Marine Fishes Read Chapter 9 Pages 154- 178
Chordates • All chordates have (at least during some period of their life) • Dorsal nerve cord • Gill slits • Notochord • Post-anal tail • These are the 4 basic characteristics of all chordates.
Bridging the gapChordates w/o backbone • Tunicates • Not fish but chordates • Lancelets: Not a Vertebrate, but a Chordate • Chordate characteristics throughout life- • But no backbone • Subphylum Cephalochordata
The Fishes Note: The term fish refers to a single fish or a group of the same species of fish. Fishes refer to more than one species of fish.
Fish • Structurally simplest living vertebrates • Probably ~30,000 species • At least half of all known vertebrate species are fishes • At least half of all known fishes are marine • First appeared about 500 million years ago and were the first vertebrates • every other vertebrate has ultimately descended from a fish-like ancestor
Three major groups of Fish • Jawless fishes (Agnatha) • Cartilaginous fishes (Chondrichthyes) • Sharks and rays (elasmobranchs) • Ratfishes (chimeras) (Holocephalins) • Bony fishes (Osteichthyes) • Lobe-finned fishes • Ray-finned fishes
Jawless Fishes • Most primitive living fishes • Feed by suction with a round, muscular mouth and rows of teeth • Long, cylindrical body • No paired fins or scales • Lampreys are parasites on other fishes and suck on their blood; hagfish typically feed on dead animals
Cartilaginous Fishes • Sharks, rays, skates, chimeras (ratfishes) • Skeleton is made of cartilage, which is lighter and more flexible than bone • Moveable jaws with well-developed teeth • Paired lateral fins for efficient swimming • Rough skin due to placoidscales
Sharks • In some form, sharks have been around for about 400 million years. • Even before dinosaurs roamed the earth, sharks hunted through the oceans! They're such good survivors that they've had little need to evolve in the last 150 million years. • Scientific Information: Sharks belong to the class of fish, Chondrichthyes. • More on Sharks to come in a later lecture!!!
Skates Oviparous (lay eggs) Mermaids purse Do not have barbs, have thorns on their dorsal area or tails Placement and number vary Small teeth Rays Viviparous (bare Live young) Have Barbs Above tail In general, larger Tail almost 2x’s as long as body Plate Like Teeth Skates vs. Rays
Skates and Rays • Flattened body • Large pectoral fins
Rat Fishes (Chimeras) • Bizarre-looking, primarily deep-sea, cartilaginous fishes • Have only one pair of gill slits instead of 5-7 • Have a long rat-like tail • Feed on crustaceans and molluscs
Cartilaginous skeleton made of cartilage possess movable jaws mostly with powerful teeth. mouth is located ventrally (under the head). presence of paired lateral fins allows for efficient swimming. skin is covered with small scales that have the same composition as teeth. Bony Skeleton made (at least partially) of bone Thin, flexible, overlapping scales along the body A flap of bony plates and tissue known as the gill cover, or operculum, that protects the gills Protruding jaws with more freedom of movement than cartilaginous fish The presence of a swim bladder helps buoyancy and compensates for the relatively heavier bony skeleton Highly maneuverable fins Cartilaginous vs. Bony Fish
Extinct No More • Subclass Sarcopterygii-Once known only for fossils and thought to be extinct for 60 million years-Named Latimeriachalumnae • Preserved specimen of the Coelacanth is located in the HMNH
Next Up Fish Form and Function