Simocephalus

Simocephalus sp. are large, 3-4 mm in length, round animals that are covered in a bivalve carapace. The head, which contains a single compound eye, is not covered by this carapace but instead is surrounded by a hood (see figure 3). Attached to the head are a very small rostrum and the first antennules, which contain olfactory setae (Balcer et al. 1984). The mouthparts of Simocephalus sp. are small and they lack maxillipeds. Simocephalus sp. uses its second antennae as swimming appendages while the five thoracic legs are used for filtering food or respiration. The dorsal side of the thorax is called the brood pouch, an extension of the carapace, and is where the eggs are held (see fig. 5). While several of the members of family Daphnidae have a tail spine, Simocephalus lacks this feature. One of the most important features in differentiating between species is the post abdominal claw (see fig. 4). The difference in pectin on these claws is the only thing that separates three Great Lakes species from one another (Balcer et al. 1984, Thorp and Covich 1991).