Pseudotothyris obtusa can be diagnosed from all congeners by having the upper pharyngeal toothplate bearing 20-30 teeth (vs. 32-47 in Pseudotothyris ignota, 31-36 in Pseudotothyris janeirensis); ceratobranchial 5 bearing 12-15 teeth (vs. 15-31 in Pseudotothyris ignota, 18-23 in Pseudotothyris janeirensis). It further differs from Pseudotothyris ignota by having the anterior margin of snout completely covered by

odontodes (vs. anterior margin of snout with an odontode-free band); first anal-fin pterygiophore contacting the 12th vertebra (vs. 13th); and metapterygoid-hyomandibula suture reduced, the bones not contacting each other dorsally to the suture (vs. metapterygoid and hyomandibula contacting each other dorsally to the suture). It can be differentiated from Pseudotothyris janeirensis by having scattered plates covering the abdomen partial or totally (vs. abdomen almost naked, except for one to three lateral abdominal plates and one to two preanal plates); spinelet absent (vs. present); three transverse dark saddles on the dorsum (vs. transverse dark saddles on the dorsum absent); subocular cheek plate generally present (vs. always absent); and odontodes on lateral plates randomly distributed (vs. odontodes aligned in well-defined series) (Ref. 116384).