Intertidal
Guides
Garypus
Garypus is a genus of pseudoscorpions in the family Garypidae, comprising at least 20 described species. These arachnids are primarily restricted to seashore habitats, occupying supralittoral and littoral zones in tropical and subtropical regions. The genus was established by Ludwig Carl Christian Koch in 1873 and shows highest diversity in the Indo-West Pacific region. Species-level taxonomy remains incompletely resolved, with many species known from single localities.
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.
Grapsidae
shore crabs, marsh crabs, talon crabs
The Grapsidae are a family of crabs commonly known as shore crabs, marsh crabs, or talon crabs. The family's monophyly remains unconfirmed, with some taxa potentially belonging to other families. The family currently comprises ten genera and approximately forty species, including two fossil genera. Members occupy diverse coastal habitats ranging from rocky intertidal zones to pelagic environments.
Grapsus
lightfoot crabs
Grapsus is a genus of lightfoot crabs in the family Grapsidae, comprising eight recognized species distributed across tropical and subtropical rocky shorelines. Members are characterized by their flattened bodies and long, slender legs adapted for rapid movement across intertidal rocks. The genus has been extensively studied for mitochondrial genome architecture and phylogenetic relationships within the Grapsoidea superfamily.
Grapsus grapsus
Sally Lightfoot Crab, Red Rock Crab, Abuete Negro
Grapsus grapsus is a common intertidal crab native to the Pacific and Atlantic coasts of the Americas. Adults display highly variable coloration ranging from brownish-red to mottled yellow and pink, while juveniles are darkly colored for camouflage on volcanic substrates. The species is renowned for its agility and rapid escape response, making it difficult to capture. It occupies rocky shorelines just above the spray zone and has been documented engaging in cleaning symbiosis with marine iguanas in the Galápagos.
Habroscelimorpha dorsalis
Eastern Beach Tiger Beetle
Habroscelimorpha dorsalis, the eastern beach tiger beetle, is a coastal tiger beetle species found on sandy beaches along the Atlantic and Gulf coasts of North America, ranging from the northeastern United States through Florida and into Mexico. Adults are active during summer months, foraging in intertidal zones for small invertebrates. The species has a two-year life cycle with larvae that construct vertical burrows in beach sand. One subspecies, H. d. dorsalis (Northeastern beach tiger beetle), is federally listed as threatened due to habitat loss from coastal development and recreational disturbance.
Halacaridae
halacarid mites, marine mites
Halacaridae is a family of meiobenthic mites comprising over 1,100 described species in 64 genera, representing the largest marine radiation of arachnids. Members occupy marine, brackish, and freshwater habitats worldwide, from intertidal zones to deep-sea hydrothermal vents. The family exhibits diverse feeding strategies including predation, algivory, scavenging, and parasitism.
Halacaroidea
halacarid mites, marine mites
Halacaroidea is a superfamily of mites within the order Trombidiformes, commonly known as halacarid or marine mites. This group comprises the only truly marine arachnids, having successfully colonized intertidal and subtidal habitats worldwide. Halacarids are microscopic predators and scavengers that inhabit marine environments ranging from coastal waters to abyssal depths, with some species also occurring in brackish and freshwater habitats.
Halocoryza
Halocoryza is a genus of small, intertidal ground beetles (Carabidae) restricted to tropical and subtropical coastal habitats. The genus comprises four described species distributed across shorelines of the Atlantic, Pacific, and Indian Oceans, including Caribbean islands and the Gulf of Mexico. All species are nocturnal predators associated with sandy or coralline substrates near mangroves, coral reefs, or seaweed accumulations. The genus is characterized by reduced flight capability, slow running speed, and adaptations for burrowing in coastal sediments.
