Sheaderia, Kim & Sikorski & O’Reilly & Boxshall, 2013

Kim, Il-Hoi, Sikorski, Andrey, O’Reilly, Myles & Boxshall, Geoff A., 2013, Copepods associated with polychaete worms in European seas, Zootaxa 3651 (1), pp. 1-62 : 38

Sheaderia n. gen.

Diagnosis. Body elongate, dorso-ventrally flattened, comprising cephalothorax, well-defined pedigerous somites 2 to 5, narrower genital double-somite and 1-segmented free abdomen. Caudal ramus with 4 setae. Antennule 5- segmented. Antenna 4-segmented, with 3 claws on third segment and 4 claws on fourth. Mandible with 1 distal blade articulated at base. Maxillule lobate, with 4 distal setae. Maxilla 2-segmented; distal segment stout, with 2 stout setae and spinulose pad. Maxilliped 3-segmented, second segment with 2 inner setae, terminal segment with 1 seta and spinulose pad distally. Legs 1–2 biramous, each with 2-segmented rami densely ornamented with spinules; setation much reduced. Leg 3 represented by lobe bearing 1 apical seta. Leg 4 absent. Leg 5 2-segmented, proximal segment unarmed, distal segment with 3 setae.

Type species: Sheaderia bifida n. gen. et n. sp. by original designation.

Etymology. The new genus is named in honour of Dr Martin Sheader who first found this parasite in the North Sea and sent it to GAB for study. Gender feminine.

Remarks. On the basis of the absence of leg 4 and the possession of a lobate leg 3, this new copepod appears closely related to the type genus of the family, Clausia . The type species C. lubbockii was recorded as an associate of an ascidian by Bocquet and Stock (1960) but is reported here to be an associate of polychaetes. C. lubbockii exhibits a suite of characters that are relatively plesiomorphic compared to the new genus: it has a 4-segmented abdomen (2-segmented abdomen in the new genus), 6-segmented antennules (5-segmented), 2 spiniform elements on the mandible (1 blade), leg 5 comprising 1 seta-bearing proximal segment (seta absent in the new genus) and 4 setae-bearing distal segment (3 setae), and shorter caudal rami. However the new genus retains a more plesiomorphic condition to the antenna: it has four expressed segments, compared to only three in Clausia . The labrum of the new genus is unique in having dorsal and ventral plates; such a structure has never been reported in the Clausiidae . The combination of plesiomorphic, autapomorphic and apomorphic character states is sufficient to justify the establishment of the new genus, although this family and related families are in need of comprehensive revision.