TAXA TABLE
 

Hypostominae is diagnosed by one unique characteristic: lower lobe oof the hypural plate longer than upper (123:1). Other characteristics that are considered synapomoprhic for the Hypostominae are: a long accessory process on the first ceratobranchial )7:2, reversed in some groups), a small canal plate (83: 1), a V-shaped spinelet (148: 0), and a posteroventral ridge on the basipterygium (173: 1)

With the exclusion of some genera formerly in Hypostominae but the inclusion of Ancistrinae, Hypostominae becomes the largest of the loricariid subfamilies in number of species (~360 currently valid species) and genera 3040).  Size is incredibly variable within the subfamily including small members such as Lithoxus (50 mm) and the largest of all loricariids, Rhinelepis and Acanthicus (1000+ mm).  Hypostomines are typically bulkier than other loricariids and generally have thicker plates than neoplecostomines.  The tribe and generic descriptions provide more information on the diversity of forms.

The best character to distinguish the Hypostominae from most other loricariids is the development of the spinelet.  In all the Hypostominae, the spinelet is large and V-shaped and clearly slides under the nuchal plate whereas it is square or absent in most other loricariids and, when present, does not slide under the nuchal plate.  Some hypoptopomatines have a triangular spinelet, but these species can be distinguished from the Hypostominae by a completely or nearly completely exposed pectoral girdle (vs. at most some odontodes supported by the coracoid laterally), and by having the fenestrae of the pterotic-supracleithrum larger ventrally than dorsally (vs. all fenestrae of about equal size).  Delturus also has a triangular spinelet but can be distinguished by the presence of an adipose fin with a postdorsal ridge of median plates (all hypostomines with a postdorsal ridge lack an adipose fin).  Chaetostoma, Cordylancistrus, Dolichancistrus, Leptoancistrus\, and some Ancistrus have the spinelet covered in skin; these species can be separated from the other loricariid subfamilies by the presence of evertible cheek plates with hypertrophied odontodes.  Hypostominae further differs from Lithogenes by being completely plated; and from Loricariinae by having a round, oval, or triangular cross-section of the caudal peduncle (vs. rectangular and depressed).

Armbruster, J.W. 2004. Phylogenetic relationships of the suckermouth armored catfishes (Loricariidae) with emphasis on the Hypostominae and the Ancistrinae. Zoological Journal of the Linnean Society 141:1-80.