Isopod
Guides
Aegidae
aegid isopods
Aegidae is a family of marine and freshwater isopod crustaceans characterized by temporary parasitic relationships with fish hosts. Adults attach to hosts to feed on blood or tissue, then detach to digest meals. The family is distinguished from related Cirolanidae by having only three pairs of hook-like pereiopods rather than seven. Members occur in diverse aquatic habitats from shallow coastal waters to deep ocean environments, with some species documented at depths exceeding 2000 meters.
Armadillidium nasatum
Nosy Pill Woodlouse
Armadillidium nasatum is a large woodlouse species native to Western Europe, particularly Britain, that has been introduced to North America and other regions. It reaches up to 21 mm in length and is distinguished from congeners by a rectangular protrusion ("nose") at the apex of the head and a rounded tail tip with incurved sides. Unlike some relatives, it does not form a complete ball when enrolled. The species exhibits synanthropic tendencies and prefers drier habitats than most woodlice.
Armadilloniscus
Driftclingers
Armadilloniscus is a genus of terrestrial isopods (woodlice) in the family Detonidae, first described by Uljanin in 1875. The genus contains at least 30 described species, commonly referred to as driftclingers. These organisms are part of the diverse crustacean fauna found in various terrestrial and coastal environments.
Aselloidea
Waterslaters and allies
Aselloidea is a superfamily of freshwater and subterranean isopods within the suborder Asellota. Members are primarily aquatic, with many lineages adapted to life in groundwater, caves, and karst systems. The superfamily includes families such as Asellidae (common freshwater isopods), Stenasellidae, and Atlantasellidae. Some representatives exhibit remarkable morphological specializations for subterranean existence, including reduced eyes and elongated appendages.
Asellota
Asellotes
Asellota is a suborder of isopod crustaceans comprising approximately one-quarter of all marine isopods. The group exhibits remarkable ecological diversity, occurring in marine, freshwater, and subterranean habitats from shallow coastal waters to abyssal depths, including hydrothermal vents. Members possess distinctive morphological specializations including a complex copulatory apparatus that distinguishes them from other isopods. The suborder has undergone multiple independent colonizations of deep-sea environments, with some lineages showing extensive radiation in these habitats.
Atlantoscia floridana
Florida Fast Woodlouse
Atlantoscia floridana is a terrestrial isopod (woodlouse) in the family Philosciidae. The species has been documented in North America, South America, and Africa, indicating a broad transatlantic distribution. It is known to be relatively fragile compared to other woodlice but naturally high in calcium content. In captive settings, it shows preferences for specific humidity gradients.
Brackenridgia
woodlice
Brackenridgia is a genus of small terrestrial isopods (woodlice) in the family Trichoniscidae, established by Ulrich in 1902. The genus contains nine described species distributed primarily in North America, with several species exhibiting troglomorphic adaptations for cave-dwelling. Species in this genus are typically found in moist, dark microhabitats including caves, forest litter, and rocky crevices.
Caecidotea racovitzai australis
Caecidotea racovitzai australis is a subspecies of freshwater isopod in the family Asellidae. It was originally described as Asellus racovitzai australis by Williams in 1970. The subspecies belongs to a genus of aquatic isopods commonly found in groundwater and cave habitats.
Carpias
Carpias is a genus of small marine isopods in the family Janiridae, established by Richardson in 1902. Members of this genus belong to the suborder Asellota, a diverse group of mostly benthic crustaceans. The genus contains multiple described species found in marine environments. Records of this genus in biodiversity databases remain limited, with few documented observations.
Carpias minutus
Sargasso Witcher
Carpias minutus is a marine isopod species in the family Janiridae, commonly known as the Sargasso Witcher. The species was described by Richardson in 1902. It is associated with the Sargasso Sea ecosystem, a unique pelagic habitat in the North Atlantic Ocean characterized by floating Sargassum seaweed. The species has been recorded from Bermuda and coastal Brazil (Rio de Janeiro and São Paulo states).
Cassidinidea ovalis
Cassidinidea ovalis is a species of isopod crustacean in the family Sphaeromatidae. Originally described by Thomas Say in 1818 as Naesa ovalis, this species has been reclassified into the genus Cassidinidea. The genus Cassidinidea is part of the sphaeromatid isopods, a group commonly known as pill bugs or sow bugs, though this particular genus tends toward more elongated, less strongly convex body forms than the classic 'pill bug' shape.
