They can be kept with rays, ive made that mix but they are known to turn and can rasp at the rays...... I feed mine a variety of dry feed, frozen foods and meaty feed.....
And i believe that there are a few species of procilodus, and some reigonal variants.
they've been known to suck slim coats. i keep mine with 3 bichirs and havn't had problems with them sucking yet. mine will eat anything, pellets, wafers, bloodworms...