Haustoriidae
Haustoriidae is a family of amphipod crustaceans characterized by stout, robust bodies adapted for burrowing in sandy sediments. They are dominant members of intertidal and shallow subtidal sandy beach communities along the Atlantic coast of North America, with some species extending into the Gulf of Mexico and Pacific coast. The family radiated during the Eocene, with the Pacific-endemic genus Eohaustorius representing the most basal lineage, diverging approximately 31 million years ago. Haustoriidae are distinguished from other amphipod families by their specialized morphology for sand-burrowing and their limited dispersal capabilities, which have resulted in strong population structure and cryptic diversity across their range.
Haustorius canadensis
Haustorius canadensis is a sand-burrowing amphipod in the family Haustoriidae, found in sandy beach ecosystems of northern New England. The species exhibits a mixed annual–biennial life history, with approximately half the population reproducing after one year and the remainder after two years. It is a dominant member of intertidal macro-infauna communities, co-occurring with Acanthohaustorius millsi and Amphiporeia virginiana. Population dynamics show seasonal movements upshore in spring and downshore in autumn and winter.
Hemigrapsus
Hemigrapsus is a genus of varunid crabs containing fifteen recognized species. The genus is naturally distributed almost exclusively in the Pacific Ocean, with one species endemic to the Atlantic coast of South America. Two species—H. sanguineus and H. takanoi—have been introduced from East Asia to the North Atlantic region, where they have established invasive populations along European coasts and the eastern United States. One species, H. estellinensis, is considered extinct; it was endemic to a hypersaline spring in the Texas Panhandle.
Hemigrapsus nudus
Purple Shore Crab
The purple shore crab (Hemigrapsus nudus) is a small intertidal crab native to the Pacific coast of North America. It shelters under rocks in the mid to high intertidal zone and feeds primarily on green algae, particularly sea lettuce. The species is distinguished from similar shore crabs by its purple coloration and smooth carapace lacking prominent teeth or spines between the eyes.
Hemigrapsus sanguineus
Asian shore crab, Japanese shore crab
Hemigrapsus sanguineus is a small intertidal crab native to the northwestern Pacific Ocean. It has become a highly successful invasive species in North America and Europe, first detected in New Jersey in 1988. The species exhibits broad physiological tolerance, thriving across wide ranges of salinity and temperature. Its rapid population growth and competitive superiority over native crabs have raised significant ecological concerns, though habitat specificity for complex rocky shorelines may limit its impact in some systems.
Heterocerus insolens
Heterocerus insolens is a species of variegated mud-loving beetle described by Miller in 1994. It belongs to the family Heteroceridae, a group of small beetles specialized for life in muddy, riparian, and intertidal environments. The species is known from North America and shares the family traits of fossorial adaptations and tolerance to water-saturated substrates.
Hippoidea
mole crabs, sand crabs, sand fleas
Hippoidea is a superfamily of decapod crustaceans within the infraorder Anomura, commonly known as mole crabs or sand crabs. These highly specialized burrowers inhabit sandy beaches worldwide, with the exception of polar regions. Members of this superfamily are characterized by their inability to walk; instead, they use modified thoracic legs for digging into sand. The superfamily comprises three families: Hippidae, Albuneidae, and Blepharipodidae. Hippoidea is considered the most basal lineage within Anomura, with the other three superfamilies (Paguroidea, Galatheoidea, and Lomisoidea) being more closely related to each other than to Hippoidea.
Hypocharassus
Hypocharassus is a genus of long-legged flies (Dolichopodidae) comprising five described species distributed across the Nearctic, Oriental, and Palearctic regions. The genus is the sole member of the tribe Hypocharassini within subfamily Hydrophorinae. Species are associated with marine and coastal habitats, with adults flying low over wet sand and larvae inhabiting intertidal zones. The Korean species H. cavitarsus represents the first Palearctic record, expanding the genus's known range.
Hypocharassus pruinosus
A marine dolichopodid fly inhabiting the intertidal zone. Larvae develop in decaying seaweed and algal mats in the supralittoral zone, with four larval instars before pupation. Adults are associated with the same marine coastal habitat. The species shows physiological adaptations to tolerate salinity and periodic submersion.
