Marine
Guides
Acartia
Acartia is a genus of marine calanoid copepods comprising the majority of species in the family Acartiidae. They are small, planktonic crustaceans found primarily in temperate coastal and estuarine waters worldwide. The genus includes ecologically important species such as A. tonsa, which is among the most abundant and well-studied estuarine copepods globally. Acartia species serve as key intermediaries in aquatic food webs and are increasingly used as model organisms for studying coastal plankton dynamics, thermal ecology, and phylogeographic patterns.
Achelous
Achelous is a genus of swimming crabs in the family Portunidae, established by De Haan in 1833. These marine brachyuran crabs are characterized by their flattened, streamlined bodies and modified fifth pereiopods adapted for swimming. The genus includes commercially significant species such as A. spinimanus, a fishery resource in southeastern Brazil, and A. hastatus, distributed across the Atlantic-Mediterranean region. Species within this genus exhibit habitat preferences related to sediment type and depth, with some showing age and sexual segregation patterns typical of portunid crabs.
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.
Aeginina
skeleton shrimp
Aeginina is a genus of caprellid amphipods containing at least two described species: Aeginina longicornis and Aeginina aenigmatica. These small crustaceans are commonly known as skeleton shrimp due to their elongated, stick-like appearance. The genus was established by Norman in 1905 and occurs in marine environments of the North Atlantic.
Amblopusa
Amblopusa is a genus of intertidal aleocharine rove beetles in the family Staphylinidae, established by Casey in 1893. Members of this genus inhabit marine intertidal zones along Pacific coastlines. The genus includes at least two recognized species: A. brevipes Casey and A. vancouverensis Yoo & Ahn, described from Vancouver Island, Canada.
Amphibalanus
acorn barnacle
Amphibalanus is a genus of acorn barnacles in the family Balanidae, established by Pitombo in 2004 to accommodate species formerly assigned to Balanus. The genus contains multiple species including the widespread and economically significant Amphibalanus amphitrite and A. improvisus. These barnacles are characterized by their conical calcareous shells, cemented base, and planktonic larval stages culminating in a settlement-competent cyprid stage. Several species have become established outside their native ranges as invasive biofouling organisms in ports and harbors worldwide.
Amphiporeia
Amphiporeia is a genus of gammaridean amphipods in the family Bathyporeiidae, comprising at least three described species: A. gigantea, A. lawrenciana, and A. virginiana. These small crustaceans are characteristic inhabitants of sandy marine and estuarine substrates along the Atlantic coast of North America, where they exhibit specialized burrowing behavior and tidal swimming activity. The genus is notable for pronounced sexual segregation within the sediment, seasonal population fluctuations, and reproductive strategies involving multiple broods per year. Species within Amphiporeia function as important components of benthic food webs, serving as both detritivores and prey for demersal fish.
Amphiporeia virginiana
Amphiporeia virginiana is a sand-burrowing amphipod crustacean described by Shoemaker in 1933. It is a dominant inhabitant of high-energy sandy beaches along the Atlantic coast of North America, from Nova Scotia to South Carolina. The species exhibits distinctive tidal migration behavior, swimming into the water column during flood tides and burrowing into sediments during ebb tides. Females brood eggs and young in a ventral marsupium.
Anilocra
Fish Lice
Anilocra is a genus of marine isopods in the family Cymothoidae, commonly known as fish lice. Members are obligate external parasites of teleost fishes, attaching to host skin and feeding on blood. The genus exhibits sequential hermaphroditism, with individuals beginning life as males and transitioning to females as they grow. Parasitism by Anilocra species has been documented to reduce host growth rates, fecundity, and survival.
Anomura
anomurans, hermit crabs, king crabs, porcelain crabs, squat lobsters, mole crabs, blanket-hermit crabs
Anomura is an infraorder of decapod crustaceans distinguished by their 'differently-tailed' body plan, including hermit crabs, king crabs, porcelain crabs, squat lobsters, and mole crabs. Multiple lineages within this group have independently evolved crab-like body forms through carcinisation. Anomura is the sister group to Brachyura (true crabs), together forming the clade Meiura. Members possess ten pereiopods, but the last pair is reduced and often concealed within the gill chamber, leaving only eight visible walking legs—a key diagnostic feature separating them from true crabs.
