They are the only aquatic Xindi and have bodies shaped like a cetacean, with long arms and webbed hands that presumably allow them to manipulate tools. They operate in water-filled spaceships. Their ships are the largest and most powerful of the Xindi fleet, but also some of the less maneuverable.
The Aquatics are often regarded as the most enigmatic Xindi species. They are infamous for their tendency to over-analyze and for taking an extraordinary amount of time to reach a decision, due to their thoughtful and cautious nature. There is even a Xindi-Primate saying that states that "it is easier to count the stars in the sky, than for an Aquatic to reach a decision". The Primates, however, do admit that sometimes it is the Aquatic's prudence that keeps the council from breaking apart.
The Aquatic language is similar to a whale song and they are known to use sonar. They keep their mouths shut when speaking, instead using two openings on the sides of their gills. Like the Xindi-Insectoids' the Xindi-Aquatics' language could not be translated by universal translators of the 22nd century. Like all Xindi, they possess a pair of small ridges on the cheeks.