Introduction to Animals
All Materials © Cmassengale
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
- Have some type of skeletal support
- Exoskeletons found in arthropods cover the outside of the body but limit size
- Endoskeletons found in all vertebrates are found inside the body & are made of cartilage &/or bone
- Worms have fluid-filled internal cavities giving them skeletal support
- Sponges have the simplest skeleton
- May be sessile (attached & non-moving) or motile (able to move around)
- Muscular tissue provides energy for movement
- 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
- Most vertebrates have a backbone or spine made of repeating bones called vertebrae that protect the spinal cord
- Some show cephalization (have a head with sensory organs concentrated there)
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)
DORSAL
ANTERIOR | POSTERIOR |
VENTRAL
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
RADIAL SYMMETRY | BILATERAL SYMMETRY |
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)
INCOMPLETE | COMPLETE |
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)
- Schizocoely occurs in protostomes where the coelom develops when mesoderm masses split
- Enterocoely occurs in deuterostomes
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
Body Coverings
- Integument is the outer covering of an animal
- Terrestrial vertebrates have water-tight outer coverings
- Integuments of amphibians allow gas exchange through the skin
- Adaptations of integuments include scales, fur, hair, & feathers to protect and insulate the body
Excretory System
- Rid animals of wastes, help conserve water, & filter wastes from the blood
- Ammonia is a toxic waste that must be gotten rid of by an animal’s body
- Kidneys filter blood in vertebrates
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