The Genesis leeches
The Genesis worm, formed from the leeches
Genesis worms were creatures native to the Genesis Planet in 2285.
They were initially formed from microbes on Captain Spock's torpedo tube brought to the planet from the USS Enterprise after Spock's funeral. Throughout their short existence, the worms evolved very quickly from microbes to their adult form. The worms were also aggressive. They attacked a Klingon strike team led by Kruge. (Star Trek III: The Search for Spock)
The Lower Decks Campaign Guide gives their scientific name as macrobacillus halodurans genesisi.