<i>Cyrtoctenus wittebergensis</i>sp. nov. (Chelicerata: Eurypterida), a large sweep-feeder from the Carboniferous of South Africa

ABSTRACT Cyrtoctenus wittebergensis sp. nov. is described from a unique holotype from the Witteberg Group of the Cape Supergroup. It is a giant hibbertopteroid eurypterid having combs and specialised movable spines of crytoctenid type (Størmer &amp; Waterston 1968) on the more distal podomeres of the second to fourth prosomal appendages. The function of the combs and their associated movable spines is discussed and it is suggested that together they formed a unique adaptation of eurypterid structures to sweep filter-feeding, the combs forming the filters and the spines the cleaners. The digestive tract is remarkably preserved and shows a spiral valve, posterior to the stomach, which is interpreted as an adaptive feature in this large arthropod to increase the absorptive area of the gut. The new evidence provided by the South African specimen has required the re-interpretation of the disarticulated Cyrtoctenus specimens previously described from Europe. Disjecta membra recently obtained from the Tournaisian of Foulden, Berwickshire, which may belong to Cyrtoctenus , are described and show characters previously unknown in Scottish material but similar to certain features in the South African specimen. The taxonomic relationships within the Hibbertopteroidea are discussed in the light of the new combination of characters found in C. wittebergensis . Two families are recognised in the superfamily, the Hibbertopteridae, including Hibbertopterus and Campylocephalus , and the new family Cyrtoctenidae which is here erected to include Cyrtoctenus, Dunsopterus and possibly also Hastimima .