Open circulatory system which does not participate in the transport of `O_2` occurs in

Options

A. Echinodermata
B. Annelida
C. Arthropoda
D. Vertebrata

Answer

To answer the question regarding the open circulatory system that does not participate in the transport of oxygen, we can follow these steps:

### Step 1: Understand the Concept of Open Circulatory System
An open circulatory system is a type of circulatory system where the blood is not always contained within blood vessels. Instead, it flows freely through cavities in the body, bathing the organs directly in blood.

**Hint:** Recall the characteristics of open versus closed circulatory systems.

### Step 2: Identify Organisms with Open Circulatory Systems
Open circulatory systems are commonly found in invertebrates, such as arthropods (like insects and crustaceans) and some mollusks. These organisms rely on diffusion for gas exchange rather than a dedicated respiratory system.

**Hint:** Think about which groups of animals have simpler body structures and may not require complex circulatory systems.

### Step 3: Consider the Role of Oxygen Transport
In organisms with an open circulatory system, the hemolymph (the fluid equivalent to blood) may not carry oxygen in the same way that blood does in closed systems. For example, many arthropods use tracheal systems for gas exchange, where oxygen is delivered directly to tissues without the need for hemolymph to transport it.

**Hint:** Reflect on how different organisms adapt their respiratory systems based on their environment and physiology.

### Step 4: Conclude on the Specific Organism
Given that the question asks for an open circulatory system that does not participate in the transport of oxygen, we can conclude that this is characteristic of certain arthropods, such as insects, which utilize a tracheal system for oxygen transport instead.

**Hint:** Consider specific examples of organisms that fit this description, such as insects.

### Final Answer
The open circulatory system that does not participate in the transport of oxygen occurs in certain arthropods, such as insects.