Animal Kingdom
I.
General characteristics of Animals:
A. Multicelled—tissues, organs, organ systems
B. Heterotrophs—eat or absorb nutrients from other organisms
C. Aerobic respiration—require oxygen
D. Reproduce sexually and sometimes asexually
E. Motile—movement
F. Life cycle include a period of embryonic development
 Germ tissue layers--ectodermic, mesodermic, and endodermic (these
tissues give rise to animal tissues and organs)
II.
Diversity in Body Plan:
 The similarities and differences in different species can be compared with
respect to five basic features:
A. Body symmetry—most animals are either radial or bilateral symmetry
1. Radial symmetry: means having body parts arranged regularly around
a central axis. (example: spokes of a bike wheel)
2. Bilateral symmetry: means having right and left halves that are mirror
images of each other.
(ex: humans—anterior (head) and posterior (anus))
B. Cephalization—means having sensory structures and nerve cells
concentrated in the head or anterior.
1. Bilateral species and cephalization evolved together
C. Gut—is a body region where food is digested and then absorbed.
1. First, some species have saclike gut with one opening—a mouth for
food entry and waste exit
2. Second, complete digestive system that has two openings (mouth and
anus)
D. Body cavities—these structures separate the gut and the body wall of most
bilateral species.
1. One type of body cavity is the coelom (humans)—this space allows
internal organs to expand and operate freely.
2. Some animals (flatworms) do not have a coelom but are packed solidly
with tissue
3. (roundworms) however, have a false coelom.
E. Segmentation—consist of a series of body units that may or may not be
similar to one another
1. Example: earthworms have repeating body segments
2. Example: Insects are segmented into the head, thorax, and abdomen
3. Example: humans are segmented into the head and the abdomen
Evolution of the Animal Kingdom
I.
Evolutionary Origin of the Animal Kingdom:
A. Animals are believed to have evolved from protistan-like ancestors.
B. The first animals were soft-bodied.
C. Fossil evidence shows that these ancestral forms had given rise to all major
animals phyla
D. Now, there are 30+ animal phyla Invertebrates (mostly) and Vertebrates
II.
Phylum Porifera (Invertebrate): Sponges
A. Many animals have with several levels of anatomical organization. However,
in sponges, they consist of a few types of cells loosely arranged into a tissue.
B. Thus, sponges are the simplest animals
C. Mainly ocean dwellers, but several species live in fresh water
D. They fasten to the ocean bottom where they filter tiny food particles from the
water, usually bacteria and other microscopic organisms, and ingest them by
phagocytosis
E. Asymmetric body with no true tissue or organs
F. Reproduce sexually and asexually (budding or fragmentation)—small
fragments that break away from the body can grow into new sponges
III.
Phylum Cnidaria (Invertebrate): jellyfishes, corals, sea anemones, hydra, etc.
A. Most live in the marine habitats, but some species are found in fresh water
B. Most are sessile or slow-moving animals but are still efficient predators
because they possess special stinging cells called cnidocytes
C. Bodies are radially symmetric and contain a single opening that’s lined with
tentacles. Also location of mouth
D. The central body cavity of Cnidarian is called gastrovascular cavity—
location where food is digestion
E. Reproduce sexually or asexually
IV.
Phylum Platyhelminthes (Invertebrate): flatworms, tapeworm, flukes
A. Approximately 20,000 species in this phylum
B. Dwell in marine and freshwater environment; free-living parasites
C. Range in size from nearly microscopic species to tapeworms that are over
twenty meters in length
D. Saclike gut or one ended gut (mouth only)
E. Bilateral symmetry
F. Hermaphrodite (both sexes in one body)
V.
Phylum Nematoda (Invertebrate): roundworms, hookworms
A. Display two evolutionary advances over the flatworms—
 They have a complete, one-way digestive tract that runs from mouth to
anus
 A cavity between their digestive tract and body wall with specialized
organs
B.
C.
D.
E.
F.
Dwell in fresh and salt water as well as in soil
Most are small, but some may reach lengths of a foot or longer
Parasites of living animals (undercooked pork) and plants
Commonly found in human intestines (third world countries)
Bilateral and false coelom (body cavity) filled with fluid—because it is not
surrounded by mesoderm derived tissue
G. Contain dorsal and ventral nerve cord
H. Male and Female species: a single female worm may deposit up to 200,000
fertilized eggs in the course of one day.

