Morgan's hermit crab (Calcinus morgani)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Arthropoda · Class: Malacostraca · Order: Decapoda · Family: Diogenidae · Genus: Calcinus.

Accepted name: Calcinus morgani · Authority: Rahayu & Forest, 1999 · Taxonomic status: accepted · AphiaID: 367449.

Synonyms and superseded combinations recorded for this taxon: Calcinus areolatus Rahayu & Forest, 1999.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=367449 (CC BY 4.0). Accessed 2026-09-25.

Biology and life history (SeaLifeBase)

Measured values published by SeaLifeBase for Calcinus morgani. Only fields the database actually holds for this species are shown; these are database values, not aquarium guidance.

Depth range: 0–80 m · Habitat zone: reef-associated · Aquarium trade: never/rarely.

SeaLifeBase notes: Inhabits coral and rock reefs in shallow subtidal and lower intertidal areas (Ref. 8423).

Source: SeaLifeBase species summary (SpecCode 92402) — https://www.sealifebase.se/summary/Calcinus-morgani.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-25.

Distribution and occurrence records (GBIF)

512 georeferenced occurrence records for Calcinus morgani are published through GBIF from 37 countries or marine areas. The map above plots 132 distinct locations from a sample of 512 records, omitting 11 inland records that carry an institution's coordinates rather than a collection site; it shows where the species has been observed and reported, not a modelled range.

Most records by country or area: Australia (150); Chinese Taipei (74); Japan (36); French Southern Territories (25); French Polynesia (24); Northern Mariana Islands (22); Indonesia (21); South Africa (21); Guam (15); Papua New Guinea (15); New Caledonia (13); Philippines (12); Vanuatu (10); Madagascar (7); Fiji (6).

Marine regions with a valid WoRMS distribution record: Mayotte Disputed area: France / Comoros; Wallis and Futuna Exclusive Economic Zone; French Polynesian Exclusive Economic Zone; Réunion Exclusive Economic Zone; New Caledonian Exclusive Economic Zone; Halmahera.

Source: GBIF Occurrence Search (taxonKey 4311577) — https://www.gbif.org/occurrence/search?taxon_key=4311577&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=367449 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-25.

Description and natural history (Wikipedia)

This hermit crab has a shield 1.15 to 1.4 times as long as it is broad. The rostral lobe is triangular and the lateral projections very small and blunt. The eye-stalks have inflated bases and are nearly as long as the shield. The left cheliped (claw) has four to six robust calcified teeth on its cutting edge and the dactyl has two to four teeth on its cutting edge.

The right cheliped is somewhat smaller with fewer teeth. The surfaces of both are dotted with small tubercles and low protuberances. The third pair of pereopods (walking limbs) have a brush of setae (bristles) near the claw while the other pereopods have scattered setae.

The shield is whitish with dark brown margins, the eye-stalks are bright blue with brown bases, the antennal appendages are dark brown and orange, the chelipeds are dark brown with white tips and white tubercles, and the pereopods are dark brown with white bands near the claws. This hermit crab was at one time thought to be synonymous with Calcinus gaimardii but that species has the front half of the shield dark brown and lacks the bright blue on the eye stalks which are entirely orange, apart from a little blue on the corneas.

Calcinus morgani is found in the tropical and subtropical Indo-Pacific region, its range extending from Madagascar to western, northern and eastern Australia, the Philippines, Indonesia and other western Pacific island groups. It is typically found in the intertidal zone of coral reefs and on rocky shores exposed to strong wave action. This is in contrast to C. gaimardii which prefers sheltered inlets and is found subtidally.

Source: Wikipedia: Calcinus morgani — https://en.wikipedia.org/wiki/Calcinus_morgani (CC BY-SA 4.0). Accessed 2026-09-25.