Anurida maritima
seashore springtail, rock springtail
Anurida maritima is a cosmopolitan springtail confined to the intertidal zone, where it forms dense aggregations of up to several hundred individuals on rock-pool surfaces. This wingless collembolan exhibits unique adaptations to marine conditions, including a vestigial furcula that prevents jumping and hydrophobic body hairs that enable it to remain on water surfaces. The species demonstrates complex behavioral rhythms synchronized with tidal cycles and survives winter through egg diapause. Recent genetic studies have revealed cryptic speciation within this morphospecies, with distinct mitochondrial and nuclear lineages now recognized.
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.
Atheta novaescotiae
Atheta novaescotiae is a species of rove beetle described in 2006. It inhabits marine seashore environments in eastern North America. The species exhibits adaptations convergent with those of Tarphiota, a genus of rove beetles specialized for similar coastal habitats.
Balanus nubilus
giant acorn barnacle
Balanus nubilus is the world's largest barnacle species, reaching up to 15 cm in diameter and 30 cm in height. It possesses the largest known muscle fibers of any barnacle, making it historically significant for muscle physiology research. This northeast Pacific species is a filter feeder that attaches to hard substrates including rocks, pier pilings, and other animals at depths up to 90 meters.
Barce husseyi
Barce cf-husseyi is an amphipod crustacean in the family Phliantidae. The 'cf.' designation indicates the specimen resembles Barce husseyi but definitive identification requires further verification. Amphipods in this genus are typically marine, benthic organisms associated with hard substrates or sediments.
Bathyporeiidae
Bathyporeiidae is a family of amphipod crustaceans containing two genera: Amphiporeia and Bathyporeia. These small, laterally compressed marine invertebrates are primarily known from shallow coastal waters of northern Europe. The family was formally established by d'Udekem d'Acoz in 2011.
Cafius
coastal rove beetles
Cafius is a genus of relatively large rove beetles in the family Staphylinidae, comprising approximately 8 described species in North America and approaching 50 globally. The genus originated in the early Miocene (ca. 17.91 Ma) along the coasts of Europe and Australia, with subsequent diversification driven by transoceanic dispersal via ocean surface currents. Species are obligate inhabitants of coastal marine environments, particularly sandy intertidal zones. The genus is notable for its global distribution across temperate and tropical coastlines and its biological adaptations to saline, dynamic shoreline habitats.
Calanidae
Calanidae is the largest family of calanoid copepods, containing ecologically dominant genera including Calanus, potentially the most abundant metazoan genus on Earth. Members inhabit marine environments from surface waters to depths exceeding 400 m, with distributions spanning polar, temperate, and tropical oceans. The family exhibits significant vertical stratification and seasonal abundance patterns, with some species performing ontogenetic vertical migrations for overwintering. Calanidae species play critical roles in marine food webs as primary consumers and prey for fish and higher trophic levels.
Calappa flammea
Flame Streaked Box Crab
Calappa flammea is a marine crab species in the family Calappidae, commonly known as the Flame Streaked Box Crab. It is distributed in the Western Atlantic Ocean. The species was first described by Herbst in 1794 as Cancer flammeus.
Calappidae
Box Crabs
Calappidae is a family of marine crabs commonly known as box crabs, comprising approximately 16 genera including both extant and fossil taxa. Seven genera are known only from the fossil record, with calappid fossils documented from the Cretaceous to Recent (66.043 Ma to present) across Europe, the United States, Mexico, Central America, Australia, and Japan. The family is characterized by a distinctive box-like carapace morphology and is distributed in tropical and temperate marine waters worldwide.
