Which is not characteristic of echinoderms

Options

A. Endodermal skeletal system
B. Bilateral symmetry
C. Free floating larva
D. Water vascular system.

Answer

To determine which option is not a characteristic of echinoderms, we will analyze each of the provided options step by step.

### Step 1: Understand Echinoderm Characteristics
Echinoderms are a group of marine animals that include starfish, sea urchins, and sea cucumbers. They have several defining characteristics, including a water vascular system, a calcareous endoskeleton, and bilateral symmetry in their larval stage.

### Step 2: Analyze Each Option
1. **Endodermal**: This term refers to the innermost layer of cells or tissue in an embryo. Echinoderms do not have an endodermal skeletal system; instead, they have a mesodermal skeletal system made of calcareous plates or ossicles. Therefore, this option is likely the correct answer.

2. **Skeletal System**: Echinoderms have a unique skeletal system composed of calcareous structures. This is a characteristic feature of echinoderms.

3. **Bilateral Symmetry**: Echinoderm larvae exhibit bilateral symmetry, which is a characteristic of their early development. However, adult echinoderms typically display radial symmetry.

4. **Free Floating Larvae**: Echinoderm larvae are indeed free-floating in the water column during their early life stages. This is a characteristic feature of echinoderms.

5. **Water Vascular System**: This is a unique feature of echinoderms, consisting of a network of water-filled canals that aid in locomotion and feeding.

### Step 3: Conclusion
After analyzing all the options, the one that does not align with the characteristics of echinoderms is the **endodermal skeletal system**. Echinoderms possess a **mesodermal skeletal system**, making this the correct answer.

### Final Answer
The option that is not characteristic of echinoderms is **endodermal skeletal system**.

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