Raninidae is a family of unusual crab

Crab

True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...

s named for their frog

Frog

Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...

-like appearance, taken by most scientists to be quite primitive. These animals closely resemble the (unrelated) mole crabs, due to parallel evolution

Parallel evolution

Parallel evolution is the development of a similar trait in related, but distinct, species descending from the same ancestor, but from different clades.-Parallel vs...

 or convergent evolution

Convergent evolution

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

. 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 abdomen

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

s of raninids are not curled under the cephalothorax

Cephalothorax

The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...

.

The earliest fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 attributable to the family Raninidae dates from the Albian

Albian

The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...

.

Taxonomy

The 46 extant and 183 extinct species in the famila Raninidae are arranged among 34 genera in 7 subfamilies:

• Subfamily Cyrthorhininae
  • Cyrtorhina
• Subfamily Lyreidinae
  • †Hemioon
  • †Lyreidina
  • Lyreidus
  • Lysirude
  • †Rogueus
  • †Macroacaena
  • †Tribolocephalus
• Subfamily Notopodinae
  • Cosmonotus
  • †Eumorphocorystes
    Eumorphocorystes
    Eumorphocorystes is a genus of crab belonging to the Raninidae subfamily Notopodinae. The genus lived in the late Cretaceous of Belgium. Rathbun referred specimens from the Pacific Northwest Oligocene to this genus....
    
    
  • †Lianira
  • †Lovarina
  • Notopus
  • †Ranidina
  • †Raniliformis
  • Ranilia
  • Umalia
• Subfamily Ranininae
  • †Lophoranina
  • Ranina
  • †Raninella

• Subfamily Raninoidinae
  • †Bicornisranina
  • †Cenocorystes
  • †Cristafrons
  • Notopoides
  • Notosceles
  • †Quaslaeviranina
  • Raninoides
• Subfamily Palaeocorystinae
  • †Cretacoranina
  • †Eucorystes
  • †Heus
  • †Notopocorystes
• Subfamily Symethinae
  • Symethis
• incertae sedis
  Incertae sedis
  , is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
  
  
  • †Araripecarcinus
  • †Sabahranina