Characteristics which are common to the Arthropod, Mollusk, Echinoderm and Chordate lines are a (an)

Options

A. segmentation and a coelom
B. endoskeleton and a coelom
C. compound eye and segmentation
D. coelom and a parietal eye.

Explanation

To solve the question regarding the characteristics common to Arthropods, Mollusks, Echinoderms, and Chordates, we will analyze each option provided in the question step by step.

### Step 1: Understand the Characteristics
We need to identify which characteristics are common among the four groups: Arthropods, Mollusks, Echinoderms, and Chordates.

### Step 2: Analyze Each Option
1. **Segmentation and Coelom**:
- Segmentation refers to the division of the body into repetitive segments. This is a characteristic of Arthropods and Chordates. Echinoderms also exhibit some form of segmentation, while Mollusks do not show true segmentation. However, all these groups possess a coelom (a body cavity).
- **Conclusion**: This option has some truth but is not entirely correct for all groups.

2. **Endoskeleton and Coelom**:
- An endoskeleton is present in Chordates and some Echinoderms, but it is absent in Arthropods and Mollusks, which have exoskeletons or shells.
- **Conclusion**: This option is incorrect as not all groups have an endoskeleton.

3. **Compound Eye and Segmentation**:
- Compound eyes are primarily found in Arthropods. Chordates have simple eyes, and Echinoderms and Mollusks do not have compound eyes.
- **Conclusion**: This option is incorrect as compound eyes are not a common characteristic.

4. **Coelom and Parietal Eye**:
- While all these groups have a coelom, the term "parietal eye" refers specifically to a type of eye found in some vertebrates and is not a common feature across all groups.
- **Conclusion**: This option is incorrect.

### Step 3: Identify the Correct Answer
After analyzing all the options, the first option (Segmentation and Coelom) is the most accurate, as segmentation is a characteristic of Arthropods and Chordates, and coelom is present in all four groups.

### Final Answer
The correct answer is **Segmentation and Coelom**.

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