Cnidaria Ctenophora

• What are Cnidarians generally classified as?

  Simple animals
• What type of tissues do Cnidarians possess?

  True tissues
• Are most Cnidarians sessile or motile?

  Most are sessile, but several are motile
• What is a nematocyst?


  A specialized stinging organelle found in Cnidocytes
• What triggers the firing of a nematocyst?

  Small stimuli
• What is the velocity and acceleration achieved by the tiny thread that bursts from a nematocyst?

  Velocity of 2 meters/sec and acceleration of 40,000× gravity
• How does a nematocyst affect its prey?

  It instantly penetrates and injects a paralyzing toxin
• What happens when a small animal brushes against a Cnidarian's tentacles?

  It is speared with hundreds or thousands of nematocysts and quickly immobilized
• How many species are there in the phylum Cnidaria?

  Over 9,000 species
• What are some examples of Cnidarians?

  Hydroids, sea anemones, and sea jellies
• What role do Cnidarians play in ocean ecosystems?

  They are architects of the ocean floor, producing reefs and coral islands
• What unique cells do Cnidarians possess?

  Cnidocytes
• Where are cnidocytes located in Cnidarians?

  In the invaginations of ectodermal and some endodermal cells
• How many types of cnidae can cnidocytes produce?

  Over 20 types
• What is the function of a nematocyst?


  To inject toxin for prey capture or defense
• What material are nematocysts made of?

  Chitin-like material
• What covers the end of a nematocyst capsule?

  The operculum
• What features may the filament of a nematocyst have?

  It may have tiny barbs or spines
• What is the cnidocil in cnidocytes?

  A trigger-like modified cilium
• What causes the discharge of a nematocyst?

  The combination of tensional forces and high osmotic pressure
• What happens when a nematocyst is stimulated to discharge?

  Water rushes in, increasing hydrostatic pressure
• What is the result of the operculum opening in a nematocyst?

  The filament is rapidly launched from the capsule
• Which Cnidarians can seriously harm humans?

  Only a few box jellyfishes and the Portuguese man-of-war
• What is the fossil history of Cnidarians?

  They have the longest fossil history with specimens from over 700 million years ago
• Where are Cnidarians typically found?


  Widespread in marine habitats, mostly in shallow warm tropical regions
• What types of environments do Cnidarians inhabit?

  Marine and some freshwater environments, but none are terrestrial
• How many traditional classes of Cnidaria are there?

  Four traditional classes
• What are the four traditional classes of Cnidaria?

  Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa
• What is the largest class of Cnidaria?

  Anthozoa
• What is unique about the class Staurozoa?

  It has no medusae in its life cycle but has a polyp topped by a medusa-like region
• What is the body plan of Cnidarians generally described as?

  Dimorphic
• What are the two forms of Cnidarians?

  Polyp and medusa
• What is the polyp form adapted for?

  A sedentary or sessile lifestyle
• What is the medusa form adapted for?

  A free-living and floating existence
• What is the structure of a polyp?

  A tubular body with the mouth directed upward and surrounded by tentacles
• What does the mouth of a polyp lead into?

  A blind gastrovascular cavity
• How do polyps attach to their substrate?

  By a pedal disc at the aboral end
• How do polyps reproduce?

  Asexually by budding, fission, or pedal laceration
• What happens if a bud detaches from a polyp?


  It forms a clone
• What happens if a bud remains attached to a polyp?

  It becomes a colony with a shared gastrovascular cavity