Sponges and Cnidarians

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Sponges and Cnidarians

• Biology I Chapter 26

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The Animal Kingdom

• Multicellular
• Eukaryotic
• Heterotrophs
• Cells lack cell walls
• 95 are invertebrates

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What Animals Do to Survive

• Feeding
• Respiration
• Circulation
• Excretion

• Response
• Movement
• Reproduction

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Trends in Animal Evolution

• Cell specialization and levels of organization
• Early development
• Body symmetry
• Cephalization
• Body cavity formation

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SPONGES
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Sponges

• Phylum Porifera
• Have tiny openings, or pores,
  all over their bodies
• Sessile they live their entire life
  attached to a single spot
• They are animals! Why?

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Sponges are Animals!!!

• Multicellular
• Heterotrophic
• No cell walls
• Contain a few specialized cells

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Form and Function in Sponges

• Have nothing resembling a mouth or gut
• Have no tissues or organ systems
• Simple functions are carried out by a few
  specialized cells

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Asymmetrical

• Have no front or back ends, no left and right
  sides
• A large, cylindrical water pump
• The body forms a wall around a large central
  cavity through which water flows continually

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Choanocytes

• Specialized cells that use flagella to move a
  steady current of water through the sponge
• Filters several thousand liters/day

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Osculum

• A large hole at the top of the sponge, through
  which water exits
• The movement of water provides a simple mechanism
  for feeding, respiration, circulation and
  excretion

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Simple Skeleton

• Spicule a spike-shaped structure made of
  chalk-like calcium carbonate or glasslike
  silica in hard sponges
• Archaeocytes specialized cells that make
  spicules

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Feeding

• Filter feeders
• Sift microscopic
  food from the water
• Particles are engulfed by
  choanocytes that line the body cavity

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Respiration, Circulation, Excretion

• Rely on the movement of water through their
  bodies to carry out body functions
• As water moves through the cavity
• Oxygen dissolved in the water diffuses into the
  surrounding cells
• Carbon dioxide and other wastes, diffuse into the
  water and are carried away

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Response

• No nervous system
• Many sponges protect themselves by producing
  toxins that make them unpalatable or poisonous to
  potential predators

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Reproduction

• Sexually or asexually
• A single spore forms both eggs and sperm usually
  at different times

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Sexual Reproduction

• Internal fertilization Eggs are fertilized
  inside the sponges body
• Sperm are released from one sponge and carried by
  currents to the pores of another sponge

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Asexual Reproduction

• Budding
• Gemmules groups of archaeocytes surrounded by
  spicules

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Ecology of Sponges

• Ideal habitats for marine animals such as snails,
  sea stars, sea cucumbers, and shrimp
• Mutually beneficial relationships with bacteria,
  algae and plant-like protists
• Many are green due to these organisms living in
  their tissues

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Ecology of Sponges

• Attached to the seafloor and may receive little
  sunlight
• Some have spicules that look like cross-shaped
  antennae
• Like a lens or magnifying glass, they focus and
  direct incoming sunlight

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CNIDARIANS
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Cnidarians

• 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

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Cnidocytes

• Stinging cells that are located on their
  tentacles
• Used for defense and to capture prey

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Nematocyst

• A poison-filled, stinging structure that contains
  a tightly coiled dart
• Found within cnidocytes

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Form and Function in Cnidarians

• Only a few cells thick
• Simple body systems
• Most of their responses to the environment are
  carried out by specialized cells and tissues

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Radially Symmetrical

• Central mouth surrounded by numerous tentacles
  that extend outward from the body
• Life cycles includes a polyp and a medusa stage

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Body Plan

• Polyp cylindrical body with arm-like tentacles
  mouth points upward
• Medusa motile, bell-shaped body mouth on the
  bottom

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Feeding

• 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

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Respiration, Circulation, Excretion

• Following digestion, nutrients are usually
  transported throughout the body by diffusion
• Respire and
  eliminate wastes
  by diffusion
  through body walls

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Response

• 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

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Response

• Statocysts groups of sensory cells that help
  determine the direction of gravity
• Ocelli eyespots made of cells that detect light

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Movement

• Hydrostatic skeleton a layer of circular muscles
  and a layer of longitudinal muscles that enable
  cnidarians to move

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Reproduction Sexually and Asexually

• 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

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Groups of Cnidarians

• Jellies (formerly jellyfishes)
• Hydras and their relatives
• Sea anemones
• Corals

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Ecology of 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