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Questions and Answers
Which of the following are classes of Cnidarians? (Select all that apply)
Which of the following are classes of Cnidarians? (Select all that apply)
- Hydrozoa (correct)
- Mollusca
- Anthozoa (correct)
- Cubozoa (correct)
- Scyphozoa (correct)
- Staurozoa (correct)
What is a key feature of Class Anthozoa?
What is a key feature of Class Anthozoa?
No medusa stage.
Which of the following are subclasses of Class Anthozoa? (Select all that apply)
Which of the following are subclasses of Class Anthozoa? (Select all that apply)
- Ceriantipatharia (correct)
- Hexacorallia (correct)
- Hydrozoa
- Octocorallia (correct)
- Scyphozoa
All members of Subclass Hexacorallia are freshwater species.
All members of Subclass Hexacorallia are freshwater species.
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What are tube anemones?
What are tube anemones?
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Sea anemones harbor symbiotic ______ that live in their tissue.
Sea anemones harbor symbiotic ______ that live in their tissue.
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Explain how coral reefs form.
Explain how coral reefs form.
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What is a major factor threatening the health of coral reefs? (Select all that apply)
What is a major factor threatening the health of coral reefs? (Select all that apply)
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Define protandrous.
Define protandrous.
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Match the following subclasses with their characteristics:
Match the following subclasses with their characteristics:
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Study Notes
Cnidarians Overview
- Five classes of Cnidarians: Hydrozoa, Scyphozoa, Cubozoa, Anthozoa, Staurozoa (proposed).
Class Anthozoa Characteristics
- No medusa stage; only polyp form exists.
- Exclusively marine species.
- Large gastrovascular cavity divided into compartments.
- Comprises three subclasses: Hexacorallia, Ceriantipatharia, and Octocorallia.
Subclass Hexacorallia
- Hexamerous body plan, characterized by six-fold symmetry.
- Includes sea anemones and hard corals.
Sea Anemones
- Larger and heavier polyps than those of hydrozoans.
- Exclusively marine, found in coastal areas worldwide.
- Attach to substrates using pedal discs at their base.
- Features tentacles around an oral disc and a cylindrical body.
- Carnivorous and capable of gliding and swimming.
- Can retract tentacles and oral discs when threatened.
Mutualistic Relationships of Sea Anemones
- Host symbiotic dinoflagellates (algae) within their tissues.
- Some live on hermit crab shells; clownfish seek shelter among them.
Reproduction in Sea Anemones
- Sexual reproduction: Dioecious or monoecious (hermaphroditic) species, with protandrous individuals producing sperm first.
- Asexual reproduction occurs through pedal laceration, longitudinal and transverse fission, and budding.
Hard/True Corals
- Resemble miniature sea anemones and reside in self-secreted calcareous cups (exoskeleton).
- Form massive colonies with a thin layer of living coral over the exoskeleton.
Subclass Ceriantipatharia
- Hexamerous body plan, including tube anemones and thorny corals.
- Few species known, living primarily in warm sea environments.
- Unique unpaired compartments in their gastrovascular cavities.
Tube Anemones
- Solitary creatures that live buried in soft sediments.
Thorny or Black Corals
- Colonial organisms that attach to firm substrates.
Subclass Octocorallia
- Octomerous body plan with eight pinnate tentacles and unpaired complete septa.
- Includes soft and horny corals like sea fans and sea pens.
- All species are colonial; gastrovascular cavities communicate through solenia.
Coral Reef Formation
- Composed of calcium carbonate exoskeletons accumulated over thousands of years.
- Living organisms primarily inhabit the top layer of the reef.
- Hermatypic corals are crucial for reef formation, requiring conditions of warmth, light, and undiluted seawater.
- Typically found in shallow waters between 30 degrees north and south latitude.
Symbiotic Relationship with Dinoflagellates
- Photosynthetic zooxanthellae inhabit coral tissues, providing food and recycling waste products.
Threats to Coral Reef Health
- Nutrients from fertilizers and sewage lead to excessive algal growth, obstructing sunlight.
- Overfishing of herbivorous fishes exacerbates algal overgrowth.
- Pollution from pesticides, oils, and sediments negatively affects reefs.
- Global warming results in coral bleaching, as warm water forces corals to expel zooxanthellae.
- Increased atmospheric CO2 acidifies oceans, complicating calcium carbonate precipitation necessary for coral structures.
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