Deep Sea Anglerfish: Bioluminescent Lures and Mating Strategies

The deep sea anglerfish, specifically the suborder Ceratioidei, represents one of the most remarkable examples of evolutionary adaptation in the ocean's midnight zone. These fish use a modified dorsal fin spine tipped with a bioluminescent lure to attract prey in complete darkness, and some species employ a reproductive strategy called sexual parasitism where dwarf males permanently fuse to much larger females. This article examines the biology of the bioluminescent lure, the bacterial symbionts that produce light, and the mating strategies that ensure reproduction in one of Earth's most challenging habitats. The content is intended for students, researchers, life-science professionals, and informed general readers seeking a rigorous overview of current scientific understanding.

Taxonomic Context and Evolutionary History

The anglerfishes belong to the teleost order Lophiiformes, a diverse array of marine fishes ranging from benthic shallow-water dwellers to highly modified deep-sea midwater species. According to a mitogenomic perspective published in BMC Evolutionary Biology, the order comprises 321 living species placed in 68 genera, 18 families, and 5 suborders, with approximately half of the species diversity occupied by deep-sea ceratioids distributed among 11 families [7]. More recent phylogenetic work published in PLOS ONE in 2025 indicates that the anglerfishes and allies, now classified under Lophioidei, include over 400 carnivorous species renowned for their remarkable hunting behavior employing a modified first dorsal-fin spine to lure prey [9].

The evolutionary transition from benthic ancestors to pelagic deep-sea habitats occurred during a period of major global warming 50 to 35 million years ago, according to research published in Current Biology [10]. This transition coincided with the origins of sexual parasitism, which is thought to increase the probability of successful reproduction once a mate is found in the midnight zone, Earth's largest habitat [10]. The same study found that the rapid transition of ancestrally benthic anglerfishes into pelagic habitats was enabled by synergistic trait interactions, including the loss of adaptive immune genes and sexual body size dimorphism [10].

The phylogenetic relationships among anglerfish lineages have been challenging to resolve. The mitogenomic analysis from 2010 recovered monophyly for all higher taxa with the exception of the Thaumatichthyidae, where Lasiognathus was deeply nested within the Oneirodidae [7]. The 2025 total-evidence approach combining ultraconserved elements, mitochondrial DNA sequence data, and morphological characters revealed a monophyletic Lophioidei positioned as the sister group to the Tetraodontoidei within a broader acanthuriform radiation [9]. Goosefishes emerge as the stem anglerfish lineage, forming a sister clade with frogfishes and batfishes, while coffinfishes and deep-sea anglerfishes form another clade [9].

The Bioluminescent Lure

Anatomy of the Esca and Illicium

The bioluminescent lure of deep-sea anglerfish consists of two primary structures. The illicium is the modified first dorsal-fin spine that extends forward from the head, and the esca is the distal bulbous tip that contains the light-producing bacterial symbionts. In nine of the eleven ceratioid families, females possess a bioluminescent lure that contains bacterial symbionts, according to research published in Nature [8]. The bacteria are extracellular and tightly packed in tubules that communicate with the exterior, releasing bacteria into the gut of the host or the surrounding sea water [8].

The morphology of the esca varies considerably among species and is often used as a diagnostic character for species identification. For example, a new species of Himantolophus described from the Andaman Sea differs from other members of the H. albinares-group in having a unique illicial and escal morphology with a simple basimedial and a pair of basilateral filaments on the esca [18]. Similarly, intraspecific variation in escal appendages has been documented in Himantolophus azurlucens, with researchers noting variation in the escal appendages of the second and third recorded specimens of this rare species [19].

Bacterial Symbionts and Light Production

The luminous symbionts of deep-sea anglerfishes are bacteria related to the genus Vibrio but form unique lineages distinct from known luminous bacteria. Phylogenetic analysis of 16S ribosomal RNA gene sequences from light organs showed that anomalopid and ceratioid symbionts are not known luminous bacteria but are new groups related to Vibrio species [8]. These symbionts are characterized by host specificity, deep divergence between symbionts from different genera or families, and possibly parallel divergence of hosts and symbionts [8].

