BIOL 111 – Part 2 (lect 10-21) C. Aikins LECTURE 10: CNIDARIANS & PLATYHELMINTHES Lecture Outline • Embryonic development • Symmetry • Parasitism Animal Characteristics 1. Eukaryotic 2. Heterotrophic 3. Multicellular 4. No cell walls 5. Motile at some life stage 6. Diplontic life cycle **most animals also have tissues **most undergo unique embryonic development pattern Embryonic development • Zygote – diploid cell resulting from union of two haploid gametes (1st cell of 2nd generation) • Embryo – young animal or plant while it is still contained within a protective structure (e.g. seed coat, egg shell or uterus) • Two major processes occur during embryonic development o Cleavage – cell division . Process forming many cells from one cell o Gastrulation – in-folding . Process forming embryonic tissue layers (2-3) from one layer of cells • Zygote (cleavage and more cleavage) morula (solid ball) blastula (hollow ball) (gastrulation begins, making a blastopore) Gastrula Gastrula • An embryo at the stage following a blastula, when it is a hollow cup-shaped structure having 2-3 embryonic cell layers • These are called germ layers : o Ectoderm . outermost layer . develops into epidermis, nervous system o Endoderm . Inner lining of blastopore . Develops into the lining of the digestive and respiratory system o *** Organisms with 2 germ layers are diploblastic o Mesoderm . Inner lining . Develops into most internal organs: muscles, skeletal system, heart, stomach o *** Organisms with 3 germ layers are triploblastic • Archenteron o Hollow space past blastopore o Develops into digestive space (gut cavity) • Blastopore o Develops into mouth or anus Importance of more sophisticated embryonic development = ? • Make tissues o Enable body organization o Allows for more complex movement and activties • Makes Gut o Enables extracellular digestion . Larger particles can now be digested Types of Symmetry • Asymmetrical o No axis divides body into equal halves o Ex some sponges • Radially symmetrical o Symmetry along a central axis o Ex cnidarians • Bilateral symmetry o Single axis divides body into equal halves . Typically means there is a head o Called the midsagittal plane (between eyes) o Ex platyhelminthes PHYLUM Cnidaria • Jellyfish, sea anemones, corals, hydrozoans • ~11,000 species o mostle marine o microscopic to many meters o carnivorous (though they can have mutualistic relationship with algae) • diploblastic • nervous and muscular tissue simple body plan: • mouth/anus (from blastopore) • gastrovascular cavity (“blind gut” from archenteron) • gastrodermis (cell layer lining gut, from endodermis) • mesoglea (inner jelly) • epidermis (outer cell layer, from ectoderm) two body forms • poyp o sessile o ex sea anemone (can awkwardly move base if necessary) • medusa o motile o oral side down o ex jellyfish • most lifecycles include both body plans How do Cnidarians obtain energy? • Carnivorous, using cnidocysts to capture prey, inject prey with venom & stick to prey o Cnidocyst fires our nematocysts • Extracellular digestion in gastrovascular cavity • Corals can obtain a large portion of their energy from symbiotic algae (which are photosynthetic) Nervous system • Very simple • Nerve net • Little to no integration or processing of signals • Provide direct lines of communication between sensors and effectors (muscles) Reproduction • Asexual reproduction o Budding • Sexual reproduction o Medusa release sperm and egg planula larva poyp Cnidarian Diversity • Class Hydrozoa o Polyp dominant phase, most species alternate between polyp and medusa o Eg Hydra • Class Scyphozoa o Medusa is dominant, polyp is reduced o Eg jellyfish • Class Anthozoa o “flower animal” o Polyp is dominant, no medusa o Eg corals and anenomes CLASS Hydrozoa • Hydra o Freshwater o No medusa stage o Move by gliding, somersaulting or floating o 2-5mm • Portuguese man-of-war o Colonial polyps and medusas . Specialized cells for different functions . Gas-filled float . Tropical, subtropical oceans CLASS Scyphozoa • Jellyfish o Large amounts of mesoglea o Some nematocyts strong enough to be felt by humans o Prey on fish larvae and zooplankton o Important food for leatherback turtles o Eg Cassiopeia . “upside down jelly” . symbiotic algae in tentacles (need light) . tolerates low O2 conditions, and gets O2 and nutrients from symbionts CLASS Anthozoa • Sea anemones o Retracts tentacles in defence o Mutualistic (+/+) relationships with fish and shrimp . Exude mucus that prevents nematocysts from firing, and are protected. Prevent other fish from eating anemones • Corals o Mutualistic relationship with zooxanthellae (a dinoflagellate) o Secrete CaCO3 exoskeleton = reefs o Coral bleaching . Serious recent ecological problem . zooxanthellae expelled (eventually