To solve the question "Diversity in the habitat not seen in," we need to analyze the options provided: Porifera, Annelida, Mollusca, and Echinodermata. Here’s a step-by-step breakdown of the solution:
### Step 1: Understand the Question
The question is asking which of the given phyla does not exhibit diversity in its habitat. This means we need to identify the phylum that has the least or no variation in its species or habitat types.
### Step 2: Analyze Porifera
Porifera, commonly known as sponges, are known for their high diversity. They inhabit various marine environments and exhibit a wide range of forms and structures. Therefore, Porifera cannot be the answer as they have significant diversity.
**Hint:** Look for organisms that are known for their variety in forms and habitats.
### Step 3: Analyze Annelida
Annelids, or segmented worms, also show considerable diversity. They can be found in various environments, including freshwater, marine, and terrestrial habitats. While their diversity is not as high as Porifera, they still exhibit a moderate level of diversity. Thus, Annelida cannot be the answer.
**Hint:** Consider the environments where segmented worms are found and their adaptations.
### Step 4: Analyze Mollusca
Mollusca is another phylum known for its diversity. It includes a wide range of organisms such as snails, clams, and octopuses, which occupy various habitats from terrestrial to aquatic environments. Mollusca is recognized as having the second highest diversity among animal phyla. Therefore, this option also cannot be the answer.
**Hint:** Think about the different types of mollusks and where they live.
### Step 5: Analyze Echinodermata
Echinodermata, which includes starfish, sea urchins, and sea cucumbers, generally have less diversity compared to the other three phyla. They are primarily marine organisms and do not exhibit the same level of variation in species or habitats as Porifera, Annelida, or Mollusca. In fact, Echinodermata is often characterized by a more uniform structure and lifestyle.
**Hint:** Focus on the characteristics of marine organisms and their habitat variations.
### Step 6: Conclusion
After analyzing all the options, it is clear that Echinodermata is the phylum that exhibits the least diversity in its habitat. Therefore, the correct answer to the question is Echinodermata.
### Final Answer
The correct answer is **Echinodermata**.
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