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General Features of Animals • Animals are a diverse group that are characterized by several features – animals are heterotrophs – all animals are multicellular and lack cell walls – most animals are able to move from place to place – most animals reproduce sexually Five Transitions in Body Plan • 1. 2. The evolution of animals is marked by five key transitions to the body Evolution of tissues • • – – 3. only the sponges (Parazoa) lack both defined tissues and organs all other animals (Eumetazoa) have true tissues Evolution of bilateral symmetry • • sponges also lack any definite symmetry and grow as irregular masses virtually all of the Eumetazoa have a definite shape and symmetry radial symmetry means the parts of their bodies are arranged around central axis bilateral symmetry means that the body only has left and right mirror images Evolution of a body cavity • a body cavity makes possible the evolution of efficient organ systems • 4. supports organs, distributes materials, and fosters complex developmental interactions Evolution of deuterostome development • bilateral animals can be divided into two groups based on differences in the pattern of embryonic development • • 5. protostomes include flatworms, nematodes, mollusks, annelids, and arthropods deuterostomes include echinoderms and chordates Evolution of segmentation • segmented animals are assembled from a succession of similar segments We will know this chart by the end of class today Sponges: The Simplest Animals • Sponges are members of the phylum Porifera – They lack true tissues and organs but instead are comprised of masses of specialized cells embedded in a gel-like matrix – the body of a sponge is perforated by tiny holes • unique flagellated cells, called choanocytes, line the body cavity of the sponge and draw water in through the pores • the sponge is a “filter-feeder” that ingests any suspended food particles trapped by the choanocytes as the water flows by Cnidarians and Ctenophora • All animals other than sponges have symmetry and tissues • Two phyla exhibit radial symmetry (Radiata) - bodies are organized around a central axis • Cnidaria – jellyfish, corals, and sea anemones » Carnivores – first animals to use extracellular digestion – occurs in gastrovascular cavity » Stinging cells are called cnidocytes » Each stinging cell or cnidocyte has a harpoon called a nematocyst » Exist in two forms • Medusae – free floating umbrella shaped • Polyps – cylindrical shaped, usually attached to a rock • Ctenophora – comb jellies Polyp Medusae Bilateral symmetry • From here on out, all organisms we describe have bilateral symmetry • All bilateral animals have three embryonic layers that develop into the tissues of the body – Ectoderm, endorderm, mesoderm Flatworms • Flatworms are in the phylum Platyhelminthes • They have a gut with only one opening – called the pharynx – Food taken in and waste expelled from here • No other body cavity besides the digestive system – acoelomates • From here on out, all organisms have a body cavity. Important advance for 3 reasons – Circulation – Movement – Organ function • Pseudocoelomate – body cavity located between mesoderm and endoderm • Coelomate – body cavity located within mesoderm Pseudocoelomates: Nematoda and Rotifera • All pseudocoelomates lack a defined circulatory system, but most have a oneway digestive tract (meaning mouth and anus now) • In all pseudocoelomates, the pseudocoel serves as a hydrostatic skeleton • muscles can work against the rigidity of the fluidfilled cavity • Nematodes – unsegmented worms with a cylindrical (i.e., round) body – covered by a flexible, thick cuticle that is shed as they grow in a process called molting – About 50 species of nematodes regularly parasitize human beings • Trichinella causes trichinosis after consuming raw or undercooked pork • From here on out, all organisms we discuss are coelomates Mollusks • The only major phylum of coelomates without segmented bodies are the mollusks (phylum Mollusca) • Basic body design • a head and foot – the foot is muscular and may function in locomotion, attachment, or food capture • a central visceral mass – contains the body’s organs • a mantle – a heavy fold of tissue that surrounds the visceral mass – respiratory organs are positioned on the inner surface of the mantle • 3 major groups – gastropods • use the muscular foot to crawl and their mantle often secretes a single, hard protective cell • all terrestrial mollusks are gastropods – bivalves • secrete a two-part shell with a hinge and filter-feed by drawing water into their shell – cephalopods • have a modified mantle cavity that permits jet propulsion and, in most groups, the shell is reduced or absent Pearls • In mollusks with shells, – the outer layer of the shell consists of horny material that is rich in protein – the inner layer of the shell consists of pearly material that is used as mother-of-pearl • pearls are formed in clams and oysters when a foreign object becomes lodged between the mantle and the inner shell • the mantle coats the foreign object with layer upon layer of shell material to reduce irritation Annelids • The first segmented animals to evolve were the annelid worms (phylum Annelida) • Segmentation is the building of a body from a series of similar segments – a small change in an existing segment