Arthropods

Arthropoda is the most diverse group of animals on the planet. They are invertebrate animals with an exoskeleton, a segmented body, and jointed legs. To grow, arthropods need to shed their external skeleton and form or find a new one. Their respiratory systems are varied, from cutaneous osmotic transfer of oxygen, gills, or lungs. Arthropods have complex eyes, nervous systems, and behaviours.

Decapods

Decapods are crustacean animals, a group separated from other arthropods by their double set of antennas and by their typical larval forms. Other groups of arthropods, insects and spiders, are also included in the NWT General Status Ranks.

Most crustaceans live in a marine habitat, but some are found in freshwater or even terrestrial habitats. Crustaceans are diverse and include Branciopods (freshwater clam shrimps), Thecostracans (barnacles), the Malacostracans (including the best-known crustaceans such as the lobsters, shrimps, prawns, crabs, and krill), and other groups such as the Copepods. Parasitic crustaceans include woodlice (Class Malacostraca, Order Isopoda), a plant parasite, and fish lice (Class Branchiura) living on fish.

As their name implies, decapods (Class Malacostraca) have ten feet (five pairs of legs). All species of decapods known to be present in the NWT are marine, living in the NWT portion of the western Arctic Ocean. No freshwater decapods, such as the freshwater crayfish, are known to occur in the NWT.

Decapod shrimps have elongated abdomens, two pairs of long antennae, and slender legs. The most numerous family of decapod shrimps in the NWT is the Hippolytidae (broken-back shrimps otherwise known as cleaner shrimp). All freshwater “shrimps” found in lakes and rivers of the NWT are not decapods.

So far, all crabs seen in the NWT are from two families, members of separate infraorders, the true crabs and anomurans. The only true crabs found here are large Oregonids: the snow crab and Arctic lyre crab. Anomurans are called “crabs” but, unlike the true crabs, they seem to have only eight legs, as one pair is very small or sometimes hidden. These specialised legs are used to clean gills. The only anomuran found in the NWT is a member of the hermit crab family. These have a soft abdomen protected by a construction of discarded shells, typically from gastropods (snails). With a curved body and modified hind limbs, hermit crabs are specially adapted to fit and secure themselves to the inner whirls of such shells, until a time when they become too large and must move to a new home.

There are 20 known species of decapods confirmed present in the NWT.