''Paralomis'' is a widely distributed, highly speciose, and morphologically diverse

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of king crabs in the subfamily Lithodinae.

Description

Like all king crabs, ''Paralomis'' has

evolved Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

-like appearance through a process called

carcinisation Carcinisation (American English: carcinization) is a form of convergent evolution in which non-crab crustaceans evolve a crab-like body plan. The term was introduced into evolutionary biology by Lancelot Alexander Borradaile, who described it a ...

. ''Paralomis'' has either a pentagonal or pyriform

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

. At the very front, its

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

consists of one short, conical spine projecting forward in the middle and one or more pairs of spines angled upward around the base. Like all king crabs, the gastric region, directly behind the rostrum, is elevated above the others. Like ''

Lithodes ''Lithodes'' is a genus of king crabs. Today there are about 30 recognized species, but others formerly included in this genus have been moved to ''Neolithodes'' and ''Paralomis''. They are found in oceans around the world, ranging from shallow t ...

'' and ''

Neolithodes ''Neolithodes'' is a genus of king crabs in the subfamily Lithodinae. They are found in all major oceans, both in high and low latitudes. Although there are records from water as shallow as in cold regions, most records are much deeper, typical ...

'', the cardiac region – directly behind the gastric region, separated by a deep groove – is triangular. Its three pairs of walking legs – morphologically similar, with the middle pair typically being the longest – are not covered at their bases by the carapace. In adults, the undersides of the dactyli feature horn-like spines. The

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

is more calcified than in other king crab genera: the second segment is undivided, the third segment has fused submedian and marginal (outer) plates, and segments three, four, and five are all entirely calcified.

Distribution

''Paralomis'' is present in four of Earth's five oceans – namely the

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

Indian Indian or Indians may refer to: Associated with India * of or related to India ** Indian people ** Indian diaspora ** Languages of India ** Indian English, a dialect of the English language ** Indian cuisine Associated with indigenous peoples o ...

, and Southern – as well as all seven continents. They are found from the very shallow

intertidal zone The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

to the deep, perpetually dark

abyssal zone The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. The word ''abyss'' comes from the Greek word (), meaning "bottomless". At depths of , this zone remains in perpetual darkness. It covers 83% of the total area ...

. The deepest known species of ''Paralomis'' is ''Paralomis bouvieri, P. bouvieri'', which has been discovered living at .

Taxonomy

''Paralomis'' was described in 1856 by zoologist Adam White (zoologist), Adam White and named for its similarity to the genus ''Hairy stone crab, Lomis''. In 1895, marine biologist James Everard Benedict incorrectly placed ''Paralomis granulosa'', the genus' type species, under the genus ''

''. Benedict therefore dissolved the genus and created two now-defunct ones – ''Leptolithodes'' and ''Pristopus'' – for other members of ''Paralomis''. ''Paralomis'' is closely related to ''Echidnocerus'', and the monospecific genus ''Glyptolithodes'' – nested Cladistics, cladistically inside ''Paralomis'' – may simply be a species of ''Paralomis''. ''Paralomis'' contains over 70 species – more than any other king crab genus – and is the most Morphology (biology), morphologically diverse genus in the subfamily Lithodinae. It contains one fossil species, ''Paralomis debodeorum'', which lived in New Zealand in the Middle Miocene, Middle–Late Miocene. ''Paralomis'' is distinguished from other king crabs by its Abdomen#Arthropoda, abdominal segments: the second is undivided, and the third, fourth, and fifth are entirely calcified. Current scientific consensus is that ''Paralomis'' is monophyletic, although within this group, carcinologist Shane T. Ahyong in 2010 identified several informal subgroups of ''Paralomis''. ''Paralomis'' relationship to other king crabs can be seen in the following cladogram:

Species

''Paralomis'' contains the following species:

References

External links

* * {{Portal bar, Crustaceans King crabs Decapod genera Taxa named by Adam White (zoologist)