3.4: The Animal Kingdom
pg. 111
The kingdom of animalia contains 35 different phyla. Reptiles, birds
and fish only represent a single phyla. 95 % of the remaining animals
are found in the other 34 phyla. The largest number of animals (800
000) are found in the Phylum Arthropoda.
What is an Animal?
Animals have the following characteristics;
- Eukaryotic, multi-cellular organisms, and do not have cell walls.
- They are heterotrophs, which ingest and digest their food.
- Mobile, or have the ability to move, in at least one stage of their
lives.
- Reproduction is sexual, producing an embryo that undergoes
stages of development.
Characteristics used to Classify Animals
Invertebrate: an animal that does not have a backbone.
Vertebrate: an animal with an internal skeleton and a backbone.
Animals can be classified by whether they have a backbone or not.
95% of animals are invertebrates, other characteristics used to classify
animals are;
- Levels of organization
- Segmentation
- Number of body layers
- Movement
- Symmetry and body plans
- Reproduction
- Body cavity
Figure 3.23: About 95 percent of animals are invertebrates.
(A) Sponges live in aquatic environments, attached to solid surfaces such as rocks, coral,
or the shell of another animal.
(B) Sea anemones use their stinging tentacles to catch food.
(C) Sea cucumbers feed on dead and decaying matter.
Levels of Organization
Animals are classified by looking at their structure, tissue, and organ
systems. All animals have cells organized into tissues, except for
sponges.
Cells → tissues → organs → organ systems → organism
Number of Body Layers
All animals express three body layers, except for sponges and
cnidarian (hydras and jellyfish). These layers are: ectoderm (skin,
nerve tissue and some organs), mesoderm (muscles, blood, kidneys
and the reproductive organs), and endoderm (lungs, liver, pancreas,
bladder, and the stomach lining). These layers are developed during
embryo development.
Figure 3.24: Most animals develop three layers of cells at an early stage in the growth of the
embryo.
Symmetry and Body Plans
Asymmetrical body plan: organisms have an irregular shaped body
plan; for example, the sponge.
Radial symmetry: a body plan that can be divided along any plane
through a central axis, into roughly equal halves. (Hydra, jellyfish, and
starfish)
Bilateral symmetry: a body plan that can be divided along one plane,
through the central axis, into equal halves. (Worms, insects and
vertebrates)
Figure 3.25: (A) the cnidarian that is known as a hydra shows radial symmetry. (B) The turtle
shows bilateral symmetry.
Body Cavities
Coelom: a fluid filled body cavity that provides space for the
development and suspension of organs and organ systems.
Coelomates: are organisms that have a coelom. (Worms. mollusks,
insects and vertebrates)
Acoelomates: are organisms that do not have a fluid filled space.
(coral, jellyfish and flatworms)
Figure 3.26: (A) Acoelomate animals have flattened bodies. (B) Coelomate animals have a
body cavity in which complex internal organs can develop.
Segmentation
Segmentation is the division of the body into repetitive sections, or
segments. The advantage to segments, is if a segment gets damaged
the other segments are unaffected.
Segments also allow for greater mobility and complex patterns of
movement of the organism.
Movement
As organisms evolved, nerve and muscle tissue developed in
organisms. This allowed for complex and fast movements. Some
organisms are sessile as adults, sponges and anemones.
Reproduction
Most animals reproduce sexually, using gametes (haploid),
fertilizations leads to the development of a zygote (diploid).
Fertilization can either be external or internal.
Invertebrate Animals
Invertebrates are aquatic and terrestrial organisms, found in most
ecosystems on Earth. The organisms have existed for hundreds of
millions of years.
Sponges and Cnidarians
Phylum Porifera – are found in both marine and freshwater
environments. They have an asymmetrical body plan and no tissues.
The sponges are only two layers of cells, with each cell living
independently of each other. The sponge is a sessile organism when it
reaches adulthood. They feed by passing water through channels and
trapping food particles.
Phylum Cnidaria – marine and freshwater organisms; such as, a
Hydra, Jellyfish, Anemones and Coral. These organisms are also made
up of only two layers of cells, yet they have tissues. They have muscle
tissue to allow movement, and a nerve network to coordinate these
movements (to capture prey and swim). They have a digestive system,
one opening, two directional. Sting tentacles capture the prey and
deliver it to the mouth, where the prey enters the gastro-vascular
cavity for digestion. Cnidarians express a radial symmetrical body
plan.
Figure 3.28: (A) Sponges are animals that have no tissues, no organs, and an asymmetrical
body plan. (B) Corals are cnidarians that can form reef environments.
Two Body Forms
Polyp: the tube-shaped sessile body form of cnidarian.
Medusa: the umbrella-shaped, free swimming body form of cnidarian.
Figure 3.29: There are two basic forms of cnidarians: polyps and medusae. (A) Polyps, such
as adult sea anemones, are sessile. (B) Medusae, like the jellyfish shown in the photo, are
mobile.
Worms
Phylum Platehelminthes: (flatworms) are Acoelomates that have
three layers of cells. They express a simple nervous system, a
gathering of nerve cells creating an eye spot, a simple brain at a head
region. (Tapeworms, flukes, and free-living planarians)
Cephalization: the concentration of nerve tissue and receptors at the
anterior end of an animal’s body.