Genomic analysis published in mBio revealed that deep-sea anglerfish symbiont genomes are reduced in size by about 50% compared to free-living relatives [6]. These genomes show a striking convergence of genome reduction and loss of metabolic capabilities with a distinct lineage of obligately host-dependent luminous symbionts. The losses include reductions in amino acid synthesis pathways and abilities to utilize diverse sugars [6]. However, the symbiont genomes have retained a number of categories of genes predicted to be useful only outside the host, such as those involved in chemotaxis and motility, suggesting that they may persist in the environment [6].

The genomes contain very high numbers of pseudogenes and show massive expansions of transposable elements, with transposases accounting for 28 and 31% of coding sequences in the symbiont genomes [6]. Transposon expansions appear to have occurred at different times in each symbiont lineage, indicating either independent evolutions of reduction or symbiont replacement [6]. These results suggest ongoing genomic reduction in extracellular luminous symbionts that is facilitated by transposon proliferation [6].

Environmental Acquisition of Symbionts

A key question in anglerfish biology concerns how these bacterial symbionts are transmitted between generations. Research published in eLife in 2019 addressed this question by analyzing bacteria-host codivergence across six diverse anglerfish genera [4]. Most of the anglerfish species surveyed shared a common species of symbiont, and only one other symbiont species was found, which had a specific relationship with one anglerfish species, Cryptopsaras couesii [4]. Host and symbiont phylogenies lacked congruence, and there was no statistical support for codivergence broadly [4].

The researchers also recovered symbiont-specific gene sequences from water collected near hosts, suggesting environmental persistence of symbionts [4]. Based on these results, they concluded that diverse anglerfishes share symbionts that are acquired from the environment, and that these bacteria have undergone extreme genome reduction although they are not vertically transmitted [4].

Further support for environmental acquisition comes from a study of ceratioid anglerfishes of the Gulf of Mexico published in FEMS Microbiology Ecology [5]. Bioluminescent symbiont amplicon sequence variants were absent from larval ceratioid samples but were found at all depths in the seawater, with highest abundance found at mesopelagic depths [5]. As adults spend the majority of their lives in the meso- and bathypelagic zones, the trend in symbiont abundance is consistent with their life history [5]. These findings support the hypothesis that bioluminescent symbionts are not present throughout host development, and that ceratioids acquire their bioluminescent symbionts from the environment [5].

Biofluorescence in the Esca

Beyond bioluminescence, at least one anglerfish species exhibits biofluorescence. A 2022 study published in the Journal of Fish Biology documented biofluorescence in an oceanic anglerfish, the Pacific footballfish [3]. Green biofluorescence was observed in small spots on the distal surface of the esca [3]. While the wavelength of bioluminescent light is unknown for this species, it is possible that light produced by this species also results in biofluorescent emission that may create a more complex lure for attracting prey or mates [3]. Biofluorescence has been observed in a variety of fishes but is rare in deep-sea environments where light from the surface cannot reach [3].

Sexual Dimorphism and Reproductive Biology

Extreme Size Differences Between Sexes

Deep-sea anglerfishes exhibit one of the most extreme examples of sexual size dimorphism among vertebrates. Females are substantially larger than males, and this dimorphism is linked to the reproductive strategy of sexual parasitism. Research published in Current Biology found that sexual body size dimorphism, variably present in anglerfishes outside the ceratioid radiation, likely promoted their transition into the bathypelagic zone [10].

The extreme size difference means that males and females occupy different ecological niches. Females are active predators with fully developed lures, while males are much smaller and must locate females in the vast darkness of the deep ocean. The olfactory and visual systems of males are often highly developed to detect chemical or visual cues from females.

Sexual Parasitism

Sexual parasitism is the most distinctive reproductive adaptation of ceratioid anglerfishes. Reproduction in certain deep-sea anglerfishes involves the permanent attachment of dwarf males to much larger females and fusion of their tissues leading to the establishment of a shared circulatory system [11]. This unusual phenomenon enables anglerfishes to maximize reproductive success in the vast and deep oceans, where females and males otherwise rarely meet [11].

Ceratioids are the only vertebrates that possess sexual parasitism, wherein males temporarily attach or permanently fuse to females to mate [10]. The Current Biology study showed that the origins of sexual parasitism coincided with the transition of ancestrally benthic anglerfishes into pelagic habitats during a period of major global warming 50 to 35 million years ago [10].

