parts of the
telson)
Carcinosoma was first described under the name
Eurysoma (meaning "wide body", deriving from
Greek εὐρύς, "wide", and
Latin soma, "body") 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. The
Eurysoma specimens had been discovered in deposits of Early Pridoli age in the Kokomo Formation of Indiana alongside several other eurypterid specimens, all of which at the time were referred to
Eurypterus lacustris (though Claypole noted in the same paper that this may have been done hastily). Later in the same year, Claypole discovered that the name
Eurysoma was
preoccupied and thus not available to be used for his genus of eurypterids. Claypole replaced the name
Eurysoma with the new name
Carcinosoma. and
soma, "body". 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. 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. As
Eusarcus had been named in 1875, fifteen years earlier than
Carcinosoma, its name had priority and replaced
Carcinosoma. 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. In 1934, 59 years after it had been described,
Eusarcus was recognized as a name preoccupied by a
harvestman. The Norwegian geologist
Leif Størmer proposed that the name of the taxon should be next oldest available and valid name for the genus,
Carcinosoma. 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. 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. The reasons for proposing the name during the circumstances of the time remains unknown, but critique from contemporary researchers of Strand for his studies in systematics and an apparent desire to name as many taxa as possible may explain the situation somewhat. As it was seen as completely unnecessary at the time, Strand's
Eusarcana was overlooked and not even mentioned in subsequent eurypterid studies. 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. Kjellesvig-Waering could differentiate
C. harleyi from
C. punctatum based on
C. harleyi lacking serrations on the eighth podomere of the swimming leg and the serrations of the ninth podomere being less developed.
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. 43804, BGS GSM89561 and GSM89568). Due to a close resemblance of the swimming legs,
C. punctatum is assumed to have been similar in appearance to
C. newlini.
C. punctatum can be distinguished from
C. newlini by the serration along the margin of the distal podomeres of
C. punctatum being more pronounced.
C. harleyi, from the Late Ludlow epoch, was described mainly based on specimens previously known (some having been reported by Salter as early as 1859) but previously referred to
Eurypterus punctatus. 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. Noted as moderately large in size by Kjellesvig-Waering, the
holotype specimen of
C. harleyi (No. 89434 in the collection of the
Geological Survey and Museum in London) is a fragment of a swimming leg measuring in length. The nearly complete lack of serrations in the joints of
C. harleyi makes the species very distinct from
C. punctatum and other species of
Carcinosoma. In 1964, both
C. punctatum and
C. harleyi were still recognized as part of
Carcinosoma following an emended diagnosis of the genus by Kjellesvig-Waering and American paleontologist Kenneth Edward Caster, though
C. harleyi was only tentatively recognized. Further species recognized at the time were
C. libertyi and
C. logani (both from Ontario, Canada;
C. logani was later found to be a
crustacean and not a eurypterid at all),
C. spiniferum (from New York, United States),
C. newlini (from Indiana, United States),
C. scorpioides and
C. scoticus (both from Scotland). Out of these species, only
C. newlini and
C. scorpioides preserve the swimming legs, where the diagnostic characters of the genus are, which makes the assignment of the other species to
Carcinosoma less secure. Kjellesvig-Waering and Caster also recognized
Eusarcus and
Carcinosoma to be distinct genera when revising the superfamily Carcinosomatoidea, and coined the replacement name
Paracarcinosoma to designate the species previously assigned to
Eusarcus.
E. scorpionis was designated the
type species. 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. In 2025, Lamsdell reclassified
C. spiniferum as a species of
Eusarcana and reclassified both
C. scorpioides and
C. scoticus as species of the new genus
Cruinnopterus.'''''' In 2025, Belgian paleontologist Peter Van Roy, along with his coauthors Jared C. Richards and Javier Ortega-Hernández described isolated appendages of a carcinosomatid eurypterid from the
Early Ordovician Fezouata biota of
Morocco. They tentatively assigned these specimens to
Carcinosoma due to their robustness and erected the new species ?
Carcinosoma aurorae, diagnosed by the paired articulating spines being of unequal length, the "positions of long and short spines alternating between
podomeres," and the teeth of the gnathobases being "long and slender," to contain them. == Classification ==