Chiridotea coeca
sand isopod, Surf Sandmole
Chiridotea coeca is a marine isopod crustacean commonly known as the sand isopod or Surf Sandmole. It inhabits sandy substrates in the western Atlantic Ocean, where it constructs burrows and exhibits distinctive swimming behavior when displaced. Adults reach approximately 15 mm in length and are specialized for fossorial life in intertidal and shallow subtidal zones.
Cirolana
Cirolana is a genus of marine isopod crustaceans in the family Cirolanidae, established by William Elford Leach in 1818. The genus name derives from an anagram of 'Carolina,' originally the French 'Cirolane' for an unknown woman named Caroline. Species occupy diverse marine habitats including intertidal zones, shallow coastal waters, and anchialine caves. The genus exhibits considerable diversity, with species groups such as the 'parva-group' recognized in Indo-Malayan and Australasian waters.
Cubaris
Reclined Pill Woodlice
Cubaris is a genus of woodlice (terrestrial isopods) in the family Armadillidae, established in 1833 with Cubaris murina as the type species. The genus contains more than 100 described species, though it has become a wastebasket taxon with many species placed in it that do not fit the original description. Species in this genus are capable of conglobation (rolling into a ball) and have been widely used in ecotoxicity testing due to their sensitive behavioral responses to soil contaminants. Several Cubaris species, particularly undescribed forms such as "Rubber Ducky," have become popular in the pet trade.
Cubaris murina
little sea isopod, little sea roly poly, little sea pillbug, little sea pill woodlouse
Cubaris murina is a small terrestrial isopod (woodlouse) in the family Armadillidae, notable for its ability to conglobate—roll into a complete ball when disturbed. The species reaches approximately 11 mm in length and 5 mm in width. It has a remarkably broad geographic distribution spanning tropical and subtropical regions across multiple continents, with populations in the Caribbean, South America, Southeast Asia, and the Pacific. The species has become popular in the exotic pet trade due to its bioactive utility in terrariums and the development of several color morphs through selective breeding.
Cylisticus
Cylisticus is a genus of woodlice (terrestrial isopods) in the family Cylisticidae, containing at least 70 described species. These soil-dwelling crustaceans are found in tropical and temperate regions, where they inhabit the upper soil layers. At least one species, C. convexus, has been studied as a tropical soil decomposer with limited vertical dispersal ability. The genus is part of the diverse oniscidean fauna contributing to litter breakdown and nutrient cycling.
Cymothoida
Predaceous and Parasitic Isopods
Cymothoida is a suborder of isopod crustaceans comprising more than 2,700 described species across four superfamilies. Members are predominantly carnivorous or parasitic, distinguished by specialized mouthparts including a mandible with a tooth-like process adapted for cutting or slicing. The group includes diverse lifestyles ranging from free-living scavengers to obligate parasites of fish and crustaceans.
Diplocheta
Rock Slaters
Diplocheta is an infraorder of terrestrial isopods commonly known as rock slaters. Members of this group are adapted to coastal and intertidal environments, showing morphological specializations for life in these habitats. The group was established by Vandel in 1957 and includes the family Ligiidae. These isopods represent an evolutionary transition between fully marine and fully terrestrial lifestyles.
Elthusa
Elthusa is a genus of cymothoid isopods comprising approximately 40 described species of obligate fish parasites. Species in this genus are characterized by branchial parasitism, attaching to the gill filaments of marine fish hosts where they feed on blood and tissue fluids. The genus has a worldwide distribution with records from the Atlantic, Indian, and Pacific Oceans. Several species have been described from South Africa, New Caledonia, Taiwan, and Japan, with some exhibiting host specificity while others parasitize multiple fish species.
Elthusa californica
Elthusa californica is a marine parasitic isopod in the family Cymothoidae. It attaches to the gill chambers of fish hosts and feeds on blood and tissue. The species occurs along the Pacific coast from California to Peru. Originally described as Lironeca californica, it was later transferred to Elthusa following taxonomic revision.
