Which one of the following groups of animals is bilaterally symmetrical and triploblastic

Options

A. Sponges
B. Ctenophores
C. Coelenterates ( Cnidarians)
D. Aschelminthes (Roundworms )

Answer

To determine which group of animals is bilaterally symmetrical and triploblastic, we can follow these steps:

### Step 1: Understand Bilateral Symmetry
Bilateral symmetry refers to a body plan in which the left and right sides of an organism are mirror images of each other. If you were to cut the organism down the middle, both halves would be similar in shape and structure.

**Hint:** Look for organisms where you can draw a line down the middle and see two similar halves.

### Step 2: Understand Triploblastic Organisms
Triploblastic organisms are those that have three germ layers: ectoderm, mesoderm, and endoderm. This is in contrast to diploblastic organisms, which only have two germ layers (ectoderm and endoderm).

**Hint:** Remember that triploblastic means "three layers," while diploblastic means "two layers."

### Step 3: Evaluate the Options
1. **Sponges (Porifera)**: These organisms are asymmetrical and do not have any defined body symmetry. They are also diploblastic, having only two germ layers.

2. **Ctenophores**: These are biradially symmetrical and diploblastic, meaning they also do not have three germ layers.

3. **Cnidarians (e.g., jellyfish, corals)**: Like ctenophores, they are radially symmetrical and diploblastic.

4. **Aschelminthes (roundworms)**: These organisms are bilaterally symmetrical and triploblastic, having all three germ layers.

**Hint:** Compare the symmetry and germ layer characteristics of each group to identify the correct one.

### Step 4: Identify the Correct Answer
From the evaluation, the only group that is both bilaterally symmetrical and triploblastic is the **Aschelminthes** (roundworms).

**Final Answer:** The correct answer is **Aschelminthes**.