Cephalocarida

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AbstractThe discovery of Cephalocarida, a marine taxon of blind crustaceans, in the mid twentieth century has contributed considerably to the debate on arthropod phylogeny and evolution. Many features of Cephalocarida, such as their thoracopod-like maxilla, their combined enditic filter feeding and swimming, and their second-order olfactory centre in the brain, have been traced back to the ground pattern of Tetraconata, Mandibulata, or even Arthropoda. The thirteen species described to date are morphologically similar. The cephalocarid body is divided into a cephalon comprising the pre-antennular region and five segments (antennular, antennar, mandibular, maxillular, and maxillar), which are fused and covered by a large horseshoe-shaped cephalic shield; a thorax comprising nine broadly homonomous limb-bearing segments, an abdomen comprising ten limbless segments, and a terminal, non-segmental telson with a furca. Although their habitats are ecologically diverse and distributed worldwide, ranging from the intertidal to the deep sea, all Cephalocarida live in the benthos of sediments with a nutrient-rich flocculent upper layer of sunken detritus.