Metacarcinus

Metacarcinus crabs are distinguished from related genera by an oval carapace approximately two-thirds as long as its maximum width, with poorly defined regions that are smooth or gently colored. The front margin bears five spines including the inner orbits, with the median spine projecting lower than the others; the total length of these front edges equals 26–34% of the maximum carapace width. The anterolateral margins carry 9–10 spines of variable shape, and the lateral margins are edged and may bear one spine. The cheliped propodus has an upper margin meeting the distal margin at approximately 120°, armed with sharp spines, granules, or a smooth keel, with typically four tubercles on the outer surface. The cutting edges of the claw fingers bear sharp teeth, and the fixed finger has two teeth: one median and one on the lower margin.

Extant species occupy marine coastal waters, with estuaries functioning as nursery habitats for juvenile stages. Metacarcinus magister occurs in the Northeast Pacific from Alaska to California, inhabiting sandy or muddy substrates from the intertidal zone to depths exceeding 200 meters. Metacarcinus edwardsii occupies North Patagonian estuaries and adjacent coastal waters.

Northeast Pacific Ocean (M. magister: Alaska to California; M. gracilis: Alaska to Baja California); southeastern Pacific Ocean (M. edwardsii: Chile and Argentina); southwestern Pacific Ocean (M. novaezelandiae: New Zealand); North Atlantic (M. starri: extinct, fossil only). Fossil species documented from Oligocene to Pliocene deposits in Washington, California, Alaska, and Japan.

• Carcinonemertes errans - parasiteEgg predator; larvae settle on crab exoskeleton and migrate under abdominal flap within 24 hours, completing metamorphosis to juvenile worms after 48 hours on host
• Heterosaccus - parasiteRhizocephalan barnacle parasitizing M. novaezelandiae in New Zealand

Development includes zoeae and megalopae larval stages preceding settlement to the benthos. In M. magister, megalopae exposed to environmental stressors exhibit delayed molting to the first juvenile stage. Females possess ventral-type seminal receptacles capable of retaining sperm across molts and even after egg extrusion, with stratification of multiple ejaculates from different males observed.

Megalopae and early juveniles exhibit reversible tetany (partial or full paralysis) when exposed to neonicotinoid pesticides; recovery occurs upon transfer to clean water. Onset of partial tetany precedes full tetany, with degree and reversal dependent on concentration and exposure duration. Juveniles selectively integrate and modify dietary fatty acids, biosynthesizing long-chain polyunsaturated fatty acids (LCPUFA) including DHA when dietary sources are insufficient.

Juvenile stages utilize estuarine nursery habitats, contributing to ecosystem connectivity between estuarine and coastal marine environments. As mid-to-upper level predators, they influence benthic community structure through predation. The genus serves as host to specialized parasites including egg predators and rhizocephalan barnacles.

Metacarcinus magister supports major commercial fisheries along the U.S. West Coast and in Canada, with management complicated by environmental stressors including hypoxia and ocean acidification. Metacarcinus edwardsii is the most heavily harvested crab in Chile. Both species face research interest regarding reproductive biology and resilience to male-biased fishing due to female sperm storage capacity. Contemporary oyster aquaculture provides juvenile habitat comparable to historical native oyster beds.

• CancerFormerly included Metacarcinus species; distinguished by carapace shape, front margin spine configuration, and cheliped propodus angle (~120° in Metacarcinus versus different proportions in Cancer)
• RomaleonAnother genus segregated from Cancer; Metacarcinus differs in carapace proportions and front margin structure

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Functional morphology of the seminal receptacle in the crab Metacarcinus edwardsii
• North Patagonian estuaries appear to function as nursery habitats for marble crab (Metacarcinus edwardsii)
• Population and maternal variation in the sensitivity of Dungeness crab Metacarcinus magister zoeae to elevated CO2
• Larval settlement of the nemertean egg predator Carcinonemertes errans on the Dungeness crab, Metacarcinus magister
• Movement Patterns and Distributional Shifts of Dungeness Crab (Metacarcinus magister) and English Sole (Parophrys vetulus) During Seasonal Hypoxia
• Juvenile Dungeness crabs (Metacarcinus magister) selectively integrate and modify the fatty acids of their experimental diets
• A Comparison of the Juvenile Dungeness Crab Metacarcinus magister Habitat Provided by Contemporary Oyster Aquaculture Versus Historical Native Oysters in a U.S. West Coast Estuary
• Occurrence of Heterosaccus (Cirripedia: Rhizocephala) in the New Zealand Crab Metacarcinus novaezelandiae (Decapoda: Cancridae) and Distribution of Other Rhizocephala in the South Pacific
• Response of megalopae and early stage juveniles of the Dungeness crab, Metacarcinus magister Dana, 1852 (Decapoda: Brachyura: Cancridae), to a neonicotinoid pesticide
• When does hypoxia affect management performance of a fishery? A management strategy evaluation of Dungeness crab (Metacarcinus magister) fisheries in Hood Canal, Washington, USA