3454lablecture2 - Lecture 2 PHYLUM CNIDARIA Tissue level of...

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Lecture 2 PHYLUM CNIDARIA Tissue level of organization, simple nerve net Diploblastic – two tissue layers: Epidermis: outer skin, contains cnidocytes, epitheliomuscular cells, interstitial cells, neurosensory cells Gastrodermis: lines gastrovascular cavity, nutritive muscular cells, interstitial cells, gland cells Mesoglea – nonliving gelatinous layer in middle Mouth serves same function as anus Circular muscles elongate body Longitudinal muscles shorten body Life cycle Polyp (sessile form) – asexual reproduction Medusa (mobile form) – sexual stage, gonochoristic Class Hydrozoa – both stages dominant Class Schyphozoa – Medusa stage dominant Class Anthozoa – Only Polyp stage General life cycle: Sperm and egg meet externally, form zygote, form actinula (or planula) larvae, form polyp stage, asexual buds from polyp form medusa stage and cycle starts over
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PHYLUM CNIDARIA CLASS HYDROZOA – all medusa have characteristic velum ORDER HYDROIDEA Hydra – single polyp, no medusa stage
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3454lablecture2 - Lecture 2 PHYLUM CNIDARIA Tissue level of...

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