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Apalone
Temporal range: Late Miocene - recent, 12–0 Ma Possible Eocene and Late Cretaceous occurrence
Spiny softshell turtle, Apalone spinifera
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Family: Trionychidae
Subfamily: Trionychinae
Genus: Apalone
Rafinesque, 1832
Species

3 recognized species, see article.

Synonyms

Mesodeca Rafinesque, 1832
Platypeltis Fitzinger, 1835
Glalypeltis Cope, 1860 (ex errore)
Callinia Gray, 1869
Euamyda Stejneger, 1944
Platyrettis Kirsch, 1944 (ex errore)[1]

Apalone is a genus of turtles in the family Trionychidae. The three species of Apalone are native to freshwater habitats in North America; they are the only living softshell turtles from the Americas (other American softshell turtles are only known from fossil remains).[2]

Geographic range

[edit]

Most Apalone species are restricted to the United States, though the range of the spiny softshell, A. spinifera, extends into southern Canada and northern Mexico.

Fossil evidence suggests that Apalone may have reached as far south as Costa Rica during the Pliocene.[2]

Taxonomy

[edit]

Apalone is a fairly new classification, resurrected by Meylan in 1987,[3] assigned to North American species of the genus Trionyx. They are still listed as Trionyx in some texts. (Trionyx now refers specifically to certain softshell species found mainly in Africa.)

Molecular phylogenetic studies generally suggest that Apalone is most closely related to the highly endangered Asian genus Rafetus, with the two genera most likely diverging during the Late Eocene. The ancestral Apalone most likely crossed from Asia into North America via Beringia, taking advantage of the warm climate during the Eocene.[4][5]

Species

[edit]

The following three species are recognized as being valid.[6]

Nota bene: A binomial authority in parentheses indicates that the species was originally described in a genus other than Apalone.

Fossil taxa

[edit]

One definitive fossil species is also known, A. amorense Valdes, Bourque & Vitek, 2017 from the late Miocene (late Clarendonian) of Florida (Alachua Formation).[7]

In addition, two other potential fossil species, generally placed in "Trionyx" sensu lato, may belong to Apalone: Apalone latus (Gilmore, 1919) from the Campanian-aged Dinosaur Park Formation of Alberta, Canada and Apalone leucopotamica (Cope, 1891) from the late Eocene-aged Cypress Hills Formation of Saskatchewan. These two species are much older than any other remains assigned to Apalone, and even predate the presumed divergence of the genus based on molecular phylogenies. However, none of these have been rigorously tested, and the placement of these genera within Apalone may just be a result of homoplasy.[2][7]

Sexual dimorphism

[edit]

Turtles of the genus Apalone exhibit marked sexual dimorphism. In carapace length, females grow to about twice the size of males. In males, the claws on the front feet are longer than those on the back feet, but in females, the claws on the back feet are longer. In males, the stout tail extends well beyond the posterior edge of the carapace, but in females, the relatively thinner tail barely reaches the edge of the carapace.[8]

Behavior

[edit]

Apalone turtles are fast swimmers that chase down their prey in water. They feed mainly on fish. They also like the comfort of sand as their bedding.

References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Apalone

View on Grokipedia
from Grokipedia
Apalone is a of softshell in the family , consisting of three extant species native exclusively to freshwater habitats across . These medium- to large-sized aquatic reptiles are characterized by their distinctive soft, leathery lacking epidermal scutes, elongated tubular snout adapted for , and webbed feet that enable rapid swimming and burrowing into sandy or muddy substrates. The is distinguished from other trionychid genera by morphological features such as reduced osteoderms and specific cranial adaptations, as established in phylogenetic revisions. The three recognized species are the (Apalone ferox), the smooth softshell turtle (Apalone mutica), and the (Apalone spinifera), with the latter exhibiting multiple adapted to regional variations. Apalone ferox is endemic to the , particularly and Georgia, where it inhabits slow-moving rivers and canals. Apalone mutica ranges from the westward to , favoring large rivers with sandy bottoms for burrowing and foraging. Apalone spinifera, the most widespread, extends from southern through the central and to , occupying diverse aquatic environments including lakes, ponds, and coastal bays. Apalone species are primarily carnivorous, preying on fish, crustaceans, insects, and amphibians using their quick strikes and gape-and-suck feeding mechanism facilitated by the tubular snout. They exhibit sexual dimorphism, with females generally larger than males, and engage in elaborate courtship behaviors involving mounting and head bobbing during the breeding season. Nesting occurs on sandy banks, where females lay clutches of 10–30 eggs, though populations face threats from habitat loss, pollution, and collection for the pet trade, leading to varying conservation statuses across species and subspecies.

