Lusus

On the planet of Alternia, lusus were creatures left to care for the young of the main intelligent inhabitants in place of biological parents, for reasons that have yet to be described. Possessing a wide variety of shapes and sizes, lusus were placed in a unique relationship with their wards.

For one thing, lusus were the ones to teach the young both how to survive and how to interact with others of their own kind in the proper way. On the other hand, said young were charged with keeping their lusus fed and healthy, lest they be "culled" for its death resulting from failing to take care of it.

As of Alternia's destruction, the only two lusus seen - Those of Vriska Serket and Equius Zahhak - Were killed on-screen. More likely than not, the majority of them are dead.

Vriska Serket's Lusus
A gigantic spider, the lusus taking care of Vriska Serket was quite troublesome for her to deal with. It normally took to intimidation to motivate her into feeding it, which only worked efficiently around her adolescence, when Vriska started bringing FLARPers she had defeated and killed for the lusus to devour.

Vriska's own words made it clear that the lusus was more of a burden than a companion, and that it had always intended to eat Vriska should she have ever failed to procure sustenance for it. Yet as Vriska said that the lusus was half-blind, nearly deaf, and could hardly move, this was likely more a threat to keep her working.

Despite all of this, Vriska and her lusus could cohabitate peacefully for the most part. As well, when her lusus used its body as a shield to protect Vriska, from massive boulders dropped by the Catenative Doomsday Dice Cascader's faulty activation and demolishing the remains of Equius Zahhak's hive, Vriska opted to use her Fluorite Octet to kill it out of mercy rather than leave it to suffer.

Aurthour
The lusus caring for Equius Zahhak was a bizarre creature, to say the least. Solid white, like all lusus, he resembled a centaur with a bald head, prominent nose, and handlebar mustache. As well, his abs and pecs were ludicrously well defined, and at his mid-abdomen hung a functional udder.

He was stated to be a particularly strong, sturdy lusus, though this didn't save him from bruising at so much as being patted on the head while his master and ward was holding back. Unlike Vriska Serket and her lusus, Equius and Aurthour were very friendly towards each other, and Aurthour regularly made it clear that he didn't hold occasional injuries against Equius.

Upon the event that caused Alternia's destruction, a meteor blew a gaping hole in Equius's hive, through which Aurthour violently fell to his death. Upon the hive and its mesa disappearing, Aurthour's body was brought through with it while lying upon a wide ledge that he'd landed upon. It is unknown how well, or even if Equius recovered from this happening.

Trivia

 * While Aurthour matches with his paired youth's theme on Sagittarius, Vriska Serket's lusus is only matched with the Scorpio sign by both spiders and scorpions being arachnids.