The longhorn decorator crab is a very common sight on the pacific northwest coast. Their shell or carapace is about 4.5 cm wide at the adult stage. You can find the longhorn decorator crab from Alaska to Mexico with very large populations on the south coast.
You have the best chance of spotting them during extreme low tides, you will see them moving about on the kelp and weeds. They can be seen at depths of 3 meters to 1200 meters.
They are pale orange in color and sometimes they have bands of darker color on their legs. The carapace is horned and slender, sort of pear-shaped. This crab decorates itself quite profusely and they will quite often be confused with the Slender Decorated Crab that is a bit smaller at the adult stage.
The Longhorn Decorator crab is an important food source for some fishes and animals, including cabezon and otters.
These decorator crab shells do not grow, but the crab does. To solve this problem, a crab must molt as it grows, shedding its old exoskeleton and growing a larger one. The old shell loosens as a new one forms beneath it. When the old shell splits, the soft animal crawls out. Before its new shell hardens, the crab absorbs water and expands to a size larger than before the molt. While the new shell is hardening, the crab must hide from its predators.
Longhorn Decorator crabs recycle their living decorations during the molting process, they remove the anemones, sponges and other decorations from their old shell and use them to decorate their new shell.
The population of these decorator crabs is not in danger at the moment, however, oil spills and ocean warming is becoming a problem.