Physical Description

General Morphology

Apalone turtles, belonging to the genus of North American softshell in the family , exhibit a highly specialized morphology adapted for an aquatic lifestyle, characterized by a streamlined, flattened body that facilitates rapid movement through water and effective on river bottoms. The shell lacks the rigid keratinous scutes typical of most , instead featuring a leathery, flexible covering that reduces weight and enhances hydrodynamic efficiency while allowing for . This skin-like dermal layer over the and plastron promotes , with up to 64% of loss occurring through the skin during submersion. The carapace is ovoid and dorsoventrally flattened, composed of a thin bony plate overlain by tough, leathery skin that provides flexibility at the margins and aids in burrowing into substrates without the hindrance of hard plates. In contrast to hard-shelled turtles, the plastron is also leathery and flexible, with reduced ossification of its underlying bones—such as the highly modified and diminutive entoplastron, epoplastra, and hypoplastra—resulting in a smaller, hingeless structure that exposes the pale, translucent undersurface and minimizes drag during swimming. The prolonged, tubular snout, protruding from a flattened head, functions as a snorkel, enabling the turtle to breathe at the water's surface while keeping its body submerged; it terminates in round nostrils positioned inferiorly, each with a fleshy ridge or flap along the inner margin that helps seal against water ingress during dives. The limbs are adapted for in water, with all four feet fully webbed and equipped with three claws per (and sometimes ) for efficient , steering, and occasional digging. Coloration enhances in aquatic environments, with the dorsal typically olive to brown, often accented by dark spots, streaks, or mottling that blend with muddy substrates; the plastron and ventral surfaces are pale yellow to white, providing contrast for display but remaining inconspicuous when viewed from below. These traits are generally consistent across the genus, though manifests primarily in size differences, with females larger than males.

Size and Sexual Dimorphism

Species of the genus Apalone exhibit considerable variation in adult body size, with carapace lengths ranging from approximately 20 to 70 cm depending on the species and sex. Females generally attain larger sizes than males, reaching up to 50-70 cm in carapace length; for instance, the (Apalone ferox) represents the largest species, with females commonly measuring 28-63 cm (males 15-30 cm) and a record of 73.6 cm. In contrast, males typically measure 11-32 cm, such as 11.4-17.8 cm in Apalone mutica and 12.7-23.5 cm in Apalone spinifera. Sexual dimorphism is pronounced across the genus, with females significantly larger and more robust than males to support production and carrying. Males possess longer, thicker tails to facilitate and more concave plastrons, adaptations that aid in copulation. This size disparity can be as extreme as females being 3-5 times larger than males in A. ferox. Growth in Apalone species follows a pattern of rapid juvenile development that slows after , allowing individuals to reach adult sizes over several years. Males typically mature in 4-5 years at smaller sizes, while females require 12-13 years or longer due to their greater ultimate size. In the wild, reaches 20-30 years, though some A. spinifera may exceed 50 years. Juveniles of Apalone have smaller, more rounded shells compared to the elongated, flattened form of adults, with coloration and patterns resembling mature individuals but often featuring distinct spots or ocelli on the . As they age, the shell elongates and becomes more streamlined, aligning with the leathery structure typical of the .

