Oedignathus

Lore & Background

Oedignathus is distinguished from other king crabs in the subfamily Hapalogastrinae by the presence of numerous tubercles on the only slightly flattened chelipeds and legs, and by the paucity of spines and setae. Other genera have flattened chelipeds covered in setae and legs with several large spines. The species Oedignathus inermis lives in pairs under purplish coralline algae that encrust rocks around the low tide mark, and may be found at depths of 0–45 m. In the littoral zone, it is associated with mussel beds, but it spends more time in the sublittoral zone. Larvae are released in January and February, at a similar time to other hermit crabs, perhaps to coincide with seasonal blooms of plankton for the larvae to feed on. O. inermis is preyed upon by birds such as the American black oystercatcher.

Reader's Guide

Oedignathus is notable as the sole genus in the subfamily Hapalogastrinae with a single species, Oedignathus inermis. Its morphological distinction—numerous tubercles on the chelipeds and legs, with few spines and setae—sets it apart from related king crabs. The species' ecological niche under purplish coralline algae and its association with mussel beds in the littoral zone, alongside a deeper sublittoral presence, illustrate its adaptability across tidal zones. The timing of larval release in January and February, synchronized with other hermit crabs and likely with plankton blooms, reflects a reproductive strategy tied to seasonal food availability. Its range spans from California to the Chukchi Sea, the Russian Far East, and disjunctly around Japan, indicating a broad but fragmented distribution. Predation by the American black oystercatcher highlights its role in coastal food webs. The genus name, from Greek roots meaning 'swell' and 'jaw', references a key anatomical feature. As the only member of its genus, Oedignathus represents a distinct evolutionary lineage within the king crabs.

Did You Know?

• Oedignathus is the only species in its genus.
• It is known by the common names granular claw crab, paxillose crab, and tuberculate nestling lithode crab.
• Its larvae are released in January and February, coinciding with other hermit crabs.
• It is preyed upon by the American black oystercatcher.