noun, plural: isopods
Any of the members of the order Isopoda, which is a taxonomic group characterized mainly by having a dorsally flattened, segmented body covered with a rigid exoskeleton, thoracic limbs of identical morphology and orientation, and abdominal limbs involved in gas exchange
Isopods are crustaceans that include woodlice and many other related species. Some of them are parasites of crabs and shrimps. Most are aquatic, found in the sea and in freshwater. There are also terrestrial species, living in moist, cool habitats. They belong to the order Isopoda of the subphylum Crustacea.
The isopods are characterized by having a dorsally flattened body covered with a rigid exoskeleton. They do not have a carapace but only a protective shield on the head. The head (called a cephalon) bears unbranched antennae. Some of the isopods have two pairs of antennae; the first pair is vestigial in terrestrial isopods. The pereon (thorax) has eight pereonites (thoracic segments); the first segment though is fused with the head. The seven segments bear a pair of pereopods (thoracic limbs). As for the pleon (abdomen), there are six pleonites (abdominal segments). The first five of the pleonites bear a pair of pleopods (i.e. abdominal limbs involved in respiration). The pelopods of aquatic isopods serve as gills and are used for propulsion. The last segment of the pleon bears a pair of uropods.
- Kingdom: Animalia
- Phylum: Arthropoda
- Subphylum: Crustacea
- Class: Malacostraca
- Order: Isopoda