Classified as part of the family Carcinosomatidae, the genus contains three species, E. acrocephalus, E. obesus and E. scorpionis, from the Silurian-Devonian of Scotland, the Czech Republic and the United States respectively.

[1] Overall, Eusarcana is mostly similar in appearance to other carcinosomatid eurypterids, particularly Carcinosoma which shares its forwardly positioned eyes, and is primarily defined by the small degree of spinosity on its second to fifth pair of appendages and its curved telson.

[3] Eusarcana was first described as "Eusarcus" by the American geologists August R. Grote and William Henry Pitt based on fossils recovered from the Pridoli-age Buffalo Waterlime of New York State.

Furthermore, the genus of Grote and Pitt was seemingly based solely on outlines and shape, which prompted some researchers, such as the prominent English geologist Henry Woodward, to regard the genus as lacking generic characters and as such being invalid, referring E. scorpionis to Eurypterus on the grounds that several British species of Eurypterus, notably E. scorpiodes and E. punctatus (today recognized as species of Carcinosoma), were similar in shape.

[1][6] E. acrocephalus (sometimes referred to erroneously as "E. acrocephala") can be distinguished from the other two species by the strongly recurved lateral sides of its carapace, the oval mesosoma and the first segment of the metasoma being unusually wide and short for the genus.

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.

[6] 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.

With Eusarcana not having large and powerful pincers like the larger pterygotid eurypterids, which not only represented potential competitors but also dangerous predators, the only obvious organ it could use for defense was the pointed and sharp tail spike.

The fact that the tail has been preserved as curved in several fossil specimens proves that it would have been flexible in life, with the apparent curvature of the spike on its end making it a dangerous weapon.

If curved forwards over the rest of the body, the spike would be positioned with its point turned upwards, effectively acting similar to a scimitar.

Though the state in which the specimens have been preserved does not allow determination of either the absence or presence of a poison canal or pores for transferring the venom to potential victims, the shape of Eusarcana suggests that it was a rather slow and inactive animal that was not very agile, possibly adapted for burrowing or ambush predation.

In such a lifestyle, a venomous and agile tail spike would greatly aid in securing prey and defense in absence of other prehensile and powerful organs with long reach.

[14] The Silurian-aged fauna of the same general area, also preserving E. acrocephalus, were home to other eurypterids Erettopterus, Pterygotus and Acutiramus, a less diverse assemblage of trilobites (Otarion, Scharyia and Prionopeltis), crustacean Ceratiocaris, cephalopods (including Cycloceras and Corbuloceras), ostracods, gastropods, crinoids, conodonts and bivalves.

[15] Silurian E. obesus from the United Kingdom lived in a marine environment also home to other eurypterids Nanahughmilleria, Pterygotus, Slimonia, Carcinosoma, Parastylonurus and Erettopterus as well as phyllocarid crustaceans, xiphosurans, gastropods and anaspid fish Birkenia.

[16] In Silurian deposits of New York, E. scorpionis occurs together with a diverse fauna of eurypterids composed of Buffalopterus, Dolichopterus, Erettopterus, Eurypterus, Pterygotus and Acutiramus.