Calappa

Weber, 1795

box crabs, shame-faced crabs

Species Guides

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Calappa is a of marine crabs in the Calappidae, commonly known as box crabs or shame-faced crabs. The "box crab" derives from their characteristically bulky, often rounded , while "shame-faced crab" refers to the posture of their large chelae (claws), which fold up to cover the front of the body as if hiding the . within this genus exhibit highly specialized claw adapted for shell-opening , primarily feeding on gastropod mollusks. The genus has a broad geographic distribution across tropical and subtropical marine waters, with both extant and fossil records documented from the Miocene to present.

Flamed Box Crab by FWC Fish and Wildlife Research Institute. Used under a CC BY 2.0 license.Calappa flammea by FWC Fish and Wildlife Research Institute. Used under a CC BY 2.0 license.<div class="fn"> Calappa marmorata (Florida, June 1860)</div> by Burkhardt, Jacques. Used under a Public domain license.

Pronunciation

How to pronounce Calappa: /kəˈlæpə/

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Identification

Calappa are distinguished from other calappid crabs by their robust, often box-like that is typically broader than long, with a rounded or arched outline. The most distinctive feature is the markedly asymmetrical chelipeds: the right claw is enlarged and modified with a broad, flat tooth on the dactyl and paired on the propodus, specialized for crushing gastropod shells; the left claw has elongated, pointed fingers for extracting prey. The chelae fold tightly over the carapace, concealing the mouthparts. Carapace ornamentation varies by species and may include , , or smooth areas; fresh coloration ranges from pale to reddish-brown.

Images

Habitat

Marine benthic environments, primarily on soft substrates including sand, detritus bottoms, and muddy sediments. Some occur on mixed substrates of sand with rock and boulders. Depth range varies by species: commonly reported from shallow coastal waters to upper continental shelf depths (approximately 50–150 m), with some records from deeper waters.

Distribution

Tropical and subtropical marine waters worldwide. Extant documented from the Indo-Pacific (including Philippines, East China Sea, southern Taiwan Strait), eastern Pacific (southeastern Gulf of California), and Atlantic-Mediterranean regions (central and eastern Mediterranean, Adriatic Sea). Fossil records extend the temporal range to the Middle Miocene, with specimens reported from Italy, Hungary, Poland, Austria, Malta, Spain, and Pliocene-Pleistocene Mediterranean localities.

Diet

Gastropod mollusks (snails) are the primary prey, accessed through specialized shell-opening . Stomach content analysis of C. granulata indicates additional consumption of crustaceans (20.28%), cephalopods (10.58%), fish (3.4%), and shellfish (0.28%). C. ocellata has been observed feeding on the mussel Brachidontes domingensis.

Life Cycle

with separate sexes. Reproductive documented in several : females carry on pleopods (berried condition). C. convexa reproduces year-round with peaks from April to August; mean of 638,885 eggs per female. C. philargius exhibits twin spawning events in January–April and August–October, with peak in February. C. granulata size at 50% female maturity estimated at 66.92 mm length, males at 59.25 mm.

Behavior

Highly specialized shell-opening using asymmetrical claws: the right claw applies crushing force to the gastropod shell aperture, while the left claw extracts the soft body or enclosed hermit crab. This represents a distinct feeding among brachyuran crabs. C. hepatica has been documented as a "nuclear " in a temporary feeding association with the flowery flounder Bothus mancus in the Indo-Pacific, where the crab's foraging activity exposes prey for the fish.

Ecological Role

of shelled mollusks and other benthic . The specialized shell-opening allows exploitation of gastropod resources unavailable to many other predators. As a nuclear , C. hepatica facilitates opportunistic foraging by predatory fishes. Epibiotic associations documented: serpulid polychaetes recorded on C. granulata with 29.3% .

Human Relevance

Subject to commercial and artisanal fisheries in several regions. C. convexa is commonly caught as by-catch in spiny lobster (Panulirus spp.) gillnet fisheries in southern Sinaloa, Mexico. C. philargius supports an increasing claw-only fishery in China, with claws yielding approximately 36.28% of whole body weight; whole-body and claw-only trade documented using trawl and trap gears. C. granulata and other occasionally appear in Mediterranean fisheries.

Sources and further reading