Isopoda
Order of crustaceans including woodlice and gribbles.
Isopoda is an order of crustaceans whose members are collectively called isopods. They include both aquatic species, such as gribbles, and terrestrial species, such as woodlice. Isopods have a rigid, segmented exoskeleton, two pairs of antennae, seven pairs of jointed limbs on the thorax, and five pairs of branching appendages on the abdomen used in respiration. Females brood their young in a pouch under the thorax called the marsupium. The name Isopoda derives from Greek roots meaning 'equal foot,' referring to their seven pairs of similarly shaped legs.
- field
- Crustacean order
- known_for
- Diverse feeding methods, terrestrial and aquatic forms, brood pouch (marsupium), and ability to roll into a ball (volvation)
- marine_species
- Around 4,500
- freshwater_species
- Around 500
- terrestrial_species
- Around 5,000
Lore & Background
Isopods are classified within the arthropods and have a chitinous exoskeleton and jointed limbs. They are typically flattened dorsoventrally, though many species deviate, particularly parasitic forms and those in deep sea or groundwater habitats. Their color varies from gray to white, or in some cases red, green, or brown. Size ranges from Microcerberidae species at 0.3 mm to the deep sea giant isopod Bathynomus spp. at nearly 50 cm. The dorsal surface is covered by overlapping, articulated plates. The body plan consists of a head (cephalon), a thorax (pereon) with seven segments, and an abdomen (pleon) with six segments. The head is fused with the first thoracic segment to form the cephalon. There are two pairs of unbranched antennae, the first pair being vestigial in land-dwelling species. The eyes are compound and unstalked. The seven free thoracic segments each bear a pair of unbranched pereopods used for locomotion, giving the order its name. In mature females, some limbs have oostegites that form a brood chamber. The first five abdominal segments each bear a pair of biramous pleopods used for gas exchange and, in aquatic species, as gills and propulsion. The last segment bears a pair of biramous uropods.
Reader's Guide
Around 4,500 species are marine, mostly on the sea floor; about 500 are freshwater; and 5,000 are terrestrial woodlice (suborder Oniscidea). In the deep sea, members of the suborder Asellota predominate. The largest isopod is in the genus Bathynomus, and some large species are fished commercially for human food in Mexico and Japan. Some isopod groups have evolved a parasitic lifestyle, particularly as external parasites of fish, and can cause significant economic loss to commercial fisheries. In reef aquariums, parasitic isopods can become a pest. The order is divided into eleven suborders, including Asellota, Cymothoida, Oniscidea, and others. Isopods first appeared in the fossil record during the Carboniferous period, represented by primitive, short-tailed members of the suborder Phreatoicidea, which were then marine organisms with a cosmopolitan distribution.
Did You Know?
- The name Isopoda comes from Greek roots meaning 'equal foot,' referring to their seven pairs of similarly shaped legs.
- Females brood their young in a pouch under the thorax called the marsupium.
- Some terrestrial isopods can roll into a ball (volvation) as a defense mechanism or to conserve moisture.
More in Other Invertebrates 1-22
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