The Thalassinidea are soft-bodied crustaceans, pale in colour and with a soft, flexible abdomen longer than the thorax. All are burrowers with one or a pair of long flattened chelipeds or nippers. The carapace covers the thorax and gills and bases of the diverse legs.

The second leg always has a fringe of long setae or hairs. Ghost shrimps (family Callianassidae) usually have one cheliped much longer than the other and with sharp pincers at the end. Sponge Shrimps (families Axiidae and Upogebiidae) have a pair of chelipeds of the same size. Their rostrum extends over the eyes and is furry or spikey.

Reproduction

Like all decapod crustaceans, female thalassinideans carry the developing eggs attached to hairs on the pleopods under the abdomen. When they hatch, the zoea larvae swim for weeks in the plankton before settling to start their own home.

Burrowing

All ghost shrimps are burrowers, either making complex tubular branching burrows in muddy and sandy sediments or living in crevices under rocks and corals. This burrowing behaviour make them an important part of the marine environment. During feeding and burrow construction, they are continuously processing the sediment causing mixing and transportation of particles and gases. Each species creates a unique burrow plan which in turn has a different effect on the sediment and nutrient dynamics of the system. The presence of burrows ultimately increases the oxygen content of the sediment leading to a healthier system. Sponge shrimps live in short burrows or cavities under rocks or inside sponges.

Fish Bait

Ghost shrimps are used as bait by fisherman. A specially designed hand-held "yabby pump" is placed over the burrows in intertidal sandy mud and the inhabitants sucked out. Fishermen call ghost shrimps Bass yabbies (after Bass Strait) or one-armed bandits (because of their one long cheliped). Recent studies on their behaviour show how useful these burrowing crustaceans are in keeping the sediment healthy and fisherman would be wise to select an alternative bait and allow the ghost shrimps to continue their important work.