Which of the following is not a characteristic feature of Hemichordates?
(a) Exclusively marine
(b) Excretion by proboscis gland
(c) Notochord present only in anterior half of body
(d) Respiration by gills

Options

A. Exclusively marine
B. Excretion by proboscis gland
C. Notochord present only in anterior half of body
D. Respiration by gills

Answer

To determine which of the following is not a characteristic feature of Hemichordates, we will analyze each option provided:

1. **Option (a): Exclusively marine**
- Hemichordates are indeed exclusively marine organisms. They are found only in marine environments and do not inhabit freshwater. Therefore, this is a characteristic feature of Hemichordates.

2. **Option (b): Excretion by proboscis gland**
- Hemichordates utilize a proboscis gland for excretion. This gland plays a crucial role in their excretory system. Hence, this is also a characteristic feature of Hemichordates.

3. **Option (c): Notochord present only in anterior half of body**
- In Hemichordates, the notochord is indeed present but is restricted to the anterior half of the body. This is a defining characteristic of this group. Thus, this option is also a characteristic feature.

4. **Option (d): Respiration by gills**
- Hemichordates do not have true gills. Instead, they have pharyngeal gill slits that are used for respiration. The term "gills" implies a structure that is not present in Hemichordates, making this option not a characteristic feature of the group.

Based on the analysis, the correct answer is:
**(d) Respiration by gills** is not a characteristic feature of Hemichordates.