Immune System Adaptations

The permanent fusion of genetically disparate individuals would normally trigger an immune rejection response in vertebrates. However, deep-sea anglerfishes have evolved remarkable immune system modifications that prevent this rejection. An even more surprising phenomenon relates to the observation that joining of genetically disparate male and female anglerfishes does not evoke a strong anti-graft immune rejection response, which occurs in vertebrates following allogeneic parabiosis [11].

Recent studies demonstrated that the evolutionary processes that led to the unique mating strategy of anglerfishes coevolved with genetic changes that resulted in loss of functional genes encoding critical components of the adaptive immune system [11]. These genetic alterations enabled anglerfishes to tolerate the histoincompatible tissue antigens of their mate and prevent the occurrence of reciprocal graft rejection responses [11].

The reconstruction of the evolutionary history of anglerfishes and the loss of immune genes supports that permanently fusing clades have convergently degenerated their adaptive immunity [10]. While the exact mechanisms by which anglerfishes defend themselves against pathogens have not yet been deciphered, it is speculated that during evolution, anglerfishes adopted new immune strategies that compensate for the loss of B and T lymphocyte functions and enable them to resist infection by pathogens [11].

The immune gene loss is not universal across all anglerfish lineages. A survey of the adaptive immune genes of the polka-dot batfish Ogcocephalus cubifrons, representing the suborder Ogcocephaloidei, found that this species has a canonical complement of adaptive immune genes and does not exhibit any of the adaptive immune changes previously identified in monkfish and oceanic anglerfish [12]. The study found that the O. cubifrons genome encodes the core genes needed to mount adaptive T and B cell responses, including those necessary for rearranging and editing antigen receptors, the antigen receptors themselves, as well as the co-receptors, signalling molecules, and antigen presenting molecules needed for B cell and T cell development and activation [12]. Work to date has identified the loss of specific adaptive immune components in two of the five Lophiiformes sub-orders, Lophioidei and Ceratioidei, while no anomalies have been identified in Antennaroidei and Chaunacoidei [12].

At a Glance

Species Diversity and Distribution

Global Distribution Patterns

Deep-sea anglerfishes are distributed throughout the world's oceans, primarily in mesopelagic and bathypelagic zones. The western North Atlantic has been documented to harbor significant ceratioid diversity, with research combining morphology and DNA barcoding to characterize species in this region [17]. The Tropical Eastern Pacific has yielded records of Ceratias uranoscopus, with a specimen collected at a depth of 1000 m off the Pacific coast of Panama representing the first verified occurrence record of this species and genus in that region and an extension of about 7000 km east on the species' previously known distribution [16].

New species continue to be described. A new species of Himantolophus was described from a single specimen collected off the east coast of the northern Andaman and Nicobar Islands, India [18]. Two specimens of Himantolophus azurlucens were collected off the Pacific coast of northern Japan, representing the first records from the western North Pacific and only the second and third records of the species since the original description [19]. The researchers determined that a previous record from the Atlantic was erroneous [19].

Morphological Variation

The morphology of deep-sea anglerfishes varies considerably among species, particularly in the structure of the esca and its appendages. These structures are often species-specific and serve as important taxonomic characters. For example, the new Himantolophus species from the Andaman Sea differs from other members of the H. albinares-group in having a unique illicial and escal morphology with a simple basimedial and a pair of basilateral filaments on the esca [18].

DNA barcoding has revealed remarkably low intraspecific genetic variation of cytochrome c oxidase subunit I within the genus Himantolophus, despite the morphological diversity observed [19]. This suggests that morphological characters, particularly those of the esca, may evolve more rapidly than mitochondrial DNA markers in some lineages.

Practical Assessment Steps for Researchers

For researchers studying deep-sea anglerfish, whether examining museum specimens, planning field collections, or analyzing genetic data, the following assessment framework provides a structured approach.

Step 1: Verify Specimen Identity

Confirm the suborder and family of the specimen using established taxonomic keys. For ceratioids, verify the presence of the illicium and esca in females. Document the morphology of the esca including the presence, number, and arrangement of filaments and appendages. Compare against species descriptions in the primary literature, noting that escal morphology is often diagnostic at the species level [18], [19].

