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Marine FishesChapter 12
12.1 Protochordates and Jawless Fishes
Chordates – animals having dorsal nerve cord, notochord, and pharyngeal gill slits at some stage of
development; includes all protochordates and vertebrates.
Protochordates –primitive invertebrate chordates: tunicate, lancelet, acorn worm
Vertebrates – higher chordates; all have a skeleton, back bone, skull, and brain
Tunicates – sessile protochordates; larval stage has primitive chordate traits
Lancelet – fishlike protochordate; adult retains all three primitive chordate traits
Acorn worm – wormlike protochordate; adults has dorsal nerve cord and gill slits
Protochordates
Jawless Fishes
Jawless Fishes – parasitic, jawless, retains larval notochord (no true backbone), and lack true scales
Warm Up 1: What am I ?
Hagfish
Lamprey
Jawless Fishes – modern diversity
lampreys
Jawless Fishes – modern diversity
Class Chondrichthyes
Cartilaginous fishes
12.2 Cartilaginous Fishes
Cartilage – flexible connective tissue, composed of cells and protein
Cartilaginous fishes characteristics: – have cartilage skeleton, gill slits, placoid scales,
Examples include: sharks, skates, and rays
Can vary greatly in external appearance.
They do not increase in size as the fish grows, instead new scales are added. Placoid scales are often referred to as denticles.
Placoid scales consist of a flattened rectangular base plate which is embedded in the fish, and variously developed structures, such as spines, which project posteriorly on the surface. The spines give many species a rough texture.
Placoid scalesPlacoid scales of the Broadnose Sevengill Shark.
Gill slits – in cartilaginous fish, visible opening for breathing Spiracles - in cartilaginous fish, breathing holes on dorsal side
behind each eye Sharks have a sense of smell that detect incredibly
diluted substances. Sharks have a “conveyor belt” of multiple rows of teeth- They
swing into place as old teeth wear out and fall away. Both have lateral lines – lines of sensory hair along the length of
the body that detect water motion and vibrations.
Some have electroreception – the ability to sense minute electricity created by muscles and nerves.
Sharks and rays have organs called ampullae of Lorenzini which you can see as visible pits near their snouts used to detect the electrical current.
Characteristics of Cartilaginous Fishes
Structures and Behavior of Sharks
• Lateral line organ – line of sensitive sound receptors along each side of a fish’s body
(See picture )
• Ampullae of Lorenzini –in shark, nerve receptors in tiny pores in snout, which detect electric fields of other animals
Jaws of Sharks• Six to 20 rows of replaceable
teeth which face backwards to prevent the escape of prey
Shark Teeth• Bites prey, then tears it apart by tossing head back and forth
• Rows of backup teeth replace lost ones
• May grow and use 20,000 teeth in a lifetime
Reproduction Sharks and rays produce fewer, but
more mature offspring.
The male deposits sperm in the female via a pair of organs called claspers (pair of organs usually between pelvic fins that transfer sperm)
• eggs are laid (like birds) • eggs hatch inside the mother and then are
born • Shark pups grow inside the mother (like
humans)
• Other sharks and skates have external developments, development is within an egg casing called “mermaid’s purse”. Can take more than a year to develop.
Figure 8.26
megamouth shark
Megachasma pelagios
Pygmy shark
Squaliolus laticaudus
Rhincodon typus
Whale shark
Mitsukurina owstoni
Goblin shark
Shark Diversity
Nearly 850 spp. of sharks, 350 exhibit typical body morphology.
Variations on this theme are common.
Great White, Carcharodon carcharias
MakoGreat White
Isurus oxyrinchus
Carchariniformes – basking sharks, filter feeder
Great White Shark• Up to 3000 teeth at one time
• Up to 23 feet in length
• Feed on sharks, sea lions, fish, rays, whales
Tiger SharkWill eat fish, turtles, crabs, clams, mammals, sea birds, and other sharks.
Hammerhead
Shark• From 12 – 20 feet long
• Unlike other sharks, they form schools
Mako Shark• The fastest shark, and among the fastest fish
• Feed on schooling fish
Bull Shark
• Aggressive and swims in shallow water
• Swims close to shore and can live in fresh water rivers and lakes for awhile
Whale Sharks• Largest sharks AND largest
fish
• Up to 46 feet long and 15 tons
• Filter feeders – eat mostly plankton and krill
Shark Diversity
HW: Draw the external Anatomy of a SHARK
Special Attributes of Rays
Superorder Batidoidimorpha of subclass Elasmobranchii consists of therays, which includes skates and guitarfish. Ray anatomy is well suited to life on sandy
bottoms or midwater. Specially adapted to life in midwater are
the eagle ray and manta ray. Pectoral fins have become “wings” that
stretch forward over the gills and are fused to the sides of the head.
Shoulder girdles are flattened and many bones are fused together for rigidity.
No longer need a tail for swimming, the tail has become a defensive whip in some species.
Rays literally fly through the water. The largest rays are mantas with wingspans
exceeding 8 meters (26 feet). Like the largest shark, the mantas feed on plankton.
Skates
Skates
• Stocky tail with no stinging spine
• Two lobes on pelvic fin
• Thorn-like scales on midline of back and tail
Rays
• long tail with stinging spine at midway
• Single lobes on pelvic fin
• No thorn-like scales
Skates and rays spend most of their lives near (on) the
ocean floor eating molluscs, squid, and small fish.
Yellow stingray, Urolophus jamaicensis
Blue spotted ray, Taeniura lymma
Skates (order Rajiformes)
•pelvic fin divided into two lobes•tail relatively stocky, no spine
Rays (order Myliobatiformes)
•each pelvic fin with one lobe•tail relatively slender to whip-like spine