Classified as part of the family Carcinosomatidae, which the genus lends its name to, Carcinosoma contains seven species from North America and Great Britain.

Carcinosoma was among the largest eurypterids, with isolated fossil remains consisting of a 12.7 centimeters (5.0 in) long metastoma (a plate overlaying the coxae of the first six appendages) of the species C. punctatum indicating a full length of 2.2 meters (7.2 ft).

By surveying the distribution of fossilized pigment cells and comparing them with those of modern scorpions, scientists were able to see the pattern and specific colors C. newlini would have possessed in life.

The gnathobases ("tooth-plates" on the coxae used when feeding) were completely black, as were the telson (the posteriormost division of the body) whose color contrasted with the preceding and adjacent brown segment.

[2] Carcinosoma was first described under the name Eurysoma (meaning "wide body", deriving from Greek εὐρύς, "wide",[5] and Latin soma, "body"[6]) by British American geologist and paleobotanist Edward Waller Claypole in 1890, who named the type species of the new genus E. newlini in honor of a C. E. Newlin who had collected the fossils.

[6] In 1868, English geologist and paleontologist Henry Woodward named a new species of Eurypterus, E. scorpioides, based on fossils from Lanarkshire, Scotland.

[9] Another species of Eurypterus, E. scoticus was named in 1899 by Scottish zoologist and paleontologist Malcolm Laurie based on fragmentary remains recovered in deposits of Llandovery age in Scotland.

[10] In 1912, American paleontologists John Mason Clarke and Rudolf Ruedemann noted that Carcinosoma was sufficiently similar to the related eurypterid Eusarcus to be designated as synonymous with it.

At this time, the combined genus of Eusarcus contained several species that are today seen as Carcinosoma, including C. newlini, C. scoticus and C. scorpioides, which Clarke and Ruedemann had referred to the genus on account of their similarities with C. newlini and species previously referred to Eusarcus.

During the preparation for his paper on the issue, Størmer also discussed the situation with fellow Norwegian researcher Embrik Strand, who helped confirm that Carcinosoma was not preoccupied.

[12] Strand would subsequently propose the replacement name Eusarcana in 1942, despite the problem having been dealt with by Størmer, who he had been in contact with, eight years earlier.

[12] In 1961, American paleontologist Erik N. Kjellesvig-Waering classified Eurypterus punctatus (originally described as Pterygotus punctatus by English paleontologist and prominent eurypterid researcher John William Salter in 1859) as Carcinosoma punctatum and named a new species C. harleyi based on fossils from the Ludlow epoch of the Welsh Borderland.

[3] C. punctatum was diagnosed by Kjellesvig-Waering in 1961 based on the considerably pronounced serrations of the distal parts of its swimming leg, but the diagnosis is only valid for the lectotype specimen of the species, BGS GSM89435 (compromising the distal parts of a swimming leg discovered in deposits of Middle Ludlow age in the Mocktree Shale of Leintwardine in Herefordshire, England), and four other specimens from the same locality (BMNH 39389, BMNH In.

Recognized by Kjellesvig-Waering as distinct, the species is named in honor of John Harley, one of the earliest collectors of eurypterid fossils in the region.

89434 in the collection of the Geological Survey and Museum in London) is a fragment of a swimming leg measuring 5 centimeters (2.0 in) in length.

Caster and Kjellesvig-Waering made no mention of Embrik Strand or Eusarcana, and they were likely not aware of the existence of the previous name.

In 2012, American paleontologists Jason A. Dunlop and James Lamsdell designated Paracarcinosoma as a junior synonym of Eusarcana per the taxonomic laws of priority.

Eusarcana is more likely to have relied on its telson, taking the shape of a sharp and curved stinger similar to that of scorpions and potentially capable of injecting venom.

[3] The flat metasoma of Carcinosoma was probably used as at least partially as aid when swimming, suggested by the pretelson being slightly expanded in comparison to other eurypterids.

In the fossil deposits of the Welsh Borderland, examples of Carcinosoma occur together with representatives of the pterygotid genera Erettopterus and Pterygotus over a period of millions of years (though other eurypterids, such as Salteropterus, Dolichopterus, Hughmilleria, Eurypterus, Marsupipterus, Mixopterus, Parahughmilleria, Slimonia, Tarsopterella and Stylonurus are also present in lesser numbers).

The third and final recognized type of fauna is one dominated by hughmilleriids and stylonurids, generally alongside sandy bottoms and with few other associated fossils.