Jellyfish-M are anti-personnel mines with skittering tentacles, able to rapidly move towards the enemy in a pack but are easily dispatched with assault rifle fire. When activated they have a purple light on their backs that turns red when about to explode. Let the Marines handle these
Jellfish-L are area superiority guided mobile explosives easily capable of destroying a light bunker, basically the Jellyfish-M in larger form and with more armor. When heavily damaged the green lights on their back turn red and moves faster, signaling it is close to exploding. Use shotguns, anything to kill them as far from the IFV as possible.
The larger ones thankfully only appear in one mission.