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Phylum Cnidaria • jellyfish, hydras, sea anemones, coral Cnidaria • have cnidocytes (stinging cells) which contain a nematocyst (harpoon-like structure) for stinging and paralyzing prey – located on tentacles discharged nematocyst barbs coiled nematocyst Tentacle Cuticle of prey Thread Nematocyst “Trigger” Thread discharges Cnidocyte Thread (coiled) Cnidaria • Radial Symmetry • • made up of two tissue layers – endoderm and ectoderm separated by mesoglea Have two body forms: polyp and medusa Polyp Mouth/anus Tentacle Medusa Gastrovascular cavity Endoderm Body stalk Mesoglea Ectoderm Tentacle Mouth/anus – Some cnidarians alternate between the 2 body forms: • polyp – sessile, usually perform asexual reproduction • medusa – free floating, usually perform sexual reproduction Feeding polyp Reproductive polyp Medusa bud ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps Haploid (n) Diploid (2n) Gonad Medusa Egg SEXUAL REPRODUCTION Sperm FERTILIZATION Zygote 1 mm Key MEIOSIS Developing polyp Mature polyp Planula (larva) • Class Hydrozoa – hydras, Obelia, and Portuguese Man-of-War – usually alternate between polyp and medusa stages Portuguese Man-of-War • Class Scyphozoa – true jellyfish – have medusa as their primary body form Jellies • Class Anthozoa – exists only as polyps, sea anemones and coral Sea anemone (class Anthozoa) • Class Cubozoa – “box jellies”, sea wasps, marine, box-shaped medusae, potent venom Sea wasp (class Cubozoa) Reproduction • • • asexual reproduction by budding sexual reproduction by producing sperm in testes and eggs (ova) in ovaries fertilized egg becomes a larva which develops into an adult Digestion • • food is taken in and wastes are expelled through the same opening – mouth digestion and circulation occur in the gastrovascular cavity Polyp Mouth/anus Tentacle Medusa Gastrovascular cavity Endoderm Body stalk Mesoglea Ectoderm Tentacle Mouth/anus Cnidaria • • have nerve tissue for coordinated movement tissue level of organization
