This was first hinted at during the end of the Monster Hunter World: Iceborne presentation of Acidic Glavenus at San Diego Comic-Con 2019.
The three new subspecies have finally been revealed and they are;
Viper Tobi-Kadachi is imbued with a poison attack
Nightshade Paolumu releases sleep breath upon hunters
Coral Pukei-Pukei attacks with a water barrage instead of poison.
Below are three subspecies gameplay. (video source Arekkz Gaming)