Which structures are the primary organs of attachment in the tapeworm scolex shown in the diagram?

The diagram shows the scolex (head) of a tapeworm, which is adapted for attachment to the host's intestine.

• I points to the rostellum, which is the anterior-most part of the scolex.
• II points to the hooks located on the rostellum. Hooks are used for firm anchorage.
• III points to the suckers. Suckers create suction to hold onto the intestinal lining.
• IV points to the neck region, from which new proglottids are formed. The neck is not directly involved in attachment.

The primary organs for attachment in a tapeworm are the hooks and suckers. In the given diagram, these are labeled as II (hooks) and III (suckers).

Let's evaluate the options:

• A. III and IV: Suckers and Neck. The neck (IV) is not an attachment organ.
• B. I and II: Rostellum and Hooks. While hooks (II) are for attachment, the rostellum (I) is the region that bears the hooks, not an attachment organ itself in the same functional sense as hooks or suckers.
• C. I and III: Rostellum and Suckers. Similar issue with I.
• D. II and III: Hooks and Suckers. These are the two main types of structures specifically designed for attachment to the host's intestinal lining.

Therefore, the organs for attachment are the hooks (II) and suckers (III).

The final answer is $\boxed{\text{D}}$