coral will die) . due to a variety of factors increasing water temperature increasing UV radiation pollution disease (bacteria) PHYLUM Platyhelminthes • “flatworms” • ~25,000 species • terrestrial (moist) or aquatic habitats • “free-living” (scavengers) or parasitic • 1mm to 10m • Tripoblastic • Move by cilia (at some stage in life) Body plan • Head o Eyespots with photoreceptors (know general direction of light) o Auricles – chemoreceptors “smell” • Highly branched digestive tract • Mouth on the back? • Bilateral symmetry Cephalization • The presenence of a head brings about cephalization • Concentration of neurons and sensory structures at the anterior end o Enables directed locomotion and behaviour o Senses encounter new environment first • Sensory structures o Mechanorecepors (touch) o Chemoreceptors (taste/smell) o Photoreceptors (light) Simple nervous system • Longitudinal nerve cords • Cerebral ganglion o Connection of nerves o “primitive brian” How do Platyhelminthes eat and breath? • Very high surface area/volume ratio • No respiratory system • No circulatory system • Have pharynx and highly branched digestive cavity o Brings nutrients across body • Some have no digestive cavity or mouth! (eg parasite) Platyhelminthes diversity • Free living o Class Turbellaria • Parasitic (+/-) o Class Monogenea . mostly ectoparasitic, on the outside o Class Trematoda . Mostly endoparasitic, live within o Class Cestoda . Endoparasitic CLASS Turbellaria • Free-living, planarians • Tubular pharynx, halfway down body • Amazing ability to regenerate o Anterior end will always develop into a head • Reproduce asexually by fission and sexually (mostly hermaphroditic) CLASS Monogenea • Ectoparasites • Flukes = flat body with suckers CLASS Trematoda • Endoparasites • Flukes • Schistosomiasis o Disease rarely causes death but can damage internal organs and impair growth in children o Common in Asia, Africa and S. America o Life cycle 1. Mature flukes in blood vessels of human intestine 2. Blood flukes reproduce sexually in human host. Fertilized eggs exit host in feces 3. Eggs develop in water into ciliated larvae. Larvae infect snails – intermediate host (shorter transitional stage) 4. Asexual reproduction within snail results in another type of motile larvae 5. Larvae penetrate skin and blood vessels of humans – primary host (organism reaches maturity and sexual reproduction) cycle repeats CLASS Cestoda • Endoparasites • Tapeworm • Habitat: intestines of vertebrates • Host-specific (different species have different hosts) • Adaptation o Scolex – suckers, hooks o Proglottids – reproductive sections • No mouth, no digestive system • Protective cuticle forms around embryos & terminal proglottid breaks off, passed via feces LECTURE 11: NEMATODES & ANNELIDS Lecture outline • Embryonic development (Part 2) o Formation of digestive tract • body cavities • Body segmentation • Nematodes • Annelids DIGESTIVE TRACT • Development of a digestive tract enables o Specialization of gut regions o Sequential food processing o Continuous operation . Continuous processing of food • Development o Protostomes . “first is mouth” . Blastopore mouth . New opening anus o Deutrostomes . “second is mouth” . blastopore anus . new opening mouth PROTOSTOME ANIMALS • Lophotrochozoans o Have one of the following characteristics (some may have lost it secondarily, or it only developed in some of the groups) o Lophophore – ciliated feeding/gas exchange structure o Trocophore - a ciliated free-living larval form o We’ll be looking at Flatworms, Annelids and Mollusks • Ecdysozoans o Have an external covering secreted by epidermis that must be shed in order to grow o We’ll be looking at nematodes, and arthropods BODY CAVITIES • Another major difference among protostomes is the presence and type of body cavity • There are three different body plans with regard to body cavities • Coelom = cavity (greek root) • Acoelomate o No coelom o Solid except digestive space o Have ectoderm muscle layer (mesoderm) Mesenchyme (unspecialized cells derived from mesoderm) gut (endoderm) • Pseudocoelomate o “false coelom” o mesoderm lines the outside of the coelom . does not completely line cavity, doesn’t wrap gut o have ectoderm muscle layer (mesoderm) pseudocoel (cavity) internal organs/gut • Coelomate o Mesoderm lines the entire cavity as a “peritoneum” . Lining derived from mesoderm o Ectoderm muscle (mesoderm) peritoneum (mesoderm) completely wrapping internal organs/gut o Many advantages . Isolates gut from body movement . Provides a hydrostatic skeleton that can assist in support and movement . Acts as a storage reservoir for gametes, wastes, etc… . Provides a space for organ development WAYS TO MAKE A COELOM • Schizocoely o Splitting within the mesoderm o Protosomes