Remipedia
Remipedia is a class of blind crustaceans found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Sea, and the Atlantic Ocean. The first described remipede was the fossil "Tesnusocaris goldichi" (Lower Pennsylvanian). Since 1979, at least seventeen living species have been identified in subtropical regions around the world. Description. Remipedes are long and comprise a head and an elongate trunk of up to thirty-two similar body segments. They lack eyes and pigmentation. Biramous swimming appendages are laterally present on each segment, and the  animals swim on their backs. They are generally slow-moving. They are the only known venomous crustaceans, and have fangs connected to secretory glands, which inject a combination of digestive enzymes and venom into their prey. Remipedia have a generally primitive body plan compared to other extant crustaceans, and are the only extant pancrustaceans to lack significant postcephalic tagmosis. Previously regarded as 'primitive', remipedia have since been shown to have enhanced olfactory nerve centers (a common feature for species that live in dark environments). History of classification. The class Remipedia was erected in 1981 by Jill Yager, in describing "Speleonectes  lucayensis" from the Bahamas. The name "Remipedia" is from the Latin "", meaning "oar-footed". Historical phylogeny based on morphology and physiology has placed Remipedia under Mandibulata, in the subphylum Crustacea, and distinct from Hexapoda. New research in evolution and development reveals similarities between larvae and postembryonic development of remipedes and Malacostraca, singling Remipedia as a potential crustacean sister group of Hexapoda. Similarities in brain anatomy further support this affinity, and hexapod-type hemocyanins have been discovered in remipedes. Recent analysis based on nuclear protein-coding genes implies that remipedes (along with Cephalocarida) are the sister group of arthropods most closely  related to insects. Remipedia and Cephalocarida are grouped together form the clade Xenocarida. The extant lineages Xenocarida, Vericrustacia, Oligostraca, and Hexapoda together form the proposed class Pancrustacea. The clade names Anartiopoda or Miracrustacea ('surprising crustaceans') has been proposed for the monophyletic clade containing xenocarids and hexapods. Classification. Thirty extant species are recognized as of early 2022, divided among eight families and twelve genera. All are placed in the order Nectiopoda. The second order, Enantiopoda, comprises the fossil species "Tesnusocaris goldichi" and "Cryptocaris hootchi".