Step 2: Assess Symbiont Presence and Identity

If the specimen has an intact esca, preserve samples for bacterial analysis. Use 16S rDNA sequencing to identify symbionts and compare against known ceratioid symbiont sequences [5]. Note that symbionts may not be present in larval specimens, as environmental acquisition appears to occur later in development [5]. For genomic studies, be aware that symbiont genomes are approximately 50% reduced compared to free-living relatives and contain high numbers of pseudogenes and transposable elements [6].

Step 3: Evaluate Reproductive State

For females, examine the ovaries for maturity and look for evidence of attached males. For males, assess size relative to females and look for evidence of attachment or fusion. Document the degree of tissue fusion if a male is attached, noting whether a shared circulatory system has been established [11].

Step 4: Consider Immune Gene Status

If conducting genomic analyses, survey the adaptive immune gene repertoire. Note that Lophioidei and Ceratioidei have lost specific adaptive immune components, while Antennaroidei, Chaunacoidei, and Ogcocephaloidei retain canonical immune gene complements [12]. The loss of adaptive immune genes is associated with the ability to tolerate tissue fusion in sexually parasitic species [10], [11].

Step 5: Document Environmental Context

Record collection depth, location, and associated environmental data. Note that symbiont abundance in seawater is highest at mesopelagic depths, consistent with the depth distribution of adult ceratioids [5]. Distribution records can contribute to understanding species ranges, as demonstrated by the significant range extension documented for Ceratias uranoscopus in the Tropical Eastern Pacific [16].

Records and Measurements

Morphometric Data

Standard morphometric measurements for anglerfish specimens include standard length, head length, illicial length, and escal dimensions. Meristic data include fin ray counts and vertebral counts. These data are essential for species identification and for documenting intraspecific variation [16], [19].

Genetic Data

DNA barcode sequences, particularly cytochrome c oxidase subunit I, provide valuable data for species identification and for assessing genetic variation within and among species. The genus Himantolophus shows remarkably low intraspecific genetic variation in this marker despite morphological diversity [19].

Symbiont Data

For symbiont studies, record the bacterial species or amplicon sequence variants present, the depth and location of collection, and the life stage of the host. Note that most ceratioid species share a common symbiont species, with only one other symbiont species found in a specific relationship with Cryptopsaras couesii [4].

Collection Records

Document collection events with precise locality data, depth, gear type, and date. The specimen of Ceratias uranoscopus collected in 1973 off Panama remained unstudied for decades before being recognized as a significant range extension, highlighting the importance of preserving and reexamining museum specimens [16].

Common Failure Patterns in Research and Observation

Misidentification of Species

The morphological similarity among some anglerfish species, particularly in the absence of intact escal structures, can lead to misidentification. The erroneous Atlantic record of Himantolophus azurlucens demonstrates that distribution records must be verified against specimen data [19]. Researchers should confirm species identity using both morphological and genetic data when possible.

Overlooking Symbiont Variation

Early assumptions of strict host-symbiont codivergence have been overturned by genomic studies showing that symbionts are environmentally acquired and shared across diverse anglerfish genera [4]. Researchers should not assume that symbiont identity correlates with host taxonomy.

Incomplete Life History Data

The absence of symbionts in larval specimens could be misinterpreted as a lack of symbiosis if researchers do not account for the timing of environmental acquisition [5]. Similarly, the absence of attached males on females does not indicate that sexual parasitism does not occur in a species, as males may be free-living until they encounter a female.

Ignoring Immune System Context

Studies of anglerfish reproduction that do not account for the unique immune system adaptations may misinterpret the absence of graft rejection as a general property of fish immunity. The loss of adaptive immune genes in sexually parasitic lineages is a derived condition, not a general fish trait [10], [11], [12].

Limitations of Current Knowledge

Incomplete Taxonomic Sampling

Many deep-sea anglerfish species are known from only a handful of specimens, and some from a single individual. The new Himantolophus species from the Andaman Sea was described from a single specimen [18], and Himantolophus azurlucens was known from only one specimen for decades before two additional specimens were collected [19]. This limited sampling constrains our understanding of intraspecific variation and geographic distribution.

Gaps in Symbiont Biology

While genomic studies have revealed that ceratioid symbionts have highly reduced genomes and are environmentally acquired, many questions remain. The mechanisms by which larvae acquire symbionts from the environment are not fully understood, and the factors that determine which symbiont species colonize a given host are unclear [4], [5], [6].