Species with a coelom:
A. Coelom—a type of body cavity located between the gut and the body wall.
B. Animals with a coelom belong to two main groups:
1. Protosomes—a bilateral animal in which the first indentation in the
early embryo develops into the mouth.
 annelides, mollusks, and arthropods
2. Deuterostomes—any of the bilateral animals, in which the first
indentation in the early embryo develops into the anus.
 echinoderms and chordates
VI.
Phylum Annelida (Invertebrate): earthworms, leeches, segmented worms
A. Most distinctive evolutionary feature is their segmented body
B. Typical annelid possesses a head region, a segmented body, and terminal
portion with an anus
C. Rings are called Segments
D. Along the body is a saddle-like enlargement called a clitelum, involved in
reproduction
E. Approximately 9,000 species
F. True Coelom
G. Annelids possess complex, closed circulatory systems—aortic arches
H. Primitive brain and ventral nerve cord that connects the brain to other areas of
the body
VII.
Phylum Mollusca (Invertebrate): clams, snails, squid, slugs, oysters
A. Approximately 50,000 species
B. They are unsegmented coelomates with soft bodies
C. All mollusks possess a thick, muscular foot for creeping, holding, catching
prey, and swimming
D. Gastropod (belly-foot)-- snails, slugs
E. Bivalves (shell opens and closes like a hinged double door)—obtain particles
of food by filtering them from the water
F. Open circulatory system that includes a heart that pumps blood through a
series of blood vessels
G. Cephalopods--squids, octopus, etc.
VIII.
Phylum Arthropoda (Invertebrate): insects, crabs, lobsters, ticks, centipedes,
millipedes, spiders, mites, etc.
A. Most successful organism on earth—success is measured by having the most
species in the animal kingdom, producing lots of offspring, occupy most
habitats, effective defenses, exploit new resources
B. Over one million species
C. Highly specialized in tasks such as feeding, walking, sensing, and reproducing
D. Arthropod characteristics:
1. Hardened exoskeleton (periodically shed in a process called molting,
which enable the arthropod to grow)
2. Specialized segmentation body plans (segments do not repeat as they
do in earthworms)
3. Jointed appendages
4. Specialized respiratory structures
5. Efficient nervous system and sensory organs
IX.
Phylum Echinodermata (Invertebrates): sea stars, sea urchins, brittle stars, sea
cucumbers
A. Species have spiny skins that are made up of hard, calcified plates that form a
type of skeleton just under their epidermis
B. No segmentation in their bodies and no head region
C. Radial symmetrical
D. Decentralized nervous system permits response to be made in all directions
E. Coelom—water vascular system
X.
Phylum Chordata (Vertebrates): sea squirt, kin , lancelet, jawless fishes, bony
fishes, amphibians, reptiles, birds, mammals
A. Approximately 45,000 different species
B. A few chordates lack backbones and are therefore known as invertibrates, but
the vast majority have backbones and are vertebrates
C. Four features that are evident in chordate embryos and, in many species, these
persist into adulthood:
1. Pharyngeal gill slits—which are perforations in the wall of the
pharynx near the digestive tract. As fish develop, these slits give rise
to gills, which in land-based vertebrates such as humans, they close
and disappear.
2. Notochord—a long rod of flexible tissue (not cartilage or bone) is
found in the embryo, beneath the nerve cord. It lends support and
consists of large cells encased in a tight covering of tissue, and
disappears as the vertebral column appears.
3. Hollow dorsal nerve cord---which runs above and parallel to the
notochord and gut. In humans, it developed into the spinal cord.
4. Tail—which extends past the anus, at the far end of the digestive tract,
and is a muscular projection. It disappears in many vertebrates
(humans) as the embryo develops.
VERTEBRATES

Invertebrate Chordates:
A. Sea squirts (urochordates/ tunicates)
1. Dorsal nerve cord, notochord, pharynx
2. Free-swimming forms that look like tadpoles
3. Strong tail to propel the animal forward
B. Lancelets (cephalochordates)
1. Dorsal nerve cord, notochord, pharynx
2. Use segmented muscle on both sides of a full-length notochord for
swimming
Bonus: How did we get from invertebrates (i.e. sea squirts, lancelets) to vertebrates?
Evolutionary Trends Among the Vertebrates

Shift from notochord to the vertebral column
1. Proved to be a stronger internal skeleton for muscles to work

Part of the nerve cord expanded and developed into a complex brain

This expansion began after jaws evolved
1. 1st jaws were modified gill-supporting structures--New feeding
possibilities

Nervous systems and sensory organs developed afterwards

Fins ---appendages that help propel, stabilize, and guide the body through
water
1. fins were also the starting point for the legs, arms, and wings seen
among amphibians, reptiles, birds, and mammals

Gas exchange structures:
1. As fishes became larger and more active, oxygen uptake distribution
improved
2. Gills developed into lungs
3. Enhanced modification of the heart
The First Vertebrates:
I.
Fish—(ray, shark, herring, etc.)
 Some primitive fish such as the lampreys and hagfish have no jaws called
Ostracoderms
 Ostracoderms disappeared when (jawed fish) Placoderms began their
adaptive radiation
 The shark and ray have skeletons of cartilage (Class Chondrichthyes)
 Herring has bony skeleton (Class Osteichthyes)
 Fish require a constant stream of water forced over the gills in order to obtain
oxygen
II.
Class Amphibia: three groups (salamanders, frogs and toads, Caecilains)
 First land vertebrates
 Return to the water to lay their eggs
 Breath through their lungs and skin, and the constantly lose water through
their skin, so must remain in moist habitats
III.
Class Reptilia: alligators, turtles, lizards, snakes, etc.
 First vertebrates to escape dependency on water
 Escape by 2 adaptations
1. internal fertilization
2. new kind of egg—contain stored food and water for the developing
embryo
 Most reptiles lay eggs; some give birth to fully formed offspring
 All have scaly skin that resist drying out
 All can adjust their internal body temperature by changes in physiology and
behavior
Example: Sun-tanning on rock and road
Example: turtle basking, looking in same direction
IV.
Class Aves: animals with feathers
 Descended from bipedal reptiles
 Resemble reptiles in many internal structures, their horny beaks and scaly
legs, and their egg-laying habit
 Feathers are used for flight and as insulation to maintain constant elevated
body temperatures



V.
Lungs have outpockets in which additional air can accumulate
Heart rate is extremely high
Eggs produced by birds have hard shells and are highly resistant to
dehydration
Class Mammalia:
 By definition, mammals nourish their young with milk, and have elevated
body temperatures and a four-chambered hearts
 Young develop internally in the uterus—exceptions are the monotremes (egglaying mammals) and the marsupials, whose young develop in pouches
outside the body
 Hair
 Specialized teeth to kill, cut, and chew before swallowing it