Myopsida

Myopsida is an order of decapodiform cephalopods consisting of neritic squids distinguished by a transparent corneal membrane that covers and protects their large, image-forming eyes, a feature absent in the related order Oegopsida.^[1][2] This order falls within the subclass Coleoidea and superorder Decapodiformes, encompassing around 50 species that typically inhabit shallow coastal and continental shelf environments rather than the open ocean.^[3][1] Key morphological characteristics of Myopsida include a funnel groove that forms a shallow depression (less pronounced than in Oegopsida), ten arms with two elongate tentacles equipped with sucker-lined clubs for prey capture, and suckers bearing chitinous rings.^[2] Unlike octopods, which have eight arms, myopsid squids possess this decapod arrangement, and they lack the photophores common in many oceanic cephalopods.^[1] Their eyes, while complex and vertebrate-like in structure, are adapted for near-shore vision, with the corneal covering providing protection in turbid or shallow waters.^[2] Additionally, myopsids share traits with sepioids, such as a beak without a pronounced angled point and the presence of accessory nidamental glands in females for egg protection.^[1] The order comprises two accepted families: Australiteuthidae, which is monotypic and contains only Australiteuthis aldrichi from Australian waters, and Loliginidae, a diverse family with approximately 50 species across about a dozen genera, including economically vital taxa like Loligo (now often reclassified as Doryteuthis or similar) and Heterololigo.^[3][1] Phylogenetic studies indicate that Myopsida forms a clade within Decapodiformes, though its exact relationships to Oegopsida and Sepioidea remain debated due to conflicting molecular evidence.^[1] Myopsid squids are predominantly demersal or semi-pelagic in neritic zones, ranging from intertidal areas to depths of around 500 meters, and are distributed globally in temperate and tropical seas.^[2] They exhibit short life cycles, often lasting one to two years, with semelparous reproduction where adults spawn once before dying; females deposit eggs in gelatinous masses attached to substrates such as seaweed, rocks, or artificial structures.^[2] Diet consists mainly of fishes, crustaceans, and other invertebrates, captured via jet propulsion and tentacle strikes.^[2] Loliginid species, in particular, support major global fisheries, contributing significantly to seafood markets for calamari and bait, with annual catches exceeding hundreds of thousands of tons as of the 2010s; for instance, species like the California market squid (Doryteuthis opalescens) form the basis of the largest cephalopod fishery in the United States.^[1][4] Their abundance and accessibility make them important subjects for ecological and aquaculture research.^[2]

Taxonomy and classification

Higher classification

Myopsida belongs to the kingdom Animalia, phylum Mollusca, class Cephalopoda, subclass Coleoidea, superorder Decapodiformes, and order Myopsida, as established by d'Orbigny in 1841.^[3][5] This placement positions Myopsida within the coleoid cephalopods, which are characterized by internal shells and advanced nervous systems, distinct from the externally shelled nautiloids.^[3] In some taxonomic schemes, Myopsida is alternatively treated as the suborder Myopsina under the broader order Teuthida, which encompasses various decapodiform squids.^[6] This classification reflects historical groupings where Myopsida and related taxa were subordinated to Teuthida to emphasize shared squid-like features, though modern phylogenetics often elevates it to ordinal status based on morphological and molecular evidence.^[6] The superorder Decapodiformes comprises seven orders: Bathyteuthida, Idiosepida, Myopsida, Oegopsida, Sepiida, Sepiolida, and Spirulida, forming a monophyletic group distinct from the superorder Octopodiformes, which includes octopuses and the vampire squid.^[7][6] Within Decapodiformes, the squid orders are Myopsida (neritic squids) and Oegopsida (oceanic squids), while other orders include cuttlefish (Sepiida), bobtail squids (Sepiolida), and the ram's horn squid (Spirulida). This superordinal division highlights evolutionary divergences in arm structure, shell morphology, and habitat preferences, with Decapodiformes generally featuring ten arms (eight plus two tentacles) adapted for diverse marine environments.^[7] The order Myopsida is primarily distinguished from other squid orders, particularly Oegopsida, by the presence of a corneal membrane that fully covers and protects the eyes, along with the absence of a secondary eyelid.^[6] These traits enable Myopsida species to thrive in coastal, neritic waters where visual acuity in turbid conditions is advantageous, contrasting with the open, unprotected eyes of Oegopsida adapted to open-ocean clarity.^[6] Such diagnostic features underpin the ordinal separation and reflect adaptations to distinct ecological niches within Decapodiformes.^[6]

