Cnidaria - Phylum Cnidaria body wall is composed of 2 cell...

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Phylum Cnidaria: -- body wall is composed of 2 cell layer, outer ectoderm and inner endoderm with structure-less layer (mesoglea) between them - Diploblastic -- Body wall contains a single cavity, enteron (single opening surrounded by tentacles for ingestion and egestion) -- excretion, respiration by diffusion - Nervous system is a network cells -- planula larva is produced from sexual reproduction, asexual budding is another form of reproduction -- two body forms: polyp and medusa -- Dimorphic - Nematocysts (stinging threads) are used to capture prey - 11, 000 species -- Hydrozoa Scyphozoa Cubozoa Anthozoa Lifestyle Solitary or colonial Solitary Solitary Solitary or colonial Body Form 1. Polyp P A (or reduced) A (or reduced) P 2. Medusae P P P A -- anthozoans won't be mentioned -- Solitary : single organism Colonial : a group of differentiated organisms -- scyphozoans and Cubozoans are true jellyfish -- polyp form is absent in true jellyfish, swim around -- polyp is non-motile (attaches to substratum) Body Forms: -- cnidarians have two morphological types - dimorphic, they are also diploblastic -- outer ectoderm is epidermis and inner endoderm which is gastrodermis -- ectoderm = epidermis -- endoderm = gastrodermis -- b/w epidermis and gastroderis there's mesenchyma no cells = mesoglea -- mesenchyma is most prominent in medusae form (i.e. jellyfish) -- in medusae, mesenchyma is jelly like substance (acellular- no cells = mesoglea) -- have gastrovascular cavity, there's extracellular digestion taking place -- in Cnidarians, mouth and anus are in same place Polymorphic colonial forms - sessile: horizontal stratification -- multiple organisms that are associated as one, but are functionally differentiated -- mutualistic hydrozoan colony found on hermit crab shell -- colony offers protection to crab, while the crab offers food to cnidarians 1. Gastrozoid Polyps: feeding polyps with mouth and tentacles for prey capture - it gets food, and then shares it with other polyps 2. Dactylozoid: "naked" polyps without mouth or tentacles -- functions include prey capture and defence -- DEFENSE
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3. Gonozoid polyps: reproductive naked polyps without mouth, no tentacles or mouth -- produce male or female gametes/ medusae Free living polymorphic colonial forms - Physalia Physalis (Portuguese Man-O'-War) -- functionally differentiated polyp morphs -- gas-filed float (filled with Carbon monoxide) at the top: -- vertical stratification, -- Gonozoids : at top, male and female Gastrozoid: below gonozoid, with 1 single tentacle and terminal mouth for feeding Dactylozoids : very highly retractable -- used for defense and prey capture -- tentacle drags very hard behind organism, when tentacles come into prey contact, release toxins, immobilize prey, -- the tentacles are very long -- about 130 metres -- pour salt and put water over 45 degrees on stung area Distinguishing free living medusae forms: Hydrozoan Scyphozoan Velum (membranous covering) is present Velum is absent Manubrian is present Manubrian is absent (4 large oral lobes instead) Gastrovascular cavity connects to 4 radial canals and a ring canal -- this allows to get access nutrients faster
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Cnidaria - Phylum Cnidaria body wall is composed of 2 cell...

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