Marine research on cumaceans from around the world.

Cumacean Morphology

Cumaceans are assigned to the Superorder Peracarida (Martin & Davis 2001), a group characterized by the possession of ventral plates forming a brood chamber, in which the young are brooded until their release as small copies of the adults, lacking only the last pair of pereopods. The cumacean body plan consists of a bulbous cephalothorax, commonly called the carapace, composed of the head and at least the first three thoracic somites fused together, usually five free thoracic segments (pereon), and a slender abdomen of six segments (pleon), terminating in either an articulated telson or a fused pleotelson. Within these constraints, carapace design and overall body form can vary widely. Despite the variation, the basic body plan is strongly conserved and cumaceans are readily recognizable as such. The fossil record for the Cumacea is very weak, with only four species known, the oldest from the Upper Permian (Opthalmadiastylis Malzahn 1972), and fossils from the early Jurassic do not differ from extant forms (Bacescu & Petrescu 1999).

The head is composed of 5 fused segments, and bears 5 pairs of appendages. There are 2 pairs of antennae, commonly called antenna 1 and antenna 2. The antenna 1 is similar in the males and females, having 3 articles and a sensory function. The antenna 2 in the females is tiny and has no obvious function, while in the mature males the antenna 2 is very long, covered in setae, and is clearly associated with finding a mate. The other head appendages are the mandibles, the maxilla 1, and the maxilla 2, used for manipulating and eating food.

The 3 segments of the pereon that are fused to the head, and also found under the carapace, have 3 pairs of legs that are modified to help collect and process food, called maxillipeds. The maxillipeds are numbered 1-3, with 1 being the pair closest to the mandibles. The 5 free segments of the pereon each bear a pair of walking legs. The legs are biramous, meaning they have two branches. The main branch (endopod) is the walking leg. The smaller branch (exopod) may or may not be present, and is used for swimming. The first pair of walking legs is usually the longest, and may be modified with a group of long setae towards the end. Swimming exopods are typically present on the third maxilliped and the first pereopod, and may be present on the 2-4 pereopods. The males typically have more exopods than the females, although this is not always the case.

The abdomen, or pleon, is composed of 6 segments, the first 5 of which may bear paired appendages, also used for swimming (pleopods). Males may or may not have pleopods, females do not. The uropods are a pair of appendages found on the last abdominal segment, and probably are used to clean the body, as grooming behavior for cumaceans includes flexing the body and running the uropods over the carapace. The telson (tail) is found between the uropods, but is not always present.

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