Evolution and systematics

Only one fossil leptostracan has been recognized in the literature, the Permian Rhabdouraea bentzi. It has a separate family status (Rhabdouraeidae; Schram and Malzahn, 1984). However, the fossil is only that of an abdomen and makes comparison to other leptostracans difficult. The regular segmentation of the body, the trunk musculature, nervous system, circulatory system, presence of a furca, and absence of uropods indicate that the Leptostraca are primitive malacos-tracans. Three extant families are recognized: Nebaliidae (with genera Nebalia, Nebaliella, Dahlella, and Speonebalia); Nebaliopsidae (with only one genus, Nebaliopsis, and only one species, N. typica); and Paranebaliidae, containing genera Paranebalia and Levinebalia. Almost 35 species are described. There is not a common name for the leptostracans, but names such as "leaflike-shrimps," "mud-shrimps," and "sea fleas," are used in the literature.

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