Lower Invertebrates

1
Lower Invertebrates

• Simple animals

2
Phylum Cnidaria

• Corals, jellyfish, Hydras

3
Phylum Cnidaria

• True Radial symmetry
• Sac plan
• Single opening to gastrovascular cavity (gut)
  serves as mouth and anus

4
Phylum Cnidaria

• Two tissue layers
• Epidermis from ectoderm
• Gastrodermis from endoderm
• Gelatinous mesoglea between epidermis
  gastrodermis

5
Phylum Cnidaria

• Two forms
• Polyp
• Hydra, sea anemone
• Medusa
• jellyfish

6
Phylum Cnidaria

• Cnidocytes
• stinging cells for prey capture and defense

7
Phylum Cnidaria

• Class Corals Sea Anemones
• Polyp only
• Class Jellyfishes
• Medusa sexual form, with oral arms
• Polyp tiny asexual form
• Class Hydroids (possibly polyphyletic)
• Polyp only (Hydra) or polyp medusa (Obelia)

8
Phylum Porifera

• Sponges

9
Phylum Porifera

• Simplest animals (if they are animals at all)
• No true tissues
• No necessary symmetry

10
Phylum Porifera

• Four cells types in vase-like form
• Pinacocytes
• Pore cells
• Collar cells (feeding cells)
• Amoeboid cells

11
Phylum Porifera

• Four cells types in vase-like form
• Collar cells (feeding cells)
• Flagellum creates currents, turbulence
• Collar traps food particles
• Engulfed by cytoplasm.

12
Phylum Porifera

• Sponge skeletons
• Spongin
• Tough fibrous protein
• Commercial sponges
• Spicules of calcium carbonate
• Spicules of silicon dioxide
• Glass sponges