Families and genera

The order Myopsida comprises two families: the monotypic Australiteuthidae and the diverse Loliginidae.^[8] The Australiteuthidae, established in 2005, contains a single genus, Australiteuthis, and one species, A. aldrichi, which is endemic to the coastal waters of northern Australia and Papua New Guinea.^[9] This small squid reaches a maximum dorsal mantle length (ML) of approximately 2.8 cm in mature females, with males maturing at around 2.1 cm ML, and is distinguished by unique morphological features such as a photophore on the ink sac and highly modified arm suckers in males.^[9] The family Loliginidae, by contrast, encompasses the majority of myopsid diversity, with approximately 50 species distributed across 11 genera and found in temperate and tropical coastal waters worldwide.^[6] These squids are ecologically and commercially significant, with many species targeted in fisheries for food and bait due to their abundance in nearshore habitats.^[6] Key genera include:

• Afrololigo (1 species, A. mercatoris), from West African waters.
• Alloteuthis (3 species), restricted to European coastal waters, such as A. media and A. subulata, which are small to medium-sized squids adapted to temperate shelf environments.^[6]
• Doryteuthis (several species), primarily in the Americas, including D. pealeii (longfin inshore squid, formerly placed in subgenus Amerigo) and D. opalescens (California market squid), reaching up to 40 cm ML.^[6]
• Heterololigo (1 species, H. japonica), found in the northwest Pacific, characterized by distinct tentacle club morphology.^[6]
• Lolliguncula (2 species), in the western Atlantic and eastern Pacific, such as L. brevis, a small squid (up to 15 cm ML) prevalent in estuarine habitats.^[6]
• Loligo (several species), cosmopolitan in temperate regions, including L. vulgaris (European waters) and L. forbesii (northeastern Atlantic), the largest myopsid at up to 93.7 cm ML.^[6]
• Loliolus (several species), Indo-Pacific, like L. hardwickei, adapted to coral reef and seagrass areas.^[6]
• Notiololigo (1 species, N. suttoni), from southern African waters.
• Nototodarus (2 species), in the southern hemisphere, such as N. gouldi (Australia and New Zealand), commercially harvested for its fast growth.^[6]
• Pickfordiateuthis (1 species, P. pulchella), a dwarf squid (ML ~2 cm) from the Gulf of Mexico, recognized as a distinct genus in taxonomic revisions based on morphological differences in arm suckers and gladius structure.^[6]
• Sepioteuthis (several species), Indo-Pacific reefs, including S. lessoniana (bigfin reef squid), known for schooling behavior and reaching 30 cm ML.^[6]
• Uroteuthis (several species), Indo-Pacific, such as U. edulis (Japanese common squid), a major fishery species exceeding 30 cm ML.^[6]

Overall, Myopsida includes about 51 species, with Loliginidae accounting for the bulk and driving much of the order's economic value through global squid fisheries.^[6] Taxonomic revisions, such as the elevation of Pickfordiateuthis and clarification of generic boundaries via morphological and molecular data, continue to refine this classification.^[10]

