B I O LO GY 1 1 2

SPONGES AND CNIDARIANS

SPONGES

• Phylum Porifera• Multicellular and heterotrophic• No cell wall and few specialized cells• Live their entire life attached to a surface• They eat by sifting microscopic food in water• Choanocytes are specialized structures that help move

water through their body cavity• Water enters through pores and leaves through the

osculum (a large hole at the top of the cavity)

GETTING EVERYTHING IT NEEDS

• Digestion is intracellular• Takes place inside the

cells

• Not only is food provided using this sifting action but also everything for respiration, circulation and excretion

SPONGES AND REPRODUCTION

• Reproduce sexually and asexually• Sexually• Eggs are fertilized internally• Zygote develops into a larva• Larva is the immature stage of the organism that looks

different from the adult• They are motile• Carried by the ocean to the floor and grow into an adult

sponge

• Asexually• By budding

CNIDARIANS

• Phylum Cnidaria• Soft-bodied carnivores that have stinging

tentacles arranged in circles around their mouth

• Simplest animals that have body symmetry and specialized tissues

• Exhibit radial symmetry

• Central mouth with several tentacles

TWO DISTINCT LIFE STAGES

• Polyp• Cylindrical body with

arm-like tentacles and usually do not move

• Lives attached to the surface with its mouth pointing upward

• Medusa• Bell-shaped body with

a mouth at the bottom• Free swimming

CNIDARIANS AND DIGESTION

• Possess a gastrovascular cavity• Digestive chamber with one opening• Foods and wastes enter and leave this opening

• Nutrients are transported throughout body by diffusion

• Oxygen and wastes are diffused through the body walls

CNIDARIANS AND RESPONSE TO STIMULI

• Gather information from their environment using specialized sensory cells• nerve nets• a network of nerve

cells that together let cnidarians detect stimuli

CNIDARIANS AND BODY STRUCTURE

• Possess a hydrostatic skeleton• Consists of layers

of circular muscles as well as longitudinal muscles that, with the digestive cavity, allow it to move

CNIDARIANS AND REPRODUCTION

• Asexual – by budding

• Sexual – external fertilization in water

CLASSIFICATION OF CNIDARIANS

• Jellyfish• Live mostly as medusas

• Hydras• Grow in branching colonies• Ex. Portuguese man-of-war

• Sea Anemones and Corals• Only have a polyp stage• Colonial• Polyps grow together in large numbers• Secrete an underlying skeleton of calcium carbonate• Form coral reefs

PORTUGUESE MAN-OF-WAR

CORAL REEFS