Carcinosomatidae is a family of extinct arthropods in the class Eurypterida. Up to 30 centimetres (11.8 in) long, these eurypterid

Eurypterid

Eurypterids are an extinct group of arthropods related to arachnids which include the largest known arthropods that ever lived. They are members of the extinct order Eurypterida ; which is the most diverse Paleozoic chelicerate order in terms of species...

s are found from the Ordovician

Ordovician

The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...

 to the Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 periods.

Description

Carcinosomatids were characterized by small to large exoskeletons with scattered minute tubercules or raised tongue-shaped scales. The prosoma (head) was subtriangular, with small compound eyes at the front. The chelicerae (claws in front of the mouth) were small. The walking legs were covered with long spines, and the second pair of walking legs was the longest. The preabdomen, the front portion of the body, was broad and ovate, while the postabdomen was cylindrical and narrow. The telson

Telson

The telson is the last division of the body of a crustacean. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked "tail" called the caudal furca is often present. Together with the...

 was a curved spine. The family contains four genera with at most 14 species:

• Carcinosoma
  Carcinosoma
  Carcinosoma is a genus of an extinct arthropod. Up to 30 cm long, these eurypterids were found in New York and in other states of the United States. It is from the Late Silurian.-Description:...
  
  Claypole, 1890
• Eocarcinosoma Caster & Kjellesvig-Waering, 1964
• Paracarcinosoma Caster & Kjellesvig-Waering, 1964
• Rhinocarcinosoma
  Rhinocarcinosoma
  Rhinocarcinosoma is a genus of Silurian eurypterid, with a triangular carapace, laterally positioned eyes, and a curved telson. In 2002, a new species was described from the Dô Son Formation of the Dô Son Peninsula of northern Vietnam.-Species:...
  
  Novojilov, 1962