Physical characteristics

Eye and vision

Myopsida, the order of squids commonly known as myopsid squids, possess a distinctive ocular anatomy characterized by large, prominent eyes covered by a transparent, fused corneal membrane that seals the eye from direct contact with seawater. This membrane, a thin, smooth, and turgid layer of skin lacking musculature, protects the underlying lens and retina while facilitating light refraction, a feature unique to Myopsida among decapodiform cephalopods. The term "Myopsida" derives from the Greek "myops," meaning "closed" or "shut eye," reflecting this sealed structure that contrasts with the open, unprotected eyes of related groups. Unlike Oegopsida, whose eyes are directly exposed to seawater without such a covering, Myopsida rely on the corneal membrane to prevent debris ingress in coastal environments.^[6] The visual system of Myopsida is adapted for high-resolution imaging in near-shore, often turbid waters, with eyes proportionally large relative to body size— for instance, in species like Doryteuthis pealeii, the eyeball diameter can reach 8–18% of mantle length. The retina features a single layer of rhabdomeric photoreceptors with dynamic screening pigment migration: in light-adapted states, pigments spread distally to shield against excess brightness, while in dark-adapted conditions, they concentrate basally to maximize sensitivity, enabling effective vision in variable coastal lighting. This setup supports binocular vision through convergent eye movements facilitated by additional extrinsic muscles, enhancing depth perception for close-range prey detection. Although Myopsida generally possess a single visual pigment (rhodopsin) tuned to blue-green wavelengths, suggesting limited color discrimination compared to vertebrates, their chromatophore-based camouflage implies behavioral responses to environmental hues, potentially via polarization sensitivity or intensity cues. Light organs and photophores are absent or rudimentary, distinguishing them from bioluminescent Oegopsida and underscoring reliance on ambient light rather than self-generated illumination.^[11][6] Functionally, the sealed corneal membrane limits eye growth potential compared to the expandable open eyes of Oegopsida but offers advantages in preventing water entry and maintaining clarity amid sediment-laden coastal currents, thus optimizing detection of predators and prey in low-visibility, neritic habitats typically shallower than 200 meters. Paralarval stages exhibit positive phototaxis, with eyes sensitive to surface light cues that guide vertical migration, as observed in Doryteuthis opalescens at mantle lengths of 2.5–3.2 mm. Overall, these adaptations prioritize acuity and stability in dynamic, particle-rich waters over the broad-depth versatility seen in oceanic squids.^[6][11]

Body structure

Myopsida exhibit a torpedo-shaped body adapted for agile swimming in coastal waters, characterized by a muscular mantle that houses the internal organs and provides the primary means of locomotion through jet propulsion. The mantle is elongated and cylindrical, often with a posterior narrowing or tail-like extension that enhances hydrodynamic efficiency. Embedded within the dorsal mantle is a well-developed gladius, a chitinous internal shell that extends nearly the full length of the mantle, offering rigidity to support rapid movements without compromising flexibility.^[12][13] The head region features eight shorter arms and two longer tentacles, all equipped with simple suckers bearing chitinous rings but lacking hooks or swiveling mechanisms, distinguishing Myopsida from the more complex sucker arrangements in Oegopsida. These suckers are arranged in two rows on the arms and four rows on the tentacular clubs, facilitating prey capture and manipulation. The tentacles, used primarily for grasping, can be partially retracted into shallow pockets or depressions on the anteroventral surface of the head for protection when not in use. A pair of fins, typically rhomboidal or triangular in shape, is located at the mantle's posterior end, aiding in propulsion, steering, and stabilization during swimming.^[12][13] Size varies significantly across species, with mantle lengths ranging from as small as 2 cm in Pickfordiateuthis to up to 93.7 cm in Loligo forbesii, reflecting adaptations to diverse predatory and foraging strategies within neritic habitats. Internally, the body relies on a hydrostatic skeleton formed by the mantle cavity, which fills with water and expels it forcefully through the funnel for jet propulsion, enabling bursts of speed. The digestive system includes a stomach, caecum, and ink sac that discharges melanin-based ink for defense, while females possess only a functional left oviduct, with the right rudimentary or absent, and accessory nidamental glands that produce coatings for egg capsules.^[12] Sexual dimorphism is evident in both structure and size, with males featuring a hectocotylus—a modified arm, often the fourth left ventral arm, specialized for sperm transfer via spermatophores—while females lack this modification. Size differences occur between sexes, with females larger in some species and males in others, such as male Loligo forbesii reaching nearly double the mantle length of females.^[12][13]