Idotea urotoma
blunt-tailed isopod
Idotea urotoma, the blunt-tailed isopod, is a marine isopod species inhabiting low intertidal and shallow subtidal zones along the northeastern Pacific coast. It exhibits color polymorphism that matches its algal or seagrass substrate, providing camouflage. The species is distinguished by a broadly triangular telson margin lacking a distinct median projection.
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.
Janiridae
Janiridae is a globally distributed family of marine isopods in the suborder Asellota, comprising over 170 species across approximately 23 genera. The family exhibits remarkable bathymetric range, from intertidal zones to hadal depths exceeding 6,000 meters. Most species inhabit shallow shelf waters within 100 meters depth, though several genera have colonized deep-sea environments including whale falls, hydrothermal vents, and abyssal plains. The genus *Jaera*, predominantly northern hemisphere in distribution, includes the notable deep-sea specialist *Jaera tyleri*, discovered on whale bones in the Southern Ocean at 1,445 meters depth—the first *Jaera* species documented in the southern hemisphere. Janiridae demonstrates broad environmental tolerance to salinity, temperature, and oxygen stress.
Jassa marmorata
Marbled Scud
A tube-building amphipod native to the northeast Atlantic Ocean, now introduced to northeast Asia. Distinguished by greyish coloration with reddish-brown markings and a maximum length of 10 mm. Notable for exhibiting two distinct male morphs with alternative mating strategies: larger 'major' males that fight for access to females, and smaller 'minor' males that sneak copulations. Constructs protective tubes from detritus and algae fragments bound with mucus secretions.
Leptopodomorpha
shore bugs, spiny shore bugs
Leptopodomorpha is an infraorder of true bugs (Hemiptera: Heteroptera) comprising over 380 species across four families. The group is commonly known as shore bugs or spiny shore bugs due to their association with riparian and intertidal habitats. The family Saldidae dominates the infraorder with approximately 350 species and is notable for jumping ability. The remaining families—Leptopodidae, Omaniidae, and Aepophilidae—are considerably smaller, with Leptopodidae containing about 30 species and the latter two families being highly reduced.
Leptuca crenulata
Mexican fiddler crab
The Mexican fiddler crab is a small intertidal crab formerly classified in the genus Uca but transferred to Leptuca in 2016. Females exhibit active mate searching behavior, which is notable as this represents a reversal of typical sex roles in fiddler crabs where males usually search for mates. The species inhabits intertidal mudflats and shows the characteristic sexual dimorphism of fiddler crabs, with males possessing one greatly enlarged claw used for signaling and combat.
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 exotica
sea roach, wharf roach, wharf louse
Ligia exotica is a large intertidal isopod commonly known as sea roach or wharf roach. It inhabits rocky coasts and harbor walls in the supralittoral zone just above the high water mark. The species has a complex taxonomic history with uncertain native origins, though molecular evidence points to East and Southeast Asia as the center of diversity. It has spread globally via human maritime activity and comprises multiple cryptic genetic lineages that may represent distinct species.
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.
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.
Limnichidae
Minute Marsh-loving Beetles
Limnichidae is a family of small beetles in the superfamily Byrrhoidea, comprising at least 30 genera and 350 described species. The family exhibits considerable ecological diversity: while many species inhabit water-adjacent habitats such as riparian zones and coastal areas, others are fully terrestrial in leaf litter or arboreal environments. The subfamily Hyphalinae is uniquely specialized for intertidal marine habitats, with larvae capable of activity in seawater—a rarity among beetles. The oldest known fossils date to the mid-Cretaceous Burmese amber.
Limulidae
Horseshoe Crabs
Limulidae is a family of marine arthropods comprising four extant species: Limulus polyphemus in North America and three Indo-Pacific species (Tachypleus tridentatus, T. gigas, and Carcinoscorpius rotundicauda). These organisms possess a distinctive horseshoe-shaped prosoma, long telson, and compound eyes. Populations are declining globally, with T. tridentatus classified as Endangered by the IUCN. The family is notable for its ancient evolutionary lineage and biomedical importance due to hemolymph containing endotoxin-sensitive coagulation factors.
