Marine Fishes
Chapter 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
Protochordates
 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
Jawless Fishes
 Jawless Fishes – parasitic,
jawless, retains larval
notochord (no true
backbone), and lack true
scales
Warm Up 1: What am I ?
Jawless Fishes – modern diversity
Hagfish
Lamprey
Jawless Fishes – modern diversity
lampreys
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 scales
Placoid scales of the Broadnose Sevengill Shark.
Characteristics of Cartilaginous Fishes
 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.
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
• 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
Shark Teeth
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
Megachasma pelagios
Squaliolus laticaudus
Pygmy shark
megamouth shark
Shark Diversity
Whale shark
Goblin shark
Mitsukurina owstoni
Rhincodon typus
Nearly 850 spp. of sharks, 350 exhibit typical
body morphology.
Variations on this theme are common.
Mako
Great White
Isurus oxyrinchus
Carchariniformes – basking sharks,
filter feeder
Great White, Carcharodon carcharias
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 Shark
Will 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
• Largest sharks AND largest
fish
• Up to 46 feet long and 15
tons
• Filter feeders – eat mostly
plankton and krill
Whale Sharks
Shark Diversity
HW: Draw the external Anatomy of a SHARK
Special Attributes of Rays
 Superorder Batidoidimorpha of subclass Elasmobranchii consists of the
rays, 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