Ch 27 - Intro to Animals

What are the major evolutionary trends in animals? 1.Level of cellular organization and specialization 2.Body plan – symmetry 3.Degree of cephalization (head region) 4.Type of body cavity 5.Segmentation 6.Structure of digestive system 27.1 Characteristics of Animals

Invertebrate Groups Simplest animals; Contains the greatest number of animal species; Most found in water Do not have a __________________! 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 Ventral is the belly or lower surface Anterior 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 Areas

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) more complex, usually motile organisms, such as worms, arthropods, and all vertebrates 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

Zygote undergoes rapid cell divisions known as cleavage to become hollow ball of cells called blastula (except sponge) 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 (Textbook p. 597 ) 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 Some animals form a third germ layer in the middle called mesoderm

Opening may become the mouth or the anus Protostomes develop __________ from blastopore Deuterostomes develop an _________ from blastopore

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 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 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)

Support Systems Sponges are supported by spicules 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 system All animals are __________________________ Sponges have specialized cells to capture & digest their food Cnidarians have one opening into their gastrovascular cavity where food enters & wastes leave; called a ________________ digestive system Annelids, arthropods, & vertebrates have a __________ digestive system in which food enters the mouth, is digested, & wastes leave through the anus 27.2 Tissues and organs

Circulatory system Transports oxygen and nutrients to cells & carbon dioxide and wastes away from cells Sponges, cnidarians, & flatworms don't have a circulatory system Closed systems, blood remains in blood vessels at all times until it reaches cells (earthworms & vertebrates) 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 –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 covering Integument 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

Reproduction 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) –Each individual functions as both male and female. –Usually produced at different times so self-fertilization does not occur.

Reproduction Echinoderms, arthropods, mollusks, & vertebrates have separate sexes & exchange sperm Internal fertilization occurs inside the body of the female & fewer numbers of sperm & eggs are produced. On land, egg and sperm need to remain moist. Also serves as protection. External fertilization occurs outside the body. Most aquatic animals release male and female gametes near one another in the water. Egg is fertilized outside the female’s body. –Developing eggs may be kept inside or outside the body. –Land – may have hard shell or kept internally (most mammals) –Water – may have jelly-like shell or kept internally (some sharks)

Kinds of Animals Kingdom Animalia contains about 35 major divisions called phyla, depending on how certain organisms are classified. See the phlylogenetic tree with the evolutionary milestones. (This is a hypothesis)