Porcellanidae

Distinguished from true crabs (Brachyura) by the reduced fifth pair of walking legs, which are folded beneath the carapace and not visible dorsally—giving the appearance of only four pairs of legs rather than five. The flattened body form and delicate, often translucent exoskeleton are characteristic. Large claws are typically asymmetrical. Identification to genus and species requires examination of carapace shape, rostrum morphology, and details of cheliped and ambulatory leg structure.

Marine environments, primarily intertidal and shallow subtidal zones. Many species occupy rocky shores, coral reefs, and rubble habitats where they shelter in crevices, under stones, or within dead coral. Some species are commensal, living in association with sponges, cnidarians (sea anemones, corals, sea whips), bivalve mollusks, or other marine invertebrates. The flattened body form is a specific adaptation for life in narrow, confined spaces.

Worldwide in marine waters, with greatest diversity in the Indo-West Pacific region. Documented from New Caledonia and the Loyalty Islands (31 species), Singapore, India (30 species, including two endemic species in the Gulf of Mannar), Cuba and the Caribbean (23 species), Japan, and southeast Africa. Distribution patterns show strong regional variation with some species having restricted ranges while others are broadly distributed.

• sea whips (Ellisellidae) - commensalLissoporcellana flagellicola specifically associated with unbranched sea whips
• sponges - commensalVarious Porcellanidae species
• cnidarians - commensalIncluding sea anemones and corals
• bivalve mollusks - commensalSome species show specialized morphological adaptations for this lifestyle

Many species form heterosexual pairs, with evidence from Pachycheles rudis suggesting long-term monogamous pairings and size-assortative mating. Both sexes exhibit aggression toward conspecific strangers. Pair formation involves agonistic interactions, with females appearing dominant in established pairs. Autotomy of appendages occurs readily when individuals are disturbed or attacked. Megalopae (post-larval stage) exhibit competency periods, settling behavior, and post-settlement aggregation.

Commensal species may serve as indicators of host organism health and distribution. Their specialized adaptations to narrow habitats contribute to biodiversity in rocky intertidal and coral reef crevice communities.

Occasionally collected for marine aquarium trade due to their attractive appearance and interesting behaviors. Subject of scientific research on crustacean mating systems, commensalism, and biogeography. No significant commercial fishery value.

• Brachyura (true crabs)Porcellanidae superficially resemble true crabs but can be distinguished by the reduced, hidden fifth pair of walking legs; true crabs display all five pairs of walking legs. Porcelain crabs also have a more flattened, delicate body form and are in the infraorder Anomura rather than Brachyura.
• Galatheidae (squat lobsters)Both are in the superfamily Galatheoidea and share the characteristic of having a long abdomen folded beneath the body; Porcellanidae typically have a broader, more crab-like carapace and are generally smaller with more delicate claws.

Despite the common name 'porcelain crabs,' they are not true crabs (Brachyura) but rather members of the infraorder Anomura, making them more closely related to hermit crabs and squat lobsters. The name refers to their smooth, often shiny exoskeleton and delicate nature, not to any taxonomic relationship to true crabs.

• commensal
• flattened body
• autotomy
• pair bonding
• intertidal
• cryptic habitat

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Porcellanidae (Crustacea: Decapoda: Anomura) from New Caledonia and  the Loyalty Islands
• Checklist of the Porcellanidae (Crustacea: Decapoda: Anomura) of India
• On some commensal decapod crustaceans from Singapore (Palaemonidae and Porcellanidae)
• Competency, settling behavior, and postsettlement aggregation by porcelain crab megalopae (Anomura : Porcellanidae)
• Systematics and biogeography of Cuban porcelain crabs (Decapoda: Anomura: Porcellanidae)
• New record of Lissoporcellana demani Dong & Li, 2014 (Decapoda, Anomura, Galatheoidea, Porcellanidae) from southeast Africa
• Size-assortative Pairing and Mate Recognition by the Thickclaw Porcelain Crab Pachycheles Rudis Stimpson, 1858 (Anomura, Porcellanidae)
• A new species of Lissoporcellana (Crustacea: Decapoda: Anomura: Porcellanidae) from Okinawa, southwestern Japan
• Integrative Phylogenetic and Morphological Analyses Reveal Two New Species of Porcellanid Crabs and Resurrect Porcellanella picta Stimpson, 1858 (Decapoda: Porcellanidae).