Paralomis

Lore & Background

Paralomis was described in 1856 by zoologist Adam White and named for its similarity to the genus Lomis. In 1895, marine biologist James Everard Benedict incorrectly placed Paralomis granulosa, the genus' type species, under the genus Lithodes, dissolving Paralomis and creating two now-defunct genera—Leptolithodes and Pristopus—for other members. Paralomis is closely related to Echidnocerus, and the monospecific genus Glyptolithodes, nested cladistically inside Paralomis, may simply be a species of Paralomis.

Like all king crabs, Paralomis has evolved a crab-like appearance through carcinisation. Its carapace is either pentagonal or pyriform, with a rostrum consisting of one short, conical spine projecting forward and one or more pairs of spines angled upward around the base. The gastric region is elevated, and the cardiac region is triangular, separated by a deep groove. The three pairs of walking legs are morphologically similar, with the middle pair typically longest, and are not covered at their bases by the carapace. In adults, the undersides of the dactyli feature horn-like spines. The abdomen is more calcified than in other king crab genera: the second segment is undivided, the third segment has fused submedian and marginal plates, and segments three, four, and five are all entirely calcified.

Paralomis is present in four of Earth's five oceans—the Atlantic, Pacific, Indian, and Southern—as well as all seven continents. They are found from the intertidal zone to the abyssal zone, with the deepest known species, P. bouvieri, discovered at 4152 m. Current scientific consensus holds that Paralomis is monophyletic, although carcinologist Shane T. Ahyong in 2010 identified several informal subgroups within the genus.

Reader's Guide

Paralomis holds significant importance as the most speciose and morphologically diverse genus in the subfamily Lithodinae, with over 70 species. Its wide distribution across four oceans and all seven continents, from shallow intertidal zones to abyssal depths of over 4000 meters, underscores its ecological adaptability. The genus is distinguished from other king crabs by its unique abdominal structure: the second segment is undivided, and the third, fourth, and fifth are entirely calcified. Its evolutionary relationships are notable: Paralomis is closely related to Echidnocerus, and the monospecific Glyptolithodes may be nested within it. The genus includes one fossil species, Paralomis debodeorum, from the Middle–Late Miocene of New Zealand. Taxonomic history includes a period of confusion when James Everard Benedict incorrectly placed the type species under Lithodes and created two now-defunct genera. Current consensus supports monophyly, though informal subgroups have been proposed. The genus' morphological diversity and global presence make it a key subject for understanding carcinisation and deep-sea adaptation among king crabs.

Did You Know?

• Paralomis contains over 70 species, more than any other king crab genus.
• The deepest known species, P. bouvieri, lives at 4152 m.
• Its abdomen is more calcified than in other king crab genera, with segments three, four, and five entirely calcified.