Chapter 42 - Animal Evolution: Introduction to the Metazoans and Eumetazoans

metazoa

multicellular animals

sponge characteristics

most basal metazoans

- Sponge bodies lack tissues and guts but have skeletal support
- Sponges are chemically exotic
- Most sponges are marine, a few percent of species are fresh water
- Habits include filter feeding, sex, and a larval stage

parazoans

Sponge bodies lack organized tissues and guts
- multiple cell types scattered throughout a sponge body

Mostly marine with a few freshwater species

Suspension feeders

Benthic (bottom-dwelling)

Specialized cell types (food collection, skeletal secretion, etc.)

Lack organized tissues

They come in a wide variety of body forms
- Some are vase-shaped & hollow in the center
- Some are full of chambers and passages
- Fans, globes, etc.

choanocytes

flagellated collar cells, generate a water current through the sponge and ingest suspended food

what are sponge larvae

blastulae that either drift away to settle (recruit) somewhere nearby or are retained in the parent

chemically exotic

- Chemicals aid in competitive interactions
- Defend against predators and competitors
- Provide natural pharmaceuticals

Sponges are loosely organized which means....

Cell suspensions can reassemble into functional sponge bodies .....(over and over and over again)!

what are sponge skeletons made of

collagen and/or mineralized spicules

Eumetazoa

animals with true tissues
- Tissues arise from cell lines that differentiate early in development, in the blastula or gastrula stage

diploblast structure

have an ectoderm and endoderm, with gelatinous material between.

ectoderm

outermost tissue layer

Forms the skin and nervous system

endoderm

innermost tissue layer

Formed during gastrulation

Forms the gut

radial symmetry

- Many planes of symmetry
- Top and bottom
- Like a flower pot

bilateral symmetry

- One plane of symmetry
- Left and right side
- Top and bottom
- Front and back ends
- Like a car

characteristics of radially symmetrical animals

• Radially symmetrical animals are usually attached to a surface, or they float
• They are equally likely to encounter food, predators, etc. from any direction
• They typically have a diffuse nerve net that intercepts info from all directions
• No central nervous system

Characteristics of Cnidaria

• Diploblastic
• Radially Symmetric
• Tentacles around mouth for catching prey
• Tentacles have cnidocytes (stinging cells)
• Blind Gut (single mouth/anus)
• A species can have a polyp stage, medusa stage, or both
• Solitary or colonial

Ctenophora characteristics

• Diploblastic and radially symmetrical, like the Cnidaria
• Pelagic, marine
• Predators; most catch prey with sticky tentacles that hang down under the 'umbrella' body.
• This orientation allows for effective prey capture with little effort.
• Swim by beating rows of cilia