Diagnosis: This species is distinguished from its congeners by the autapomorphic reduced ossified suprapreopercular canal. In auchenipterids the suprapreopercle is a short canal bone lying above the preopercle and containing the dorsal end of the opercular lateral line canal, which passes through it and enters the pterotic; and among centromochlines, this canal bone may vary. In some forms (as in Centromochlus perugiae, C. heckelii, and C. existimatus, a suprapreopercular ossification is absent, but in most forms it is present as a tube, completing the space between preopercle and the pterotic. In G. bockmanni, the suprapreopercle is not represented as a tube. This small canal bone is an incompletely ossified tube between the preopercle and the pterotic, with the bony portion located close to the preopercle. A fully ossified suprapreopercle was not detected in G. bockmanni. Glanidium bockmanni further differs from its congeners (albescens, ribeiroi, catharinensis, melanopterum, and leapardus in having a small adult size 29-48 mm SL (vs. 70-195 mm SL); lower jaw of equal size (vs. slightly prognathous); first nuchal plate absent (vs. present); low number of vertebrae 32 (vs. 3440); anal fin with 7 branched rays (vs. 8-11); and a less voluminous muscle adductor mandibulae A2 associated with a discrete concavity between sphenotic and pterotic (vs. thickened A2 associated with a quite pronounced concavity). It very closely resembles G. cesarpintoi , but can be distinguished from it due to larger post-cleithral process (20% SL vs. 16% SL); shorter mesethmoid (15% HL vs. 25% HL); adipose fin present (vs. absent); and pectoral-fin spine with antrorse spinules on anterior margin (vs. retrorse in cesarpintoi) (Ref. 56311).