Excirolana
Excirolana is a genus of marine isopod crustaceans in the family Cirolanidae, comprising approximately 15 described species. Members are specialized inhabitants of exposed sandy beaches in tropical and warm temperate regions worldwide. The genus is characterized by ovoviviparous reproduction, in which embryos develop internally within paired uteri rather than in an external brood pouch. This reproductive mode is considered an adaptation to the harsh environmental conditions of intertidal sandy habitats.
Excirolana chiltoni
sand piranha
Excirolana chiltoni is a small intertidal isopod, commonly called 'sand piranha,' inhabiting sandy beaches of the Pacific Rim from Japan and Korea to Colombia. Adults reach approximately 8 mm in length and form dense aggregations exceeding 1,000 individuals. The species exhibits ovoviviparous reproduction with direct development, a 2-year lifespan, and pronounced spatial segregation during breeding.
Exosphaeroma diminutum
Exosphaeroma diminutum is a small marine isopod in the family Sphaeromatidae, described by Menzies and Frankenberg in 1966. The species epithet 'diminutum' reflects its notably small body size relative to congeners. Like other Exosphaeroma species, it belongs to a group of crustaceans commonly known as marine pillbugs or rolly pollies, which are relatives of terrestrial isopods. The species has been recorded from Saint Thomas in the Caribbean region.
Exosphaeroma inornata
Exosphaeroma inornata is a sphaeromatid isopod originally described by Dow in 1958 from California. The species was later synonymized with E. media George and Stromberg 1968 from San Juan Island, Puget Sound, with differences between original descriptions attributed to author errors or phenotypic variations. It is a wide-ranging intertidal species with documented occurrence from San Diego, California north to San Juan Island, Washington, though a significant distribution gap exists between Humboldt Bay and Puget Sound.
Floridoscia
Floridoscia is a genus of terrestrial isopods (woodlice) in the family Philosciidae, described in 1984 by Schultz and Johnson. As members of the suborder Oniscidea, these crustaceans are fully adapted to land. The genus is endemic to Florida and contains species restricted to this region.
Floridoscia fusca
Florida Rufous Woodlouse
Floridoscia fusca is a terrestrial isopod species in the family Philosciidae, commonly known as the Florida Rufous Woodlouse. It is native to North America and belongs to the suborder Oniscidea, which encompasses the majority of terrestrial isopods. The species was described by Schultz and Johnson in 1984.
Gnathostenetroidoidea
Gnathostenetroidoidea is a superfamily of asellotan isopods established by Kussakin in 1967. Members are predominantly small crustaceans adapted to cryptic habitats, including both freshwater groundwater systems and marine interstitial environments. The superfamily includes families such as Protojaniridae and Caecostenetroididae. Documented species exhibit reduced or absent eyes and morphological specializations for subterranean or interstitial life.
Gnorimosphaeroma
Gnorimosphaeroma is a genus of marine and estuarine isopod crustaceans in the family Sphaeromatidae. Species in this genus inhabit intertidal and shallow subtidal environments, with documented occurrences in algal beds, sedge marshes, and wood debris habitats. The genus shows behavioral adaptations for humidity detection and orientation, and includes species with annual semelparous life histories.
Gnorimosphaeroma noblei
Gnorimosphaeroma noblei is a marine isopod in the family Sphaeromatidae, described by Menzies in 1954. It is a small crustacean capable of conglobation (rolling into a ball), a defensive behavior common in pill isopods. The species occurs in the temperate North Pacific region. Like other sphaeromatids, it inhabits marine intertidal and shallow subtidal zones.
Gnorimosphaeroma oregonense
Oregon pill bug, Oregon pillbug
Gnorimosphaeroma oregonense is a small intertidal isopod crustacean commonly known as the Oregon pill bug. It inhabits tidal pools and intertidal zones along the Pacific coast from California to Alaska. The species has been documented at depths up to 24 meters.
Idotea
Idotea is a genus of marine isopod crustaceans inhabiting cold temperate waters. The taxonomy remains unresolved, with many currently recognized species potentially representing synonyms or candidates for reassignment to other genera. Members are associated with seaweed habitats and exhibit flexible habitat selection behaviors. The genus includes species with distinct physiological adaptations to different oxygen regimes.
