Raninidae Temporal range: | |
---|---|
Lyreidus tridentatus | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Malacostraca |
Order: | Decapoda |
Suborder: | Pleocyemata |
Infraorder: | Brachyura |
Section: | Raninoida |
Superfamily: | Raninoidea |
Family: | Raninidae De Haan, 1839 |
Genera | |
See text |
Raninidae is a family of unusual crabs, sometimes known as "frog crabs", on account of their frog-like appearance. They are taken by most scientists to be quite primitive among the true crabs. They closely resemble the (unrelated) mole crabs, due to parallel evolution or convergent evolution. In both groups, the claws are modified into tools for digging, and the body is a rounded shape that is easy to bury in sand. Unlike most other true crabs, the abdomens of raninids are not curled under the cephalothorax.
They spend most of their time buried in the sand with their eyes popping out so they can grab unaware prey. They also emerge for mating. [1] Raninids are omnivores and some have been found to have consumed Sardinella, crab, shrimp, bivalve, ray, hydroid, copepod, and squid. [2]
The earliest fossil attributable to the family Raninidae dates from the Albian. [3]
Raninids' dorsal surfaces have varying textures: smooth, pitted, granular, inclined or fungiform nodes, eroded, scabrous or terraced. Raninids have a strongly specialized respiratory mechanism. They lack Milne-Edwards openings and have modified antennae which they inhale through. They generally have posterior branchial orifices. They have eight pairs of vertically arranged gills all of which are functional. Their abdomens are short, incompletely folded, and have six freely articulated somites and a small telson. Raninids also lack a sterno-abdominal cavity. [4]
Frog crabs are marine animals. Depending on the species they can be found at varying depths. Members of this family have been found to live at depths ranging anywhere from 1m to over 900m. [5] The 46 species are distributed across pan-tropical regions with certain regions having many species and others only one. Some species are found across various regions while others can only be found in one specific region. [6]
Sexual dimorphism is seen in both extant and extinct members of this family. Sexually dimorphic characteristics of the abdomen are seen throughout the family, though throughout the subfamilies there are varying styles and degrees of development. [7]
Some other sexually dimorphic characteristics include males being larger, having more developed anterolateral carapace teeth, larger chelae, and different setae on the P1 propodus and dactylus as compared to those of the females. [1]
Unlike other Podotremates, Raninids' spermatheca opens anteriorly on sternite 7 rather than at the extremities of sternal suture 7/8. The formation of the spermathecal chamber, which doesn't differ much from the usual podotreme configuration, is done by the separation of the two laminae which compose endosternite 7/8. In all raninoids, spermathecal apertures are close to each other, separated by medial line, recessed in medial depression, and located in proximity to the female gonopore. Female gonopores are found on P3 coxae and male gonopores on P5 coxae. There is a variety in shapes when it comes to the male sexual gonopods showing strong diversity. In reproduction sperm is ejaculated to the base of the G1. It is then picked up by the spoon-like G2 and placed in the distal portion of the G1, before being transferred through the G1 ejaculatory channel into the spermatheca. [1]
The taxonomic status of Raninidae has varied greatly with academics citing various information learned about them to try and discern where they belong. Where these creatures fit evolutionarily has been a topic of debate and study ever since the 18th century. Their status varying so much over the years can in part be attributed to the unusual characteristics of raninids. There are still ongoing debates surrounding the raninoid lineage. [1]
The 46 extant and 183 extinct species in the famila Raninidae are arranged among 34 genera in 7 subfamilies: [8]
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen), usually hidden entirely under the thorax. They live in all the world's oceans, in freshwater, and on land, are generally covered with a thick exoskeleton, and have a single pair of pincers. They first appeared during the Jurassic Period.
Carcinisation is a form of convergent evolution in which non-crab crustaceans evolve a crab-like body plan. The term was introduced into evolutionary biology by L. A. Borradaile, who described it as "the many attempts of Nature to evolve a crab".
The Sesarmidae are a family of crabs, previously included in the Grapsidae by many authors. Several species, namely in Geosesarma, Metopaulias, and Sesarma, are true terrestrial crabs. They do not need to return to the sea even for breeding.
Johngarthia is a genus of crabs in the land crab family Gecarcinidae, formerly included in the genus Gecarcinus, and containing six species. The genus bears the name of John S. Garth, a 20th century naturalist who specialized in crabs and other arthropods.
