Questions and Answers
Can animals be asymmetric? Explain with examples.
Yes, sponges are not symmetric.
Define radial symmetry and provide examples of animals with radial symmetry.
Having symmetry around a central axis. Examples include jellyfish and sea anemones.
What is the difference between the aboral and oral side of an animal?
Aboral = away from the mouth; oral = closer to the mouth.
Define bilateral symmetry and give examples of animals with bilateral symmetry.
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How do animals with bilateral symmetry differ from those with radial symmetry?
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Is either form of symmetry superior? Explain why or why not.
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Define the following terms: anterior/posterior; dorsal/ventral; proximal/distal; superior/inferior; lateral.
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When did animals first appear in the fossil record?
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Why did 19th century biologists view the Cambrian period as the starting point of animal life?
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What is so interesting about the Cambrian Period?
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What is so interesting about the Burgess Shale?
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Approximately when did the first animals appear in the fossil record?
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What is the importance of the Cambrian explosion?
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What is unusual about the animal fossils found at the Burgess Shale?
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Briefly characterize the phylum Porifera.
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Are sponges symmetric, asymmetric or both? Explain.
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What kind of cell types exist in a sponge? Briefly describe their roles.
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Sponges are considered to lack tissues. Explain.
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Describe the structure and function of choanocytes.
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How does a sponge feed and what do they feed on?
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What are spicules? What are they made of and what is their function?
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Do all sponges have spicules? What are spongin fibers?
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What is the significance of the observation that all cells in a sponge are genetically identical?
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What are the differences between asconoid, syconoid, and leuconoid sponges?
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Explain why many species within the phylum Porifera are hermaphrodites.
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Briefly describe the life cycle of a typical sponge.
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Can sponges move at any time in their life cycle? When?
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What is the purpose of extracting chemicals from different sponge species?
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Study Notes
Symmetry in Animals
- Animals can exhibit different types of symmetry: asymmetric, radial, and bilateral.
- Sponges are an example of asymmetric animals, lacking a definitive shape.
- Radial symmetry is characterized by symmetry around a central axis, seen in jellyfish and sea anemones.
- Bilateral symmetry features two mirror-image halves, allowing clear front and back, seen in dogs and humans.
Structure and Terminology
- Aboral refers to the side away from the mouth, while oral is closer to the mouth.
- Directionality in bilateral animals aids movement and perception, facilitating interaction with the environment.
- Descriptive terms include:
- Anterior: front
- Posterior: back
- Dorsal: back
- Ventral: belly
- Proximal: close to body
- Distal: farther from body
- Superior: above
- Inferior: below
- Lateral: outside
Fossil Record and Evolution
- First animals appeared approximately 550 million years ago.
- The Cambrian period is crucial, marking an explosion of life and the emergence of major animal groups.
- The Burgess Shale contains unique soft-bodied fossils, providing insights into early animal life and diversity.
Characteristics of Porifera
- The phylum Porifera includes about 5000 living species of sea sponges, classified into three groups: Hexactinellida, Demospongia, and Calcarea.
- Sponges reproduce both sexually and asexually and rely on structures called spicules for support.
- They lack specialized tissues, demonstrating a simple cellular organization.
Cellular Composition
- Sponges consist of various cell types:
- Spicules: provide structural support and deter predators.
- Choanocytes: flagellated cells that create water currents for filter feeding.
- Amoebocytes: mobile cells that distribute nutrients and can form gametes.
Feeding and Chemical Processes
- Sponges filter organic materials and microscopic life from seawater for nourishment.
- Spicules are needle-like structures providing support, varying in shape across species.
- Some sponges secrete spongin fibers, collagen-like materials that contribute to structure.
Life Cycle and Mobility
- Many sponges are hermaphrodites, capable of producing both male and female gametes.
- The typical life cycle involves the release of sperm into water, formation of free-swimming larvae, and settlement to develop into adults.
- Sponge larvae are the only mobile stage, highlighting biodiversity and evolutionary complexity.
Research and Chemical Extraction
- Research on sponge species focuses on extracting chemicals for potential medicinal use, as sponges release toxins for survival and competition in their habitats.
- These studies aim to understand the natural function of sponge metabolites and their applications in treating human ailments.
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Description
Explore the fascinating world of animal symmetry, including asymmetric, radial, and bilateral forms. Learn essential terms that describe animal structure and orientation, as well as the importance of these features in movement and interaction. Discover how these features relate to the evolutionary history of animals.
