Isopods (Isopoda) are one of the biggest orders by species richness in the class of crustaceans (Crustacea). They inhabit very diverse habitats, from deep sea, fresh water till land, including parasitic species. Among 52 000 described species of crustaceans more than 10 000 belong to the order of isopods. That include around 5 000 sea, around 950 freshwater and more than 4 000 terrestrial species, and each year more species are described. They are very old group of animals, the fossil record dates back to the Carboniferous period (Paleozoic), at least 300 million years ago. The name Isopoda derives from the Greek ISO meaning "same" and POD meaning "foot", owing to very similar legs.
Isopods differ from other crustaceans with 7 pairs of thoracic legs (walking legs) and 5 pairs of abdominal legs, used for respiration, but also as additional copulatory organ within males. These are relatively small crustaceans, of 0.5 mm and even up to 50 cm (deep sea species giant isopod; Bathynomus giganteus), but most species are large from 0.5 to 3 cm. Most species are separated sexes, except for some marine parasites that are hermaphrodites, and the first part of the life cycle of males, which later transform into females. In some species parthenogenesis is observed, namely that females reproduce independently, and the young derives from unfertilized eggs. The female carries the eggs in brood pouch, where the young develop. Young emerge from brood pouch as an independent individual, very similar to adult crustaceans. Because the outside of the body consists of solid chitinous cuticle, when growth is several times they moult and so reject the old cuticle (ecdysis). They feed with mostly everything, algae, moss and dead organic matter (detritus) and are an important link in the decomposition of dead matter. They are also an important segment of food to various predators.
Recent studies have identified numerous new species of isopods for Croatia and science. Unfortunately threats endangering the caves and their inhabitants. The Red Book of Croatian Cave Fauna included 12 terrestrial and 15 aquatic isopods.
Jana Bedek -