Download Introduction to Animals

Introduction to Animals
Characteristics
 All multicellular (metazoans) & eukaryotic
 Cells lack cell walls & come in a variety of shapes
 Ingestive heterotrophs (take in food & internally digest it)
 Store food reserves temporarily as glycogen in the liver
 May be sessile (attached & non-moving) or motile (able to move
around)
 Reproduce sexually
 Show levels of organization including cell, tissue, organ, & system
 Most show division of labor among cells
 Cells are specialized for particular functions
 Cell junctions hold individual cells in a tissue together
Invertebrate Groups
 Simplest animals
 Contains the greatest number of animal species
 Most found in water
 Do not have an backbone
 Includes sponges, cnidarians, flatworms, roundworms, annelids
(segmented worms), mollusks, arthropods, & echinoderms
Vertebrate Groups
 More complex animals
 Most have a backbone
 Includes fish, amphibians, reptiles, birds, & mammals
Body Areas
 Dorsal is the back or upper surface
 Ventral is the belly or lower surface
 Anterior head or front end
 Posterior is the tail or hind end opposite the head
 Oral surface in echinoderms is where the mouth is located
(underside)
 Aboral surface in echinoderms is the surface opposite the mouth (top
side)
Body Symmetry
 Symmetry is the arrangement of body parts around a central plane or
axis
 Asymmetry occurs when the body can't be divided into similar
sections (sponges)
 Radial symmetry occurs when similar body parts are arranged around
a central point like spokes on a wheel (echinoderms)
 Most animals with radial symmetry are sessile (attached) or sedentary
(move very little)
 Bilateral symmetry occurs when animals can be divided into equal
halves along a single plane (right & left sides that are mirror images)
 Animals with bilateral symmetry are more complex, usually motile
organisms, such as worms, arthropods, and all vertebrates
 Animals with bilateral symmetry show cephalization & have anterior
& posterior ends
Segmentation
 Occurs whenever animal bodies are divided into repeating units or
segments
 Found in more complex animals
 Earthworms show external segmentation, while humans show internal
segmentation (vertebrae of the backbone)
 Segments may be fused together such as cephalothorax covering
chest & head of a crayfish
Tissue Development
 All animals reproduce sexually, but some also reproduce asexually
(sponges bud & flatworms fragment)
 Zygote is the fertilized egg all animals form from
 Zygote undergoes rapid cell divisions known as cleavage to become
hollow ball of cells called blastula
 Blastocoel is the central cavity of the blastula
 Blastula invaginates (folds inward at one point) to form an opening &
two cell or germ layers; process called gastrulation
 New cup-shaped structure with 2 cell layers is called the gastrula
 Archenteron is the deep cavity of the gastrula that forms the
primitive gut
 Inner germ layer called endoderm & outer germ layer called ectoderm
 Opening may become the mouth or the anus
 Protostomes (mollusks, arthropods, & annelids) develop mouth from
blastopore, while deuterostomes (echinoderms & vertebrates)
develop an anus from blastopore
 Some animals form a third germ layer in the middle called mesoderm
 Cells differentiation during development changing their shapes to fit
their function (neurons or nerve cells become long to conduct
messages)
Cleavage
 Protostomes have spiral cleavage in which embryonic cells divide in a
spiral arrangement
 Deuterostomes have radial cleavage or embryonic cell division
parallel or perpendicular to the vertical axis of the embryo
 Protostomes have determinate cleavage ( embryonic cells can't form
a new organism if separated)
 Deuterostomes have indeterminate cleavage ( embryonic cells can
form other organisms if separated such as identical twins)
Germ Layers
 Form the tissues, organs, & systems of an animal
 Found in the embryo of all animals except sponges (have specialized
cells but no tissues)
 Ectoderm (outer) forms skin, nerves, & sense organs
 Endoderm (inner) forms the digestive & respiratory organs & systems
 Mesoderm (middle) forms muscles, circulatory system, reproductive &
