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Section 12.2 – Sponges and Cnidarians
Characteristics of Sponges
- Found in warm, shallow water
- Few live in fresh water – dull colors
- Salt water sponges are brightly colored
- Most have asymmetry, but some are radial
- Adult sponges live attached – sessile
- Sponges live in colonies
Sessile- Organisms that remain attached to one place during their
lifetime
Body Structure
- Hollow tube – body
- Small openings – pores
- Only cells – NO tissues
- Body wall has 2 cell layers
- Collar Cells - Line the inside of the sponge
- Spicules- Sharp pointed structures that form the skeleton of
the sponge
Obtaining Food and Water
- Sponges filter food through their pores
- O2 is taken from the water
- Water carries away wastes
Reproduction
- Reproduce sexually and asexually
Hermaphrodite – produce both eggs and sperm
A sperm CANNOT fertilize its own eggs.
After an egg is released, if fertilized, it will form a larva.
Asexual reproduction occurs by budding and regeneration.
Cnidarians
- Examples – coral, sea anemones, hydras and jellyfish
- Most live in salt water
- Some form colonies – hydra and coral
Body Forms
1) Polyp - Shaped like a vase, Sessile, Ex – Sea Anemones, Coral
and Hydra
2) Medusa – bell-shaped and free swimming, Ex. Jellyfish
Body Structure
- Radial symmetry
- One body opening
- Two cell layers
- O2 and CO2 are exchanged in the H2O
- Have nerve cells called a nerve net
- Have tentacles – arm-like structures that surround the mouth
of cnidarians
- Tentacles have stinging cells that paralyze prey
Obtaining Food
- Are predators – use stinging cells
Reproduction
- Sexual – egg and sperm
- Asexual – Budding