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Chapter 23 Invertebrates: Learning Goals What Are the Key Features Of

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Chapter 23 Invertebrates: Learning Goals What Are the Key Features Of Chapter 23 Invertebrates: Learning Goals . What Are the Key Features of Animals? . Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . What Are the Major Animal Phyla? . You should be able to match the common name to the Phyla and explain it’s impact on humans What Are the Key Features of Animals? . Animals possess all of the following characteristics – Multicellularity – Their cells lack a cell wall – They obtain energy by consuming other organisms – Most reproduce sexually – They are motile at some point in the life cycle – They are able to respond rapidly to external stimuli Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Most animal phyla that currently populate Earth were present by the Cambrian period (544 million years ago) – The scarcity of pre-Cambrian fossils led systematists to search for clues about the evolutionary history of animals by examining features of: –Anatomy –Embryological development –DNA sequences 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Certain features represent evolutionary milestones, and mark major branching points on the animal evolutionary tree – The appearance of tissues – The appearance of body symmetry – Protostome and deuterostome development An Evolutionary Tree of Some Major Animal Phyla Fig. 23-1 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Lack of tissues separates sponges from all other animals – Tissues are groups of similar cells that carry out a specific function (e.g., muscle) – Sponges are the only modern-day animals that lack tissues Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Animals with tissues exhibit either radial or bilateral symmetry – Symmetrical animals have an upper (dorsal) surface and a lower (ventral) surface – Symmetrical animals are divided into two groups: –Animals that exhibit radial symmetry –Animals that exhibit bilateral symmetry Body Symmetry and Cephalization central axis anterior plane of symmetry plane of symmetry posterior (a) Radial symmetry (b) Bilateral symmetry Fig. 23-2 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Animals with radial symmetry can be divided into roughly equal halves by any plane that passes through the central axis – Animals with radial symmetry have two embryonic tissue (germ) layers – Ectoderm, which is an outer layer that covers the body, lines its inner cavities, and forms the nervous system – Endoderm, which is an inner layer that lines most hollow organs – Bilaterally symmetrical animals have three embryonic tissue (germ) layers – A layer of mesoderm between the ectoderm and endoderm 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Bilaterally symmetrical animals have heads – Animals with bilateral symmetry can be divided into mirror-image halves only along one plane that runs down the midline – These animals exhibit cephalization, the concentration of sensory organs and a brain in a well-defined head, with definite anterior (head) and posterior regions Body Symmetry and Cephalization central axis anterior plane of symmetry plane of symmetry posterior (a) Radial symmetry (b) Bilateral symmetry Fig. 23-2 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Most bilateral animals have body cavities – Body cavities are fluid-filled cavities between the digestive tube and the outer body wall 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Body cavity structure varies among phyla – The most common body cavity is a coelom, a fluid-filled body cavity that is completely lined with mesoderm –Phyla with animals that have this type of body cavity are called coelomates, and include annelids, arthropods, mollusks, echinoderms, and chordates (which include humans) Body Cavities The body cavity is The body cavity is partially, There is no cavity completely lined with tissue but not completely, lined with between the body wall derived from mesoderm tissue derived from mesoderm and digestive tract body wall body wall coelom pseudocoelom body wall digestive digestive digestive tract tract tract digestive digestive digestive cavity cavity cavity (a) “True” coelom (b) “False” or pseudocoelom (c) No coelom (annelids, chordates) (roundworms) (cnidarians, flatworms) Fig. 23-3 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? – A body cavity that is not completely surrounded by mesoderm is known as a pseudocoelom –Phyla with animals that have this type of body cavity are called pseudocoelomates and include roundworms, such as nematodes Body Cavities The body cavity is The body cavity is partially, There is no cavity completely