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) • • • • 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 • • • • • • 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 • • • • 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 • • • • • 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