BIOL 1202 Chapter : Biology 1202 Chapter 33
Chapter 33: Invertebrates
Most Recent Hypothesis About Animal Phylogeny
1. No true tissues
2. Diploblastic; two tissue layers
3. Triploblastic; 3 tissue layers
Concept 33.1: Sponges are basal animals that lack true
tissues
• Porifera: Phyla Calcarea & Silicia
o Live in both fresh and marine waters
o Lack true tissues and organs
o Asymmetrical body
Sponges
• Sponges are suspension feeders
o Filter water passing through their bodies
Q: Water movement through a sponge would follow what
path?
A: Pore>spongocoel> osculum
Concept 33.2: Cnidarians are an ancient phylum of
eumetazoans
Cnidarians
• A wide range of sessile and floating forms including
jellyfish, corals, and hydras
• Simple diploblastic, radial body plan
o Body plan is a sac with a central gastrovascular
cavity
o Single opening serves as both mouth and anus
o Mesoglea layer between epidermis and
endodermis (gastrodermis)
Cnidarians Body Plans
• Polyp form is generally sessile
• Medusa form moves freely in water by passive drifting
and contractions of the bell
Defining Feature of Cnidarians
• Cnidocytes
o Unique cells that function in defense and the
capture of prey
• Stimulus causes the cell to evert releasing thread
• Some cnidocytes sting, others just entangle prey
Document Summary
Most recent hypothesis about animal phylogeny: no true tissues, diploblastic; two tissue layers, triploblastic; 3 tissue layers. Concept 33. 1: sponges are basal animals that lack true tissues: porifera: phyla calcarea & silicia, live in both fresh and marine waters, lack true tissues and organs, asymmetrical body. Sponges: sponges are suspension feeders, filter water passing through their bodies. Concept 33. 2: cnidarians are an ancient phylum of eumetazoans. Cnidarians body plans: polyp form is generally sessile, medusa form moves freely in water by passive drifting and contractions of the bell. Defining feature of cnidarians: cnidocytes, unique cells that function in defense and the capture of prey, stimulus causes the cell to evert releasing thread, some cnidocytes sting, others just entangle prey. Concept 33. 3: lophotrochozoans, a clade identified by molecular data, have the widest range of animal body forms. Flatworms: phylum platyhelminthes, triploblastic development, but acoelomate. Have: light-sensitive eyespots, centralized nerve net w/anterior ganglia, gastrovascular cavity w/ 2-way pharynx.
