Ctenophore Ctenes - Lecture notes 7 PDF

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lecture notes on ctenophores and platyhementhes...

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Ctenophore Ctenes o 8 bands of cilia o Used for  Locomotion  Moving through canals o Will refract light to create rainbow waves o Largest organisms to move through ciliary action o Feeding  Collobasts (sticky cells) on tentacles catch prey  Prey brought up to mouth via muscular contractions  Food digested in pharynx and passes through stomach out to gastrovascular canals  Eat plankton - zooplankton  Focus on jelly organisms o Ctenophore Gut  Pass through gut - implications for the evolutionary timeline of through guts and anuses  Unclear if this is convergent evolution or if through guts evolved earlier and were lost in some taxas  Phylum Platyhelminthes o Body symmetry review  Radial - universally symmetrical  Bilateral - one plane of symmetry o Bilateral Cephalization  The concentration of sensory and feeding structures at the head of the organism  Dorsal = top side  Ventral = bottom side  Anterior = front end  Posterior = Back end o Bilateral Body Cavity Functions  Hydrostatic skeleton  Movement  Support  Excretion  Reproduction  Circulation  Nerve / sense organs o Bilateral Hydrostatic Skeletons  Lophotrochozoa (“squishies”)  Without cuticle  muscle s for layers  Hydrostatic support leads to lengthening and thickening at the same time  Peristaltic motion good for burrowing  Ciliary movement possible for small animals or certain parts  Ecdysozoa (“crunchies”)  With cuticle to provide rigidity  Muscles do not form layers, attached to bend cuticle elements  Hydrostatic support will lead to a more whip-like motion

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 No ciliary movement possible Bilateral Body Cavity Types  Acoelomates  No cavity, compact organization  Mesoderm mostly solid mass of tissue  Pseudocoelomates  Cavity without epithelial lining  Organs lie free within this cavity  Coelomates  Cavity lined with epithelial lining  Organs surrounded by peritoneum Platyhelminthes Diversity  Platyhelminthes Characters  Acoelomate  Three tissue type  Incomplete gut  Organ system  Hermaphroditic  Dorsoventrally compressed  Taxa  Class Proseriata  Flatworms  Class Trematoda  Flukes  Cohort Cestoda  Tapeworms  *cohort - group of orders, less than class* o Proseriata Epidermis  Ciliated cells  Rhabdoids  Secrete mucus  Produced by gland cells in the skin or mesenchyme  Three muscle arrangements  Longitudinal  Circular  Diagonal  Mesenchyme  Loosely organized cells between body wall and organs  Mainly amoeboid cells, extracellular matrix, muscle fibers, and connective tissue o Trematoda Epidermis  Disorganized surface  Spines  Pinocytotic vesicles  Thin basement membrane o Cestoda Epidermis  Surface covered by microtriches  Folds to increase surface area and nutrient intake  Food vacuoles  Syncytial zone

More open flow of cytoplasm creating the covering of the organism  Thicker baseement membrane o *Tegument* - allow for direct absorption of nutrients o Proseriata Feeding Strategies Active carnivores  Known barnacle hunters Detritivores Herbivores Symbiotic with algae o Digestive system Mouth → Pharynx → Enteron Pharynx  Simple - short, ciliated tube  Complex - additional folds Increasing size leads to increasing complexity of gut Basic sac-like gut Triclad intestine - 3 main branches Multibranched gut Diverticulata - extensions of the gut that facilitate absorption by the organism o Proseriata Osmoregulation and Waste Protonephridium  Same space for ultrafiltration and reabsorption o Reproduction Asexual - binary fission o Regeneration Cells in mid-body region relatively undifferentiated (neoblast)  Can become either head of tail as needed o Review First triploblastic organisms Show cephalization 3 groups  Class proseriata - flatworms  Class trematoda - tapeworms  Cohort cestoda - flukes Variety of feeding strategies  Proseriata - carnivores, herbivores, detritovores, symbiotic  Trematoda and cestoda - parasites  Proseriata regenerate o Cestoda and trematoda lifestyle Both parasitic Feeding and reproduction tightly linked  Simultaneous fertilization Require hosts, multiple hosts for different life stages o Feeding apparatuses parasitic flatworms Cestoda  Tapeworms  Hooks and suckers Trematoda 

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Flukes Suckers, oral and lateral o Cestoda lifestyle Cysticerus is unique to cestoda Larvae become cysticerus, which is transmitted  

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