Leptostracans possess a segmented body divided into three main regions: the head (cephalon), thorax, and abdomen. Unlike many other crustaceans, they lack a carapace, and their exoskeleton is relatively soft and flexible. Their head bears a pair of compound eyes and two pairs of antennae, with the first pair often being longer and more prominent. The thorax typically consists of seven segments, each bearing a pair of appendages, while the abdomen comprises six segments with appendages modified into pleopods, used primarily for swimming. Leptostracans also possess a telson, a tail spine that aids in locomotion and balance.
The order includes around 30 described species, distributed across three families: Nebaliidae, Leptostracidae, and Thysanocarididae. Nebaliidae is the most diverse family, containing species such as *Nebalia bipes*, which is commonly found in temperate coastal regions. These crustaceans are generally small, ranging from a few millimeters to a couple of centimeters in length, and exhibit a transparent or semi-transparent exoskeleton, allowing their internal structures to be visible.
Leptostracans play a role in marine ecosystems as both predators and prey. They primarily feed on detritus, small invertebrates, and organic particles, using their appendages to filter or grasp food. Their life cycle involves several molting stages as they grow, and some species exhibit sexual dimorphism, with males and females differing in size or appendage structure.
Due to their small size and specialized habitats, leptostracans are not well-studied compared to other crustacean groups. However, they provide valuable insights into the evolutionary history of Malacostraca and contribute to the biodiversity of marine environments. Their unique adaptations and ecological roles make them an interesting subject for further research in crustacean biology.