Phylum Nematoda: round worms (hookworm, pinworm and vinegar
eel) that live in all habitats, and can be free-living or parasitic.
Cylindrical and tapered ate one end.
Phylum Annelida: segmented worm, are long tube-like organisms
that are divided into a series of ringed segments. These worms have a
distinct head region with a brain and a number of organ systems
(digestive, circulatory, nervous, excretory, and reproductive). The
digestive system is a two opening (mouth and anus) and one
directional.
Figure 3.31: Segmented worms, like this earthworm, are coelomates that are segmented on the
inside as well as on the outside.
Mollusks
Phylum Mollusca: there are over 100 000 species, making them the
second most diverse animal phylum. They express bilateral symmetry.
Mollusks have a soft body plan surrounded by a hard shell.
Mantle: a membrane that surrounds a mollusk’s internal organs.
The mantle creates a calcium carbonate shell, protecting organ
systems; such as, digestive, circulatory, respiratory, excretory,
reproductive and nervous).
The octopus has a relatively large brain, and is capable of learning
complex tasks.
Figure 3.32: Three of the major classes of mollusks are (A) the bivalves, represented here by a
file clam; (B) the gastropods, represented by a land snail; and (C) the cephalopods,
represented by an octopus.
Echinoderm
Phylum Echinodermata: made up of sea stars, sea urchins, sea
cucumbers and sand dollars. These organisms express radial
symmetry, spiny endoskeletons (internal skeleton), and tube feet
(fluid-filled, similar to suction cups).
Arthropods
Phylum Arthropoda: is the largest animal phylum. (Spiders,
scorpions, crustaceans [lobsters], and insects) They have moveable
jointed legs and body segmentation. These organisms have an
exoskeleton.
Exoskeleton: is an external skeleton that protects organs, provides
support for muscle attachments, and protects against water loss and
predation.
Table 3.5: Characteristics of Arthropod Groups
Vertebrate Animals
Phylum Chordata: (50 000 species)
Most chordates are vertebrates, have a notochord which eventually
develops into a spine, brain and spinal cord.
Notochord: a flexible, rod-shaped structure found in chordate
animals; during vertebrate development it is replaced by the spine.
Cartilage: the flexible, non-bony tough material found in vertebrate
endoskeletons.
Fish (half of all vertebrates are fish, developed 400 million years ago)
Found in fresh water and saltwater habitats. The lamprey is the oldest
living vertebrate. Jaw less fish, uses suction mouth to latch onto their
food. Cartilage endoskeleton
Fish use gills to obtain oxygen from the water.
Bony fish have an air sac that allows them to rise and sink in the
water, called a swim bladder.
Figure 3.35: (A) the sea lamprey is thought to be the most ancient of all living vertebrates. It
is jawless and has a cartilaginous skeleton. This species uses its mouth to hold on to and
penetrate the bodies of prey. (B) The cartilaginous fish include the sharks and rays, like this
manta. (C) The bony fish include the vast majority of the Earth’s current fish diversity, such
as Ontario’s pumpkinseed sunfish.
Amphibians (360 million years ago) (frogs, toads, and salamanders)
The first limbs were modified fins. They have lungs, and also use their
skin to gas exchange, and reproduce externally.
Figure 3.36: In Ontario, there are representatives of the two major amphibian orders. The
bullfrog (A) is an anuran (frogs and toads), and the spotted salamander (B) is a urodelan
(salamanders and newts).
Reptiles (300 million years ago)
There are four major groups (three orders): lizard and snakes, turtles,
crocodilians. Reptiles have a three chambered heart, share the
ventricle. These animals are ectothermic.
Ectothermy: the reliance on the environmental heat for determining
internal body temperature.
Use lungs for gas exchange. Reproduction is done by internal
fertilization, and they lay shelled eggs on land. (amniotic egg)
The incubation temperature will determine the sex of the offspring.
Figure 3.37: In the three orders, the four major groups of living reptiles are the snakes,
lizards, turtles, and crocodilians. The eastern foxsnake (A), five-lined skink (B), and wood
turtle (C) are all Ontario residents. The gavial (D) is an endangered species on the Indian
subcontinent.
Birds (150 million years ago)
(Related to at least one group to dinosaurs)
Birds are edothermic and have a four chambered heart.
Endothermy: the use of metabolic heat to maintain a high, constant
body temperature.
Bones are light weight and hollow, and adaptation for flying, a
toothless skull (beak) and a compact body plan for weight reduction.
Figure 3.39: (A) Black-capped chickadees are small songbirds whose range covers parts of
Canada and the United States. (B) Ostriches are large birds that do not fly. They live in desert
and grassland regions of Africa.
Mammals
Females have mammary glands that produce and secrete milk to
nourish developing young. Mammals also have hair that has multiple
functions, defense, sensory detection, waterproofing communication,
insulation and camouflage.
Mammals are endothermic animals, with a four chambered heart,
highly developed brains.
There are three main groups; momotremes, marsupials, and placental
mammals.
Mammary gland: a mammalian gland that produces and secretes milk
for nourishing developing young.
Placenta: an organ in the pregnant uterus that exchanges nutrients and
oxygen between the mother and developing offspring.
See Table 3.6, page 123 for characteristics of each group.
Table 3.6: Characteristics of Mammal Groups
Section 3.4: Review, questions 1 – 15, page 124