Taxonomy and Phylogeny

Extant Species

The genus Apalone comprises three extant species of softshell turtles native to North America, all belonging to the family Trionychidae. Established by Rafinesque in 1832 with Apalone hudsonica (now a synonym of A. spinifera) as the type species, the genus was revised by Meylan in 1987 to recognize its monophyly based on morphological and later molecular evidence. Recent genetic studies using mitochondrial and nuclear DNA sequences have confirmed the monophyly of these three species, distinguishing Apalone from other trionychid genera. Apalone ferox, the Florida softshell, is the largest in the , with females reaching a maximum length of up to 67 cm, while males are smaller at 15–32 cm. It features a smooth, leathery lacking spines or tubercles along the anterior margin, and its overall coloration is typically olive to brown with subtle mottling. No are recognized, and the is distinguished from congeners primarily by its greater size and entirely smooth shell texture. Apalone mutica, known as the smooth softshell, has a smooth without trailing spines, similar to A. ferox but smaller, with females attaining a maximum length of 35.6 cm and males up to 17.8 cm. Coloration varies from grayish-olive to tan, often with darker flecks, providing minor differentiation from the more uniformly colored A. ferox. Two are recognized: the nominal A. m. mutica (midland smooth softshell) and A. m. calvata (Gulf smooth softshell), differing slightly in texture and distribution patterns. Apalone spinifera, the spiny softshell, is the most widespread and is characterized by a bearing trailing spine-like along the anterior and posterior edges, contrasting with the smooth shells of the other two . Females grow to a maximum length of 54 cm, with males reaching 30 cm; coloration ranges from olive-brown to gray, sometimes with dark spots or rings that are more pronounced in juveniles and certain . Six are currently recognized, including the nominal A. s. spinifera (eastern spiny softshell) and A. s. aspera (Gulf Coast spiny softshell), which exhibit variations in prominence and pigmentation intensity. Interspecies differences within Apalone are most evident in shell texture—smooth in A. ferox and A. mutica versus spiny in A. spinifera—along with maximum size (A. ferox being the largest) and subtle color variations that aid in identification but are less diagnostic than structural traits.

Fossil Record

The fossil record of the Apalone documents its evolutionary history within the family , with the earliest definitive records of the genus appearing in the of . Fossils attributable to Apalone are known from the mid-Campanian Judith River Group (approximately 80 million years ago), representing some of the oldest evidence for the North American trionychine lineage and indicating early diversification of softshell turtles in freshwater environments of western . These early specimens suggest that Apalone was already distinct from more basal trionychid groups, such as the plastomenines, which dominated North American assemblages during the and . Key extinct taxa within Apalone include A. latus from the () of , , and A. meadei from the of , both of which exhibit shell morphologies transitional between more rigid ancestral forms and the highly flexible carapaces of modern species. Later fossils, such as A. floridensis from the Clarendonian of (approximately 9–10 million years ago), further illustrate the genus's persistence and adaptation in southeastern , with carapaces showing reduced ossification compared to contemporaneous trionychids. These taxa highlight Apalone's role in post-Cretaceous trionychid recovery following global extinction events. Phylogenetically, Apalone is placed within the subfamily Trionychinae of , forming the to the of Asian trionychine genera (such as Pelodiscus and Amyda); molecular clock analyses calibrated with fossils estimate the divergence of Apalone from this Asian around 76 million years ago (), with the family originating in approximately 109 million years ago, likely involving dispersal across . Evolutionary trends in the Apalone lineage include progressive shell flexibility, with early fossils displaying more ossified and rigid structures akin to plastomenines, evolving toward the leathery, reduced and elongate ("snorkel") seen in extant species, adaptations enhancing ambush predation in aquatic habitats. This progression aligns with major radiations during the –Early Eocene and , coinciding with warming climates and expanding freshwater systems.

