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