Habitat and distribution

Geographic range

Myopsida exhibit a global distribution confined to coastal and continental shelf waters, predominantly in temperate and subtropical latitudes, ranging from intertidal zones to depths of approximately 500 m, while being notably absent from polar regions. This pattern reflects their preference for neritic environments in tropical to temperate seas worldwide, excluding extreme cold waters.^[14][15] Recent studies indicate that climate change is influencing their distributions, with ocean warming projected to increase habitat suitability in northern latitudes for some species, such as poleward expansions for Doryteuthis pealeii and D. opalescens, while potentially contracting southern ranges (as of 2023).^[16][17] The family Australiteuthidae is highly restricted, with its sole species, Australiteuthis aldrichi, occurring only in northern Australian waters, including the Joseph Bonaparte Gulf of Western Australia and inshore areas of the Northern Territory, as well as adjacent Papua New Guinean seas. In marked contrast, the more diverse family Loliginidae displays a cosmopolitan range across multiple ocean basins. For example, Doryteuthis pealeii (synonym Loligo pealeii) inhabits the western North Atlantic from Newfoundland southward to Venezuela, favoring shelf habitats. Similarly, Loligo vulgaris is widespread in the eastern Atlantic, from the North Sea and British Isles to southwest Africa, encompassing the entire Mediterranean Sea.^[18][19][20] Loliginid distributions extend prominently into the Indo-Pacific, where genera such as Uroteuthis thrive, with species like U. duvaucelii spanning from the Indian Ocean and Red Sea eastward to the South China Sea and Philippine Sea, northward to Taiwan. In southern ocean realms, Nototodarus species, including N. sloanii and N. gouldi, are confined to waters around New Zealand and southern Australia, from Queensland to Western Australia and across the Tasman Sea. A representative temperate-subtropical species, Doryteuthis opalescens, predominates in eastern Pacific upwelling zones, particularly along the California Current from Baja California to Alaska, with peak abundances off central California.^[21][22] Latitudinal patterns underscore a dominance in temperate and subtropical zones, with species richness peaking in regions like the Indo-West Pacific and eastern Atlantic, driven by historical biogeographic processes such as Tethys Sea closure and Atlantic expansion. Myopsids undertake short seasonal migrations tied to spawning grounds; for instance, Loligo forbesii in the northeast Atlantic performs temperature-influenced movements, migrating eastward earlier in warmer conditions to reach breeding areas in the English Channel and North Sea. These migrations typically involve inshore-offshore shifts over hundreds of kilometers, aligning with reproductive cycles rather than long-distance oceanic travel.^[14][23]

Ecological niche

Myopsida squids primarily inhabit neritic and demersal environments, favoring coastal waters over continental shelves and slopes, often at depths from the intertidal zone to around 700 meters. They show a preference for sandy or muddy bottoms, where many species engage in bottom-oriented foraging, though some venture into open water for schooling behaviors that provide defense against predators.^[6] These cephalopods are strictly carnivorous, preying on a variety of marine organisms including crustaceans such as shrimp, crabs, euphausiids, and mysids; small teleost fishes like myctophids and herring; and other cephalopods, with cannibalism observed in several species. Juveniles typically consume planktonic prey like copepods, transitioning to larger items as they grow, employing ambush tactics by extending tentacles to capture prey near the seafloor or pursuing it actively in the water column.^[6][24] Myopsida serve as key prey in marine food webs, targeted by larger predatory fish such as tuna and sharks, seabirds, and marine mammals including dolphins, seals, and sperm whales. To evade these threats, they deploy defensive strategies like ejecting ink clouds to disorient attackers and rapid jet propulsion for escape.^[24][25] In terms of behavioral ecology, many Myopsida exhibit diurnal activity patterns, with increased foraging and movement during daylight hours, complemented by schooling in open water to reduce individual predation risk. Symbiotic associations are uncommon, though some species interact with cleaner fish that remove ectoparasites, providing mutual benefits in reef-associated habitats.^[26]