Liparocephalini
Liparocephalini is a tribe of rove beetles (Staphylinidae: Aleocharinae) comprising approximately 5 genera and more than 20 described species. The tribe is notable for its specialized colonization of intertidal marine habitats, representing a rare ecological transition among beetles. Phylogenetic studies indicate that ancestors of Liparocephalini originated in beach littoral zones and subsequently colonized rocky reef areas in the low tidal zone through intermediate tidal zones.
Lophopanopeus bellus
black-clawed crab, Blackclaw Crestleg Crab
Lophopanopeus bellus is a small crab native to the Pacific coast of North America, ranging from Alaska to California. The species is characterized by its rounded carapace with low tubercles, black claws, and highly variable coloration. Two subspecies are recognized: L. b. bellus in the northern portion of the range and L. b. diegensis in the southern portion. The species is notable for being parasitized by the barnacle Loxothylacus panopaei.
Lysmata
cleaner shrimp, peppermint shrimp
Lysmata is a genus of marine caridean shrimp distinguished by its unique sexual system of protandric simultaneous hermaphroditism. The genus includes two main ecological groups: cleaner shrimp that live in pairs and remove parasites from fish, and peppermint shrimp that often live in aggregations and consume pest anemones. All studied species begin life as males before maturing into functional simultaneous hermaphrodites capable of both producing and fertilizing eggs. Members of this genus are heavily targeted by the ornamental aquarium trade, with some species commanding high prices.
cleaner-shrimppeppermint-shrimpprotandric-simultaneous-hermaphroditismornamental-aquarium-tradecoral-reefmutualismAiptasia-controlhermaphroditeeuhermaphroditemale-phasecaridean-shrimpLysmatidaeHippolytidaetropical-marinetemperate-marinerock-reefsponge-habitatintertidalpair-bondingaggregationsectoparasite-removalfish-cleaningaquacultureconservationfisheries-managementmisidentificationcryptic-speciesgenetic-homogeneityoutcrossingreciprocal-fertilizationegg-incubationmoltingocean-acidificationwarmingbehavioral-ecologyreproductive-ecologyPanamaGulf-of-MexicoLakshadweepSouthern-CaliforniaArabian-SeaCaribbeanIndian-OceanLysmata-amboinensisLysmata-debeliusLysmata-boggessiLysmata-wurdemanniLysmata-bahiaLysmata-intermediaLysmata-californicaLysmata-hochiStenopus-hispidusMedon
Medon is a genus of rove beetles in the family Staphylinidae, subfamily Paederinae. Species are small, typically found in soil and leaf litter habitats, with some taxa occurring in intertidal zones along coastlines. The genus is distributed across the Palearctic region, with significant diversity in Turkey (23+ species) and East Asia. Several species have been described in recent decades, indicating ongoing taxonomic refinement.
Megalorchestia corniculata
beach hopper
Megalorchestia corniculata is a beach-dwelling amphipod in the family Talitridae, commonly known as a beach hopper. It inhabits sandy intertidal zones along the Pacific coast of North America. The species plays a significant ecological role as a consumer of marine wrack, contributing to nutrient cycling in coastal ecosystems.
Melanderia
Melanderia is a genus of long-legged flies (family Dolichopodidae) endemic to the West Coast of the United States. Members of this genus inhabit the intertidal zone, an unusual habitat for dolichopodid flies. Adults possess modified labellae that resemble mandibles, a distinctive morphological adaptation. The genus comprises four described species divided into two subgenera: Melanderia and Wirthia.
