Open blood vascular syste is present in

Options

A. cephalochordates
B. cyclostomes
C. urchordates
D. vertebrates

Answer

To determine which group of animals has an open blood vascular system, we can analyze each option provided in the question:

1. **Cephalocordate**:
- Cephalocordates, such as lancelets, possess a closed blood vascular system. This means that their blood circulates within vessels and does not freely flow in the body cavity.

2. **Cyclostome**:
- Cyclostomes, which include jawless fish like lampreys and hagfish, also have a closed blood vascular system. Their blood is contained within blood vessels, similar to cephalocordates.

3. **Urocordate**:
- Urocordates, or tunicates, exhibit an open blood vascular system. In this system, the blood is not entirely contained within vessels and can flow freely in the body cavity, which is characteristic of an open circulatory system.

4. **Vertebrate**:
- Vertebrates, which include mammals, birds, reptiles, amphibians, and fish, have a closed blood vascular system. Their blood circulates through a network of vessels.

Based on this analysis, the group that possesses an open blood vascular system is **urocordates**.

### Final Answer:
The open blood vascular system is present in **urocordate** (option 3).