Heart to pump blood evolved for the first time in

Options

A. Annelids
B. Arthropods
C. Roundworms
D. Flatworms

Answer

To solve the question "Heart to pump blood evolved for the first time in," we will analyze the options provided and understand the evolutionary context of the circulatory system in different phyla.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the first instance of a heart evolving to pump blood in the evolutionary history of animals.

2. **Reviewing the Options**: The options given are:
- A) Annelids
- B) Arthropods
- C) Roundworms
- D) Flatworms

3. **Analyzing Each Option**:
- **Flatworms**: Flatworms (Phylum Platyhelminthes) do not have a circulatory system. They rely on diffusion for nutrient and gas exchange. Therefore, they do not have a heart.
- **Roundworms**: Roundworms (Phylum Nematoda) possess a pseudocoelom, which acts as a fluid-filled cavity. They do not have a true circulatory system or heart; instead, the pseudocoelomic fluid functions in circulation.
- **Arthropods**: Arthropods (Phylum Arthropoda) have an open circulatory system where blood flows through sinuses rather than enclosed blood vessels. They do have a heart, but it is not the first instance of a heart in the evolutionary timeline.
- **Annelids**: Annelids (Phylum Annelida) are characterized by a closed circulatory system. They have blood vessels that act similarly to a heart, allowing for more efficient circulation of blood.

4. **Conclusion**: Based on the analysis, the first instance of a heart to pump blood evolved in **Annelids**. They exhibit a more complex circulatory system compared to the other groups mentioned.

### Final Answer:
The heart to pump blood evolved for the first time in **Annelids**.