11.9.4 Protostomes and Deuterostomes

Question 1

Protostomes and Deuterostomes

Answer 1

• The coelomates can be taxonomically grouped intoprotostomes and deuterostomes based on differences that occur during development.
• Protostomes have spiral and determinant cleavage, and deuterostomes have radial and indeterminate cleavage.
• Protostomes have schizocoelus development, and deuterostomes have enterocoelus development.
• In protostomes, the blastopore develops into the mouth. In deuterostomes, the blastopore develops into the anus.

Question 2

note

Answer 2

• Review: As a group, the coelomates have a body cavity lined on both sides with tissue derived from the mesoderm.
• The phylogenetic tree on the left depicts the fact that the coelomates are taxonomically grouped into protostomes and deuterostomes. The groupings are based on fundamental differences that occur during development.
• Protostomes include molluscs, annelids, and arthropods.
• Deuterostomes include the echinoderms, chordates, and several other lesser-known phyla.
• During embryonic development cells continually divide, a process called cleavage. The cleavage pattern is indicated by the position of the cells relative to the embryo’s polar axis. In protostomes, each new cell forms at an angle that is oblique to the polar axis. The pattern is referred to as spiral cleavage since the dividing cells spiral outward from the polar axis. In deuterostomes, cells form at right angles to the polar
  axis, a pattern called radial cleavage because the cells form a radius outward from the polar axis.
• In protostomes, cells are determinate, meaning that their developmental fate is fixed. In deuterostomes, the cells are indeterminate, meaning that the cells of the embryo are identical and any single cell has the potential of developing into a complete organism.
• Review: In all coelomates, the coelom originates from
  mesoderm.
• In protostomes, the coelom forms by schizocoelous
  development, so-named because the coelom forms from the splitting of cells in the mesoderm. In deuterostomes, the coelom is formed by an evagination of the archenteron, the primitive gut. The process is called enterocoelus development.
• The word protostome literally translates as “first mouth”. Early in embryonic development the opening called the blastopore forms. The blastopore, first opening, of a protostome forms the mouth, and the anus forms subsequently at the other end. In a deuterostome, the blastopore forms the anus and the mouth forms subsequently at the other end. The name deuterostome translates as “second mouth.”
• Review: Hans Spemann and Hilde Mangold determined that during gastrulation the cells at the dorsal lip of the blastopore are the primary inducers of cell differentiation.
• Because genes control development, we can determine phylogenetic relationships by looking at developmental patterns. Spemann and Mangold performed their experiment on salamanders, which are deuterostomes.
• Question: What experimental outcome would be expected if the same experiment were performed on protostomes?

Question 3

For animals that have it, spiral cleavage becomes evident

Answer 3

• at the third cell division.

Question 4

Which of the following is descriptive of deuterostomes?

Answer 4

• radial and indeterminate cleavage, anus develops from blastopore

Question 5

What two terms are used to further divide and label the organisms classified as the coelomates?

Answer 5

• protostomes and deuterostomes

Question 6

What type of cleavage do protostomes display?

Answer 6

• Spiral and determinant

Question 7

Which of the following are deuterostomes?

Answer 7

• humans

Question 8

Which of the following is descriptive of protostomes?

Answer 8

• spiral and determinate cleavage, mouth develops from blastopore

Question 9

The word “schizocoelous” literally translates as

Answer 9

• of a split cavity

Question 10

Which of the following characteristics are associated with protostomes?
The mouth develops from blastopore.
The presence of a coelom.
Enterocoelous development.
Exhibits determinate cleavage.
Schizocoelous development.
Anus develops from blastopore.
Exhibits spiral cleavage.
Includes sea urchins.
Absence of coelom.
Includes insects.

Answer 10

• 1, 2, 4, 5, 7, 10

Question 11

What characteristic is used to further divide the animals classified as coelomates?

Answer 11

• the development, migration, and fate of tissues

Question 12

Which of the following are not branch points in the phylogenetic tree of animals?

Answer 12

• radial symmetry / bilateral symmetry
• coelomate / acoelomate
• radial cleavage / spiral cleavage
• All of these are branch points.