Idotea metallica
metallic isopod
Idotea metallica is a neustonic marine isopod in the family Idoteidae, commonly known as the metallic isopod. It is recognized by its metallic blue coloration and blunt, squared-off telson. The species inhabits drifting objects at the sea surface, forming persistent local populations on floating patches of debris. It has a worldwide distribution in open ocean waters but is competitively inferior to coastal congeners such as Idotea baltica, limiting its persistence in nearshore environments.
Idoteidae
Common Valvetails
Idoteidae is a family of aquatic isopod crustaceans in the suborder Valvifera, distributed globally in marine and freshwater habitats. The family includes approximately 20 genera and numerous species, with highest diversity in temperate coastal waters. Members range from free-living forms in macroalgae and seagrass beds to commensal species associated with other marine organisms. The family has been extensively studied in Australia, New Zealand, the northeastern Pacific, and the North Atlantic.
Jaera
Jaera is a genus of small marine isopods in the family Janiridae, comprising more than 20 described species. The genus is notable for the Jaera albifrons species complex, a group of closely related, sympatric species that exhibit fine-scale habitat partitioning along intertidal shores. These isopods are euryhaline, capable of osmoregulation across wide salinity ranges from freshwater-influenced areas to fully marine conditions. The group has been extensively studied for its ecological differentiation, reproductive isolation, and as a model for understanding speciation processes in marine environments.
Janiroidea
Witchers
Janiroidea is a superfamily of marine isopods in the suborder Asellota, established by G. O. Sars in 1897. It comprises 25 families, with Paramunnidae and Munnidae as the two largest and most diverse. Members occupy a remarkable depth range from shallow littoral zones to hadal trenches exceeding 8,000 meters. The superfamily exhibits substantial morphological diversity, including adaptations for interstitial, benthic, and deep-sea habitats.
Ligia
rock lice, sea slaters, wharf roach
Ligia is a genus of large isopods in the family Ligiidae, commonly known as rock lice or sea slaters. These crustaceans inhabit intertidal and supralittoral zones on rocky coastlines worldwide, with most species showing limited dispersal capacity and allopatric distribution patterns. Some species have become fully terrestrial in high-humidity environments. The genus exhibits complex phylogeographic patterns in East Asia, with cryptic species and overlapping lineages documented through molecular studies.
Ligia baudiniana
Central American Seaslater
A large intertidal isopod (sea slater) native to the Greater Caribbean region, reaching 25–30 mm in body length. Distinguished from congeners by long uropods exceeding two-thirds body length and brush-like structures on the first pair of legs in males. Exhibits strong habitat fidelity to natural mangrove forests and rocky intertidal zones, with documented sensitivity to coastal development. Serves as intermediate host for digenean trematodes.
Ligia occidentalis
Western Sea Slater
Ligia occidentalis is a supralittoral isopod inhabiting rocky shorelines along the eastern Pacific coast. The species occupies the high intertidal zone, hiding in crevices above the high tide line during daytime to avoid desiccation and emerging nocturnally to feed. It is distinguished from the sympatric Ligia pallasii by longer uropods, larger eyes set closer together, and a sleeker body form. The species harbors mycoplasma-like bacteria as hepatopancreas symbionts and shows remarkable morphological stasis across highly genetically divergent allopatric lineages.
Ligia oceanica
sea slater, common sea slater, sea roach
Ligia oceanica is a large intertidal isopod reaching up to 35 mm in length, making it the largest species in the suborder Oniscidea. Native to rocky Atlantic coasts of Europe, it has been introduced to eastern North America and Atlantic islands. This semelparous species inhabits the supralittoral zone, hiding in rock crevices by day and emerging nocturnally to feed. Molecular phylogenetics suggests closer affinity to marine isopod suborders Valvifera and Sphaeromatidea than to terrestrial woodlice, challenging traditional classification.
Ligia pallasii
Sleepy Seaslater, Rock Louse, Sleepy Sea Slater
Ligia pallasii is a large, semiterrestrial isopod in the family Ligiidae, commonly known as the sleepy seaslater or rock louse. It is among the largest sea slaters, reaching 25–30 mm in body length. This species inhabits the high intertidal zone along the Pacific coast of North America, from the Aleutian Islands to northern California. It exhibits nocturnal scavenging behavior, feeding primarily on algae and organic matter, and seeks shelter in moist microhabitats during daylight hours to avoid desiccation.