lined with tissue but not completely, lined with between the body wall derived from mesoderm tissue derived from mesoderm and digestive tract body wall body wall coelom pseudocoelom body wall digestive digestive digestive tract tract tract digestive digestive digestive cavity cavity cavity (a) “True” coelom (b) “False” or pseudocoelom (c) No coelom (annelids, chordates) (roundworms) (cnidarians, flatworms) Fig. 23-3 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Bilateral organisms develop in one of two ways based on embryological development – Protostome development – In these animals, the body cavity forms within the space between the body wall and the digestive cavity – These animals include nematodes, arthropods, annelids, and mollusks – Deuterostome development – In these animals, the body cavity forms as an outgrowth of the digestive cavity – Echinoderms and chordates are deuterostomes • Embryonic Development Protostomes Blastopore forms mouth first Deuterostomes Blastopore forms anus first • Molecular sequences 23.3 What Are the Major Animal Phyla? . Sponges have a simple body plan – Sponges belong to the phylum Porifera and are found in most marine and aquatic environments –Sponges do not move, but occur in a variety of sizes and shapes –They may reproduce asexually by budding, where the adult produces miniature versions of itself that drop off and assume an independent existence –They may reproduce sexually through fusion of sperm and eggs An Evolutionary Tree of Some Major Animal Phyla Fig. 23-1 The Diversity of Sponges Fig. 23-4 23.3 What Are the Major Animal Phyla? . Some sponges contain chemicals useful to humans – A number of chemicals within sponges have proved to be valuable medicines –The drug spongistatin is an emerging treatment for the fungal infections that sicken AIDS patients –Some medicines derived from sponges include some promising new cancer drugs 23.3 What Are the Major Animal Phyla? . Sponges lack true tissues and organs – The sponge body is perforated by tiny pores through which water passes, and by fewer, large openings through which water is expelled – As water passes through the sponge, oxygen is extracted, and microorganisms are filtered out and digested by individual cells The Body Plan of Sponges (water flow out of the sponge) epithelial cell pore spicules (water flow into the sponge) amoeboid cell pore cell collar cell (water flow) Fig. 23-5 Cnidaria – Sea Anemone . Radial symmetry . Two tissue layers . Filled with water . Nematocysts - stinging organelles that release toxins 23.3 What Are the Major Animal Phyla? . Cnidarians are well-armed predators – Sea jellies, sea anemones, corals, and hydrozoans belong to the phylum Cnidaria – These animals are mostly marine and are all carnivorous predators – The cells of cnidarians are arranged into distinct tissues, including a contractile muscle-like tissue and an organized nerve net An Evolutionary Tree of Some Major Animal Phyla Fig. 23-1 Cnidarian Diversity Fig. 23-6 Echinoderms - starfish . Endoskeleton . Coelom (cavity lined with tissue)forms from gut tube tissue . Deuterostomes . Water vascular system . Tube feet (locomotion) 23.3 What Are the Major Animal Phyla? . Echinoderms have a calcium carbonate skeleton . The phylum Echinodermata includes sand dollars, sea urchins, sea stars, sea cucumbers, and sea lilies – Echinoderm larvae exhibit bilateral symmetry; adults show radial symmetry The Diversity of Echinoderms Fig. 23-27 Platyhelminthes - flatworms . Bilateral symmetry . 3 tissue layers . Cephalization (nerve mass) . True organs and organ systems . Aceolomate (no body cavity) . Parasitic forms 23.3 What Are the Major Animal Phyla? . Some flatworms are harmful to humans – Tapeworms can infect people who eat improperly cooked beef, pork, or fish that has been infected by the worms –Tapeworm larvae form encapsulated resting structures, called cysts, in the muscles of these animals –The cysts hatch in the human digestive tract, and the young tapeworms attach themselves to the lining of the intestine 23.3 What Are the Major Animal Phyla? . Some flatworms are harmful to humans (continued) –Tapeworms may grow to a length of more than 20 feet (7 meters), absorbing nutrients across their outer surface –They release eggs that are shed in the hosts feces, continuing the infective cycle The Life Cycle of the Human Pork Tapeworm 1 A human eats poorly cooked pork with live cysts 2 A larval tapeworm is liberated by digestion and attaches to the human’s adult tapeworm head (attachment site) intestine 6 inches 3 The tapeworm matures in a human intestine, producing a series of reproductive segments; each segment contains both male and female sex organs 8 The larvae
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