Life history

Reproduction

Myopsida exhibit a polygamous mating system in which both males and females engage in multiple matings, often with several partners over short periods. Life history details are best known for the diverse family Loliginidae; information on the monotypic Australiteuthidae remains limited.^[27] Males transfer spermatophores—elongated packets containing sperm—using a specialized arm called the hectocotylus, which is inserted into the female's mantle cavity or buccal region during mating postures such as the parallel or head-to-head positions.^[28] Female choice plays a role, as receptive females may jet away or otherwise reject unsuitable males, while male-male agonism is common among larger individuals, involving aggressive displays like fin beating and ink release to secure mating access.^[28] Multiple matings benefit females by increasing egg production rates and resulting in larger hatchlings relative to egg mass, potentially enhancing offspring survival through genetic diversity and resource allocation.^[29] Spawning in Myopsida occurs year-round but features seasonal peaks, such as in spring and summer in temperate regions, aligning with optimal environmental conditions for egg development.^[12] Females deposit eggs in gelatinous strings or finger-like capsules attached to substrates in coastal shallows, where the capsules are coated with protective mucus from the accessory nidamental glands to guard against predation and desiccation.^[30] In families like Loliginidae, batch spawning is typical, with females releasing multiple capsules sequentially over days before moving to new sites, and no parental brooding occurs as eggs are left anchored to rocks, algae, or artificial structures.^[31] Fecundity varies by species and female size, with each egg capsule typically containing 100–300 eggs, and mature females producing up to several thousand eggs across multiple batches.^[32] For example, in Doryteuthis opalescens, females deposit around 200 eggs per capsule, totaling approximately 2,000 eggs per spawning event.^[32] Eggs are fertilized internally using stored spermatophores prior to deposition, promoting potential multiple paternity within a single capsule.^[28] Environmental factors strongly influence spawning, with most species favoring warmer shallow waters (typically 10–50 m depth) where temperatures support rapid embryonic development, often coinciding with seasonal plankton blooms that provide post-hatching food for paralarvae.^[33] However, some species like Loligo forbesii spawn in deeper, cooler waters (10–150 m, occasionally up to 500 m), adapting to lower temperatures (around 8–10°C) during winter peaks in subtropical-temperate regions.^[34]

Growth and lifespan

Myopsida paralarvae typically hatch at a dorsal mantle length (DML) of 2.5–4 mm, emerging from egg capsules as planktonic larvae adapted for a brief pelagic phase before transitioning to a more benthic or nektonic lifestyle.^[35][12] This initial planktonic stage lasts approximately 1–3 months, during which the larvae exhibit rapid morphological changes, including the development of fins and chromatophores, facilitating their shift toward juvenile forms.^[36] Metamorphosis to the juvenile stage occurs swiftly, often within 4–12 weeks post-hatching, marked by increased swimming capabilities and a reduction in yolk reserves as they begin active predation on zooplankton.^[35] Growth in Myopsida is characterized by high rates, with allometric patterns where tentacles and arms elongate disproportionately after hatching, enhancing foraging efficiency as the mantle and body expand.^[37] For instance, in Loligo vulgaris, paralarvae exhibit exponential growth, achieving relative daily increases of 1.8–2.2% DML during the first 80 days, allowing them to reach 8 mm DML by the end of the planktonic phase.^[36] Overall, coastal species grow rapidly, with L. vulgaris attaining sexual maturity at 20–30 cm ML within about 1 year, influenced by warmer temperatures that accelerate somatic development and reduce time to larger sizes.^[38][39] Sexual maturity in Myopsida is reached relatively early, often at 3–6 months in coastal populations, with size at maturity varying widely from 10 cm ML in smaller species to 50 cm ML in larger ones like Loligo pealeii.^[40][41] Males generally mature slightly earlier and at smaller sizes than females, with environmental factors such as temperature modulating onset; higher temperatures promote faster maturation in subtropical cohorts.^[42] Most Myopsida exhibit semelparity, completing their life cycle in 1–2 years and typically dying shortly after spawning due to senescence.^[43] For example, L. pealeii has a lifespan of 6–12 months, with individuals spawning once before mortality, while L. vulgaris averages 12–15 months overall.^[24][38] Lifespan and growth are highly sensitive to environmental conditions, with elevated temperatures shortening duration but increasing growth velocity in temperate species.^[44]

