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CNIDARIANS
What makes Cnidarians Unique?
• Cnidarians are group of animals that are very diverse from stony coral to jellyfish. What common thread keeps this phyla of animals together?
Common Thread
• Cniadarians are DIPLOBLASTIC (2 Layers – epidermis and gastrodermis)
• TRUE TISSUES(muscular, nervous, gastric)• CNIDAE (stinging tentacles)
Diploblastic Body
• The two tissue layers are the epidermis and the gastrodermis
• Mesoglea- Jelly like portion between that separates the two layers.
True Tissues
• True tissues: muscular, nervous, gastric
Cnidae
Cnidocytes used in defense, feeding, and attachment
Some Cnidocytes can produce Nematocysts or stinging cells
Nematocysts
Food gathering and defense.
Long tube with spines that penetrates prey delivering toxin
Nematocysts
Two Body Forms
• Polyp: tentacle up (anenomes, coral, hydra)
• Medusa: tentacle down (jellyfish)
Polyp Stage
• Sessile, Asexual Reproduction, usually attached to substrate, some “walk”
Polyp Stage
• Budding• Fission
Polyp Stage
Polymorphism in polyps
Medusa Stage• Dioecious, free swimming, sexual
reproduction• Develop reproductive organs (testis and
ovaries)
Reproduction
• Sexual and Asexual reproduction• Alternation of generations
Reproduction (sexual)
• Egg and Sperm released from GVC• Once combined egg + sperm will form a
planula (free swimming larva)• Once GVC devolops forms a Polyp
Reproduction (asexual)
• Budding• Fission
Alteration of Generations
• 2 Stages: Polyp & Medusa (dimorphic)• Polyp Stage – some species asexual
reproduction by budding, usually sessile
Nutrition• Gastrovascular Cavity: Functions in
digestion, the exchange of respiratory gases, metabolic waste, and release of gametes
Nutrition• Feeding: Prey mostly small crustaceans
(copepods) • Nematocysts paralyze prey, contractile
cells move prey to mouth, GVC releases enzymes
Skeletal System
• Hydrostatic – fluid filled body (mesoglea)• Epitheliomuscular cells (longitudinal and
circular)
Nervous System
• Nerve Net – Nervous system is spread throughout entire body
• Most primitive nervous system
• Some sensory structures – ocelli sense light
Circulation, excretion, respiration
• No special structures or tissues, these life functions are carried out directly with the environment
Hydrozoa
• Alteration of generation• Mostly Marine (although a few freshwater)
Hydra
Obelia
Physalia
Scyphozoa
• True Jellyfish• Mostly found in Medusa stage• Some harmful some not to humans• Ocelli (rhodopalia) allow for Phototaxis
(move toward light)
Cubozoa
• Box Jelly Fish• Some possess
dangerous nematocysts
• Active swimmers and feeders
• Tentacles on corners of medussa
Anthozoa
• Corals & Anemones• Lack medusa stage
Anemones
• Can move slowly over some surfaces• Live as individuals but in colonies• Feed on fish and crustaceans or organic
debris
Corals
• Secrete a calcium skeleton
• Stony coral, large polyped stony corals, and soft corals
• May use symbiotic algae called zooxanthelle for autotrophism.
• Can live individually or in groups.
Zooxanthelle
• Symbiotic Algae that provides food for the coral
• Found in reef-building coral
Soft Coral• No hard calcium skeleton (although may
contain fragments inside them)
Large Polyped Stony Coral (Octocoral)
• Have both soft tissue as well as produces a hard calcium skeleton
Stony Corals
• Little soft tissue mainly hard calcium skeleton
Reef building
• Corals can grow on one another to create entire reef systems
Issues Affecting Reefs
• Many Reef Ecosystems are in peril from being destroyed.
• There are many culprits aiding in destruction of the reefs.
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