Ancinidae - Marine isopods
Ancinidae is one of the many families of marine isopods. They are somewhat related to terrestrial isopods, the most notable of which is the pill bug or roly-poly. Isopods are not insects. They differ by having 2 pair of antennae instead of 1 as in insects and by having some legs that branch. Like insects, isopods have 3 main body regions: the head, thorax and abdomen. Unlike most insects, the 3 parts are usually fused and may not be easily distinguished, especially when looking from above. Marine isopods breathe through gas exchange from the gills on their abdominal legs. When they reproduce, the female broods the eggs in a pouch, called a marsupium, located under the body. There is no larval stage. The eggs develop directly into miniature adults.
Sizes of marine isopods range from 1 mm (.04 in) to 360 mm (14.2 in) though very few exceed 50 mm (2 in) and most are 3-20 mm (less than 1 in). Their homes range from the intertidal zones on beaches to the greatest depths of the ocean (7280 m or about 24,000 ft). The largest marine isopod is the giant isopod, Bathynomus giganteus, which lives in the cold, deep waters of the sea. The shallow water varieties take refuge in various places like sand, crevices, dead shells, worm tubes, algal mats, dead wood and even in living organisms. Most are benthic (live on the bottom) and are detritus feeders or filter feeders. Some though are carnivores or parasites. The tongue-eating isopod, Cymothoa exigua, feeds on the tongues of fishes and eventually takes the place of the tongue.
In all, there about 6,250 species of marine isopods worldwide.