Marine Fishes
Chapter 8
Vertebrates
• Share characteristics with protochordates
(invert chordates)
– Single, hollow nerve cord
– Pharyngeal slits
– Notochord (between nerve cord and gut)
– Post-anal tail
• Different because they have a vertebral
column (spine)
– Protects nerve chord
– Bilateral symmetry
Types of Fishes
• Oldest and simplest vertebrates
• Most abundant
– About half of species
– 15,300 marine
• 3 major groups
– Agnatha (jawless fishes)
– Chondrichthyes (cartilaginous fishes)
– Osteichthyes (bony fishes)
Jawless Fishes (Class Agnatha)
• Lack jaw
– Feed by suction with a round mouth and rows
of teeth
• Body is cylindrical and
elongated
• Lack paired fins and
scales
• Lack true vertebrae
Classes of Jawless Fish
Hagfishes
• AKA slime eels
Lampreys
• Found in temperate regions
– Produce slimy mucus
• Breed in freshwater; marine
• Feed on dead or dying fish
as adults
• Live in burrows in cold
• Attach to other fish and suck
water
on blood
• ~20 species known
• ~30 species known
Eww… slime
Cartilaginous Fishes
(Class Chondrichthyes)
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Skeleton made of cartilage
Movable jaws with teeth
Paired lateral fins
Rough, sandpaper-like skin
– Placoid scales: pointed tip directed backward
• Sharks, rays, skates, and ratfishes
Shark Body
• Adapted for fast
• Paired pectoral fins
swimming and predatory
– Large and pointed
feeding
• 5-7 gill slits
• Fusiform: spindle-shaped • Rows of sharp, triangular
body
teeth
• Caudal fin: tail fin;
– Rows are replaced with
back row
powerful
– Heterocercal: upper lobe
longer than lower
• 2 Dorsal fins
Exceptions to the Rules
• ~ 350 living species
• Hammerhead
– Wide head; improves sensory perception
• Sawshark
– Long, flattened blade armed with teeth
• Spined pygmy shark
– Only 10 in long
• Whale Shark (largest fish)
– Up to 60 ft long; over 40 ft is rare
– Filter feeders (plankton), not hunters
Planet Earth Great White Attack
Manta Rays and Whale Shark
Rays and Skates
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450 – 550 species
Dorsoventrally flattened bodies
Demersal: live on the bottom
Gill slits underneath (5)
Eyes on the top of head
Sawfish
– Ventral slits so they are grouped with rays
Stingrays
Stingrays
• Whip-like tail with spines
• Poison glands
• Feed on clams, crabs,
fish, animals in sediment
• Damage shellfish beds
• Teeth are modified
grinding plates
Electric Rays
• Special organs that
produce electricity on
each side of head
• Shocks up to 200 volts
Manta Rays
• Fly through water
• Feed at bottom
or midwater
• Largest Manta =
23 ft
Skates
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Similar in appearance and feeding
Lack spines and whip-like tail
Some have electric organs
Lay egg cases
– Rays give birth to live young
Ratfishes
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Chimaeras
Mostly deep-water & strange-looking
One pair of gill slits covered with skin
Rat-like tail
Feed on crustaceans
and molluscs
Bony Fishes (Osteichthyes)
• ~23,000 species
– 96% of all fishes
– ½ of all vertebrates
– More than ½ live in the ocean
Skeleton Composition
• Skeleton of some bone
• Cycloid or ctenoid scales:
thin, flexible, and overlapping
– Cycloid: smooth
– Ctenoid: tiny spines along borders
– Scales made of bone and covered with skin and
mucus
– Some do not have bones
• Operculum: flap of bony plates that protects
gills
Fins
• Homocercal: lobes of caudal fin are the
same size
– Sharks are heterocercal
• Fin rays consist of membranes supported
by bony spines
– Act as rudders or used as protection
– Added maneuverability
– Sharks have stiff, fleshy fins
Mouths
• Mouth is terminal
(anterior end)
– Cartilaginous have
ventral mouths
• Jaws are protrusible
• More freedom of
movement
• Teeth can be replaced
but are not in rows
Buoyancy
• Swim bladder: gas-filled sac to adjust
buoyancy
– Cartilaginous fish have oily livers