The Question is from neet-zoology animal-kingdom , and it was created by the author Mr. BALACHANDRA.N

Question

In certain Cnidarians, the medusa stage is absent.  This phenomenon is MOST directly related to which ecological adaptation?

Mr. BALACHANDRA.N · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Cnidarian Life Cycles and Ecological Adaptations
 **Related Topics**:  Polymorphism in Cnidarians, Medusa vs. Polyp, Benthic vs. Pelagic lifestyles
 **Prerequisites**: Basic understanding of Cnidarian life history (medusa and polyp stages), ecological terms (sessile, benthic, pelagic).
## SOLUTION PATHWAY
**Given Information**:
  Medusa stage is absent in certain Cnidarians.
  We need to find the ecological adaptation most directly related to this absence.
**Method & Steps**:
 1. Analyze the role of the medusa stage in Cnidarian life cycles.
  Reasoning: The medusa stage is typically the free-swimming, sexually reproductive stage in many Cnidarians.  Its motility allows for dispersal and wider gene flow.
 2. Consider the implications of a missing medusa stage.
  Working: If the medusa stage is absent, the organism likely lacks the free-swimming, sexually reproductive phase.  This suggests a lifestyle that doesn't require wide dispersal for reproduction or survival.
 3. Relate the absence of the medusa stage to the given options.
  Reasoning:  A sessile or benthic lifestyle is consistent with an organism that doesn't need to move widely for reproduction or feeding.  Deep-sea environments, symbiotic relationships, and predation on large mobile prey are not necessarily exclusive to Cnidarians lacking a medusa stage.
 4. Final step.
  Result: The absence of the medusa stage is most directly related to a sessile or benthic lifestyle.
  Verification:  Many anthozoans (corals, sea anemones) lack a medusa stage and are benthic organisms. This confirms our reasoning.
## OPTION ANALYSIS
A :x: Deep-sea environments:  Many deep-sea Cnidarians *do* have a medusa stage.  This is not the most direct relationship.
B :x: Symbiotic relationships with algae: While some Cnidarians with symbiotic algae are benthic, the symbiotic relationship itself doesn't directly cause the absence of the medusa stage.
C :x: Predation on large, mobile prey:  Predatory lifestyle doesn't necessitate the absence of a medusa stage. Many medusae are predators.
D ✓: Sessile or benthic lifestyle:  A sessile or benthic lifestyle is strongly correlated with the absence of a medusa stage, as it eliminates the need for a free-swimming, dispersal phase.
## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the medusa and polyp stages:  Remember that the polyp is typically sessile, while the medusa is free-swimming.
  2.Assuming a correlation implies causation:  While a correlation exists between the absence of a medusa and a benthic lifestyle, this doesn't prove that one directly causes the other.  Evolutionary pressures likely resulted in both.
 **Quick Tips**:
  1. Focus on the ecological implications of a free-swimming vs. sessile lifestyle.
  2. Consider the reproductive strategies of different Cnidarian groups.

Mr. BALACHANDRA.N · Answer

Deep-sea environments

Mr. BALACHANDRA.N · Answer

Symbiotic relationships with algae

Mr. BALACHANDRA.N · Answer

Predation on large, mobile prey

Mr. BALACHANDRA.N · Answer

The correct Option is "Sessile or benthic lifestyle"

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