Questions and Answers
What is the primary difference between the development of protostomes and deuterostomes?
Which group of bilaterians develops the anus first from the blastopore?
What is the term for the hollow ball of cells formed during the cleavage stage of embryonic development?
What is the advantage of segmentation in annelids?
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What is the term for the opening to the outside during embryonic development?
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Which type of cleavage is characteristic of deuterostomes?
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What is the term for the primitive body cavity formed during embryonic development?
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Which group of bilaterians exhibits determinate development?
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What is the main advantage of segmentation in animals?
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What has been used previously to infer animal phylogeny?
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What is the main difference between traditional animal phylogeny and new phylogenies?
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What is the main characteristic that distinguishes Porifera (sponges) from other animals?
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What is the phylogenetic group that includes animals that molt their cuticles?
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What is the term for the process by which animals grow by gradual addition to the body mass?
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What is the main characteristic that distinguishes Lophotrochozoa from Platyzoa?
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What is the significance of the annelids and arthropods being separated into different clades?
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Study Notes
Closed Circulatory System
- Blood moves continuously through vessels separated from body fluids
Patterns of Development
- The basic Bilaterian pattern of development involves:
- Mitotic cell divisions (cleavage) of the egg forming a hollow ball of cells (blastula)
- Blastula indents to form a two-layer-thick ball with:
- Blastopore (opening to the outside)
- Archenteron (primitive body cavity)
Evolution of Development
- Bilaterians can be divided into two groups:
- Protostomes: develop the mouth first from or near the blastopore
- Deuterostomes: develop the anus first from the blastopore, and the mouth develops later from another region of the embryo
Differences between Protostomes and Deuterostomes
- Cleavage pattern of embryonic cells:
- Protostomes: spiral cleavage, new cells form to the right or left of previous cells
- Deuterostomes: radial cleavage, new cells form on top of previous cells
- Developmental fate of cells:
- Protostomes: determinate development, cell fate is determined early
- Deuterostomes: indeterminate development, cell fate is not determined until after several divisions
- Formation of the coelom:
- Protostomes: cells move apart to form coelom
- Deuterostomes: groups of cells pouch off to form coelom
Segmentation
- Evolution of segmentation provides two advantages:
- Allows for redundant organ systems in adults, such as in annelids
- Allows for more efficient and flexible movement, as each segment can move independently
- Segmentation appeared several times in animal evolution
Animal Phylogeny
- Traditional animal phylogeny was developed from morphological, molecular, life history, and other types of relevant data
- New phylogenies are constructed from molecular data, which may suggest different phylogenetic relationships
- Current phylogeny shares common ground with traditional phylogeny, but some parts are not firmly established
Classification of Animals
- Multicellular animals are divided into distinct phyla
- Animals are divided into two main branches:
- Porifera (Sponges): Parazoa - monophyletic
- Eumetazoa: Animals other than sponges
- Phylum Cnidaria branches off the evolutionary tree before Bilateria
- Phylum Bilateria includes deuterostomes and protostomes
Protostome Divisions
- Protostomes are divided into:
- Spiralians: grow by gradual addition to the body mass, have spiral cleavage, and include two main groups:
- Lophotrochozoa
- Platyzoa
- Ecdysozoans: animals that molt, including arthropods and many other phyla
- Spiralians: grow by gradual addition to the body mass, have spiral cleavage, and include two main groups:
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Description
This quiz covers the basics of the closed circulatory system and patterns of development in bilaterians, including cell divisions, blastula formation, and body cavity development.