can produce a new kind of segment with a different function – This allows for two important advancements 1. specialized segments • 2. the anterior segments contain sensory organs and a brain connections • • circulatory system is required because the segments are divided by partitions a nervous system allows for coordination Arthropods • All arthropods have jointed appendages, including legs, wings, antennae, and mouthparts – • Without jointed appendages, it is impossible to walk, fly, or grasp an object Arthropods also developed a rigid, chitinous exoskeleton on the outside of their body – – provides points for muscle attachment one drawback of a chitinous exoskeleton was that it prevented arthropods from reaching immense sizes Embryo development • Up to this point, all coelomates develop the same way – called protostomes • From here on out, organisms will develop in a different way - deuterostomes Echinoderms • Echinoderms (phylum Echinodermata) were the first deuterostomes to evolve – their name means “spiny skin,” which refers to an endoskeleton composed of hard, calcium-rich plates called ossicles that lies just beneath the skin – all echinoderms are bilaterally symmetrical as larvae but become radially symmetrical as adults – a key innovation in echinoderms is a hydraulic system that aids in movement called the water vascular system • it is a system of fluid-filled canals that extend into numerous, hollow tube-feet Chordates • Chordates (phylum Chordata) are deuterostome coelomates characterized by a flexible rod called a notochord that develops along the back of the embryo • 4 principal features of chordates 1. 2. 3. 4. • • • • notochord a stiff but flexible rod that forms beneath the nerve cord in the early embryo nerve cord a single dorsal hollow nerve cord pharyngeal pouches a series of pouches behind the mouth that develop into slits in some animals postanal tail a tail that extends beyond the anus, at least during embryonic development • All vertebrates are chordates – – the only non-vertebrate chordates are the tunicates and the lancelets vertebrates are distinguished by having • • backbone (comprised of a series of hollow bones) that replaces the notochord head with a skull and brain Chordate phylogenetic tree Fish • Vertebrates first conquered the sea, then the land • 4 characteristics that all fish share 1. 2. 3. 4. gills fish use gills to extract dissolved oxygen from water vertebral column all fishes have a skeleton made of either bone or cartilage single-loop blood circulation blood is pumped from the heart to the gills, to the body, and then back to the heart nutritional deficiencies fish are unable to synthesize the aromatic amino acids and must consume them in their diet The first fishes to evolve were jawless Later, predatory fishes with jaws evolved, which eventually gave rise to the sharks and bony fishes At this point, we are talking about various classes not phyla anymore – all organisms are part of the chordata phylum Sharks and rays • Sharks and rays are members of the class Chondrichthyes • Sharks evolved into fast swimmers because their cartilaginous skeleton is light and flexible Bony fishes • Bony fishes (class Osteichthyes) consist of about 30,000 species • Have a heavy internal skeleton of bone but are still buoyant because of a swim bladder – the swim bladder is a gas-filled sac that allows fish to regulate their buoyant density • Have a gill cover called the operculum – allows them to breathe without having to move Amphibians • Amphibians have five key characteristics that allowed them to successfully invade land 1. 2. 3. 4. 5. legs lungs cutaneous respiration supplements the use of lungs pulmonary veins returns oxygenated blood from the lungs to the heart for repumping partially divided heart helps to prevent the mixing of oxygenated blood with deoxygenated blood must reproduce in water and are not completely terrestrial many have a tadpole or intermediate larval phase Major groups include Frogs and Toads Salamanders and newts Caecilians Reptiles • Reptiles replaced amphibians as the dominant terrestrial vertebrates because of important features – amniotic egg • reptiles lay watertight eggs with various layers that protect and nourish the embryo – dry skin • the skin of reptiles is covered by dry scales that prevent water loss – thoracic breathing • reptiles expand and contract the rib cage to move air in and out of the lungs • Major groups – Turtles and tortoises – Crocodiles and alligators – Snakes and lizards Birds • Birds evolved from small bipedal dinosaurs – modern birds lack teeth and have only vestigial tails – they lay amniotic eggs and have reptilian scales on their feet and lower legs – birds are unique from reptiles in having • feathers--lightweight and adapted for flight • flight skeleton--rigid for attaching flight muscles; the bones are thin and hollow Mammals • Mammals share three major characteristics – mammary glands • female mammals have mammary glands that produce milk to nurse the newborns – hair • the primary function is insulation • hair is made up of dead cells filled with the protein, keratin – middle ear • all mammals have three middle ear bones that evolved from bones in the reptile jaw • 3 major groups – Monotremes – lay eggs, duck-billed platypus – Marsupials - kangaroos – placental mammals--most species of mammals today are placental mammals