KINGDOM ANIMALIA
Phylum Chordata
Class Chondrichthyes
Class Chondrichthyes
 846 species of sharks and rays
 Date to over 400 mya
 Cartilaginous endoskeleton
 Jawed
 Well-develop pectoral/pelvic fins, powefull tail fin
 Skin is rough due to numerous placoid scales
(constantly worn out/replaced)
 The notochord, which is present in the young, is
gradually replaced by cartilage. Chondrichthyes
also lack ribs, so if they left the water, the larger
species's own body weight would crush their
internal organs long before they would suffocate.
 As they do not have bone marrow, red blood
cells are produced in the spleen and special tissue
around the gonads. They are also produced in an
organ called Leydig's Organ which is only found in
cartilaginous fishes, although some do not
possess it. Another unique organ is the epigonal
organ which probably has a role in the immune
system. The subclass Holocephali, which is a very
specialized group, lacks both of these organs.
Class Chondrichthyes
• The evolution of jaws is an example of
evolutionary modification of existing
structures to perform new functions. Jaws are
modified gill arches, and allowed the
exploitation of new roles in the habitats:
predators with powerful jaws. There are two
classes of jawed fish: the cartilaginous fish and
the bony fish.
 They have jaws, lots of teeth, paired fins, and a
cartilage endoskeleton.
 Cartilaginous fish first appeared during the Devonian
Period and expanded in diversity during the
Carboniferous and Permian before nearly disappearing
during the great extinction that occurred near the end
of the Permian.
 A large group of cartilagenous fish still survives today
and is an important part of the marine fauna.
 These fish have five to seven gill slits on both sides of
the pharynx, and lack the gill covers found in bony fish.
 The chondrichthyian body is covered epidermal placoid
(or toothlike) scales. Developmental studies show the
teeth of sharks are enlarged scales.
 The largest sharks are filter feeders, not the predators
of Hollywood movies. Basking and whale sharks eat
tons of crustaceans (small krills, etc.) filtered from the
water.
 Most sharks are fast-swimming, open-sea predators.
The great white shark feeds on dolphins, sea lions and
seals (and people sometimes).
 In other words, anything is WANTS to!
Class Chondrichthyes
 Teeth = enlarge placoid scales
 Teeth form in actively growing
skin areas in mouth just behind
upper/lower jaws; skin grows,
teeth pushed over edge of jaw
and increase in size
 Teeth worn = reabsorbed or lost
 In rays, teeth fuse to form bony
plates
Class Chondrichthyes
 Internal fertilization
facilitated via unique
pelvic claspers on males
 Anamniote eggs
enscapsulated in leathery
case or retained in body
until birth of living young
Class Chondrichthyes
2 informal groups: differ
in body plan and
definition
1. Sharks (353 species)
 Powerful swimmers
 Mid-water dwelling
 Solitary predators
2. Rays (456 species)

Dorsoventrally flattened
enlarged pectoral fin – subject
to waves on muscular
contraction

Bottom-dwelling

eat shelled inverts (crush)
 Rays and skates live on the
ocean floor; their pectoral fins
are enlarged into winglike fins;
they swim slowly. Stingrays
have a venomous spine. The
electric ray family can feed on
fish that have been stunned
with electric shock of over 300
volts. Sawfish rays have a large
anterior "saw" that they use to
slash through schools of fish.
Class Chondrichthyes
 Most marine, some taxa are
estuarine or freshwater
 Range in size (from 20cm to
over 12m)
 Commercially important in
food ,
cosmeticpharmaceutical,
and medical products
 Estimated 771,400 tons of
sharks/rays harvested each
year by humans (while only
30 humans-2.6 tons
harvested by sharks)