Whatever they were, there were nine of them and they came from the sea. They had dog heads and sealion bodies when they weren’t busy shape-changing into something else.
They roamed around Rhodes or Crete and could kill anything with a poison look, so protection was not a problem and they could spend all their time gamboling around indulging in silly pranks and tomfoolery.
They upset ZEUS by messing with the weather and POSEIDON tried to flood them out which is a bit silly for things that can swim. They just moved on and can pop up almost anywhere from time to time causing havoc in coastal areas.