Ch 26- Sponges and Cnidarians
• What characteristics do all animals share?
– Members of kingdom Animalia, multicellular,
eukaryotic heterotrophs, lack cell walls
• Invertebrates- animals that do not have a
backbone
– 95% of all animal species
– Range in size from dust mites to giant squids
• Vertebrates- animals that have a backbone
– Fish, amphibians, reptiles, birds, mammals
• What essential functions do animals carry
out?
– Feeding, respiration, circulation, response,
movement, and reproduction
• What are the important trends in animal
evolution?
– High levels of cell specialization and internal body
organization in complex animals
– Bilateral body symmetry
– Front end or head with sense organs
– Body cavity
Sponges
• Why are sponges classified as animals?
– Multicellular, heterotrophic, no cell walls, contain a few specialized
cells
• Phylum Porifera
• Are sessile and filter feeders
• Body plan
– Asymmetrical, forms wall around large central cavity
– Choanocytes- specialized cells that use flagella to move steady current
of water through sponge
– Osculum- large hole at top of sponge
– Spicule- spike shaped structrure made of chalklike calcium carbonate
– Archaeocytes- specialized cells that move around within the walls of
sponge
• How do sponges carry out essential functions?
– Movement of water throughout sponge
• Characteristics of sponges
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No true tissues or organs
Food digested by collar cells and nutrients are passed to rest of body
Produce toxins
Feed on bacteria, protozoans, unicellular algae
May reproduce either sexually or asexually
• Internal fertilization
• Gemmules- groups of archaeocytes surrounded by tough layer of spicules
• Play an important role in the primary productivity of
coral reefs
Cnidarians
• What is a cnidarian?
– Soft-bodied, carnivorous animals with stinging
tentacles arranged in circles around their mouths
– Simplest animals to have body symmetry and
specialized tissues
• Cnidocyte- stinging cells, located along
tentacles
• Nematocyst- poison-filled, stinging structure
that contains tightly coiled dart
Form and Function in Cnidarians
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Polyp-sessile and vase shaped-cylindrical
Medusa-swimming and bell shaped
Radially symmetrical
Most cnidarians reproduce both sexually and
asexually
Groups of Cnidarians
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Jellfishes, hydras, sea anemones, corals
Scyphozoa-means cup animals
– Sexual reproduction
– Medusa dominant form of life cycle
– Nematocysts-poison
– Common jellyfish
Hydrozoa
– Hydras are most common freshwater, lack a medusa stage
– Sexual or asexually
– Portuguese man-of-war
Anthozoa
– Sea anemones
• Sessile, only polyps
• Coastal areas
• Tentacles and feed on fish
– Corals
• Polyps in colonies
• Calcium carbonate
• Warm clear water
• Coral reefs