Uncertainties in Evolutionary Reconstruction

The evolutionary history of anglerfishes has been challenging to reconstruct due to the lack of fresh material for a majority of the deep-sea ceratioids and the incompleteness of the fossil record across all Lophiiformes [7]. While recent phylogenomic analyses have resolved some relationships, others remain uncertain [9].

Limited Understanding of Immune Compensation

While researchers have documented the loss of adaptive immune genes in sexually parasitic anglerfishes, the mechanisms by which these fish defend themselves against pathogens have not yet been deciphered [11]. It is speculated that anglerfishes adopted new immune strategies that compensate for the loss of B and T lymphocyte functions, but these remain to be characterized [11].

Safety and Ethical Context

Specimen Handling

Researchers working with deep-sea anglerfish specimens should follow institutional guidelines for handling preserved specimens. Many specimens are stored in ethanol and require appropriate personal protective equipment. When working with fresh specimens, follow established protocols for tissue sampling and preservation for genetic analysis.

Field Collection Considerations

Deep-sea collection requires specialized equipment and vessels. Researchers should coordinate with established programs such as the DEEPEND project, which has contributed significantly to understanding deep Gulf of Mexico biodiversity including ceratioid anglerfishes [5]. Collection permits and institutional approvals are required for field work in most jurisdictions.

Ethical Use of Museum Specimens

Museum specimens represent irreplaceable scientific resources. The 1973 specimen of Ceratias uranoscopus from Panama was eventually recognized as a significant range extension, demonstrating the long-term value of preserved specimens [16]. Researchers should minimize destructive sampling and deposit voucher specimens in recognized repositories.

Professional Escalation Criteria

Researchers encountering the following situations should seek specialized expertise:

Taxonomic Uncertainty

If a specimen cannot be confidently identified using available keys and literature, consult a taxonomic specialist in Lophiiformes. The morphological complexity of escal structures and the existence of cryptic species warrant expert confirmation [18], [19].

Symbiont Identification Challenges

If symbiont sequences do not match known ceratioid symbiont lineages, consult with researchers studying bioluminescent symbiosis. The discovery of new symbiont lineages would represent a significant finding given the limited diversity documented to date [4], [8].

Anomalous Distribution Records

If a specimen is collected far outside its known range, verify the identification and document the record carefully. The Ceratias uranoscopus record from Panama extended the known distribution by approximately 7000 km, and such records require rigorous documentation [16].

Genetic Data Interpretation

If genomic analyses reveal unexpected patterns in immune gene content or symbiont genomes, consult with specialists in comparative immunology or microbial genomics. The ongoing genome reduction in symbionts and the convergent loss of adaptive immunity in hosts represent active areas of research [6], [10], [11].

Frequently Asked Questions

What is the function of the anglerfish bioluminescent lure?

The bioluminescent lure, consisting of the illicium and esca, functions primarily to attract prey in the dark waters of the deep sea. The esca contains bacterial symbionts that produce light, and the structure is positioned forward of the mouth to draw prey within striking distance. In at least one species, the Pacific footballfish, the esca also exhibits green biofluorescence that may create a more complex lure for attracting prey or mates [3].

How do anglerfish acquire their bioluminescent symbionts?

Research indicates that ceratioid anglerfishes acquire their bioluminescent symbionts from the environment instead of through vertical transmission from parents. Evidence includes the lack of host-symbiont codivergence across anglerfish genera, the presence of symbiont gene sequences in seawater, and the absence of symbionts in larval specimens [4], [5].

What is sexual parasitism in anglerfish?

Sexual parasitism is a reproductive strategy in which dwarf males permanently attach to and fuse with much larger females, establishing a shared circulatory system. This strategy maximizes reproductive success in the deep ocean where encounters between males and females are rare. Ceratioids are the only vertebrates that possess this adaptation [10], [11].

Why do anglerfish not reject attached males immunologically?

Deep-sea anglerfishes that exhibit permanent fusion have lost functional genes encoding critical components of the adaptive immune system. This genetic change allows them to tolerate the histoincompatible tissue antigens of their mate and prevents graft rejection responses. The loss of adaptive immunity coevolved with the evolution of sexual parasitism [10], [11].

Are all anglerfish species sexually parasitic?