Calliopiidae
Calliopiidae is a family of hyperbenthic amphipods distributed across the North Atlantic and North Pacific oceans. Members inhabit diverse marine environments including subtidal waters, hydrothermal vents, and the hyperbenthic zone immediately above the seafloor. The family includes the newly described genus Bathya from deep-sea hydrothermal vents and Calliopius species associated with macroalgae.
Calliopius laeviusculus
Planktonic Amphipod
Calliopius laeviusculus is a marine amphipod crustacean distributed across the North Atlantic in both European and North American waters. The species exhibits a semiannual life cycle in southern parts of its range, with overwintering adults releasing young in spring and early summer. Population dynamics are tightly coupled to seasonal food availability, particularly capelin egg deposits. Multiple generations per year occur in warmer regions, while single-generation annual cycles prevail in colder northern waters.
Callipallene brevirostris
Long-necked Sea Spider
Callipallene brevirostris is a sea spider species in the family Callipallenidae, commonly known as the Long-necked Sea Spider. It was originally described as Pallene brevirostris by Johnston in 1837 and later transferred to the genus Callipallene. The species is known from European waters and has two recognized subspecies: C. b. brevirostris and C. b. producta.
Callipallenidae
sea spiders
Callipallenidae is a family of sea spiders (Pycnogonida) established by Hilton in 1942. The family includes multiple genera distributed across Antarctic, subantarctic, and temperate waters, with notable species richness in southern Australian and Tasmanian waters. Some genera, such as Pallenella, exhibit exceptional sympatric diversity with multiple species co-occurring in the same microhabitat. Members of this family are generally small to medium-sized pycnogonids found in marine benthic environments.
Canacidae
beach flies, surf flies, surge flies
Canacidae is a family of minute Diptera commonly known as beach flies, surf flies, or surge flies. The family comprises approximately 307 species in 27 genera as of 2010, though counts vary among sources. Following McAlpine's 2007 taxonomic revision, the family now includes Tethininae as a subfamily, uniting what were previously treated as separate families. Members are predominantly intertidal specialists found along sea coasts worldwide.
Canacinae
surf flies, beach flies
Canacinae is a subfamily of small flies in the family Canacidae, commonly known as surf flies or beach flies. Members are strongly associated with intertidal marine environments, particularly rocky shore habitats in the surf zone. The subfamily includes multiple tribes and genera distributed across tropical and subtropical coastal regions worldwide, with documented occurrences in the Indo-Pacific, Afrotropical, and other oceanic regions.
Cancer
Edible Crabs
Cancer is a genus of marine crabs in the family Cancridae, comprising eight extant species and three extinct species. The genus includes economically and ecologically important species such as the European edible crab (Cancer pagurus), Jonah crab (Cancer borealis), and red rock crab (Cancer productus). These crabs inhabit littoral and sublittoral zones of temperate and cold-temperate seas, primarily in the Atlantic and Pacific Oceans. The genus is thought to have evolved from related Pacific Ocean genera during the Miocene epoch.
Cancer gracilis
Cancer gracilis is a species of true crab in the family Cancridae, originally described by Dana in 1852. It is currently recognized as a synonym of Metacarcinus gracilis. The species belongs to the diverse group of decapod crustaceans characterized by a hard carapace and ten walking legs. Like other members of the genus, it is a marine crab found in coastal waters.
Cancer irroratus
Atlantic rock crab, peekytoe crab
A medium-sized marine crab native to the western North Atlantic, ranging from Iceland to South Carolina. Adults reach 133 mm carapace width and can live up to 8 years. The species occupies depths from intertidal zones to 790 m. It has become commercially significant as the 'peekytoe crab' and has established non-native populations in Iceland via ballast water transport.
Caprella verrucosa
Caprella verrucosa is a marine amphipod species in the family Caprellidae, commonly known as skeleton shrimp. The species was described by Boeck in 1871. It is found in temperate Asian waters, with confirmed records from the South Korean part of the Yellow Sea. Like other caprellids, it exhibits a reduced body plan with elongated pereiopods adapted for clinging to substrates in marine environments.
