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Phylum Cnidaria Jelly Fishes Sea Anemones Corals Phylum Cnidaria • A.k.a Coelenterata or Radiata • Differ from sponges - have rudimentary organs Morphology • Body wall - 3 layers • Epidermis • Gastrodermis • Mesoglea Body plans • Sessile - Polyp (hydranth or hydroid) • Cylindrical stalk and oral end with tentacles Body Plan • Free swimming Medusa • Bell shaped • Mesoglea constitutes bulk Cell Types • Epithelio-muscle cells • Cover and protect • Can contract (muscular properties) • Interstitial cells • Production of gamets • Mucous secreting cells (Gland cells) • Nerve cells • Cnidocytes Cnidocyte • On Tentacles • Defense and feeding • Nematocyst • Cnidocil - trigger Nervous System • First time • Nerve net • 2 nets • Associated with epidermis and gastrodermis Classification • • • • 3 Classes Hydrozoa Scyphozoa Anthozoa Hydrozoa • Polymorphic • Polyp - Hydra • Medusa - Obelia • Simple gastrovascular cavity - no septa • No nematocysts in digestive cavity • Solitary or colonial Close-up of Hydroid Hydroid medusa Composition of Colonies • 3 types of individuals • Gastrozooid - responsible for feeding also numerous • Gonozooid - sexual reproduction • Dactylozooids - defense and food capture Life Cycles • 3 basic types • Obelia - both polyp and medusa stage • Hydra - only polyp – Asexual reproduction - budding • Physalia - Colony attached to float called Pneumatophore Scyphozoa • Exclusively marine • Medusa dominant stage • Much larger in size compared to hydrozoan medusae Scyphozoa • Mesoglea makes up large portion of body • Gastrovascular cavity divided by septa • complex system of canals in medusa to help move food and oxygen • Muscular system on outer edge of medusa • Very toxic - can kill in 30 secs or less Sense organs • 8 compound marginal sense organs – 2 sensory pits - chemoreception – 1 ocellus (eye spot) - light sensing – tactile structures - touch sensitive – 1 statocyst - orientation and balance Reproduction Anthozoa • None have medusa - Only Polyp • Hence Sessile • Several Septa in Gastro-vascular cavity • Attached to substrate by Pedal Disk Phylum - Ctenophora Combjellies or Sea Walnuts • • • • • Offshoot of Medusa like Cnidarian Transparent animals Never colonial Free swimming No nematocysts instead have COLLOBLASTS – adhesive cells Characteristics • 8 rows of fused cilia (combs) • Nervous system – nerve net • Single sense organ – Statocyst • Cydippid larva • Bioluminescence
