Perhaps you've heard of these cichlids, but you've never taken the time to look them up. They comprise primarily the Geophagus and Satanoperca genera, mostly from South America. The nickname comes from their predominant feeding method - gulping the substrate, sifting it for any nourishment, and then passing what remains through the gills.
Consisting of nearly three dozen species, these are some of the most beautiful New World cichlids, in my opinion. If you're interested in adding these to your cichlid keeping portfolio, check them out. Below are a couple of good primers from Tropical Fish Hobbyist magazine.
The Cichlid Room Companion
Tropical Fish Hobbyist
American Cichlid Assoc.
African Cichlid Hub