No. Sexual parasitism is found only in the suborder Ceratioidei, the deep-sea anglerfishes. Other anglerfish lineages, including goosefishes, frogfishes, batfishes, and coffinfishes, do not exhibit this reproductive strategy. The polka-dot batfish, for example, has a canonical complement of adaptive immune genes and conventional reproduction [12].

How many species of anglerfish exist?

The order Lophiiformes contains 321 living species placed in 68 genera, 18 families, and 5 suborders according to a 2010 mitogenomic study [7]. More recent phylogenetic work indicates over 400 carnivorous species in the broader Lophioidei group [9]. Approximately half of the species diversity is occupied by deep-sea ceratioids distributed among 11 families [7].

What is the difference between bioluminescence and biofluorescence in anglerfish?

Bioluminescence is the production of light by living organisms, in this case by bacterial symbionts in the esca. Biofluorescence is the absorption of light at one wavelength and re-emission at a longer wavelength. The Pacific footballfish exhibits green biofluorescence in small spots on the distal surface of the esca, which may enhance the complexity of the lure [3].

Where are deep-sea anglerfish found?

Deep-sea anglerfish are distributed throughout the world's oceans in mesopelagic and bathypelagic zones. They have been documented in the western North Atlantic, the Tropical Eastern Pacific, the Andaman Sea, and the western North Pacific, among other regions [16], [17], [18], [19]. Adults spend the majority of their lives in the meso- and bathypelagic zones [5].

Related Articles

• Types Of Mutations
• Types Of Mutations
• Types Of Mutations
• Dna Synthesis Diagram
• Dna Synthesis Diagram

References and Further Reading

• NCBI Literature Resources. National Center for Biotechnology Information.
• PubMed. National Library of Medicine.
• First detection of biofluorescence in a deep-sea anglerfish.. Journal of fish biology, 2022.
• Diverse deep-sea anglerfishes share a genetically reduced luminous symbiont that is acquired from the environment.. eLife, 2019.
• Characterization of the microbiome and bioluminescent symbionts across life stages of Ceratioid Anglerfishes of the Gulf of Mexico.. FEMS microbiology ecology, 2019.
• Ongoing Transposon-Mediated Genome Reduction in the Luminous Bacterial Symbionts of Deep-Sea Ceratioid Anglerfishes.. mBio, 2018.
• Evolutionary history of anglerfishes (Teleostei: Lophiiformes): a mitogenomic perspective.. BMC evolutionary biology, 2010.
• Bioluminescent symbionts of flashlight fishes and deep-sea anglerfishes form unique lineages related to the genus Vibrio.. Nature, 1993.
• A total-evidence phylogenetic approach to understanding the evolution, depth transitions, and body-shape changes in the anglerfishes and allies (Acanthuriformes: Lophioidei).. PloS one, 2025.
• Synergistic innovations enabled the radiation of anglerfishes in the deep open ocean.. 2024.
• Histocompatibility and Reproduction: Lessons from the Anglerfish.. 2022.
• A survey of the adaptive immune genes of the polka-dot batfish Ogcocephalus cubifrons.. 2023.
• Autocatalysis, Autopoiesis, and the Opportunity Cost of Individuality.. 2024.
• How is Bioluminescence Employed By Humans and in Nature. 2021.
• Photobiology of the deep twilight zone and beyond. Other Conferences, 1997.
• First record of the deep-sea anglerfish Ceratias uranoscopus Murray, 1877 (Lophiiformes, Ceratiidae) from the Tropical Eastern Pacific Ocean. Check List, 2024.
• Deep-sea anglerfish (Lophiiformes: Ceratioidei) diversity from the western North Atlantic throughout morphology and DNA barcoding. Marine Biodiversity, 2023.
• A new species of deep-sea anglerfish, genus Himantolophus (Lophiiformes: Himantolophidae) from the Andaman Sea, India.. Zootaxa, 2022.
• First Records of a Rare Deep-sea Anglerfish, Himantolophus azurlucens, from the Western North Pacific, with Comments on the DNA Barcodes of the Genus (Lophiiformes: Himantolophidae). Species Diversity, 2022.
• New Data on the Morphology and Distribution of Two Rare Species of Deep-Sea Anglerfish from the Families Linophrynidae and Himantolophidae. Journal of Ichthyology : A Translation of Voprosy Ikhtiologii, 2020.

This article is educational and does not replace institutional policy, professional advice, or applicable safety and regulatory requirements.