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Unit 6: Marine Biology
Section 1: Introduction to Chordates, Fishes,Chondrichthyes
Phylum
Chordata
Subphylum
Urochordata
Subphylum
Cephalochordata
Ex: tunicates
sea squirts
salps
Ex: lancelets
Class
Agnatha
Jawless
fish
Class
Chondrichthyes
cartilaginous
fish
Class
Osteichthyes
bony fish
Subphylum
Vertebrata
Class
Class
Reptilia
Aves
sea turtles sea birds
sea snakes
Class
Mammalia
whales, dolphins
seals, otters, dugongs
I Phylum Chordata
A. Major Characteristics
1. a single , tubular nerve cord running along the dorsal side of
the animal
a. becomes spinal cord in vertebrates
2. gill or pharyngeal slits at some point in time in the life of
the animal
3. a dorsal notocord or flexible rod for support that lies between the
nerve cord and the gut
a. replaced by a backbone in vertebrates
II Fishes
A. Important Points
1. ~ 24,000 species making up 1/2 of all the vertebrates on
earth
2. ~ 58% are marine
3. most economically important marine organism - food,
variety of products, sport, aquaria, tourism, etc. . .
4. thought to be the simplest/oldest of all living invertebrates
5. Ichthyology - study of fish
B. Common Groups of Fishes
1. jawless fishes - Agnatha
a. Hagfishes
b. Lampreys
2. cartilaginous fishes - Chondrichthyes
a. sharks
b. skates, rays
3. bony fishes – Osteichthyes
Student Notes:
III Agnatha
A. Major Characteristics
1. “jawless” fish
2. < 50 sps
3. lack jaws/no paired appendages
4. thick snake-like bodies & flattened tails
IV Chondrichthyes
A. Major Class Characteristics
1. Ex: sharks, skates, rays, chimaeras
2. possess an endoskeleton made of cartilage
a. produced by chondrocytes or cartilage cells
b. cartilage is lighter and more flexible than bone
3. jaws usually armed with well-developed teeth
4. mouth is often ventral
5. paired fins for stability, lift, propulsion
6. skin has a rough, sand-paper texture due to presence of
scales (dermal denticles)
7. ~ 850 species: two subclasses
a. Elasmobranchii - sharks and rays
b. Holocephali - chimaeras
V Anatomy – see handout
VI Physiology of Sharks
A. Body plan
1. fusiform shape
a. hydrodynamic/little drag
B. Buoyancy
1. presence of oil filled livers (reduce negative buoyancy)
C. Respiration
1. as sharks swim, water passes through mouth - over gills - out gill slits
D. Skin
1. placoid scales giving a sandpaper texture to skin
dermal denticles
E. Feeding/Digestion
1. With few exceptions, top-level carnivores
2. Teeth are continually being shed and replaced
3. spiral valve intestine (increases surface area)
Because sharks cannot move their jaws back and forth in order to chew,
when a large shark takes a bite out of a large prey, it must shake its
head back and forth to get the “chewing”
motion necessary
Jaws of some sharks can exert biting pressures in excess of 2800 kg/cm3
F. Osmoregulation (salt/water balance)
1. concentration of solutes in the body is close to that of
sea water due to retention of nitrogenous wastes (urea)
G. Reproduction
1. sharks produce a relatively small number of large, active young
2. mate late in life
3. internal fertilization
4. 3 types:
a. oviparous - egg laying (~43%) - egg cases
b. ovoviparous - eggs retained in the female until ready to hatch
c. viviparous - live bearing
H. Circulation
1. elaborate, closed circulatory system (from here on!)
2. two-chambered heart
3. single loop
I. Senses
1. sight
a. well developed, used at close range
b. tapetum lucidum
c. nictitating membrane
2. olfaction
a. well developed (1ppm)
3. Ampullae of Lorenzini
a. electroreception
4. hearing
a. sensitive to low-frequency vibrations
5. lateral line
a. row of sensory cells/nerves – sensitive to water vibrations
VII Ecology/Conservation
1. as predators, important role in keeping populations in check
2. reproductive habits make them extremely vulnerable to overfishing