Phylum Cnidaria

Symmetry Radial or Biradial Advantageous because it allows for sensory structures are evenly distributed around the body.

Diploblastic Tissue level of organization Ectoderm forms epidermis (outer layer) Endoderm forms gastrodermis (inner layer) Mesoglea contains some cells but does not have true tissues.

Cnidocytes Cnida: fluid-filled, intracellular capsule enclosing a coiled hollow tube Operculum: lid Cnidocil : stimulation of the cnidocil forces open the operculum and discharges the coiled tube.

Nematocyst Specialized cnidocyte Used in food gathering and defense Armed with spines that penetrate the prey and release paralyzing toxins Other cnidocytes Wrap around prey Sticky secretions that help in attachment

Alternation of Generations Most Cnidarians possess two body forms in their life histories. Polyp Asexual and Sessile Attaches to a substrate at aboral end Mouth is surrounded by food-gathering tentacles

Alternation of Generations Medusa Dioecious and free-swimming Shaped like an inverted bowl with tentacles hanging Mouth faces downward Swims by pulsations of the body wall

Maintenance Functions Gastrovascular Cavity Functions in digestion, respiration, excretion, and discharge of gametes Feed on small crustaceans and fish Nematocysts entangle and paralyze prey Tentacles shorten which draws food to the mouth Mucus and enzymes dissolve food in the gastrovascular cavity which are phagocytized and further digested.

Maintenance Functions Hydrostatic skeleton Water or fluids in body cavity and against which contractile elements of the body wall act. Think of a balloon Polyps: somersault, glide or inch across the substrate Medusa: swim or float

Maintenance Functions Nerve Net Simple nervous system Nerve cells located below epidermis and interconnect…this creates a nerve net. The net conducts impulses around the body in response to a localized stimulus. Response changes due to stimulus strength.

Reproduction Most are separate sexes Eggs and sperm are released into gastrovascular cavity Free swimming larva called planula Can also bud (become medusa)

Kingdom: Phylum: Classes: Animalia Phylum: Cnidaria Classes: Hydrozoa Scyphozoa Staurozoa Cubozoa Anthozoa

Class Hydrozoa Small, relatively common Mostly marine, some freshwater Alternation of generations Nematocysts are only in the epidermis Gametes are released to the outside Mesoglea does not contain cells

Class Hydrozoa Colonial Polyps Individuals are specialized for feeding, reproduction, or defending the colony Ex: Obelia, Gonionemus, Hydra (freshwater), Portuguese Man of War

Class Staurozoa All Marine Sessile, oral end looks like medusa Crawling larva…very little dispersal abilities ~100 species

Class scyphozoa All Marine “True Jellyfish” Dominant stage in life cycle is the medusa stage Most are harmless but some can be very dangerous to humans

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Class Cubozoa Medusa is cuboidal Tentacles hang from each corner Active feeders and swimmers in tropical waters Some possess dangerous nematocysts

Class Anthozoa Colonial or Solitary Lack Medusa All Marine External radial symmetry Internal biradial symmetry

Sea Anemones Solitary, large, and colorful Some attach to solid substrates, burrow in soft substrates, or live in symbiotic relationships

Sea Anemones Some move by thrashing or crawling along a surface Feed on invertebrates and small fish Asexual Reproduction: Fragmentation Sexual Reproduction Monoecious (protandry) Dioecious

Coral Stony Coral Soft Coral Look like anemones Have a calcium carbonate exoskeleton that they can retract into when threatened Soft Coral Do not have the CaCO3 exoskeleton

Symbiotic Relationships Sea anemone/Clownfish Coral/Zooxanthellae Protists that undergo photosynthesis and give the coral their color Also release carbon to build exoskeletons