Majoidea

Majoidea is a superfamily of crabs within the infraorder Brachyura, commonly known as spider crabs or decorator crabs. These crabs are characterized by their triangular or pear-shaped carapaces and long, spindly legs, often much longer than the carapace width.

Characteristics:

• Carapace: Typically triangular or pear-shaped, sometimes adorned with spines, tubercles, or other projections.
• Legs: Possess elongated legs, which contribute to their spider-like appearance.
• Decorator Behavior: Many species exhibit "decorator crab" behavior, attaching algae, sponges, and other materials to their carapaces and legs for camouflage or defense. This behavior involves specialized hooked setae that hold the decorating materials in place.
• Mouthparts: They possess mouthparts adapted for grasping and shredding food.
• Habitat: Found in a wide range of marine habitats, from shallow intertidal zones to deep sea environments.
• Diet: Their diet varies depending on the species and habitat, but commonly includes algae, small invertebrates, and detritus.

Classification:

Majoidea contains several families, including:

• Epialtidae
• Inachidae
• Inachoididae
• Majidae
• Mithracidae
• Oregoniidae

The classification of Majoidea and its constituent families has been subject to revisions based on molecular and morphological data. Some formerly recognized families have been reclassified or synonymized.

Ecological Role:

Spider crabs play important roles in marine ecosystems as both predators and prey. Their decorator behavior can also contribute to habitat complexity and biodiversity. They are preyed upon by various marine animals, including fish, seabirds, and other crustaceans.