Boreoclausia, 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 : 32-33

Boreoclausia n. gen.

Diagnosis. Body elongate, dorso-ventrally flattened, with well-defined pedigerous somites but lacking defined prosome-urosome division. Free abdomen 1-segmented. Caudal ramus with 6 setae. Antennule 5- to 7-segmented, with expanded first segment. Antenna 4-segmented, with spinulose spine on each of third and fourth segments. Mandible with 1 distal spiniform blade fused to segment or articulated at base. Maxillule lobate, with few distal setae. Maxilla 2-segmented; distal segment stout, with spinulose pad. Maxilliped 4-segmented, with spinulose pad distally on terminal segment. Legs 1–3 each with 2-segmented exopod, endopod lacking or small and lobate; setation of exopods much reduced. Leg 4 represented by papilla or lobe bearing few setae. Leg 5 absent or represented by setose papilla.

Type species: Boreoclausia recta n. gen. et n. sp., by original designation.

Etymology. The generic name Boreoclausia refers to the “boreal” distribution of the host of the type species. The ending of the genus, -c lausia, is the name of the type genus of the Clausiidae . Gender feminine.

Remarks. In order to confirm the placement of the new genus in a family, we considered the families Nereicolidae , Serpulidicolidae and Clausiidae , all of which contain polychaete-associated copepods having a moderately transformed, or reduced body form and appendages. The genera of the Nereicolidae have in common a body consisting of the cephalosome, an inflated and unsegmented metasome, and 1- or 2-segmented urosome. This body configuration is not shared with the new genus which retains well defined pedigerous somites.

When establishing the Serpulidicolidae, Stock (1979) highlighted that legs 1–4 of the female are positioned lateroventrally rather than mid-ventrally, that leg 5 of the female is enlarged, and that the number of free abdominal somites of the female is reduced to one or two. Although the new genus has only one abdominal somite, it does not share the first two traits. Legs 1–4 of Boreoclausia are located ventrally and thus not visible in a dorsal view of the body and its leg 5 is markedly reduced.

The Clausiidae includes a heterogeneous mix of genera exhibiting a broad range of modifications and appendage reductions, depending on genus. The characteristics of Boreoclausia are the elongate, linear body, with the well-articulated pedigerous somites, the possession of one free spiniform distal element on the mandible, and the rather well-developed, functional antennae, which are shared with genera of the Clausiidae . We tentatively place Boreoclausia in the Clausiidae , although the presence of the greatly reduced leg 5 of the new genus, an unusual feature for the Clausiidae , suggests that this placement should be revisited within the context of a large scale phylogenetic analysis of this cluster of families.

Currently, generic classification in the Clausiidae is mainly based on leg morphology. Within this family, Boreoclausia is similar to four other genera, Clausia , Indoclausia Sebastian and Pillai, 1974 , Pseudoclausia Bocquet and Stock, 1960 , and Spionicola , because they lack leg 4 or have a vestigial leg 4 reduced to a setiferous lobe. However, in all four of these genera both rami of legs 1 and 2 are at least 2-segmented, and none of them exhibits a strongly reduced, lobate endopod, as found in Boreoclausia . Leg 3 of Boreoclausia is similar to legs 1 and 2 in having a 2-segmented exopod and a lobate endopod. In contrast, leg 3 of the other four genera is reduced to a lobe bearing 1 or 2 setae (in Clausia , Indoclausia and Spionicola ) or to a uniramous state consisting of a onesegmented exopod without an endopod (in Pseudoclausia ). In addition, the mandible of Boreoclausia has only 1 distal element, whereas the above four genera have two elements.

Most striking is the reduction of leg 5 in Boreoclausia to a pair of setae, which is extremely unusual for the Clausiidae . Sebastian and Pillai (1974) recorded a similar form of leg 5 in their genus Stockia which was later removed by Boxshall and Halsey (2004) from the Clausiidae due to its lichomolgoid form of maxilla. We propose to establish Boreoclausia as a new genus in order to accommodate two new species.

The reduction of the endopods of the legs and the possession of a 1-segmented abdomen of Boreoclausia is reminiscent of the Serpulidicolidae , and the anterodistal process of the first antennular segment resembles that of the Spiophanicolidae (see below). However, these families differ from Boreoclausia in many other characteristics.