Mesovelia polhemusi
Mesovelia polhemusi is a marine water treader (family Mesoveliidae) described from Belize in 1990. It occupies a highly specialized habitat in tidal mangrove forests, an environment where few other aquatic insects occur. The species has been documented in southern Florida, expanding its known range beyond the type locality. It was named in honor of heteropteran specialist John T. Polhemus.
Metaltella
Metaltella is a genus of South American spiders in the family Desidae (formerly Amphinectidae), first described by Cândido Firmino de Mello-Leitão in 1931. The genus contains six species distributed across Argentina, Brazil, Chile, Peru, and Uruguay. One species, Metaltella simoni, has been introduced to North America and is now established in the southeastern United States and Canada. Members of this genus are hacklemesh weavers that construct webs with retreats. The genus is notable for its intertidal ecology in its native range and its successful establishment as an introduced species in North America.
Micralymma
Micralymma is a genus of rove beetles (Staphylinidae: Omaliinae) established by Westwood in 1837. The genus contains marine intertidal species, with M. marinum being the most documented member. Species in this genus are among the few beetles adapted to regular saltwater submersion. The genus has been recorded in both Europe and North America.
Micronaspis
Florida intertidal firefly
Micronaspis is a monotypic genus of fireflies (Lampyridae) containing a single species, Micronaspis floridana, commonly known as the Florida intertidal firefly. This rare, endemic species is restricted to intertidal salt marsh habitats along the coast of Florida and the Bahamas. It represents a classic example of geographic isolation due to its highly specialized habitat requirements.
Micronaspis floridana
Florida Intertidal Firefly, fiddler crab firefly
Micronaspis floridana is a rare, endemic firefly restricted to intertidal salt marshes along the peninsular coast of Florida and the Bahamas. The genus is monotypic, containing only this single species. It serves as a model organism for studying genetic isolation and speciation due to its highly restricted 'shoestring' geographic distribution. The species is threatened by coastal development, storm surges, and sea level rise; Hurricane Dorian severely impacted populations on Grand Bahama island.
Minuca longisignalis
longwave gulf fiddler, Gulf Marsh Fiddler Crab
Minuca longisignalis, formerly Uca longisignalis, is a fiddler crab endemic to Gulf of Mexico salt marshes. It exhibits striking reproductive seasonality characteristic of warm-temperate lineages, with ovigerous females appearing no earlier than April and peak ovigery in June. The species constructs burrows in vegetated marsh areas, with burrow density and depth varying by elevation and distance from shoreline. It co-occurs with congeners such as Uca spinicarpa, though shows substrate preferences for different clay compositions.
Neomolgus littoralis
intertidal red velvet mite
Neomolgus littoralis is a species of snout mite in the family Bdellidae, commonly known as the intertidal red velvet mite. It inhabits shoreline environments across North America, Europe, and Japan. The species reaches approximately 2 mm in length and is characterized by its red coloration, ridged abdomen, and elongated snout. It is known to prey on small insects including kelp flies.
Ocypode
Ghost Crabs
Ocypode is a genus of ghost crabs comprising 21 species distributed across tropical and subtropical sandy shores worldwide. Members are characterized by deep box-like bodies, elongated eyestalks often tipped with horn-like projections in several species, and pronounced claw asymmetry with one cheliped substantially larger than the other. They construct deep burrows in intertidal sandy or muddy substrates and exhibit primarily nocturnal activity patterns. The genus was established in 1795 and remained the sole genus in subfamily Ocypodinae until 2013, when Hoplocypode was segregated based on gonopod morphology.
Ocypodidae
Ghost and Fiddler Crabs
Ocypodidae is a family of semiterrestrial crabs comprising approximately 180 described species across 13 extant genera. The family includes two well-known groups: ghost crabs (genus Ocypode) and fiddler crabs (multiple genera including Leptuca and Minuca), plus the mangrove crabs of genus Ucides. Members are characterized by markedly unequal chelipeds in males, with the larger cheliped always exceeding carapace length. The family underwent substantial taxonomic revision in 2016, when the genus Uca was divided into 13 separate genera.