11.9.3 The Formation of Body Cavities Flashcards
1
Q
The Formation of Body Cavities
A
- The presence or absence of a body cavity (the space between the body wall and the digestive tract) can distinguish certain taxonomic groups. The body cavity is called a coelom.
- Acoelomates lack a body cavity (ex: flatworms).
- Pseudocoelomates have a body cavity that is not completely lined with tissue derived from the mesoderm (ex: roundworms).
- Coelomates have a body cavity that is lined on both sides with tissue derived from the mesoderm (ex: humans).
2
Q
note
A
- As a taxonomic group, the acoelomates lack a body cavity. The cross section of the body plan to the left indicates the lack of coelom.
- Among the acoelomates are the planarians.
The body plan of the pseudocoelomates is shown to the left. - Notice that one side of the pseudocoelom is lined with
mesoderm and the other is lined with endoderm. Among the pseudocoelomates are the roundworms (not pictured). - The coelom of the coelomates is lined with mesoderm on both sides. The coelom creates a compartment that protects complex organs and enables their independent expansion and movement. The taxonomic grouping of coelomates encompasses chordates, including humans.
- The phylogenetic tree pictured to the left illustrates the
evolutionary relationships among acoelomates, pseudocoelomates, and coelomates.
3
Q
A coelom is:
A
- a body cavity surrounded by mesoderm
4
Q
A digestive tube is characteristic of members of this group
A
- acoelomates, pseudocoelomates, and coelomates
5
Q
True or false?
The inner lining of the digestive tube in coelomates develops from embryonic ectoderm.
A
- false
6
Q
The internal complexity found in most animals was possible following the evolution of
A
- mesoderm
7
Q
Starting with the outermost layer, include all structures that would be seen in a cross section of an earthworm.
A
- ectoderm, mesoderm, coelom, mesoderm, endoderm, digestive cavity
