The Design of Organisms

The Design of Organisms

What Patterns do you see?

Body Plans• The great diversity

of plant and animal forms arises from a surprisingly small number of patterns.

• Although some organisms have complex shapes, we will begin looking at simple systems

Spheres, Tubes, and Fans• A surprisingly large

number of biological structures can be described in terms of spheres, tubes, and fans (surfaces).

Phylum Annelida: The Segmented Worms

Annelid Evolution

• Earliest fossils are about 520 to 550 million years old… right at the beginning of the Cambrian period.

Annelid Characteristics

1. Bilaterally symmetrical and vermiform (worm-shaped)

2. Triploblastic

• 3 cell layers

3. Coelom (Body Cavity)

More Characteristics

• 4. Through Gut: Mouth & Anus• 5. No true respiratory system (no respiratory

organs)

6. Simple Nervous System• Ganglia are bundles of

nerves that act somewhat like brains.

• The head contains several “cerebral ganglia”

• Along the ventral nerve cord (yellow) there are “segmental ganglia”

7. Closed Circulatory System with “Hearts”

• Annelid worms have blood and 5 pairs of “hearts” to keep it circulating.

• This is a new characteristic, not seen in simple organisms.

8. Body possesses 3 separate sections, a prostomium, a trunk and a pygidium.

• Prostomium = 1st segment, some w/ sensory organs

• Trunk = body segments

• Pygidium = end segments, contain anus.

9. Reproduction: Freaky Worms

• Some annelid worms are gonochoristic. Gonochoristic organisms, like you, have a distinct sex. Usually, there are 2 varieties, i.e. male and female.

• Most however, are simultaneous hermaphrodites, meaning that individuals have both testes and ovaries. During mating, they may act as a male or female.

Clitellum• Fertilized eggs

will be wrapped in a mucus-covered coccoon made by the clitellum, which contains the worm eggs

Label ‘er up!

• Label up your diagram!

• Skip “C”

• B = “ganglia” not brain