Paralomis is a widely distributed, highly speciose, and morphologically diverse genus of king crabs in the subfamily Lithodinae.[2][3]
Description
Like all king crabs, Paralomis has evolved a crab-like appearance through a process called carcinisation.[3]Paralomis has either a pentagonal or pyriform carapace.[3] At the very front, its rostrum consists of one short, conical spine projecting forward in the middle and one or more pairs of spines angled upward around the base.[3][4] Like all king crabs, the gastric region, directly behind the rostrum, is elevated above the others.[3] Like Lithodes and Neolithodes, the cardiac region – directly behind the gastric region, separated by a deep groove – is triangular.[3] 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.[3] In adults, the undersides of the dactyli feature horn-like spines.[3] The abdomen 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.[3]
Distribution
Paralomis is present in four of Earth's five oceans – namely the Atlantic, Pacific, Indian, and Southern – as well as all seven continents.[3] They are found from the very shallow intertidal zone to the deep, perpetually dark abyssal zone.[4] The deepest known species of Paralomis is P. bouvieri, which has been discovered living at 4,152 m (13,622 ft).[3]
Taxonomy
Paralomis was described in 1856 by zoologist Adam White and named for its similarity to the genus Lomis.[1] In 1895, marine biologist James Everard Benedict incorrectly placed Paralomis granulosa, the genus' type species, under the genus Lithodes.[5][3] Benedict therefore dissolved the genus and created two now-defunct ones – Leptolithodes and Pristopus – for other members of Paralomis.[5][3]Paralomis is closely related to Echidnocerus, and the monospecific genus Glyptolithodes – nested cladistically inside Paralomis – may simply be a species of Paralomis.[6][7][8]
Paralomis contains over 70 species – more than any other king crab genus – and is the most morphologically diverse genus in the subfamily Lithodinae.[3][4] It contains one fossil species, Paralomis debodeorum, which lived in New Zealand in the Middle–Late Miocene.[3]Paralomis is distinguished from other king crabs by its abdominal segments: the second is undivided, and the third, fourth, and fifth are entirely calcified.[3] Current scientific consensus is that Paralomis is monophyletic, although within this group, carcinologist Shane T. Ahyong in 2010 identified several informal subgroups of Paralomis.[3]Paralomis' relationship to other king crabs can be seen in the following cladogram:[6]
^ abcPoore, Gary C. B.; Ahyong, Shane T. (2023). "Anomura". Marine Decapod Crustacea: A Guide to Families and Genera of the World. CRC Press. pp. 311–317. ISBN978-1-4863-1178-1.
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