Actinopterygii: The Ray-Finned Fish
- Created by: ValentineDevil
- Created on: 25-02-19 16:03
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- Actinopterygii: The Ray-Finned Fish
- The largest group of vertebrates
- Skeleton of paired fins is formed from many small bones (fin rays) in a fan-like arrangement
- Supported at the bases of fins by parallel rows of bones called radials
- Actinopterygian Skeleton Components
- Ural region consists of highly modified vertebral elements and arches supporting the caudal fin rays
- Epicentrals or dorsal ribs are membrane bones without homologs in tetrapods
- Ural region consists of highly modified vertebral elements and arches supporting the caudal fin rays
- Skeletal support among Osteichthyans
- Last common ancestor of bony fishes had polybasal condition where proximal skeletal elements of the fin articulated with the shoulder girdle
- Pectoral fin consisted of anterior propterygium, the middle mesoterygium and the posterior metapterygium
- Lineage leading to tetrapods, the propterygium and mesoterygium were lost along with dermal fin rays; new long bones that were articulated end on end were added along the main axis (PD axis) of the metapterygium, ultimately forming the limb
- Teleosts, which are the largest group of ray-finned fish, and in some holosteans, such as the gar
- Metapterygium was lost while the propterygium and mesopterygium were retained
- No teleost shows end-on-end articulation of long bones in the pectoral fin
- Metapterygium was lost while the propterygium and mesopterygium were retained
- Last common ancestor of bony fishes had polybasal condition where proximal skeletal elements of the fin articulated with the shoulder girdle
- Primitively: Heterocercal tails (upper and lower fin lobes differ in length)
- Derived: increasing trend of tail symmetry- homocercal tail
- Fewer bones often fused up into larger elements as in triggerfish
- Net effect: skeletal elements associated with caudal fin tend to become increasingly specialised
- Become physically consolidated at the end of the tail, with clear distinction between elements associated with the tail's upper and lower lobes
- Net effect: skeletal elements associated with caudal fin tend to become increasingly specialised
- Fewer bones often fused up into larger elements as in triggerfish
- Prim: numerous bones in tail, as in salmons
- Derived: increasing trend of tail symmetry- homocercal tail
- Dorsal fin
- Prim: single fin un-subdivided
- Derived: two separate portions; usually anterior portions carries sturdy rays modified as rigid spines; posterior portion carries flexible and soft rays
- Some have an additional adipose fin posterior to the dorsal fin (small, soft and fleshy)
- Fin spines
- Prim: 0 (rays soft, flexible as in herrings)
- Der: development of hollow, robust spines, which are modified fin rays
- Various fins are often associated with poison glands
- Skull ornamentation
- Prim: Smooth-surfaced skull bones
- Der: crests, ridges, tubercles and spikes
- Jaw mechanics
- Prim: simple jaws (gar); upper jaw bones connected to skull
- Der: connection between cheekbone and posterior bone of maxilla lost
- Articulations and levers- complex movements
- Body shape
- Prim: slender, elongate, large adult sizes, fusiform heads, bodies and tails, long guts, high vertebral count (50-75), no fin spines, fins other than pectorals placed posteriorly
- Der: body highly variable, small adult body sizes, short and deep heads and bodies, short guts, low vet count (24), fins other than pectorals placed far forward, fin spines present
- Rover predators (salmon, tuna, bass): fusiform bodies, pointed heads, terminal mouths, narrow tail fins, forked tail fins, actively chasing prey, continuous swimming
- Ambush predators (pike, barracuda and needlefish): streamlined bodies, flat heads. large toothed mouths, narrow tail base, large tail fins, dorsal and anal fins situated far back, surprising prey, fast swimming
- Surface-orientated dwellers (halfbreak, killifish, and flyingfish): small bodies, flat heads, dorsally directed mouths, large often dorsally facing eyes
- Bottom dwellers (flatfish, sucker, anglerfish): flat/compressed bodies, very small subterminal mouths or very large gaping mouths, small eyes
- Reef dwellers (angelfish, surgeonfish, mandarinfish): short, compressed bodies, pectoral fins high on body, pelvic fins below pectoral fins, long dorsal and anal fins, large eyes, small mouths, short snouts
- Agile hunters (loach, eel, gunnel): very long bodies, stout heads, tapering or rounded tails, very long dorsal and anal fins running the length of the body, paired fins small or absent
- Skeleton of paired fins is formed from many small bones (fin rays) in a fan-like arrangement
- Neopterygii
- Most extant species
- Lepisosteriformes
- Gars
- Most surface periodically to take a gulp of air, doing so more frequently in stagnant or warm water (O2 conc low)
- Freshwater; brackish water; occasionally marine
- Heavily vascularized swim bladders that can effectively function as lungs
- Ganoid scales
- Elongate and very slender jaws armed with small needle-like teeth (act as simple opposable devices)
- Heterocercal tails; dorsal fin close to tail
- Gars
- Amiiformes
- Bowfin
- Long, undulating dorsal fin consisting of 145 to 250 rays, running from middle of the back to base of tail
- Ambush, predator, freshwater, near bottom of vegetated sloughs, lowland rivers and lakes, swamps and backwater area
- Swim bladder that serves to maintain buoyancy
- Allows them to breathe air by means of a small pneumatic duct that connects foregut to bladder; can also gulp air
- Bowfin
- Teleostei
- Largest radiation of verts.
- Pinnacle of ray-finned fish diversity
- Diverse habitats (poles to equator) various dentition inside oropharyngeal cavity
- Body sizes, shapes and proportions vary greatly
- Pinnacle of ray-finned fish diversity
- Movable premaxilla in upper jaw; variable degrees of jaw mobility
- Scales highly differentiated
- Reproductive strategies and biology among most complex in animal kingdom
- Perch-like teleosts: ctenoid (toothed) scales
- Largest radiation of verts.
- Basal Actinopterygians
- Very few extant species
- Polypteriformes
- Bichirs & reedfish
- Series of dorsal small fins (7-18)
- Have bifid (double edged) tips); only fins with spines; rest are soft rays
- Elongate fish
- Thick, ganoid scales
- Jaws: simple and operate as scissor-like devices
- Fleshy pectoral fins
- Slit-like spiracles on the top of their heads that are used to breathe air
- Paired ventral lungs (left lung shorter than the right)
- 4 pairs of gill arches
- Chondrostei
- Sturgeons and paddlefish
- Sturgeons: 5 rows of longitudinal bony scutes; bodies spindle-shaped; flattened snouts
- Paddlefish: the sword-shaped snout and head up to the level of the operculum are extensively covered in sensory ampullae
- Little degree of ossification
- Retain a considerable amount of cartilage in their skeletons
- Retain a spiracle
- Heterocercal tail
- Scale-less
- Sturgeons and paddlefish
- The largest group of vertebrates
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