Sponges and Cnidarians

1
Sponges and Cnidarians

• Unit VI
• Chapter 26

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What is an Animal?

• Animals, members of the kingdom Animalia, are
  multicellular, eukaryotic heterotrophs whose
  cells lack cell walls
• Invertebrates are animals that have no backbone,
  or vertebral column
• Includes over 95 of all animal species
• Vertebrates are animals that have a backbone
• Includes 5 of all animal species

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What Animals Do to Survive

• Animals carry out the following essential
  functions
• Feeding herbivores, carnivores, omnivores,
  detritivores
• Respiration take in O2 and give off CO2
• Circulation diffusion, closed/open circulatory
  system
• Excretion ridding the body of liquid and solid
  wastes
• Response nervous systems
• Movement sessile or mobile
• Reproduction asexual or sexual

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Trends in Animal Evolution

• Complex animals tend to have high levels of cell
  specialization and internal body organization,
  bilateral body symmetry, a front end or head with
  sense organs, and a body cavity

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Trends in Animal Evolution
mollusks
echinoderms
roundworms
arthropods
annelids
flatworms
chordates
cnidarians
sponges
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Early Development

• Animals that reproduce sexually begin life as a
  zygote (fertilized egg)
• The zygote undergoes a series of divisions to
  form a blastula (hollow ball of cells)
• The blastopore leads to a central tube that
  becomes the digestive tract
• A protostome is an animal whose mouth is fromed
  from a blastopore (most invertebrates)
• A dueterostome is an animal whose anus is formed
  from the blastopore (most vertebrates)

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Body Symmetry

• With the exception of sponges, all animals
  exhibit some type of body symmetry
• Radial symmetry body plan in which body parts
  repeat around the center of the body
• Bilateral symmetry body plant in which only a
  single imaginary line can divide the body into 2
  equal parts

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Cephalization

• Animals with bilateral symmetry usually exhibit
  what is called cephalization
• Cephalization is the concentration of sense
  organs and nerve cells at the anterior, or
  fromnt, end of the body

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Sponges

• Sponges are classified as animals because they
  are multicellular, heterotrophic, have no cell
  walls, and contain a few specialized cells

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Body Plan of Sponges

• Sponges are asymmetrical they have no front or
  back end
• The movement of water through the sponge provides
  a simple mechanism for feeding, respiration,
  circulation, and excretion
• Sponges are filter feeders that sift microscopic
  food particles from the water
• Sponges can reproduce either sexually or
  asexually
• In sponges, eggs are fertilized inside the
  sponges body, a process called internal
  fertilization
• Sponges do not have nervous systems that allow
  them to respond to their environment, however,
  some produce toxins to ward off predators

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Anatomy of a Sponge
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Ecology of Sponges

• Sponges play an important part in the ecology and
  survival of numerous aquatic organisms
• They usually live attached to the sea floor
• They form mutually beneficial relationships with
  bacteria, algae, and plantlike protists
• They provide a habitat for snails, sea stars, sea
  cucumbers, and shrimp

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Cnidarians

• Cnidarians are soft-bodied, carnivorous animals
  that have stinging tentacles arranged in circles
  around their mouths
• They are the simplest animals to have body
  symmetry and specialized tissues
• Cnidocytes are stinging cells that are located
  along their tentacles
• A nematocyst is a poison filled, stinging
  structure that contains a tiny coiled dart used
  to paralyze and kill prey

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Cnidarians
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Form and Function in Cnidarians

• Cnidarians are radially symmetrical
• They typically have a life cycle that includes
  two different-looking stages a polyp and a
  medusa
• A polyp is a cylindrical body with arm-like
  tentacles
• In a polyp, the mouth points upward
• Polyps are usually sessile (do not move)
• A medusa has a motile, bell-shaped body with the
  mouth on the bottom

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Life Stages of Cnidarians
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Cnidarian Activity

• After paralyzing its prey, a cnidarian pulls the
  prey through its mouth into its gastrovascular
  cavity
• Nutrients are then transported through the body
  by diffusion
• Cnidarians gather information from their
  environment using specialized sensory cells
• Most cnidarians reproduce both sexually and
  asexually
• Most sexual reproduction takes place with
  external fertilization (outside the females body)

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Groups of Cnidarians

• Cnidarians include jellyfishes, hydras and their
  relatives, and sea anemones and corals

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Ecology of Corals

• The worldwide distribution of corals is
  determined by a few variables
• Temperature
• Water depth
• Light intensity
• Many coral reefs are now suffering from human
  activity
• Recreational diving, chemical fertilizers,
  over-fishing, coral bleaching