Leptostraca (from the Greek language words for thin and shell)[
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Description
Leptostracans are usually small, typically long,[ Invertebrate Palaeontology and Evolution] They are distinguished from all other members of their class in having seven abdomen segments, instead of six. Their head has stalked , two pairs of antennae (one biramous, one uniramous), and a pair of mandibles but no .[ A phylogeny of the Leptostraca (Crustacea) with keys to families and genera][ Multicellular Animals: Volume II: The Phylogenetic System of the Metazoa]
Leptostracans have gills on their thoracic limbs, but also breathe through a respiratory membrane on the inside of the carapace. The eggs hatch as a , or "manca" stage, which lacks a fully developed carapace, but otherwise resembles the adult.
Classification
It is now accepted that leptostracans belong to the Malacostraca,
The order Leptostraca is divided into three families, with ten genus containing a total of around 40 validly described extant species:
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