Final answer:
The cricoid cartilage is unique as it is the only complete cartilaginous ring in the trachea, providing structural support to maintain the airway passage.
Step-by-step explanation:
The unique feature of the cricoid cartilage is that it is the only complete cartilaginous ring in the trachea. Unlike the other cartilages that form the trachea, which are C-shaped and not fully enclosed rings, the cricoid cartilage forms a complete ring around the trachea. This structure provides support and maintains the open passage of the trachea. Its shape is characterized by a wider posterior region and a thinner anterior region. The cricoid cartilage is also attached to the esophagus and plays a role in the voice production as it is connected to the vocal cords and muscles of the larynx.