Distribution and Habitat

Geographic Range

The genus Apalone is endemic to , with its three extant species distributed across freshwater systems from southern to . These turtles occupy a broad latitudinal range, spanning approximately 2,000 km from the in northward to the and southern . No populations have been established outside the , though minor introductions of have occurred within the and , including recent human-assisted expansions of A. spinifera into , , and Washington. Apalone spinifera, the spiny softshell turtle, exhibits the widest distribution within the genus, occurring in over 30 U.S. states and Canadian provinces, including western New York, Pennsylvania, the Dakotas, Montana, Nebraska, Wyoming, North and South Carolina, Georgia, Arizona, and New Mexico, with extensions into Ontario and Quebec in Canada and several Mexican states such as Chihuahua, Coahuila, Tamaulipas, Nuevo León, and along the Rio Grande. Isolated populations exist in areas like Vermont, New Jersey, Colorado, California, Nevada, Utah, Hawaii, and Virginia. In contrast, Apalone ferox, the Florida softshell turtle, has a more restricted range confined to the southeastern United States, primarily in South Carolina, southern Georgia, the Mobile Bay drainage in Alabama, and throughout peninsular and panhandle Florida. Apalone mutica, the smooth softshell turtle, is centered in the Mississippi River basin, ranging across states including Alabama, Arkansas, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, Tennessee, Texas, West Virginia, and Wisconsin, with a disjunct population in the Canadian River drainage of New Mexico. Historically, the genus's range was likely more continuous in northern regions, but slight contractions have occurred at northern edges due to habitat loss and degradation, particularly in the and southern , where northern populations of A. spinifera have declined in New York and A. mutica has been extirpated from Pennsylvania's . Current distributions show stability in core southern and central areas, with no significant overall range shifts reported for the genus. Overlap zones exist where A. spinifera and A. mutica co-occur, notably in central U.S. river systems such as the and drainages in states like , , and .

Habitat Preferences

Apalone , comprising species such as the smooth softshell (A. mutica), spiny softshell (A. spinifera), and softshell (A. ferox), primarily inhabit freshwater aquatic systems including rivers, large streams, lakes, ponds, marshes, and backwaters. These environments feature soft, muddy, or sandy bottoms that facilitate burrowing for concealment and . Species like A. mutica show a strong preference for large rivers with sandy substrates and bars, while A. spinifera and A. ferox tolerate a broader range of slower-flowing or stagnant waters, including reservoirs and drainage ditches. These favor slow-moving or stagnant waters with abundant aquatic vegetation for cover, which supports foraging and predator avoidance. in these habitats often includes low dissolved oxygen levels, to which Apalone species are adapted through a snorkel-like that extends above the substrate or water surface, enabling respiration while buried. They exhibit a preference for warmer waters in the range of 20–30°C, with juveniles selecting temperatures around 25–28°C for optimal activity and growth. Nesting occurs on sandy or gravelly banks, bars, and islands, typically exposed during low- periods to ensure drainage and sun exposure. Females select open, sunny sites near edges, often excavating nests in loose sand or soil up to several meters from the shore. In winter, individuals migrate to deeper pools or channels and overwinter by burrowing into muddy or sandy substrates to avoid freezing temperatures. During summer droughts or low- conditions, Apalone aestivate by embedding in mud, reducing metabolic activity to survive prolonged dry spells.

Ecology and Behavior

Diet and Foraging

Apalone turtles are primarily carnivorous, with diets consisting mainly of aquatic and terrestrial prey such as , , crustaceans (particularly ), mollusks, amphibians, and worms. They occasionally consume plant matter, including , , and , either incidentally during feeding or as minor dietary components. This opportunistic feeding reflects their role as generalist predators in freshwater ecosystems, where they exploit abundant invertebrates and small vertebrates. Foraging in Apalone involves a combination of and active pursuit strategies, enhanced by their streamlined bodies and ability to bury in soft substrates like or . Individuals often conceal themselves just below the surface in shallow , using their long necks for rapid lunges to capture passing prey such as or . They also actively search along the bottom of waterbodies, employing visual and olfactory cues to locate food under or rocks, and may pursue prey by swiftly. This dual approach allows efficient exploitation of both stationary and mobile resources in their aquatic habitats. Ontogenetic shifts in diet occur within the , with juveniles prioritizing smaller like and crustaceans due to their size limitations, while adults shift toward larger prey such as and mollusks. Feeding adaptations include powerful jaws equipped with sharp, cutting edges that enable them to seize and process tough prey, including crushing the shells of mollusks. Seasonal variations in diet and foraging intensity are pronounced, with increased consumption of and during summer when water temperatures rise and prey abundance peaks, supporting heightened metabolic activity. In winter, activity declines as individuals bury in substrates for or estivation, leading to opportunistic scavenging of carrion or reduced feeding on available resources when briefly active.