excretory systems
Larval Forms
 Some animals have indirect development & go through an immature
larval form that does not resemble the adult
 Planula is the larva of cnidarians (jellyfish, corals, & sea anemones)
 Trochophore is the larva of mollusks (squid & octopus)
 Dipleurula is the larva of echinoderms (starfish & sea urchins)
Metamorphosis
 May be complete or incomplete
 Usually found in arthropods
 Incomplete metamorphosis (egg --> nymph --> adult)
 Complete metamorphosis ( egg --> larva --> pupa --> adult)
Body Cavities
 Coelom is an internal body cavity lined with mesoderm

Animals with a coelom are called coelomate animals (annelids,
mollusks, arthropods, & vertebrates)
 Acoelomate animals do not have a body cavity but have solid bodies
(sponges, flatworms, & cnidarians )
 Pseudocoelomate animals have a body cavity only partially lined with
mesoderm (roundworms)
Body Layers
 Sponges have specialized cells but no tissues or organs
 Cnidarians (jellyfish, coral, sea anemone) have 2 body layers
(ectoderm & endoderm) with a jellylike layer called mesoglea between
for support
 Cnidarians have one body opening into a large cavity called
gastrovascular cavity
 All worms, mollusks, arthropods, echinoderms, & vertebrates have
3 cell layers (ectoderm, mesoderm, & endoderm)
Mouth & Anus Development
 Blastopore is the opening in the gastrula formed when blastula folds
inward
 Protostomes are animals that the blastopore develops into the mouth
( earthworms, mollusks, arthropods)
 Deuterostomes are animals that the blastopore develops into the anus
(echinoderms & vertebrates)
Support Systems
 Sponges are supported by spicules, while limestone cases support
corals
 Hydrostatic skeletons in worms consist of a fluid-filled body cavity
surrounded by muscles
 Arthropods have external exoskeletons that prevent water loss but
must be molted for growth to occur
 Echinoderms & vertebrates have internal endoskeletons that grow
with the organism
Digestive Systems
 All animals are heterotrophs
 Sponges have specialized cells to capture & digest their food
 Cnidarians have one opening into their gastrovascular cavity where
food enters & wastes leave; called a two-way digestive system
 Annelids, arthropods, & vertebrates have a one-way digestive
system in which food enters the mouth, is digested, & wastes leave
through the anus
Circulatory System
 Transports oxygen and nutrients to cells & carbon dioxide and
wastes away from cells
 Sponges, cnidarians, & flatworms don't have a circulatory system
 In closed systems, blood remains in blood vessels at all times until it
reaches cells (earthworms & vertebrates)
 In open systems, blood isn't always contained in blood vessels
(arthropods)
Respiratory System
 Oxygen is needed & carbon dioxide must be eliminated
 Sponges, cnidarians, flatworms, & roundworms exchange gases by
diffusion
 Mollusks & fish use gills to exchanges gases, while terrestrial
vertebrates use lungs
Nervous System
 Cephalization occurs in animals that have a distinct head at the
anterior end where sensory organs are concentrated
 Cephalization is found in more complex animals
 Sponges have specialized nerve cells, while cnidarians & flatworms
have a nerve net
 Ganglia are clusters of nerve cells found in more complex animals
 Nerve cells may specialize to detect, light, sound, etc.
 Brain interprets nerve impulses & sends a response
Reproductive System
 All animals reproduce sexually, but some also use asexual
reproduction
 Budding is asexual reproduction in which an outgrowth on the parent
organism breaks off to form a new individual (hydra)
 Sponges, flatworms, & cnidarians asexually reproduce by
fragmentation (separating into pieces & each piece making a new
organism)
 Some insects develop from unfertilized eggs by parthenogenesis
 Hermaphrodites are animals that produce both sperm & eggs
(earthworms - cross fertilize & tapeworms self fertilize)
 Echinoderms, arthropods, mollusks, & vertebrates have separate sexes
& exchange sperm
 Internal fertilization occurs inside the body of the female & larger
numbers of sperm & eggs are produced
 External fertilization occurs inside the body of the female & fewer
eggs & sperm are produced