Sesarma is a genus of terrestrial crabs endemic to the Americas.
Latreilliidae is a small family of crabs. They are relatively small, long-legged crabs found on soft bottoms at depths of up 700 metres (2,300 ft) in mostly tropical and subtemperate waters around the world. Their carapace is very small and doesn’t cover the bases of their legs, which protrude from the cephalothorax in a spider-like manner. The family and its type genus are named after Pierre André Latreille. The oldest known fossils from the Latreillidae have been dated to the middle of the Cretaceous period. It comprises seven extant species.
Ranina is a genus of crabs belonging to the family Raninidae.
Hexapodidae is a family of crabs, the only family in the superfamily Hexapodoidea. It has traditionally been treated as a subfamily of the family Goneplacidae, and was originally described as a subfamily of Pinnotheridae. Its members can be distinguished from all other true crabs by the reduction of the thorax, such that only seven sternites are exposed, and only four pairs of pereiopods are present. Not counting the enlarged pair of claws, this leaves only six walking legs, from which the type genus Hexapus, and therefore the whole family, takes its name. Some anomuran "crabs", such as porcelain crabs and king crabs also have only four visible pairs of legs. With the exception of Stevea williamsi, from Mexico, all the extant members are found either in the Indo-Pacific oceans, or around the coast of Africa.
Vultocinus anfractus is a species of crab, the only species in the family Vultocinidae. It has been found around the Philippines, Vanuatu and New Caledonia, and lives on driftwood. Its discovery forced a reappraisal of the relationships within the superfamily Goneplacoidea, and to the recognition of Mathildellidae, Conleyidae and Progeryonidae as separate families.
Heloecius cordiformis is a species of semiterrestrial crab found in mangrove swamps and mudflats along the east coast of Australia. Adults are around 25 mm (1 in) wide, with males being larger and having larger and more conspicuously coloured claws. The males wave their claws to communicate with other crabs, giving them their common name of semaphore crab. They can breathe both in air and under water, and feed at low tide on detritus in the sediment. H. cordiformis is the only species in the genus Heloecius and the family Heloeciidae.
Gelasimus vocans is a species of fiddler crab. It is found across the Indo-Pacific from the Red Sea, Zanzibar and Madagascar to Indonesia and the central Pacific Ocean. It lives in burrows up to 50 centimetres (20 in) deep. Several forms of G. vocans have been recognised, with their authors often granting them the taxonomic rank of full species or subspecies.
Guinotellus melvillensis is a species of crabs in the family Xanthidae, the only species in the genus Guinotellus. It is a benthic crab with an ovate carapace within the subfamily Euxanthinae.
Polydectus cupulifer is a species of crab in the family Xanthidae, and the only species in the genus Polydectus. Together with the genus Lybia, it forms the subfamily Polydectinae. It is found in the Indo-Pacific, ranging from Madagascar and the Red Sea in the west to Japan, Hawaii and French Polynesia in the east. P. cupulifer is densely covered with setae (bristles), and frequently carries a sea anemone in each chela (claw).
Symethis is a genus of crabs. It differs from other genera in the family Raninidae by the lack of ornamentation of the male first pleopods and by the reduced number of gills, and is therefore placed in a separate subfamily, Symethinae.
Geosesarma dennerle is a species of small land-living crabs found on Java, Indonesia.
Notopus is a genus of frog crabs from the family Raninidae, it consists of a single extant species and two extinct species.
Leptuca thayeri, known generally as the Atlantic mangrove fiddler crab or mangrove fiddler, is a species of true crab in the family Ocypodidae. It is distributed all across the Western Atlantic.
Nanhaipotamon is a genus of freshwater crabs, in the subfamily Potamiscinae, found in southern China and Taiwan. As of 2018, 18 species have been described. The genus is named after the South China Sea, for it occurs mostly in coastal areas. The genus was first described by R. Bott in 1968 as Isolapotamon (Nanhaipotamon), i.e., a subgenus of Isolapotamon.
Leptuca leptodactyla, commonly known as the thin-fingered fiddler crab or the western Atlantic fiddler crab, is a species of fiddler crab native to the western Atlantic coast of the Americas.
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