BIOL 112 Lecture 26

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Happy Halloween!

Invertebrates

Sponges

(Porifera)

• Sessile adult form, mobile larvae
• No true tissues (germ layers)
• Originally thought to be plants

Anatomy:

• Feeding cells (choanocytes/collar cells; close resemblance to choanoflagellates) collect food particles in phagocytic vacuoles
• food transferred to free-roaming amoebocytes
• Mesohyl: gelatinous "gunk" that makes up the sponge body.
• Pores allow transmission of water and food into spongocoel and out osculum

Sexual Reproduction

Sequential Hermaphrodites: produce sperm and egg at separate times.

Sperm are released into water and fertilize eggs of neighboring sponges.

Zygote becomes motile larva which then settles and develops into a new sponge.

Asexual Reproduction

Fragmentation: a broken part of a sponge will form into a new organism

Eumetazoa

Animals with true tissues

Cnidaria

• radially symmetric
• diploblastic (endo- and ectoderm; no mesoderm)
• colonial or solitary
• sessile (polyp) or mobile (medusa)
• corals and jellyfish
• predators

Anatomy:

• gastrovascular cavity: gut with radial canals (surrounding tissue is only a few layers deep; diffusion is efficient)
• single-opening mouth and anus
• tentacles (contain stinging cells called nematocysts)
• Hydrostatic skeleton
• Neural net/mesh; no central brain or ganglia
• Act on the contractile system for movement and engulfment of prey

Asexual Reproduction

Fission and budding

Sexual

Life cycle alternates between polyp and medusa form:

• Polyp produces medusa
• Medusa produces gametes
• Gametes fuse to form zygote
• zygote settles to form polyp