The Decapoda or decapods are an order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfish, shrimp, and prawns. Most decapods are scavengers. The order is estimated to contain nearly 15,000 extant species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp and Anomura including hermit crabs, porcelain crabs, squat lobsters making up the bulk of the remainder. The earliest fossils of the group date to the Devonian.
Squat lobsters are dorsoventrally flattened crustaceans with long tails held curled beneath the cephalothorax. They are found in the two superfamilies Galatheoidea and Chirostyloidea, which form part of the decapod infraorder Anomura, alongside groups including the hermit crabs and mole crabs. They are distributed worldwide in the oceans, and occur from near the surface to deep sea hydrothermal vents, with one species occupying caves above sea level. More than 900 species have been described, in around 60 genera. Some species form dense aggregations, either on the sea floor or in the water column, and a small number are commercially fished.
Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans include the word crab, all true crabs are in the sister group to the Anomura, the Brachyura.
Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They have flattened bodies as an adaptation for living in rock crevices. They are delicate, readily losing limbs when attacked, and use their large claws for maintaining territories. They first appeared in the Tithonian age of the Late Jurassic epoch, 145–152 million years ago.
Glypheidea is an infraorder of lobster-like decapod crustaceans, comprising a number of fossil forms and the two extant (living) genera Neoglyphea and Laurentaeglyphea: The infraorder was thought to be extinct until a living species, Neoglyphea inopinata, was discovered in 1975. They are now considered "living fossils", with over 256 fossil species discovered, and just two extant species.
The Diogenidae are a family of hermit crabs, sometimes known as "left-handed hermit crabs" because in contrast to most other hermit crabs, its left chela (claw) is enlarged instead of the right. It comprises 429 extant species, and a further 46 extinct species, making it the second-largest family of marine hermit crabs, after the Paguridae.
Retroplumidae is a family of heterotrematan crabs, placed in their own (monotypic) superfamily, Retroplumoidea.
The Galatheidae are a family of squat lobsters.
Galathea is a genus of squat lobsters in the family Galatheidae. It is one of the largest genera of squat lobsters that in 2008 contained 70 species. Most species of Galathea live in shallow waters.
Munidopsis is a genus of squat lobster. It is the second largest of all the genera of squat lobsters, after Munida, with over 200 species. Its members are mainly found on continental slopes and on abyssal plains. A few fossil species are also known, including specimens from the Campanian (Cretaceous).
Munida is the largest genus of squat lobsters in the family Munididae, with over 240 species.
Agononida is a genus of squat lobsters in the family Munididae. In 2022, recognizing that the genus as then defined was paraphyletic, it was divided into three lineages: Agononidasensu stricto and two new genera, Garymunida and Hexamunida. Agononida is distributed in the Indian and Pacific Oceans.
Babamunida is a genus of squat lobsters in the family Munididae. The genus occurs in the Atlantic, Indian, and Pacific Oceans, with the greatest diversity in the Pacific.
Bathymunida is a genus of squat lobsters in the family Munididae, containing the following species:
Heteronida is a genus of squat lobsters in the family Munididae. They occur in the western Pacific Ocean.
Plesionida is a genus of squat lobsters in the family Munididae. As of 2017, it contains the following species:
Munididae is a family of squat lobsters, taxonomically separated from the family Galatheidae in 2010.
Chirostyloidea is an anomuran superfamily with squat lobster-like representatives. It comprises the three families Chirostylidae, Eumunididae and Kiwaidae. Although representatives of Chirostyloidea are superficially similar to galatheoid squat lobsters, they are more closely related to Lomisoidea and Aegloidea together forming the clade Australopoda. No fossils can be confidently assigned to the Chirostyloidea, although Pristinaspina may belong either in the family Kiwaidae or Chirostylidae.
Hexamunida tenuipes is a species of squat lobster in the family Munididae. It is found off of Japan.
Babamunida hystrix is a species of squat lobster in the family Munididae. It is found off of French Polynesia and the Tuamotu Islands, at depths between about 100 and 290 metres.