Caprellidae
Skeleton Shrimp, Ghost Shrimp
Caprellidae is a family of marine amphipods known as skeleton shrimps, characterized by their slender, threadlike bodies that provide camouflage among seaweed, hydroids, and bryozoans. They exhibit extreme sexual dimorphism, with males typically much larger than females. The family contains 88 genera across three subfamilies and is distributed worldwide in marine environments from intertidal zones to deep sea depths. Some species have been documented as invasive, spreading through biofouling on aquaculture equipment.
Carcinus
Green crabs
Carcinus is a genus of crabs in the family Carcinidae, comprising two recognized species: C. maenas (the European green crab or shore crab) and C. aestuarii (the Mediterranean shore crab). The genus is notable for containing one of the world's most successful marine invasive species, C. maenas, which has established populations across temperate coastlines on multiple continents. Both species share similar ecological roles as opportunistic predators in coastal marine systems. C. aestuarii is endemic to the Mediterranean Sea and has been implicated in at least one invasion event in Japan.
Caridea
caridean shrimp, true shrimp
Caridea is a species-rich infraorder of decapod crustaceans comprising over 3,000 described species of true shrimp. Members are distinguished from other shrimp groups by their brooding reproductive strategy, lamellar gill structure, and characteristic abdominal segmentation where the second segment overlaps both the first and third. They occupy diverse aquatic habitats from freshwater streams to abyssal depths exceeding 5,000 meters, with roughly one-quarter of species inhabiting freshwater environments. The group includes commercially significant species such as Pandalus borealis and ecologically important cleaner shrimp that maintain reef fish health.
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).
Centropagidae
Centropagidae is a family of calanoid copepods comprising 14 genera and over 130 species. Members occupy diverse aquatic habitats including marine coastal waters, freshwater lakes, and saline lakes across the Southern Hemisphere, with notable concentrations in Australia, southern South America, subantarctic islands, and Antarctica. The family exhibits significant habitat diversity: marine genera include Centropages, Dussartopages, and Gladioferens; freshwater genera include Boeckella, Calamoecia, and Hemiboeckella. The genus Boeckella poppei represents the only terrestrial/freshwater invertebrate reported from all three main Antarctic biogeographic regions (subantarctic islands, maritime Antarctic, and continental Antarctic).
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.
Chironominae
non-biting midges
Chironominae is a subfamily of non-biting midges (Diptera: Chironomidae) containing over 2,000 described species across three tribes: Chironomini, Pseudochironomini, and Tanytarsini. Members are globally distributed and primarily aquatic in their immature stages. The subfamily includes economically and ecologically significant genera such as Chironomus, Polypedilum, and Tanytarsus. Adults are characterized by reduced mouthparts and do not feed; larvae are diverse in habitat specialization, ranging from freshwater lakes and rivers to marine environments and phytotelmata.
Chthamalidae
Chthamalid Barnacles
Chthamalidae is a family of small, intertidal barnacles in the superfamily Chthamaloidea. The family includes at least 56 recognized species across 14 genera. Members are distinguished by a primary shell wall of eight, six, or four plates without imbricating whorls, and a membranous or rarely calcareous basis. They occupy the highest intertidal zones, often in wave-washed habitats where other barnacle families cannot survive. Molecular studies have revealed extensive cryptic diversity, with many species separable only by DNA analysis.
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.
Cirolanidae
Cirolanidae is a family of aquatic isopod crustaceans established by Dana in 1852. The family encompasses approximately 70 genera and over 500 species, ranging from small interstitial forms to the supergiant deep-sea isopods of the genus Bathynomus that can exceed 30 cm in length. Members occupy diverse aquatic habitats including marine coastal waters, deep-sea environments, freshwater systems, and subterranean groundwater. The family is characterized by dorsoventrally flattened bodies and includes both free-living and troglobitic species.
