The Andalites are a race of sentient psionic quadrupeds originating from the same universe as the Yeerk.

In their native universe, they are a highly cultured and civilized race. However, in the Cantina Universe, they have become cloned shock-troops for the Yeerk Lost Colony and the Dread Conglomerate.
Biology
Andalites have several biological adaptations that are unique.
All five traditional senses are present in Andalites, as well as psionics. Andalite hearing is highly sensitive, comparable to Vulcans. Their vision, however, is their primary sense. Primary eyes, located inside the skull, have restricted movement but tremendous ability to judge distance. The stalk eyes which swivel on the top of the Andalite head have a keen ability to find and track even the smallest movement.
Andalite necks do not move in any direction, so an Andalite must face the direction he or she wants their primary eyes to look at.
The tactile touch of an Andalite is considered to be less sensitive than most races. However, their psionic property makes touching another being a very strong sensation.
Psionics among Andalites operates on the same basic principle as most other races. But since Andalites have no mouths they do not have traditional speech, instead using what is known as "Thought Speak". They have the capacity for symbolic language, which expresses itself in that Andalites use Thought Speak to express specific words and concise ideas, while using a more general spectrum of psionics for emotions and images. Thought Speak, as opposed to true telepathy, is a complete analog to spoken language. An Andalite can misspeak, lie, and be either articulate or inarticulate.
Without mouths, Andalites must eat through absorption of nutrients via the porous but dense hoofs they possess. Their digestive system is extremely simple, as nutrients are absorbed directly unto the blood stream through their hooves, bypassing any breaking down. The hooves act much like villi in most other races. There is a limited sense of taste in these hooves, though they appear to have a more complex sense of taste regarding liquids.
The arms of Andalites are remarkably weaker than human arms. Humans developed their upper appendages as both manipulative devices and weapons, but Andalites use their arms as simply manipulators. Their seven-fingered hands are slender and highly dexterous.
Tail blades and tremendously long spinal extensions provide Andalites with their primary weaponry. Appearing similar to scorpion tails, Andalite tails reach roughly one meter in front of the torso when fully extended. Even individuals untrained in the art of combat can instinctively move their tails faster than human vision is capable of tracking. Andalite stalk eyes, however, are up to the task.
The actual blade of an Andalite tail is scythe-like, sharpened on the underside and pointed at the end. It's composed of extremely hard keratin, although beta keratin supplements and daily buffing can strengthen them further. Some Andalites have been known to add complex braces and artificial blades to their tails, often either as tools for constructing scoops or as weapons.
Behavior
Very few herbivorous species develop higher cognitive functions, as the planning involved in hunting is often associated with the development of language, temporal perception, and abstraction.
Developing language among Andalites was a function of their community. The grazing herds built scoops on the edge of wide grassy fields, near the woods. The scoops must be near the forest to have the proper soil density, but on the field so they can graze. This meant that their territories overlapped with large predators. Andalites are much smaller than the large predators of their home world, so they would bring down threats through coordinated efforts.
Initially Andalites communicated through complex hand signals and subtle psionic implication. There is evidence, however, that the "Andalite Renaissance" where they developed Thought Speak, literature, art, and government, was instigated by a higher intelligence. Potentially a nearly-omnipotent being.
After the Renaissance, Andalite civilization began expanding towards the stars. Their global government consisted of military commanders called Princes acting as independent executives, assembling to act as a single legislative body. Judicial action seems to be a foreign concept to them, as the breaking of the law among Andalites generally results in either immediate demotion by their immediate Prince for minor offenses, and immediate death for major offenses. There is no concept of "innocent until proven guilty".
Often Andalites have displayed an extremely narrow view of gender roles. Although females are not treated as inferior by any means, there are specific jobs and behaviors that are male and specific one that are female.
Species History
Andalites evolved on a very isolated planet. After developing space travel they considered themselves alone in the universe for several decades. However, after encountering several unsavory races such as the Skirt-Na, they began developing a certain level of xenophobia.
An initial encounter with the Yeerks was an exercise in Andalite compassion, which backfired when the Yeerks attacked their Andalite benefactors and stole their technology. This reinforced Andalite xenophobia, and initiated the Yeerk Empire.
Since then the Andalite people have been in roiling internal conflict between conflicting policies advocated by various Princes; on one hand are the advocates of genocide in response to the Yeerks, while in opposition is a minority opinion that the Andalites should be encouraging younger species and helping them oppose the Yeerks independently.
This conflict has yet to resolve itself.