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How does Cnidaria fit in? Cnidaria 3 classes:Hydrozoa, Scyphozoa, Anthozoa Porifera 2 body types: polyp, medusa diploblastic 3 body types tissue level choanocytes of organization cellular level of organization Blastula stage heterotrophic multicellular eukaryote unknown common ancestor How do the Acoelomates fit in? the acoelomates Platyhelminthes Porifera Cnidaria unknown common ancestor Nemertea The Acoelomates Acoelomate Characteristics Organ level of organization Tissues are organized to for organs which are used to accomplish physiological functions Acoelomate Characteristics Triploblastic 3 Embryonic Germ Layers 3 Tissue Layers endoderm gastrodermis mesoderm mesoderm ectoderm epidermis Acoelomate Characteristics No body cavity ectoderm ectoderm mesoderm mesoderm Gut endoderm endoderm Acoelomate Characteristics Mesoderm (mesenchyme, parenchyma) Triploblastic Gut Ectoderm Endoderm Acoelomate Characteristics Bilateral Symmetry Anterior: toward the front of the body Posterior: toward the rear of the body Acoelomate Characteristics Cephalization the concentration of sensory organs in the head of the animal Eye spots Auricles Phylum Platyhelminthes the flatworms Physiology Feeding – Free-living, carnivorous – parasitic Digestion – intestine is simple or branched – incomplete system (no anus) – digestive system reduced or absent in parasitic species Physiology Osmoregulation and excretion – Protonephridia and flame cells – much excretion is via diffusion protonephridia flame cell Physiology Nervous system -ladder-like -cephalization -nervous system is reduced in parasitic species Skeletal and circulatory systems – absent Cerebral ganglia Lateral nerve cords Physiology Reproduction Asexual Sexual – usually monoecious, but most must cross fertilize – Internal fertilization (usually reciprocal) Phylum Platyhelminthes Class Turbellaria Class Trematoda Class Cestoda Class Turbellaria Free-living flatworms • move on slime trails using cilia Class Turbellaria • predatory • use a pharynx to capture prey pharynx Class Turbellaria • have a branched (or lobed) gut ClassTurbellaria Reproduction Asexual – Fission ClassTurbellaria Reproduction Sexual – internal fertilization – simple life cycle Adaptations for Parasitism • increased reproductive potential • monoecious • presence of adhesion organs (suckers, hooks) • poorly developed sensory systems • reduced, or absent, digestive system • resistant cuticle • complex life cycles with more than 1 host Class Trematoda Parasitic Flukes • endoparasitic Trematoda Life Cycle • have at least two hosts in their life cycle • final host = vertebrate Vertebrate host #1 infective stage in host muscle Vertebrate host #2 Invertebrate host eats eggs adult fluke (in host liver) Class Cestoda Parasitic tapeworms Class Cestoda 2 body regions: scolex and proglottids scolex proglottids Class Cestoda Scolex suckers rostellum Class Cestoda Proglottids • repeating segments containing reproductive organs • may be immature, mature, or gravid Class Cestoda Immature proglottids • found at the anterior end of the tapeworm • contain no noticeable sex organs Class Cestoda Mature proglottids • found in the middle of the tapeworm • contain noticeable sex organs • sperm must come from either a different proglottid or a different individual Class Cestoda Mature proglottids genital pore sperm duct vagina uterus ovary testes Class Cestoda Gravid proglottids • found at the posterior end of the tapeworm • contain fertilized eggs • entire proglottid is shed in the host’s feces uterus eggs Cestoda Life Cycle Adult tapeworm (in host intestine) Gravid proglottids Vertebrate host #2 Infective stage in host muscle eggs Vertebrate host #1 Ecology •Parasitic flatworms infect many people in some parts of the world (for example, the Chinese liver fluke infects approx. 30 million people in Asia) •Some Trematodes have display polyembyony: a single larvae can have up to 4 younger larvae developing within it •Trematodes are a model system for studying host parasite coevolution Phylum Nemertea the ribbonworms Physiology Feeding – Free-living, carnivorous – have an eversible proboscis that is not connected to the digestive system – Proboscis is used to stab prey and may have a poisonous tip (or stylet) Physiology rhynchocoel proboscis mouth rhynchocoel Physiology Digestion – intestine is unbranched – complete system (mouth and anus) This is the first animal to have an anus!!! Physiology Reproduction Asexual – Some species are capable of reproducing asexually through fragmentation and regeneration Sexual – usually dioecious – internal fertilization Physiology Osmoregulation and excretion – same as Platyhelminthes Nervous system – same as Platyhelminthes Skeletal system same as Platyhelminthes Physiology Circulation – closed circulatory system consisting of contractile blood vessels This is the first animal to have a closed circulatory system!!! Ecology •Nemerteans are mostly marine, although there are a few species found in freshwater (and even a few on land!) •They range in size from a few millimeters to 30 meters •Their biology is little known in part because they are extremely fragile and fragment easily How do the acoelomates fit in? Nemertea Platyhelminthes acoelomate Complete digestive system acoelomate Cnidaria Porifera Closed circ. system Ladder-like nervous system proboscis cephalization protonephridia organ level of organization triploblastic unknown common ancestor
