The Common Spider Crab (Libinia emarginata)
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Infraorder: Brachyura
Superfamily: Majoidea
Family: Majidae
This slow-walking scavenger is found along the entire East Coast. Harmless to humans and not particularly aggressive in general, the spider crab's main defense against predators is camouflage: the hook-like hairs on the crab's shell (carapace) hold algae and other small debris in place.
Any species of sluggish marine crab in the widely distributed family Majidae (or Maiidae). Spider crabs have a beak-shaped head; thick, rounded body; and long, spindly legs. They use a mucuslike mouth secretion to fasten algae, sponges, and other organisms to the hairs, spines, and knobby projections covering the body. Most species are scavengers, especially of carrion. Their size varies greatly. The body of the European long-beaked spider crab (Macropodia rostrata) is less than 0.5 in. (1 cm) in diameter, whereas the Japanese giant crab (Macrocheira kaempferi), whose outstretched claws can measure 13 ft (4 m) from tip to tip, is perhaps the largest known arthropod.
The Japanese spider crab, Macrocheira kaempferi, is the largest living arthropod; fully grown it can reach a leg span of almost 4 m (13 feet), a body size of up to 37 cm (15 inches) and a weight of up to 20 kg