Physical characteristics

The cephalocarid head is short and wide, and is covered with a strong dorsal head shield. Ventrally, in front of the mouth, is a large, posteriorly directed labrum, which func tions to keep food particles—moving anteriorly as a result of a feeding current set up by the thoracic appendages—from going past the mouth opening. The mouth appendages posterior to the mouth, maxillules, and maxillae are built much like the following limbs of the thorax. That is, they have a basal protopod with endites on the inner margin and epipods and exopods on the outer margin. The endopod has a more or less ambulatory function and consists of 5-6 segments. Metachronal movements of these limbs cause an anteriorly directed feeding current in the mid-ventral groove between the paired appendages. There are 20 post-cephalic somites of which the first eight are considered to belong to the thorax. The abdominal somites do not bear appendages, except for the last somite (telson or anal somite) that has a pair of posteriorly directed uniramous appendages generally referred to as caudal rami.

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