Biology Chapter 11 Notes:
Animal Diversification
1. All animals eat other organisms
2. All animals move at least at some stage of their life cycle; some animals move only during a
"larval stage" that comes early in their lives; organisms that are fastened in place during their
adult life (mussels, barnacles) are sessile
3. Animals are multicellular; generally have body parts that are specialized for different activities
Four Distinctions amongst animals: DNA and RNA analysis have helped biologists identify four
distinctions within various animals; hinges on a particular adaptation and on the question of whether or
not an animal descends from an ancestor with that adaptaion
1. Does the animal have defined tissues with specialized cells? sponges have no distinctive tissue
and some organisms are just aggregations of similar cells; other animals have defined tissues
with highly specialized functions
2. Does the animal develop with radial or bilateral symmetry? radial symmetry describes
organisms with a body structured like a pie; possible to make multiple slices going through the
centre that divide the organisms into identical pieces; tends to be slow-moving or freefloating;bilateral organisms have a left and right side that are mirror images; faster-moving and
more adept at searching for food and avoiding predators
3. During development, does the animal's gut develop from front to back, or back to front?
important distinction among bilaterally symmetrical animals with defined tissues; protosomes
(mouth first) and deuterostomes (mouth second); the gut develops from front to back in
protosomes and the first opening that forms is the mouth of the adult animals; the gut develops
from back to front in deuterostomes and the second opening becomes the mouth; this is the
most basic division of animals in terms of revealing their evolutionary relatedness
4. Does growth occur by molting or by adding continuously to the skeletal elements? bilateral
protosomes have an inportant distinction; animals that shed an exoskeleton and replacing it
with a larger one at regular intervals during their life (molting); animals can grow by adding to
the size of their skeletal elements in a more continuous manner than molting; all animals share
a common ancestor (protist) but the four distinctions help identify and organize all of the approx
36 phyla of animals
Evolutionary Success
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everything that is not extinct is evolutionary successful; never use the word higher or ower
a species is either extant or extinct; an extant species is able to find food, escape predators and
reproduce; different organisms have very different lives
emphasis on adaptation among the species and their relationship to their environment; each
species was differentiated from the other and shows specializations that adapt to the particular
niche in their environment