Reproduction

Apalone turtles exhibit seasonal reproduction, with and mating primarily occurring in spring from April to May, though a secondary period may happen in the fall for some species like the smooth softshell (Apalone mutica). During this time, males actively pursue females in aquatic environments, swimming erratically and chasing rivals, often approaching within centimeters before submerging and resurfacing. Smaller male size relative to females facilitates sex identification but does not appear to directly influence combat; instead, males employ displays such as neck extension and probing under the female's to assess receptivity. Non-receptive females respond aggressively by spinning, charging, or biting, resulting in frequent wounds on males. Nesting follows mating in through summer, typically May to , when gravid females emerge onto sandy banks or bars near to excavate flask-shaped nests using their hind limbs. These nests measure 10-25 cm deep with a narrow neck leading to an egg chamber, and females urinate to moisten the for digging before covering the with packed . Clutch sizes range from 4 to 39 , averaging 12-18, with egg dimensions around 24-32 mm in ; females often produce two to three clutches per season, proportional to body size. Eggs incubate for 60-90 days, depending on environmental conditions, with optimal temperatures of 28-32°C promoting development. Hatchlings emerge measuring 3-5 cm in length, with flexible, olive shells marked by dark dashes, and become immediately independent, dispersing to without . However, they face high mortality rates from predation by raccoons, foxes, birds, and other animals targeting nests and emerging young. Sexual maturity is reached earlier in males at 4-6 years, when they attain about 80-85 mm plastron length, compared to females at 6-9 years and larger sizes around 150-200 mm, reflecting pronounced sexual size dimorphism.

Daily and Social Behavior

Apalone turtles exhibit primarily crepuscular and diurnal activity patterns, with peak movements occurring at dawn and dusk, while nocturnal activity is less frequent. In a study of spiny softshell turtles (Apalone spinifera), approximately 53% of activity was diurnal, 37% crepuscular (16% at dawn and 21% at dusk), and only 10% nocturnal, with overall activity highest during warmer months like and minimal below 7–8°C. To avoid excessive heat, predators, or disturbance during the day, individuals often bury themselves in soft mud or sand substrates, emerging primarily for or basking in shallow waters. Basking typically occurs in the afternoon from to , accounting for about 8–14% of daily time depending on sex, often on sandbars, logs, or water surfaces. Locomotion in Apalone is highly adapted to aquatic environments, where their streamlined bodies and extensively webbed limbs enable rapid, efficient through propulsion via strokes and undulating motions. On , they are more awkward and energy-inefficient, relying on a sprawling that limits speed and distance, though they can achieve bursts of quick movement when necessary, such as during nesting migrations up to 100 m from . Overland travel is rare and typically short, as occurs rapidly outside aquatic habitats, prompting a strong preference for remaining submerged or near edges. Socially, Apalone are largely solitary outside of brief periods, with limited interactions among individuals and no evidence of complex group structures or behaviors. Males may display territorial , particularly during the breeding season in spring, by charging or biting at or unreceptive females, though overt territorial defense of areas is not strongly pronounced in all like the smooth softshell (Apalone mutica). Basking occasionally involves multiple adults of both sexes aggregating loosely on suitable sites, but these are transient and not indicative of social bonding. Defensive behaviors in Apalone emphasize rapid evasion and physical retaliation when escape is impossible. When threatened or handled, individuals often hiss audibly, lunge to bite, and use their claws to scratch, serving as a deterrent against predators or interference. Their primary escape strategy involves quick submersion into water, where they can bury rapidly into the substrate by plunging headfirst and shimmying to conceal themselves, minimizing exposure to aerial or terrestrial threats. For overwintering, turtles enter a state of by burrowing into soft bottom sediments of rivers, lakes, or streams at depths of 0.5–7 m, remaining submerged from October to April to avoid freezing temperatures and anoxic conditions. During extended dry periods or high temperatures in summer, some individuals aestivate similarly by burying in banks or substrates to conserve and reduce metabolic demands, though this is less studied and varies by and availability. Emergence from these periods typically aligns with rising water temperatures around 12°C in spring.

