVA I–III and ANDEEP I–III during the recent decade and studies of their morphology have allowed a critical, interim re-assessment of the composition of “Bradfordian” families. A synopsis of the generic composition of the “Bradfordian” families with diagnoses for the Phaennidae, Scolecitrichidae, Tharybidae, Diaixidae, Parkiidae, Rostrocalanidae and Kyphocalanidae is given with a discussion on the placement of genera within these families. A setation matrix for oral limbs of the currently described “Bradfordian” genera is presented to facilitate their identification. Finally, we give an outlook on promising approaches for elucidating relationships among “Bradfordian” families, both at the family and genera level.