Grimothea planipes, formerly known as Pleuroncodes planipes and commonly called ‘red crab‘, ‘tuna crab‘ or ‘pelagic red crab’, is a species of decapod crustacean belonging to the family Munididae within the order Decapoda. Grimothea planipes is a widely distributed species in the eastern Pacific, from California, USA, to Peru, with special abundance along the coast of Baja California and the Gulf of California in Mexico. It is found in both shallow and deep waters, from the surface to depths of 300 meters, inhabiting pelagic and benthic zones, often near continental shelves and submarine canyons.
In morphological terms, Grimothea planipes measures about 8 to 13 centimeters in total length. Its body resembles that of a characteristic lobster, being elongated and dorsoventrally flattened, with a robust bright red or orange carapace, which gives it its common name of ‘red crab‘. Its eyes are large and dark, giving it a good view of its surroundings. The abdomen is well developed, although it is somewhat shorter than what we are used to seeing in lobsters, ending in a fan-shaped tail, which it uses to swim quickly when it feels threatened. It has three pairs of thin and elongated legs (pereiopods), adapted both for swimming and for moving on the seabed. A distinctive feature to differentiate it from similar species, such as Pleuroncodes monodon, is the shape and size of the third pair of pereiopods, which in Grimothea planipes are longer and more robust, with a greater presence of setae (hairs) than in other species of the same genus. In addition, it also has a pair of pincers, with which it captures its prey.
Grimothea planipes is an omnivorous species, with very varied feeding habits. It feeds mainly on plankton, such as copepods and other small crustaceans, as well as organic debris and detritus found in the water column or on the seabed. It also consumes microscopic algae and small benthic invertebrates. This varied diet makes it a key organism in the food chain, serving as prey for numerous species of fish, seabirds and marine mammals. To feed, it uses its mouthparts and chelae (claws) to capture and manipulate its food, which is then crushed and digested in its stomach.
Reproduction of Grimothea planipes is sexual and generally occurs during spring and summer, when temperature and food availability conditions are optimal. This species shows sexual dimorphism, with males larger and more robust than females. Females carry fertilized eggs on their abdomen, attached to their pleopods (swimming legs) until the larvae hatch. The larvae pass through several planktonic stages, where they are part of the marine plankton before settling to the seafloor and metamorphosing into juveniles. This life cycle, with a prolonged planktonic phase, allows for wide geographic dispersal, which contributes to their success in different marine habitats.
A curious fact about Grimothea planipes is its massive migratory behavior. During certain periods of the year, giant swarms of this species can be observed moving in the water column, a phenomenon known as ‘red tide of lobster’. These events can have a significant impact on the ecosystem, as they attract large numbers of predators such as fish, seabirds and cetaceans that feed on these crustaceans. In addition, Grimothea planipes plays an important role in Baja California’s fishing industry, where it is caught commercially for fishmeal production and as bait for sport fishing, underscoring its economic and ecological importance in the region.
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