Original description and subsequent discoveries 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. This name derives from the
Ancient Greek εὖ, (
eu-) meaning "true", and
σάρξ (
sarx), meaning "flesh", meaning "true flesh". The designated type species was
E. scorpionis. Though Grote and Pitt did not provide a generic diagnosis for the genus, the species was well diagnosed with a number of distinctive characters. 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. In 2014, American paleontologist James Lamsdell suggested that
E. obesus may represent a juvenile of the related and contemporary
Carcinosoma scorpioides. Unlike other species of
Eusarcana,
E. obesus does not appear to possess spines on its appendages.
Carcinosoma scorpioides was referred to the new genus
Cruinnopterus by Lamsdell (2025), and
E. obesus was designated as a junior synonym of that species.'''''' Lamsdell (2025) also transferred the species
Carcinosoma spiniferum to
Eusarcana.''''
E. spiniferum
is known from the Silurian of New York, from a single prosomal appendage that preserves some elongated spines. The appendage is much less robust than the appendage of Carcinosoma newlini
, the Carcinosoma
type species, and is more similar to that of E. scorpionis
.''''
Recognition as preoccupied name It was first in 1934, 59 years after its original description, that
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 contemporary researchers critiquing 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. The naming of
Eusarcana was one of many contributions to nomenclature by Strand seen as unhelpful today. His journal
Folia Zoologica et Hydrobiologica would later re-emerge within the field to create all kinds of systematic problems that could have been avoided. Strand was also notorious for applying new species names to incomplete or poorly preserved fossils. In 1964, American paleontologists Kenneth Edward Caster and Erik N. Kjellesvig-Waering 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. With
Eusarcana all but forgotten, all subsequent researchers used
Paracarcinosoma for the genus. In 2012, American paleontologists Jason A. Dunlop and James Lamsdell noted that whilst the name
Eusarcana had been completely unnecessary (and of questionable validity, as Strand did not designate a type species) at the time of its creation, it is the oldest available valid name for the taxon and as such should constitute its name under the rules of priority, despite
Paracarcinosoma being more widely used. As such,
Paracarcinosoma was designated as a junior synonym, with all three species assigned to it being transferred to
Eusarcana. == Classification ==