Peckoltia greedoi is distinguished from P. pankimpuju by having well developed color and eyes; from all other congeners except P. ephippiata by having uniformly colored head (vs. large spots, mottling, short lines, or thick dark areas; faint spots are present in P. ephippiata, but are not obvious); from all congeners except P. braueri, P. capitulata, P. compta, P. lujani, P. oligospila, P. otali, and P. stimulata by having the abdomen largely naked posterior to the pectoral girdle (vs. only small naked patches at insertions of pelvic fins); from all congeners except P. ephippiata, P. furcata, P. lujani, P. pankimpuju, and P. sabaji by having the dentaries meet at an angle greater than 90°; from P. ephippiata by having fewer teeth 16-39 dentary, 20-38 premaxillary (vs. 39-72 dentary, 41-73 premaxilary), by having faint spots forming bands in the dorsal fin, and by having platelets maximally present below pectoral girdle and in a narrow, lateral column just posterior to pectoral fin, and below pelvic girdle (vs. platelets on the central region of the abdomen posterior to the pectoral girdle present); and by lacking slight keels on the lateral plates (vs. keels present, strongest on median series); from P. lujani by the absence of spots on the posterodorsal surface of head and nape (vs. presence of large spots), and by having the pectoral-fin spine relaxed position angled dorsally, pointing at insertion of dorsal fin (vs. pectoral-fin spine angled only slightly dorsally, pointing maximally to dorsal insertion of caudal fin) and pectoral-fin spine reaching two or more plates of the ventral series beyond the pelvic base when adpressed ventral to pelvic fin (vs. less than one plate).

It differs from Etsaputu by possessing more than six evertible cheek odontodes, the largest of which extending posterior to the eye (vs. six or fewer, the largest not extending beyond the exposed portion of the opercle). It can be diagnosed from Hemiancistrus (except ‘H.’ landoni) and Ancistomus by the presence of prominent dorsal saddles (vs. dark or light spots or entirely dark); and from all Hemiancistrus and Ancistomus by the presence of bands in the caudal fin and absence of free spots (vs. bands absent or present with some free spots) and bands in the dorsal fin (vs. spots or no markings). It can be separated from Peckoltichthys bachi by the absence of spots on the head (vs. large dark spots or mottling), by having the eyes high on the head with the dorsal rim of the orbit higher than the interorbital space (vs. low on the head, dorsal rim of orbit lower than interorbital space), and by having small plates on the abdomen (vs. relatively large).

Peckoltia greedoi closely resembles P. vittata but it can be distinguished by having the dentaries meeting at an angle >90° (vs. <90°), by having a shallower slope of the head (~30° from snout tip to orbit, vs. >45°), no change in slope of head from anterior margin of orbit to tip of parieto-supraoccipital (vs. angle becoming much shallower beyond orbits), head appearing narrower and longer when placed side-by-side with similar size specimens, abdomen without platelets between pectoral and pelvic girdles (vs. platelets present), pectoral-fin spine reaching two or more plates beyond pelvic-fin base when adpressed ventral to pelvic fin (vs. less than one plate) (Ref. 99824).

Description: Dorsal fin ii,7; anal fin i,4; pectoral fin i,6; pelvic fin i,5 (Ref. 99824).