Evolutionary history

Fossil record

The fossil record of Myopsida is limited, primarily due to the challenges of preserving their soft-bodied structures, with most evidence consisting of durable parts such as gladii, beaks, and statoliths.^[45] Recent 2025 analyses using digital fossil-mining techniques identified over 250 fossil beaks representing 40 squid species, including Myopsida, dating to approximately 100 million years ago and confirming a rapid radiation of decabrachian cephalopods during the Cenomanian stage of the Late Cretaceous.^[45] While Cenomanian gladius-bearing coleoids are known from Lebanese lagerstätten, their affinities are debated and not definitively assigned to Myopsida.^[46] Possible Jurassic precursors are suggested by gladii morphologies in teuthid coleoids from Solnhofen-type deposits, which share structural similarities with later myopsid forms, though direct assignment remains tentative.^[47] Key fossil sites include Eocene strata in North America, such as those along the east coast, where statoliths attributable to Loligo-like forms provide evidence of early diversification within the Loliginidae family.^[48] In the Oligocene of Russia, particularly the Lower Oligocene deposits of the Krasnodar region, a pyritized complete body fossil of a Loligo species represents one of the earliest well-preserved myopsid specimens, revealing details of soft-tissue anatomy.^[49] These occurrences are rare overall, reflecting the order's vulnerability to taphonomic biases against soft-bodied preservation in marine sediments.^[45] Known fossil taxa are predominantly assigned to modern families, such as early representatives of Loliginidae, including species like Loligo clarkei from Eocene horizons, which exhibit statolith morphologies akin to extant forms.^[50] In contrast, no fossils have been identified for the Australiteuthidae, a family restricted to modern, monotypic representation.^[51] Preservation typically involves isolated gladii and rostral beaks, often from exceptional lagerstätten like those in Lebanon and Russia, which suggest myopsids inhabited coastal, nearshore environments similar to many living species.^[46]

Phylogeny

Myopsida is positioned within the superorder Decapodiformes, where molecular phylogenomic analyses using transcriptomic data consistently recover it as part of a well-supported clade comprising Myopsida, Sepiida (cuttlefishes), and Oegopsida (open-eyed squids), which is sister to Sepiolida (bobtail squids).^[52] Within this clade, the majority of analyses support Myopsida + Sepiida as sister to Oegopsida, with high bootstrap support (>90%) from maximum likelihood methods such as RAxML and IQ-TREE.^[52] Earlier molecular studies using multi-gene datasets, including 18S rRNA, 28S rRNA, histone H3, 16S rRNA, and COI, similarly placed Myopsida as closely related to Oegopsida within Decapodiformes, though with varying support for the exact sister-group relationship.^[53] Divergence time estimates based on multiple nuclear genes and fossil calibrations indicate that the split between Myopsida and its closest relatives, such as Oegopsida, occurred approximately 155–210 million years ago during the Jurassic period.^[54] Morphological data corroborate the molecular placement, highlighting shared decapodiform traits such as the characteristic arm arrangement of eight arms plus two tentacles, which distinguish Decapodiformes from Octopodiformes.^[55] Myopsida is considered basal relative to more derived squid orders like Oegopsida, retaining primitive features such as a closed ocular capsule while exhibiting adaptations suited to neritic environments.^[55] Internally, phylogenies derived from mitochondrial (e.g., COI, 12S rRNA, 16S rRNA) and nuclear markers (e.g., 18S rRNA, histone H3) confirm the monophyly of the family Loliginidae within Myopsida, with bootstrap support around 71%.^[56] The smaller family Australiteuthidae serves as the sister group to Loliginidae, supporting a two-family structure for the suborder, as affirmed by phylogenomic approaches from the 2010s onward.^[56] Evolutionary trends in Myopsida reflect an adaptation from ancestral demersal or oceanic forms in early Decapodiformes to specialized coastal and shelf niches, marked by key innovations including the development of a protective corneal membrane over the eyes and the absence of tentacular hooks.^[55] These changes likely facilitated enhanced visual acuity in turbid nearshore waters compared to the open-ocean lifestyles of more derived groups like Oegopsida.^[55]

