phylum cnidaria - crestwood high school · • phylum cnidaria • hydras, jellies, sea anemones,...
TRANSCRIPT
• Phylum Cnidaria
• Hydras, jellies, sea anemones, and corals
• Soft-bodied
• Carnivorous
• Stinging tentacles arranged in circles around their mouths
• Simplest animals to have body symmetry and specialized cells
• Stinging cells that are located on their tentacles
• Used for defense and to capture prey
• A poison-filled, stinging structure that contains a tightly coiled dart
• Found within cnidocytes
• Only a few cells thick
• Simple body systems
• Most of their responses to the environment are carried out by specialized cells and tissues
• Central mouth surrounded by numerous tentacles that extend outward from the body
• Life cycles includes a polyp and a medusa stage
• Polyp: cylindrical body with arm-like tentacles; mouth points upward
• Medusa: motile, bell-shaped body; mouth on the bottom
• Polyps and medusas have a body wall that surrounds an internal space: the gastrovascular cavity
• Gastrovascular cavity: a digestive chamber with one opening
– Food enters and wastes leave the body
• Following digestion, nutrients are usually transported throughout the body by diffusion
• Respire and eliminate wastes by diffusion through body walls
• Statocysts: groups of sensory cells that help determine the direction of gravity
• Ocelli: eyespots made of cells that detect light
• Specialized sensory cells are used to gather information from the environment
• Nerve net: loosely organized network of nerve cells that together allow cnidarians to detect stimuli – Distributed uniformly throughout the body in
most species – In some species it is concentrated around the
mouth or in rings around the body
• Hydrostatic skeleton: a layer of circular muscles and a layer of longitudinal muscles that enable cnidarians to move
• Polyps can reproduce asexually by budding
• External sexual reproduction – The sexes are separate-each individual is
either male or female
– Both egg and sperm are released into the
water
• Jellies (formerly jellyfishes)
• Hydras and their relatives
• Sea anemones
• Corals
• The worldwide distribution is determined by:
– Temperature
– Water depth
– Light intensity
• Many suffer from human activity
• Coral bleaching has become common
• Global warming may add to the problem
Cnidarians True tissues, but
only two germ layers (endoderm & ectoderm)
Radial symmetry Stinging cells called
nematocysts Gastrovascular cavity
(single opening) Examples:
Jellyfish Corals Anemones
Nematocyst
Thread (coiled)
CNIDOCYTE
“Trigger”
Discharge of thread
Cuticle of prey
Tentacle
Thread
Ectoderm
Endoderm
Mesoderm
Cnidarian 2 germ layers
3 germ layers