Conservation

Population Status

The genus Apalone comprises three extant species of softshell turtles, all classified as Least Concern on the , indicating that they do not currently face a high risk of globally. Apalone ferox () is stable across its range in the , with no evidence of widespread population decline. Similarly, Apalone mutica (smooth softshell turtle) maintains a stable population trend in the basin and associated drainages. Apalone spinifera (), the most widespread , is also Least Concern overall, though some regional populations, such as those in , show localized declines. While the species level is Least Concern, certain subspecies such as A. s. atra ( Spiny Softshell) are classified as Critically Endangered. Population estimates for Apalone species reveal mixed trends, with declines observed in some portions of their ranges over the past few decades, particularly in fragmented or peripheral habitats, while core areas like the support stable or increasing numbers. For instance, A. spinifera populations in have experienced declines of up to 45% from the mid-1990s to mid-2010s due to low rates, with ongoing declines noted in recent assessments. In contrast, urban and riverine populations in the , such as those along the , exhibit resilience with no substantial overall reductions. Subspecies like A. s. aspera (Gulf Coast spiny softshell) are considered secure regionally, with no global vulnerability assessments. Monitoring efforts for Apalone populations primarily employ mark-recapture techniques to estimate abundance and survival rates, often combined with radio telemetry to track movements and habitat use. These methods have been applied in long-term studies, such as 16-year assessments in urban streams, revealing consistent in stable environments. studies using loci indicate fragmentation in some populations, particularly under anthropogenic influences, with reduced in isolated river segments compared to connected core ranges. Regional variations highlight greater security in northern populations of A. spinifera, where stable nesting and occur in large river systems, versus southern populations facing more pressure from alterations, though overall viability remains adequate. In the Gulf Coast region, A. s. aspera populations are monitored through targeted surveys showing no acute declines.

Threats and Protection

Apalone species face significant threats from anthropogenic activities that alter their aquatic habitats. Habitat loss and degradation, primarily due to river damming and channelization, disrupt natural water flows and reduce suitable sandy nesting and areas essential for their . , including and contaminants, accumulates in their softshells and affects by reducing clutch viability and hatching success in contaminated waters. Overcollection for the pet trade and markets exacerbates population declines, particularly for larger females targeted during nesting seasons. Additional risks include road mortality, as females crossing roads to nest sites are frequently killed by , and collisions with boats in altered waterways. poses emerging threats by altering seasonal water flows, increasing flood events that wash away nests, and shifting temperatures that impact and sex ratios. , such as certain predatory fish, may indirectly compete for resources in fragmented habitats, though this impact varies by region. Conservation measures include international and domestic protections to curb trade and . The (Apalone spinifera) and some subspecies, such as A. s. atra, are listed under Appendix III to monitor and regulate , a status implemented in following U.S. proposals. In Florida, commercial harvest and sale of the Florida softshell (Apalone ferox) are prohibited to prevent . Habitat restoration efforts, such as and projects in regions like and Illinois rivers, aim to recreate nesting sands and stabilize shorelines through vegetation planting and erosion control. Success stories highlight the efficacy of targeted interventions; for instance, in Vermont's protected river systems, enforcement and nest protection have led to over 85% nest success rates at key sites, contributing to local population stabilization. Recovery plans in and emphasize head-starting programs, where eggs are incubated in controlled environments to boost hatchling survival before release. Looking ahead, enhanced genetic management is crucial to maintain diversity and prevent hybridization in fragmented populations, as studies on populations underscore the role of molecular data in guiding translocation and breeding programs. Continued monitoring and adaptive strategies will be essential to address ongoing declines observed in some regions.

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  53. https://www.federalregister.gov/documents/2016/05/24/2016-11201/inclusion-of-four-native-us-freshwater-turtle-species-in-appendix-iii-of-the-convention-on
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  55. https://neiwpcc.org/2022/02/17/lake-champlain-has-a-new-ambassador-the-spiny-softshell-turtle/
  56. https://outdoor.wildlifeillinois.org/articles/smooth-softshell-turtles-a-focal-species-of-the-illinois-wildlife-action-plan
  57. https://www.herpconbio.org/Volume_16/Issue_1/Parren_etal_2021.pdf
  58. https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/recovery-strategies/spiny-softshell-apalone-spinifera-2016-proposed.html
  59. https://complete.bioone.org/journalArticle/Download?urlid=10.2744%252FCCB-1149.1
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