11.9.1 Constructing a Phylogenetic Tree of Animals: Animal Development

Question 1

Constructing a Phylogenetic Tree of Animals: Animal Development

Answer 1

• The entire animal kingdom may have descended from a single common ancestor, probably a colonial flagellated protist.
• Four key characteristics of an animal are:
1. ingestion of food
2. structural proteins for support
3. presence of nerves and muscles
4. unique embryological development
• The second major branching point of the phylogenetic tree of animals involves radial versus bilateral symmetry (no sides versus two-sided body plan.)

Question 2

note

Answer 2

• To construct a phylogenetic tree of animals, first determine the possible common ancestor. It is believed that the common ancestor was a multicellular colonial flagellated protist that lived more than 700 million years ago.
• The term colonial describes a group of cells that are
  physically adjoining, but not dependent on each other.
• The common ancestor may have looked something like the green algae Volvox, a modern colonial organism.
• General homologies among animals include:
  1. ingestion of food
  2. use of protein for structural support versus cell walls
  3. presence of nerves and muscles
  4. unique embryological development
• Review: The outgroup is a species or group of species that are more closely related to each other than to other species in their clade.
• Multicellularity is one of the few shared characteristics among sponges (the outgroup) and the rest of the animal kingdom.
• Review: The Linnaean system of taxonomy, shown below and left, uses a hierarchical system of classification with the following groupings of greater specificity. A mnemonic that is useful for remembering the order and name of the groupings is seen below and right:
  Kingdom K
  Phylum P
  Class C
  Order O
  Family F
  Genus G
  Species S
• Looking at the phylogenetic tree of animals, you can see that sponges diverged from the rest of the animal kingdom at an early point. Taxonomic classification reflects the sponge’s early divergence. Sponges, which lack true tissues, are grouped as parazoa (“besides the animals”). The rest of the animal kingdom is collectively called the eumetazoa (“true animals”).
• The eumetazoa are divided into two major branches based on differences in body symmetry:
• Members of the phyla Cnidaria (hydras and jellyfish) and Ctenophora (comb jellies) have radial symmetry. The term radial means branching out in all directions from a common center. Animals with radial symmetry have a top and a bottom, but no sides.
• Animals of the other major branch include many different phyla and are characterized by bilateral symmetry. Animals that are bilateral (two-sided) have a dorsal (top) and ventral side (underneath) side, but also have a head and a tail end.
• The term cephalization describes an evolutionary trend
  toward the concentration of sensory equipment at the anterior end of the body.

Question 3

Cephalization leads to the development of what body part?

Answer 3

• head

Question 4

Parazoa are animals with:

Answer 4

• no true tissue

Question 5

Which statement below gives the best description of a colonial organism?

Answer 5

• An organism that lives adjoined to others like itself, yet they are not fully dependent on one another.

Question 6

Sponges differ from the rest of the Animalia because:

Answer 6

• they have no true tissues or organs.

Question 7

Which type of symmetry does the body of a human display?

Answer 7

• Bilateral

Question 8

Which of the following phyla serves as the outgroup of the animal kingdom?

Answer 8

• Porifera

Question 9

Eumetazoa are animals that have:

Answer 9

• true tissue