Which of the following is not a feature of urochordates?
(a) Open circulatory system
(b) Neural gland as excretory structure
(c) Pharyngeal gill slits throughout the life
(d) Notochord in adult stage

Options

A. Open circulatory system
B. Neural gland as excretory structure
C. Pharyngeal gill slits throughout the life
D. Notochord in adult stage

Answer

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

1. **Open circulatory system (Option A)**: Urochordates, also known as tunicates, possess an open circulatory system. This means that their blood (hemolymph) is not entirely contained within vessels and can flow freely through cavities. Thus, this is a feature of urochordates.

2. **Neural gland as excretory structure (Option B)**: Urochordates do not primarily use a neural gland for excretion. Instead, they utilize specialized cells called nephrocytes for excretion. Therefore, this option is not a feature of urochordates.

3. **Pharyngeal gill slits throughout the life (Option C)**: Urochordates have pharyngeal gill slits, but these are typically present during the larval stage and may not persist throughout their adult life. However, in some species, the gill slits can be retained in the adult form. Thus, while this is a feature in some contexts, it is not universally applicable to all urochordates.

4. **Notochord in adult stage (Option D)**: Urochordates possess a notochord during their larval stage, but it is generally lost or reduced in the adult stage. Therefore, this option is also not a feature of urochordates.

Based on this analysis, the option that is not a feature of urochordates is **(b) Neural gland as excretory structure**.

### Summary of Steps:
1. Identify the features of urochordates.
2. Analyze each option to see if it aligns with the known features.
3. Determine which option does not match the characteristics of urochordates.