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• 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

• Polyp-sessile and vase shaped-cylindrical• Medusa-swimming and bell shaped• Radially symmetrical• Most cnidarians reproduce both sexually and

asexually

Groups of Cnidarians• 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