Ligidium gracile
Western Rockslater
Ligidium gracile is a species of terrestrial isopod commonly known as the Western Rockslater. It belongs to the family Ligiidae, a group of semi-terrestrial crustaceans often found in moist coastal or riparian habitats. The species is native to western North America and is distinguished from other rock slaters by its relatively slender body form. Like other ligiids, it occupies an ecological niche between fully aquatic and fully terrestrial isopods.
Ligidium kofoidi
Kofoid's Rockslater
Ligidium kofoidi is a species of woodlouse in the family Ligiidae, described by Maloney in 1930. It is a small to medium-sized terrestrial isopod found in North America. The species is rarely documented, with only a handful of observations recorded. As a member of the genus Ligidium, it inhabits moist terrestrial environments and belongs to a group commonly known as rockslaters.
Ligiidae
Rock Lice, Sea Slaters
Ligiidae is a family of large, dorsoventrally flattened terrestrial isopods commonly known as rock lice or sea slaters. These crustaceans inhabit rocky intertidal zones and adjacent coastal habitats, where they hide during daylight hours and emerge at night to scavenge. They represent the sole family within the infraorder Diplocheta and are distinguished from other woodlice by their elongated body form, large size (up to 30 mm), long antennae, and preference for marine-influenced environments. The family exhibits poor desiccation resistance and limited dispersal ability, leading to pronounced population isolation and cryptic genetic diversity across their range.
Littorophiloscia vittata
Eastern Saltmarsh Woodlouse
Littorophiloscia vittata is a woodlouse species in the family Halophilosciidae, native to the east coast of North America. It inhabits saltmarsh environments, typically found under boards and debris. The species was first described by Thomas Say in 1818. As a member of the suborder Oniscidea, it belongs to the diverse group of terrestrial isopods commonly known as woodlice or pill bugs.
Microcerberidea
Cerberuses and Pillslaters
Microcerberidea is a suborder of minute isopod crustaceans established by Lang in 1961. Members are among the smallest isopods, measuring less than 2 mm in length. They inhabit interstitial spaces in marine sediments across tropical and subtropical coastal regions.
Miktoniscus spinosus
Eastern Mikto
Miktoniscus spinosus is a small terrestrial isopod in the family Trichoniscidae, commonly known as the Eastern Mikto. It belongs to the suborder Oniscidea, which encompasses the familiar woodlice and pill bugs. The species is native to the eastern United States, with documented presence in New England. As a member of the Synocheta, it represents one of the more derived lineages of terrestrial isopods.
Nagurus
Nagurus is a genus of terrestrial isopods in the family Trachelipodidae, established by Holthuis in 1949. These woodlice are found in tropical and subtropical regions, with records from northern Europe and Southeast Asia suggesting either introduced populations or broader native distribution than currently documented. The genus comprises small to medium-sized isopods adapted to life on land.
Paracerceis
Paracerceis is a genus of marine isopod crustaceans in the family Sphaeromatidae, established by Hansen in 1905. The genus comprises at least 13 described species distributed across tropical and temperate coastal regions. The best-studied species, Paracerceis sculpta, has become a model organism for research on alternative reproductive tactics and sexual selection due to its unusual system of three discrete male morphs. Several species have been introduced outside their native ranges, including P. sculpta in Australia and Türkiye.
Pentidotea
Pentidotea is a genus of marine isopods in the family Idoteidae, established by Richardson in 1905. The genus comprises approximately 13 described species of flattened, oval-shaped crustaceans found in coastal marine environments. These isopods are members of the suborder Valvifera, characterized by their ability to roll into a ball. Species in this genus are primarily associated with algae and seagrass habitats in temperate to cold waters.
Pentidotea aculeata
Pencil Isopod
Pentidotea aculeata is a marine isopod in the family Idoteidae, commonly known as the Pencil Isopod. It inhabits the intertidal zone along the coast of California. The species was described by Stafford in 1913. Like other idoteid isopods, it is adapted to life in shallow coastal waters where it likely feeds on algae and detritus.