Mar-gite

The Mar-gite were crystalline, silicate based, aliens from outside the Orion Spur that attacked the Terran Confederacy without warning and without any communication. Despite the Terran's calls for diplomacy, the Mar-gite remained silent and aggressive and thus became one of thirteen species driven to extinction by the Terrans.

Description
Mar-gite were silicon based crystalline life forms. Five limbed with a central section, much like a Terran starfish. They had eyes at the end of their legs/arms, as well as several more ringing a central mouth. Their colors varied depending on unknown factors, either black, bone white, pink, reddish, or dark purple. Their eyes were bloodshot and rolled around in the 'sockets' often aimlessly.

Their undersides were covered in pinkish red cilia, and their teeth were calcite based. Mar-gite apparently communicated through pheromones, and smelled like pine scented cleaning products.

Culture
Mar-gite language and thought process are alien enough that no communication has ever been established successfully; either that, or they refused all communication. The only thing known is that are a spacefaring species, that they can feed on carbon-based lifeforms and have a predilection to digest them alive.

History
The Mar-gite attacked from the nearby galactic arm, using several star systems scattered roughly 25 LY apart to cross the gulf between the galactic arm and the Orion Spur. Within a year they had attacked and taken over 300 systems. It wasn't until the information about how the Mar-gite ate that the Confederacy went to war. They prefer carbon-based life forms to eat and will abandon a world once all the carbon life has been devoured. They 'ate' by grabbing onto victims and extruding acids to dissolve the life-form, devouring the nervous system last, seeming to relish the pain.

This almost caused the collapse of the Confederacy as the Senate proclaimed that perhaps if the Confederacy just gave the worlds to the Mar-gite they wanted, then they'd be sated and stop their attack. This caused riots on over 5,000 worlds, culminating in the Confederate Senate being lynched in the streets.

The Mar-gite did not communicate, so their desires and wants are unknown.

The war lasted for nearly a century, close to 300 planets were planet cracked and nearly a thousand worlds were depopulated, but they were exterminated, through planet crackers and rumors of worse. Of the 14 or so star systems they used to cross the Hub-Ways Gulf, only 4 remain. Those four are some of the most heavily defended systems outside of TerraSol itself.

Whether or not there are more Mar-gite and whether or not they were fleeing a stronger adversary is currently unknown.