 Because of this, Marco sees an opportunity and morphs into a gorilla, knocking out the Visser.The Yeerks have just captured some new specimens of aquatic species - known as Leerans.The Leerans are capable of telepathy and limited mind-reading capacity, hence the Yeerks' attempts to endow the sharks with sentience - a secret invasion is impractical due to the Leeran mind-reading abilities.