The Fishes Vertebrate Success in Water Evolutionary Perspective
The Fishes Vertebrate Success in Water
Evolutionary Perspective • Primitive Fishes can be traced back 530 million years ago • Hagfish are the most primitive fishes known • Aquatic environments have selected for certain adaptations including streamlining for moving thru a dense medium • Ability to exchange gases with water or air • Regulating buoyancy and electrolytes and detecting environmental changes
Infraphylum Hyperotreti • Hagfish are divided into 20 species • Heads supported by cartilage bars and brains enclosed by a fibrous sheath • They lack vertebrae but retain a notochord as the axial supportive structure • Four pairs of sensory tentacles surround the mouth • Ventrolateral slime glands produce copious amounts of slime • They feed on invertebrates and dead fish
Hagfish
Hagfish Mouth
Hagfish Slime
Infraphylum Vertebrata • Ostracoderms are extinct agnathans • Sluggish swimmers, Had bony armor as their only defense • Bottom dwellers, filter feeders either filtering water or muddy sediment • Some ostracoderms used bony plates around the mouth as jaws to crack mollusc shells or arthropod exoskeletons
Ostracoderms
Lampreys • Agnathans (jawless) Fish who live in fresh and marine environments in temperate regions • Most adult lampreys prey on other fish, larva are filter feeders • Mouth is sucker like with lips used for attaching • Epidermal teeth line the mouth and tongue like structure • Attach to prey with teeth and lips, tongue rasps away scales • Anticoagulant produced in saliva, feeds on blood
Lamprey
Lamprey Mouth
Lamprey
Gnathstome, Jawed Vertebrates • Jaws evolved from the anterior pair of gill arches • Permitted more efficient gill ventilation • Allowed the capture and ingestion of more food sources • Streamlining and paired fins became more important with increased activity • Paired pectoral and pelvic fins reduced the tendency to roll during swimming
Class Chondricthyes • Cartilage skeleton fish, includes sharks, rays, skates and ratfishes (chimeras) • Most are carnivores and scavengers, most are marine • Placoid scales • Elasmobranch subclass (820 species) sharks, rays, skates started in early Devonian 375 mya • Tough skin with placoid scales pointing posteriorly aids in reducing friction
Chondricthyes
Basking Shark
Sting Ray
Hammer. Head
Skate
Great White
Rat Fish
Shark Feeding • Shark teeth are modified placoid scales • The row of teeth on the outer edge is backed up by rows of teeth attached to a ligamentous band • As the outer teeth wear or break off, they are replaced • Replacement is rapid, 7 -8 days • Teeth may be adapted for shearing flesh, Top teeth cut while bottom teeth hold • Teeth may be modified for breaking shells of molluscs
Placoid Scales
Shark Senses • Ampullae of Lorenzini- Sensory pits on snout of sharks, able to detect very small electrical charges, heart beating, nerve impulse • Lateral line- detects vibrations in the water, any movement or change in water pressure around the shark • Nostrils- widely spaced on both sides of head, nostril is u shaped, not used for breathing • Eye sight- Excellent, dark eyes to absorb maximum light, nictitating membrane cover
Ampullae of Lorenzini
Ampullae of Lorenzini Structure
Lateral Line
Lateral Line System
Nictitating Membrane
Rays, Skates and Ratfish • Rays and Skates are specialized for living on the ocean floor by expanding the pectoral fins • Some have venomous spine at base of tail used for defense • Many have camoflaged their dorsal surface to blend in with the bottom • Ratfish have a single gill cover (operculum) an enlarged head with teeth shaped for crushing shells
Sting Ray Barb
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