Phylum Cnidaria 10:10 - Lecture notes 13 PDF

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Friday, 4 June y Organismal diversity

Phylum Cnidaria Radially symmetric • Jellyfish, anemones, corals, hydroids Very diverse •

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Medusoid stage definition: A hydroid has typically three lifecycle stages. The first stage is a tiny pelagic larva. The larva develops into a second, often colonial, hydroid stage. ... The medusae are released from the colony and become pelagic. The body in the medusoid stage take the shape of dome-like umbrella with tentacles along the edge :Characteristics Radial symmetry - symmetry exists around one axis - Oral:aboral axis Animals simultaneously face all compass directions • Useful to have all feeding and sensory organs available in all • : directions when Danger can approach from any direction • Food has to drift or swim into their path inadvertently • Two body forms; same internal structure • Gastric cavity •

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:Taxonomy : Class: Anthozoa • ( Sea anemones (solitary • Class Anthozoa; corynactis viridis - The jewel anemone • Class Anthozoa: Urticina Felina - The dahlia anemone • Hard and soft corals • ( (colonial Sea fans • ( Sea pens (colonial • Sub tidal • Medusoid stage in • life cycle is absent Cnidarian Taxonomy Class Scyphozoa • The jellyfish • Medusoid stage is the • most conspicuous Class Hydrozoa • Very diverse group • Mostly colonial • Benthic hydroids • Pelagic Portuguese man-of-war • Often reduced medusoid stage in life • :Morphology 1

Friday, 4 June y Main features: gut like cavity, surrounded by a solid body wall • Gut like cavity • called a Coelenteron opens to the exterior via a mouth main layers of 2 • cells = diploblastic These are called • the epidermis and the gastrodermis In between these • there is gelatinous matrix called mesoglea

Body wall :structure Most stinging cells • are found on the epidermis Lots of mucus inside • and out Gastrodermis - digestio and gonad • Mesoglea contains muscular cells • Epidermis - sensory cells and nematocysts •

:Nematocysts Found throughout the epidermis • High densities on tentacles, prey catching or defensive structures. • Some have localised high densities in gastrodermis – quell swallowed prey

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Friday, 4 June y

:Stages of attack 1. Cnidocil is stimulated 2. The ions in fluid surrounding coiled hollow tubule disassociate from macromolecules - increases osmotic pressure 3. Results in the opening of the operculum 4. Water rushes into capsule 5. Increased pressure causes coiled tubule to be everted rapidly Undischarged:

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Discharged:...