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LO February 21, 2019
Chapter 33, 34, and 35 (General Traits of Animals…
LO February 21, 2019
Chapter 33, 34, and 35
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- Describe the body plan features of animals, including presence of tissues, body symmetry, early embryonic development, presence and type of body cavity, and segmentation, stating the potential advantages of each.
(1) Symmetry:
- Radial Symmetrical Body Plan: Its parts are arranged in such a way that any longitudinal plane passing through the central axis divides the organism into halves that are approximate mirror images. e.g. Sea Anemones, Corals, and Jellyfish.
- Bilateral symmetry: body has right and left halves that are mirror images of each other. e.g. Bilateria
- Asymetrical Symmetry Lack of Symmetry (coral)
- Starfish bilateral then radial
Bilateral symmetry
- Acoelomates: have no body cavity between the digestive tract (derived from the endoderm) and the musculature layer (derived from the mesoderm).e.g. flatworm
- Pseudocoelomates: have a body cavity, the pseudocoelom, between tissues derived from the endoderm and those derived from the mesoderm.e.g roundworms
- Coelomates: have a body cavity, the coelom, that develops entirely within tissues derived from the mesoderm, and so is lined on both sides by tissue derived from the mesoderm.e.g Earthworm
(3) A body cavity.
- Ectoderm: gives rise to the outer covering of the body and the nervous system.
- Endoderm: gives rise to the digestive system, including the intestine.
- Mesoderm: the skeleton and muscles develop from this.
(2) Tissues: allowing specialized structures and functions. (except sponges).
- A zygote can give rise to any cell.
- the process is irreversible: Once a cell differentiates to serve a function, it and its descendants can never serve any other.
(4) various patterns of embryonic development.
Blastopore: the opening that connects the archenteron cavity of a gastrula stage embryo with the outside.
Protostomes
- include most bilaterians, including flatworms, nematodes, mollusks, annelids, and arthropods.
- the mouth of the adult animal develops from the blastopore or from an opening near the blastopore (protostome means “first mouth”—the first opening becomes the mouth).
- Determinate Development: the type of tissue each embryonic cell will form in the adult is determined early, often before cleavage., when the molecules that act as developmental signals are localized in different regions of the egg.
Deuterostome
- The echinoderms and the chordates (few others).
- blastopore gives rise to the organism’s anus, and the mouth develops from a second pore that arises later in development (deuterostome means “second mouth”).
- Indeterminate Development:
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- List the shared derived traits and shared ancestral traits of animals.
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Synapomorphies
- Specific-Cell-Cell Junctions
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- Hox Genes: Helps cells differentiate into what they are supposed to be.
- Electrically Excitable Cells
- Draw a phylogenetic tree of the Metazoa, including the Porifera, Cnidaria, Platyhelminthes, Annelida, Mollusca, Nematoda, Arthropoda, Echinodermata, and Chordata, rooted with the Choanoflagellates as an outgroup. Label the groups according to Protosome vs Deuterostome and Lophotrochozoa vs Ecdysozoa.
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- On the same phylogenetic tree, label the characters that distinguish each clade, using the developmental and body plan features listed in learning outcome #2.
- Explain the colonial flagellate hypothesis of metazoan origin and why it is currently favored.
The Colonial Flagellate Hypothesis proposes that multicellular organisms evolved from a single flagellated cell. it is believed that a group of these unicellular flagellates combine to form an aggregate then form a sphere which develops specialized cells (such as reproductive cells), and then fold in on themselves to create a tissue layer.
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