THE EVOLUTION OF ANIMAL DIVERSITY
I.
What is an animal?
a. Multicellular, heterotrophic eukaryotes that obtain nutrients by
ingestion
i. INGESTION  eating food
1. Distinguishes animals from fungi; internal
digestion
b. Other unique features exist in the animal life cycle
c. The transformation of a zygote into an adult animal is
controlled by specialized genes; molecular biology distinguish
animals from the other organisms
II.
The animal kingdom probably originated from colonial protests
a. First animals appeared over 600 million years ago
b. Cambrian explosion, a span of about 10 million years, that
occurred 545 million years ago
i. Saw a massive amount of animal species evolve
c. Majority of animals are invertebrates
i. INVERTEBRATES  lack a vertebral column
(backbone)
III.
Sponges have a relatively simple, porous body
a. SPONGES  phylum = PORIFERA; stationary animals that
appear so sedate the ancient Greeks believed they were plants
b. RADIAL SYMMETRY  body parts are arranged like pieces
of a pie around an imaginary central axis
c. SUSPENSION FEEDERS  filter-feeders; animals that collect
food particles from water passed through some type of foodtrapping equipment
IV.
Cnidarians are radial animals with stinging threads
a. CNIDARIANS  stingers with radial symmetry
i. Ex. Jellies, anemones, hydras, corals
ii. CNIDOCYTES  “stinging cell”
V.
Most animals are bilaterally symmetrical
a. BILATERAL SYMMETRY  divided equally by a single cut
with a mirror image on the right and left side
i. ANTERIOR  towards head
ii. POSTERIOR  towards tail
iii. DORSAL  back
iv. VENTRAL  underside, bottom, belly
VI.
Flatworms are the simplest bilateral animals
a. FLATWORMS  phylum = PLATYHELMINTHES; leaf-like
or ribbon-like animals ranging in length from 1 mm to 20 m
b. 3 groups
i. Flatworms (planaria)
ii. Flukes
iii. Tapeworms
1. *Parasitic
VII. Most animals have a body cavity
a. BODY CAVITY  fluid-filled space between the digestive
tract and the body wall
i. PSEUDOCOELOM  a body cavity that is not
completely lined by tissue derived from the mesoderm
ii. COELOM  cavity is completely lined by tissue derived
from mesoderm
b. Having a body cavity allows for better movement; larger
internal organs; and increases nutrient circulation and gas
(oxygen) circulation
VIII. Roundworms have a pseudocoelem and a complete digestive tract
a. ROUNDWORMS  phylum = NEMATODA; cylindrical
worms with a blunt head and tapered tail
i. One species is responsible for TRICHINOSIS
1. TRICHNOSIS  obtained by eating undercooked
pork
IX.
Diverse mollusks are variations on a common body plan
a. MOLLUSCA  more than 150,000 known species
i. 3 most diverse groups
1. GASTROPODS
2. BIVALVES
3. CEPHALOPODS
X.
Many animals have a segmented body
a. SEGMENTATION  the subdivision of the body along its
length into a series of repeated parts
i. Advantages
1. Flexibility and mobility
XI.
Earthworms and other annelids are segmented worms
a. ANNELIDA  a segmented body resembling a series of fused
rings
i. EARTHWOMRS
ii. POLYCHAETES
iii. LEECHES
XII. Arhtropods are the most numerous and widespread of all animals
a. ARTHROPODA  nearly 1,000,000 types; equipped with
jointed appendages and an exoskeleton of chitin
i. MOLTING  shedding of exoskeleton
ii. Ex.
1.
2.
3.
4.
Horseshoe crab
Arachnids
Crustaceans
Millipedes
5. Centipedes
XIII. Insects are the most diverse group of organisms
a. ENTYMOLOGY  study of insects
b. Largest group of arthropods
XIV. Echinoderms have spiny skin, an exoskeleton, and a water vascular
system for movement
a. ECHINODERMATA  “spiny skin”; sea stars, sand dollars,
sea urchins, sea cucumbers
i. ENDOSKELETON  internal skeleton
XV. Our own phylum, Chordata, is distinguished by four features
a. Dorsal, hollow nerve cord
b. NOTOCHORD  a flexible, supportive, longitudinal rod
located between the digestive tract and the nerve cord
c. PHARYNGEAL SLITS  gill structures in the pharynx
d. A muscular POST-ANAL TAIL
e. *MOST DIVERSE GROPU OF CHORDATES ARE THE
VERTEBRATES
XVI. A skull and a backbone are hallmarks of vertebrates
a. Skull and backbone  enclose the main parts of the nervous
system
XVII. Most vertebrates have hinged jaws
a. AGNATHANS  small group of “jawless” fishes
XVIII. Fishes are jawed vertebrates with gills and paired fins
a. CHONDRICHTHYES
b. OSTEICHTHYES
XIX. Amphibians were the first land vertebrates
a. AMPHIBIA  class that exhibits a mixture of aquatic and
terrestrial adaptations
XX. Reptiles have more terrestrial adaptations than amphibians
a. REPTILIA  class that includes snakes, lizards, alligators,
crocodiles
i. AMNIOTIC EGG  can be laid on dry land
ii. ECTOTHERMIC vs ENDOTHERMIC
XXI. Birds share many features with their reptilian ancestors
a. AVES  class of about 8,600 species of birds
i. Many questions linger about origin of birds
XXII. Mammals also evolved from reptiles
a. MAMMALIA  hair and mammary glands
i. MARSUPIALS VS EUTHERIANS (PLACENTALS)
XXIII. A phylogenetic tree gives animal diversity an evolutionary
perspective
XXIV. Humans threaten animal diversity by introducing non-native
species
a. Ex.
i. Rabbits in Australia