Leptostraca (from the
Greek words for thin and shell)[3] is an
order of small, marine
crustaceans. Its members, including the well-studied Nebalia, occur throughout the world's oceans and are usually considered to be
filter-feeders.[4] It is the only extant order in the
subclassPhyllocarida. They are believed to represent the most primitive members of their class, the
Malacostraca, and first appear in the
fossil record during the
Cambrian period.[5]
Description
Leptostracans are usually small, typically 5 to 15 millimetres (0.2 to 0.6 in) long,[7] but the largest species (
Nebaliopsis typica) can reach 4 cm, and the
SilurianCeratiocaris could grow to 75 cm.[8] They are distinguished from all other members of their class in having seven
abdominal segments, instead of six. Their head has stalked
compound eyes, two pairs of
antennae (one
biramous, one
uniramous), and a pair of
mandibles but no
maxillipeds.[4] They are the only
malacostracans with a
carapace that comprises two valves. It covers the head and the thorax, including most of the thoracic appendages, and serves as a brood pouch for the developing
embryos. Its anterior tip bears a movable
rostrum. Also unique among malacostracans is their eight pairs of thoracic appendages which have been specialized into leaf-like filter feeding organs, and are not used for locomotion. The first six abdominal segments bear
pleopods, while the seventh bears a pair of caudal furcae, which may be homologous to
uropods of other crustaceans.[9][10][11]
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
postlarval, or "manca" stage, which lacks a fully developed carapace, but otherwise resembles the adult.[5]
^
abJ. K. Lowry (October 2, 1999).
"Leptostraca". Crustacea, the Higher Taxa: Description, Identification, and Information Retrieval.
Australian Museum. Archived from
the original on September 23, 2017. Retrieved August 8, 2007.
^V. V. Petryashov (1996). "Pseudonebaliopsis atlantica gen. n., sp. n., is a new genus and a new species of Leptostraca (Crustacea, Malacostraca) from the central part of the North Atlantic". Zoologichesky Zhurnal (in Russian). 75 (12): 1892–1896.
^
abJ. Moreira; L. Gestoso; J. S. Troncoso (2003). "Two new species of Sarsinebalia (Crustacea, Leptostraca) from the Northeast Atlantic, with comments on the genus". Sarsia: North Atlantic Marine Science. 88 (3): 189–209.
doi:
10.1080/00364820310001390.
S2CID84442419.