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List characteristics that distinguish animals from organisms in the other four kingdoms.
- Multicellular eukaryotes
- Heterotrophy by ingestion
- Carbohydrate reserves as glycogen
- No cell walls
- Highly differentiated body cells (tissues to organs to organ systems)
- Nervous and muscle tissue is unique
Distinguish between radial and bilateral symmetry.
- Radial- have a top and bottom but no “sides” – can be divided along any plane for roughly equal halves
- Bilateral- have dorsal, ventral, anterior and posterior body surfaces. Exhibit “cephalization” – an evolutionary trend towards concentration of sensory structures towards the anterior end
Outline the major phylogenetic branches of the animal kingdom, which are based upon grade of organization; symmetry and embryonic germ layers; absence or presence of a body cavity; and protostome-deuterostome dichotomy.
- Symmetry- none, radial, bilateral
- Germ layers- ectoderm, mesoderm, endoderm
- Body cavity- acoelomate, pseudocoelomate, coelomate
- Coelomates divided into two lines:
- 1.The protostomes: mollusks, annelids, arthropods
- 2.The deuterostomes: echinoderms & chordates
- This division is based on cell cleavage, coelom formation, and the blastopore fate
Distinguish among acoelomate, psuedocoelomate and coelomate.
- Acoelomate- an animal body plan characterized by no body cavity between the digestive tract and outer body wall
- Pseudocoelomate- a fluid filled body cavity that separates the digestive tract and outer body wall
- Coelomate- fluid-filled body cavity completely linedwith tissue derived from mesoderm and separates the digestive from the outer body wall
Distinguish between spiral and radial cleavage.
- Spiral cleavage- cleavage in which the planes of cell division are diagonal to the vertical axis of the embryo
- Radial cleavage- cleavage during which the cleavage planes are either parallel or perpendicular to the vertical axis of the embryo
Distinguish between determinant and indeterminate cleavage.
- Determinate- the developmental fate of each embryonic cell is established very early. If a cell is isolated from the 4-cell stage the embryo will not fully develop.
- Indeterminate- early embryonic cells retain capacity to develop into a complete embryo if isolated from other cells: this type of cleavage in the human zygote results in identical twins
Distinguish between schizocoelous and enterocoelous.
- Schizocoelous- descriptive term for coelom development during which, as the archenteron forms, the coelom begins as splits within the solid mesodermal mass; this is found in protostomes
- Enterocoelous- coelom development during which the mesoderm arises as lateral outpocketings of the archenteron with hollows that become coelomic cavities; formation found in deuterostomes
Compare developmental differences between protostomes and deuterostomes including: plane of cleavage, determination, coelom formation, fate of the blastopore.
- Protostomes- Spiral cleavage, Determinate cleavage, Schizocoelous coelom formation, Blastopore
- forms the mouth
- Deuterostomes- Radial cleavage, Indeterminate cleavage, Enterocoelous coelom formation, Blastopore
- forms the anus
Describe the hypothesis about animal origins from unicellular ancestors.
- The animal kingdom probably originated from colonial protists related to choanoflagellates
- Colonial protist- an aggregate of identical cells
- can be the beginning of specialization and division of labor among a group of cells
Explain why it is difficult to resolve what the first animals looked like.
Animals diversified so rapidly that it is difficult from the fossil record to sort out the sequence of branching in animal phylogeny
Describe two views about discontinuities between Ediacaran and Cambrian fauna.
- Ediacaran- fossils appear to represent cnidarians, but soft-bodied mollusks and worms were also present
- Cambrian- the ancient animals of the Ediacaran appeared to die out early
- debate still exists on the phylogenetic conditions between the animals on the Cambrian boundary