Oregonia gracilis
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| Oregonia gracilis | |
|---|---|
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| 1855 illustration of Oregonia gracilis by James D. Dana | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Decapoda |
| Suborder: | Pleocyemata |
| Infraorder: | Brachyura |
| Family: | Oregoniidae |
| Genus: | Oregonia |
| Species: | O. gracilis |
| Binomial name | |
| Oregonia gracilis Dana, 1851 | |
| Synonyms[1][2] | |
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Oregonia gracilis, commonly known as the graceful decorator crab, is a species of crab belonging to the family Oregoniidae.[3] Like other decorator crabs it habitually attaches other organisms to its back.[4] The sessile organisms are attached to hooked setae that act as a sort of velcro attachment. This decoration provides visual and chemical camouflage thus reducing predation risk.[5] Pacific halibut are a major predator of O. gracilis. Other predators include octopus and sea otters. The main food source of O. gracilis is floating kelp and algae that they capture utilizing a waiting strategy in order to maintain cryptosis.[6]
Oregonia gracilis have three body segments: head, thorax and abdomen. Like many crustaceans, the head and thorax combine into a cephalothorax and are completely covered in a continuous exoskeleton called a carapace.
The carapace is heart shaped, a brown, tan or grey color and 5 cm in length with four pairs of long thin walking legs (pereiopods). A fifth pair of the pereiopods have pincers attached and are called chelipeds.[5] The chelipeds are used for feeding, defense, and to decorate their bodies. The chelipeds are longer than the walking legs in males and shorter than the walking legs in females. The mouth has three pairs of feeding appendages called maxillipeds. Two long stalked compound eyes protrude from the cephalothorax. Behind each eye is a large and curved postorbital spine.
Using fine hooked setae found on the carapace, the crab liberally decorates itself with algae, sponges, bryozoans and hydroids. Its shell covered in sessile organisms makes the crab camouflaged to its environment. Juveniles and adult females decorate heavily whereas adult males are sparse in their decoration.[6]