Clibanarius
Clibanarius is a genus of hermit crabs in the family Diogenidae, comprising approximately 60 valid species as of 2025. Members possess soft, asymmetrical abdomens protected within scavenged gastropod shells. While predominantly marine, the genus includes C. fonticola, the only known hermit crab species to complete its entire life cycle in freshwater. The genus exhibits broad geographic distributions, with feeding rates documented to vary with temperature.
Clunio californiensis
Clunio californiensis is a species of non-biting midge in the family Chironomidae, first described by Hashimoto in 1974. The genus Clunio is notable for its marine and intertidal habitat associations, with several species exhibiting specialized adaptations to life in coastal environments. As a member of the subfamily Orthocladiinae, this species is part of a diverse group of chironomids often found in challenging aquatic habitats.
Coelopa vanduzeei
kelp fly
Coelopa vanduzeei is a species of kelp fly in the family Coelopidae, a group of flies specialized for life in coastal environments. Like other members of this family, it is associated with decaying marine vegetation. The species was described by Cresson in 1914.
Conchoderma
goose barnacles
Conchoderma is a genus of pedunculate barnacles (goose barnacles) in the family Lepadidae. Species in this genus are obligate epibionts, attaching to mobile marine hosts including whales, fish, sea snakes, and crustaceans. They possess a flexible stalk (peduncle) that anchors them to their host and a capitulum with calcareous plates enclosing the body. The genus includes notable species such as C. auritum, which associates with whales, and C. virgatum, which has been documented on diverse hosts including fish and copepods.
Coronula diadema
whale barnacle, humpback whale barnacle
Coronula diadema is a species of whale barnacle that lives exclusively on cetacean hosts, primarily humpback whales (Megaptera novaeangliae). First described by Carl Linnaeus in 1767, this barnacle attaches to whale skin using specialized coring structures and filter-feeds on plankton. The species exhibits simultaneous hermaphroditism and forms mating groups of up to nine individuals. Its crown-like appearance gives rise to both its scientific and common names.
Coronulidae
Whale Barnacles
Coronulidae is a family of barnacles (Cirripedia) commonly known as whale barnacles, though their host associations extend beyond cetaceans to include sea turtles and crocodilians. Members are obligate epizoic species that attach to mobile marine hosts during their free-swimming larval stage. The family includes the genus Chelonibia, which exhibits exclusively passive feeding behavior—a unique trait among barnacles where the species relies entirely on host-generated water currents rather than facultatively switching between active and passive feeding modes.
Crangon
Crangon is a genus of marine shrimp in the family Crangonidae, comprising approximately 20 extant species distributed exclusively in the Northern Hemisphere. The genus exhibits a strong Pacific Ocean bias, with most species occurring in the northern Pacific, suggesting a Pacific origin. The brown shrimp Crangon crangon is the most commercially important and best-studied species, supporting significant fisheries in European waters. Several species display notable biological traits including intensive cannibalism behavior and broad environmental tolerances.
Crangonidae
crangonid shrimps, sand shrimps, brown shrimps
Crangonidae is a family of marine shrimp in the superfamily Crangonoidea, containing 24 genera and including the commercially important species Crangon crangon, the common brown shrimp. Members are primarily benthic, inhabiting coastal to deep-water sediments. The family is distinguished by partially chelate first pereiopods used in prey capture. Two fossil species are known: Crangon miocenicus from the early Miocene of Russia and Morscrangon acutus from the early Eocene of Denmark.
Ctenophora
comb jellies, sea gooseberries, sea walnuts, Venus's girdles
Ctenophora is a phylum of marine invertebrates distinguished by eight rows of fused cilia used for locomotion, called comb rows. They are the largest animals to swim using cilia. Unlike cnidarians, they lack stinging cells and instead capture prey using colloblasts—sticky adhesive cells. The phylum contains approximately 150–186 recognized species exhibiting diverse body plans, from egg-shaped cydippids with retractable tentacles to flattened benthic platyctenids and large-mouthed beroids. Ctenophores possess a decentralized nerve net without a brain, and their phylogenetic position as either the earliest or second-earliest branching animal lineage remains actively debated.