Which of the following would show pentaradial symmetry and have a calcareous endoskeleton made up of ossicles ?

Options

A. Mollusca
B. Annelida
C. Arthropoda
D. Echinodermata

Answer

To solve the question of which organism shows pentaradial symmetry and has a calcareous endoskeleton made up of ossicles, we will analyze the characteristics of the given options step by step.

### Step 1: Understand the concept of symmetry
- **Pentaradial symmetry** means that the organism can be divided into five equal parts around a central axis. This type of symmetry is commonly found in certain marine organisms.

**Hint:** Look for organisms that can be divided into five equal parts when considering their body structure.

### Step 2: Identify the endoskeleton type
- An **endoskeleton** is an internal skeleton that provides support and structure to the organism. In this case, we are looking for a calcareous endoskeleton made up of **ossicles**, which are small, calcified structures.

**Hint:** Focus on organisms known for having a calcareous structure or skeleton.

### Step 3: Analyze the options
1. **Mollusca**: These organisms have a hard outer shell and soft bodies. They do not exhibit pentaradial symmetry; instead, they generally show bilateral symmetry.

**Hint:** Remember that mollusks have shells but do not have pentaradial symmetry.

2. **Annelida**: Annelids (like earthworms) are cylindrical and exhibit bilateral symmetry. They do not have an endoskeleton made of ossicles.

**Hint:** Annelids are segmented and bilaterally symmetrical, which disqualifies them from being the answer.

3. **Arthropoda**: Arthropods (like insects and crustaceans) have a chitinous exoskeleton and also exhibit bilateral symmetry. They do not have a calcareous endoskeleton made of ossicles.

**Hint:** Arthropods have an exoskeleton and bilateral symmetry, not pentaradial.

4. **Echinodermata**: Echinoderms (like starfish and sea urchins) exhibit pentaradial symmetry in their adult forms. They have a calcareous endoskeleton made up of ossicles and are characterized by their unique water vascular system.

**Hint:** Echinoderms are known for their pentaradial symmetry and calcareous ossicles.

### Step 4: Conclusion
Based on the analysis, the organism that shows pentaradial symmetry and has a calcareous endoskeleton made up of ossicles is **Echinodermata**.

**Final Answer:** Echinodermata (Option 4)