Human interactions

Economic importance

Myopsida, particularly species within the family Loliginidae, play a significant role in global commercial fisheries, contributing to cephalopod landings that support food security and economic activity in coastal regions. According to FAO data, Loliginid squids accounted for approximately 365,000 tonnes in 2007, representing about 11.3% of the total global squid catch that year, though recent figures indicate common squids (Loligo spp.) at 334,000 tonnes in 2022, forming part of the 543,000 tonnes categorized as various squids (including Loliginidae and Ommastrephidae) that year.^[12][57] Key exploited species include Doryteuthis gahi (Patagonian squid), which sustains a major fishery around the Falkland Islands with catches varying widely—exceeding 100,000 tonnes in 2022 but dropping to around 13,000 tonnes in the 2023 second season, and the fishery closed for 2024 and the 2025 first season due to low biomass—and Doryteuthis opalescens (California market squid), the basis of the largest squid fishery in the United States, yielding over 23,500 tonnes in 2023.^{[58][59][60][25]} These squids are primarily harvested for human consumption, processed into products like calamari, and used as bait in other fisheries, with limited success in aquaculture due to difficulties in rearing larvae and high growth rates. The broader cephalopod sector, dominated by squid, generates substantial economic value, with global exports valued at USD 14.3 billion in 2022, underscoring the market importance of Loliginidae as high-quality, versatile seafood.^[61][57] Regionally, fisheries for Loligo pealeii (longfin inshore squid) in the northwest Atlantic have experienced pressures from intensive harvesting, prompting stock assessments and management to address potential overexploitation since the late 1990s. Sustainable practices in the European Union include minimum landing sizes and effort controls for species like Loligo vulgaris and Loligo forbesii, alongside FAO-recommended international guidelines to maintain stock health, though no total allowable catch quotas are applied to cephalopods.^[12][62] Non-food applications further highlight their economic utility; Loliginid squids are widely used as bait in tuna longline fisheries to attract pelagic species, improving operational efficiency in global operations. In biomedical research, the giant axons of Loligo pealeii have been instrumental since the mid-20th century, enabling foundational studies on nerve conduction and action potentials that advanced neuroscience.^[63][64]

Conservation

Myopsida populations face several anthropogenic threats, with overfishing being the primary concern due to their commercial importance in global fisheries. Species in the family Loliginidae, such as those in the genus Loligo, are heavily targeted for human consumption, leading to localized depletions in heavily fished areas, as seen in recent declines and closures in the Falkland Islands Doryteuthis gahi fishery. Bycatch in trawl fisheries exacerbates this, as juvenile and non-target Myopsida are often discarded, reducing recruitment potential. Climate change further impacts these squids by altering ocean temperatures, which shifts spawning grounds and migration patterns; for instance, warming waters have caused Loligo species to expand southward in the North Sea, potentially disrupting established ecosystems. Pollution, including ocean acidification from CO₂ emissions, adversely affects egg survival rates, as elevated pCO₂ levels hinder embryonic development in species like Doryteuthis opalescens.^{[6][65][66][60]} Conservation status for most Myopsida species remains unassessed or classified as Least Concern by the IUCN Red List, reflecting their wide distributions and high reproductive rates. However, species with restricted ranges, such as Australiteuthis aldrichi in northern Australian waters, are potentially vulnerable to habitat-specific pressures despite their current Least Concern designation. Populations of Loligo forbesii in the northeast Atlantic exhibit fluctuations linked to environmental variability and fishing intensity, though overall they are assessed as Least Concern. Few Myopsida are formally listed under international conventions like CITES.^[67][67] Ongoing conservation measures emphasize sustainable fisheries management. The FAO Code of Conduct for Responsible Fisheries provides a framework for regulating cephalopod harvests, promoting stock assessments and effort controls to prevent overexploitation. Marine protected areas (MPAs) safeguard key spawning habitats; for example, California's Channel Islands MPAs protect approximately 13% of Doryteuthis opalescens spawning grounds through seasonal closures. Research on stock assessments, such as depletion models for English Channel loliginids, informs quota setting and monitoring. Emerging techniques like environmental DNA (eDNA) metabarcoding enable non-invasive detection of rare or elusive species, enhancing biodiversity surveys in cephalopod communities.^[6][68][69] The future outlook for Myopsida is cautiously optimistic with the adoption of sustainable practices, as their short life cycles and high fecundity allow for rapid recovery under reduced fishing pressure. Continued integration of climate modeling into management plans and expanded eDNA monitoring could mitigate emerging threats, supporting stable populations in well-regulated fisheries.^[6][69]