More than 95% of all animal species are
What is a vertebrate?
an animal with an internal segmented backbone.
In contrast to a vertebrate, an invertebrate
does not have a backbone
How many groups have scientists divided animals into?
more than 30 major groups
Each classified group of animals is called?
In general, How is each phylum of animals defined?
by distinctive structural and functional characteristics.
What are the three main criteria that are used to classify animals?
body symmetry, tissue layers, and developmental patterns.
What does body symmetry refer to?
how similar an object is across a central Axis
Animals with bilateral symmetry can be divided
equally along only one plane, which splits an animal into mirror-image sides
Animals with radial symmetry have body parts arranged
in a circle around a central axis.
Bilateral animals have how many distinct layers of tissue?
Name and described the layers of tissue bilateral animals have.
1. ectoderm (outer layer); endoderm (inner layer that lines the gut); mesoderm (middle layer that develops into internal tissues and organs).
Most radial animals only have how many layers of tissue–what are they?
two layers of tissue, consisting of endoderm and ectoderm layers.
Animal developmental patterns are grouped into two major divisions:
the protostomes and the deuterostomes
In general, the major difference in development between protostomes and deuterostomes is
the structure that develops from the first opening of the digestive cavity.
For protostomes, what develops first and second?
the mouth is formed first and the anus is formed second.
For deuterostomes, what develops first and second?
the first opening forms the anus, and the mouth is formed second.
To study the evolutionary relationships among animal groups, advances in biotechnology have helped scientists use?
molecular comparisons along with structural differences
What is the phylogenetic tree is what?
evolutionary history of invertebrate animals.
Do scientists know everything they need regarding the phylogenetic tree at this point?
No. It is a work in progress and as more data are gathered, a more complete evolutionary tree can be constructed.