Class Chondricthyes
chimaeras, sharks, rays
• The cartilaginous
fishes
• Most primitive
living vertebrates
that have:
– complete vertebra
– movable jaws
– paired appendages
Chondricthyes
• Most are
predacious,
some such as
the whale
shark is a filter
feeder.
• None have a
swim bladder
– adapted to
bottom
dwelling
– Or predators
in water
column
Chondricthyes
characteristics
• Placoid scales- scales with spiny
points
– are modified anterior to form
replaceable rows of teeth- resemble
teeth of higher vertebrates
– originate from same tissues as teeth
• Other types of scales include:
– primitive bony fishes- Ganoid Scales
– more advanced bony fishes
• Ctenoid scales• Cycloid scales
Chondricthyes
characteristics
• Paired pectoral
and pelvic fins;
• - pelvic fins in
males modified as
"claspers"
• two median
dorsal fins
Chondricthyes
characteristics
• Types of tails in fishes:
– heterocercal tail- most
primitive form; spinal
column turns up
(dorsad) in fin
– diphycercal tail- spinal
column goes straight
into fin
– homocercal tail- fin
located behind spinal
column
Chondricthyes
• Nostrils (nares)• - not connected to
mouth cavity;
• - have two nasal sacs.
• Spiral valve in
intestine;
• - increases surface
area & efficiency of
digestion.
• Notochord persists
• Heart is two
chambered;
• - atrium & ventricle
characteristics
Chondricthyes
characteristics
• respiration done by 5-7
pairs of gills
• No swim bladder or lung.
• Fairly well developed
brain;
– with 10 pairs of cranial
nerves;
– well developed olfactory
bulbs
Chondricthyes
characteristics
•
•
•
•
Sexes separate;
gonads paired;
have a cloaca;
development one of three types:
– oviparous - i.e., lay eggs
– ovoviviparous- eggs retained in uterus without
attachment to female
– viviparous- eggs attach and get nutrients directly from
female.
• Some sharks possess uteri with very primitive
placentas
Chondricthyes
characteristics
• Three types of kidneys in vertebrates:
– pronephritic kidney: functional kidney of adult
hagfishes,
• and the embryos of some higher vertebrates
– mesonephritic kidney: functional kidney of sharks and
bony fishes;
• collecting duct is the Wolffian Duct, also carry sperm.
– metanephritic kidney: functional kidney of birds
reptiles and mammals;
• is drained by a ureter.
Chondricthyes
characteristics
• Lateral line
system;
– vibrations and
currents in water
• Ampullae of
Lorenzini
– Electromagnetic
forces
Chondricthyes
characteristics
• Digestive tract well
developed:
• - mouth
- pharynx
- esophagus
- stomach
- liver
- pancreas
- intestine
- spiral valve
• rectal gland– functions in regulating salt
content of blood
Chondricthyes
• Ancestor of these fishes
evolved in freshwater
– Sea water is
hyperosmotic (i.e., salt
conc. of blood less than
that of seawater)
• so they have a problem
of losing water from
there tissues.
• to prevent water loss they
retain nitrogenous wastes in
blood;
– this elevates salt conc. in
blood to be slightly higher
than sea water,
– and therefore they will not
lose water passively;
– rectal gland helps keep this
balance
characteristics
Chondricthyes
characteristics
• Features that are more advanced than
Agnathans (Cyclostomates)
–
–
–
–
–
–
Scales
2 pairs of lateral fins
moveable jaws
enamel covered teeth
3 semicircular canals (inner ear)- agnathans had two
paired reproductive organs and ducts
Chondricthyes
characteristics
• Features that make them more primitive
than boney fishes:
–
–
–
–
–
Cartilage
placoid scales
separate gill clefts
spiracle to pharynx
no air bladder
Chondricthyes
characteristics
• Interesting trivia about sharks
– Have very large livers
• 20% of body weight can be liver oil- called
squalene;
– use as fuel for long term swimming or cruising.
– Squalene important commercially in Japan as a cosmetic
and aphrodisiac.