Bony Fishes (Osteichthyes)
Superclass Osteichthyes – bony fishes
Spelling:
Osteichthyes. O,S,T,E ,I,C,H,T,H,Y,E ,S. Osteichthyes.
Taxonomic Rank: Superclass
Key Characteristics: Bony skeleton, operculum covering gills, swim bladder for buoyancy, lepidotrichia (fin rays)
Biological Context: Includes the vast majority of extant fish species. Represents a major evolutionary shift toward ossified internal support, improved respiration, and buoyancy control.
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Class Actinopterygii – ray-finned fishes
Spelling:
Actinopterygii. A,C,T,I,N,O,P,T,E,R,Y,G,I,I. Actinopterygii.
Taxonomic Rank: Class
Key Characteristics: Fins supported by bony rays, single dorsal fin (ancestrally), ganoid, cycloid, or ctenoid scales
Biological Context: Most diverse vertebrate class. Includes both basal and derived lineages. Ray-finned structure allows precise control of movement and fin shape.
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Subclass Cladistia – bichirs and reedfish
Spelling:
Cladistia. C,L,A,D,I,S,T,I,A. Cladistia.
Taxonomic Rank: Subclass
Key Characteristics: Lungs for aerial respiration, ganoid scales, dorsal finlets
Biological Context: Basal actinopterygians. Retain many ancestral traits including spiracles and ventral lungs. Found in African freshwater systems.
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Subclass Chondrostei – sturgeons and paddlefishes
Spelling:
Chondrostei. C,H,O,N,D,R,O,S,T,E,I. Chondrostei.
Taxonomic Rank: Subclass
Key Characteristics: Cartilaginous skeleton (secondarily derived), heterocercal tail, electroreception
Biological Context: Ancient lineage with reduced ossification. Sturgeons are benthic filter feeders; paddlefishes are pelagic planktivores. Vulnerable to habitat loss and overfishing.
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Subclass Neopterygii – modern ray-finned fishes
Spelling:
Neopterygii. N,E,O,P,T,E,R,Y,G,I,I. Neopterygii.
Taxonomic Rank: Subclass
Key Characteristics: Increased jaw mobility, lighter skeleton, homocercal tail, improved fin control
Biological Context: Includes Holostei and Teleostei. Represents a major radiation of actinopterygians with enhanced feeding and swimming capabilities. Marks the transition from ancestral forms to modern bony fishes.
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Division Holostei – gars and bowfin
Spelling:
Holostei. H,O,L,O,S,T,E,I. Holostei
Taxonomic Rank: Division
Key Characteristics: Ganoid or cycloid scales, functional lungs, heterocercal tail (in bowfin), elongated jaws (in gars)
Biological Context: Transitional group between basal actinopterygians and teleosts. Gars are ambush predators with armored scales; bowfin are facultative air breathers. Retain ancestral traits but show increased jaw flexibility and fin mobility.
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Division Teleostei – teleosts
Spelling:
Teleostei. T,E,L,E,O,S,T,E,I. Teleostei.
Taxonomic Rank: Division
Key Characteristics: Mobile premaxilla, homocercal tail, cycloid or ctenoid scales, swim bladder, advanced jaw protrusion
Biological Context: Most diverse vertebrate clade. Teleosts dominate freshwater and marine ecosystems. Innovations in jaw structure and fin control enabled adaptive radiation into nearly every aquatic niche.