All species are recognized by Isbrücker (1980) in Hemiancistrus except Plecostomus plecostomus panamensis which is recognized as Hypostomus panamensis.

• H. annectens (Regan 1904)
• H. aspidolepis (Günther 1867)
• H. fugleri (Ovchynnyk 1971)
• H. holostictus Regan 1913
• H.. maracaiboensis Schultz 1944
• H. panamensis (Eigenmann 1922)
• H. wilsoni Eigenmann, 1918

The H. annectens group can be diagnosed by a lateral process on the first infrapharyngobranchial, the presence of an invagination on the fifth ceratobranchial located on the posterior part of the bone between the mesial flap and the main body of the ceratobranchial, and a ligament connecting the opercle and angulo-articular (interoperculo-mandibular ligament; for discussion of the ligament see Armbruster, 1998a).  All of these characteristics are found sporadically (but rarely) throughout Loricariidae, but preliminary evidence (Armbruster, 1997) suggests that they are synapomorphic for the group.  The branchial characters are best developed in adults, and juvenile H. panamensis usually lack the process on the infrapharyngobranchial.

Largest specimen examined male, 298.5 mm SL (holotype of H. maracaiboensis, USNM 121012).  Similar in appearance to Hypostomus but with up to eight (usually one to three) hypertrophied, evertible odontodes on cheek in adults (see below).  Hypertrophied odontodes generally consisting of one to three (usually one) very-elongate, stout odontodes and four to five slender, slightly-elongated odontodes in largest adults (see above).  Some medium-sized specimens (ca. 200 mm SL) with cheek odontodes only moderately elongate (usually only one to three).  Cheek odontodes of juveniles slightly longer than in comparatively-sized Hypostomus.  Hypertrophied cheek odontodes hooked anteriorly.

Color pattern typically dark brown with small to large spots located on head, fins, and abdomen; spots becoming larger posteriorly to almost form thick stripes on caudal peduncle in some individuals.  Spots largest in H. aspidolepis and H. panamensis, medium-sized in H. annectens, H. fugleri, H. holostictus, and H. wilsoni, and smallest in H. maracaiboensis; spots in H. maracaiboensis becoming smaller with increasing body size.  All fins with spots; spots darker on membranes and fin spines than on fin rays; spots smaller on caudal fin; spots fading to brown wash distally on fins of large specimens; spots on pectoral-and pelvic-fin spines darker dorsally than ventrally.  Abdomen slightly lighter than sides.  Odontodes, particularly hypertrophied ones, white at base, gold to orange at tip.

Caudal peduncle robust, oval (almost circular) in cross-section, flattened below.  Body deep and robust (more-so in H. maracaiboensis than in other species); head greatly arched, arch continuing to dorsal fin; body sometimes with a hump between the head and dorsal fin.  Body concave dorsally from dorsal fin origin to caudal fin, narrowest just posterior to adipose-fin membrane.  Supraoccipital slightly raised, forming rounded ridge which proceeds beyond posterior tip of supraoccipital to dorsal-fin origin; supraoccipital ridge posterior to supraoccipital flanked by keels of dorsal plates.  Pterotic-supracleithrum with rounded ridge proceeding directly backwards from posterodorsal corner of orbit.  Rounded ridge present between eye and nare.

Iris with well-developed dorsal flap making eye appear bilobed; eye moderate in size, located laterally.  Maxillary barbel fairly long, flattened, almost reaching opercular opening in some specimens.  Lower lip papillose; papillae large anteriorly, becoming smaller posteriorly.  Small buccal papilla present.

Length and height of dorsal fin varies intragenerically and ontogenetically; juveniles tend to have long dorsal fins that reach the adipose fin spine.  Depressed pectoral-fin spine reaching to last ray of pelvic fin or slightly beyond.  Nuptial males with hypertrophied, anteriorly hooked odontodes on dorsal margin of distal pectoral fin spines.  Pelvic-fin spine reaching beyond last anal-fin ray.  Pectoral fin insertion on about same plane as pelvic fin insertion.  First pterygiophore of anal fin exposed ventrally, supporting odontodes (appears as plate-like structure anterior to first, unbranched anal-fin ray).  Adipose-fin membrane typically separated by 1-2 plates from anterior-most, dorsal caudal procurrent spine.  Dorsal-fin spinelet and dorsal-, pectoral-, and pelvic-fin spines well-developed, stout.  Caudal fin forked, lower lobe longer than upper.  Dorsal fin II 7; pectoral fin I 6; pelvic fin I 5; anal fin I 4; caudal fin I 14 I.

Abdomen and lower surface of head almost completely covered with small plates in adults; platelets present between pelvic fin and lower lateral row of plates in adults.  Lateral plates moderately-keeled; keels becoming weaker posteriorly.  Pterotic-supracleithrum proceeded at level of lateral line by single, medium- to large-sized plate.  Body with four rows of lateral plates from row just posterior to head to insertion of pelvic fin and five rows of plates from insertion of pelvic fin to end of caudal peduncle.  Base of caudal fin rays covered with single row of elongate, narrow plates; lateral line not continuing onto caudal fin plates.  Lateral line plates 26-28; 2-3 rows of plates between suprapreopercle and exposed opercle (usually three, but plate rows may be fused together); plates between canal plate and exposed opercle * 5; predorsal plates 3 (includes nuchal plate); interdorsal plates 5-7; plates in depressed dorsal fin 12-19; and postanal plates 12-14.  Teeth per dentary 20-38 (avg. = 25, n of dentaries = 28, n of specimens = 15), and teeth per premaxilla 20-34 (avg. = 26, n of premaxillas = 32, n of specimens = 16); teeth bicuspid, mesial cusp larger, obliquely truncate, lateral cusp small and pointed.  Jaw rami meeting at slight oblique angle at symphysis.

The group differs from Pterygoplichthys by having seven (vs. nine or more) dorsal-fin rays.  Differs from all other Hypostominae by having hypertrophied odontodes on cheek which are evertible and usually three rows of plates (occasionally two) between the suprapreopercle and exposed opercle (vs. zero to one, occasionally two).  The only species of Hypostominae with which the H. annectens group may be sympatric are Pterygoplichthys zuliaensis Weber, P. undecimalis (Steindachner), Hypostomus hondae (Regan), Hypostomus spinosissimus (Steindachner), Hypostomus tenuicauda (Steindachner) and Hypostomus villarsi (Lütken; a species probably described from the Lago Maracaibo basin and often mistakenly referred to as H. watwata Hancock; pers. obs.). The H. annectens group further differs from H. hondae by having small, thin teeth vs. large, spoon-shaped teeth and from H. spinosissimus, H. tenuicauda, and H. villarsi by having dark brown base color (vs. white to tan).  In addition, H. spinosissimus has an extremely elongate caudal peduncle in adults that is circular in cross-section (caudal peduncle short and oval in cross-section in the H. annectens group) and has elongated odontodes on the entire body of nuptial males (elongated breeding odontodes are restricted to pectoral fin spines in the H. annectens group). H. tenuicauda and H. villarsi may also have elongated odontodes on the lateral plates of nuptial males but not to the extent of H. spinosissimus (see Armbruster and Page, 1996).

Potentially sympatric Ancistrini include Ancistrus Kner, Chaetostoma Tschudi, Hemiancistrus landoni (Eigenmann), H. hammarlundi Rendahl (probably a synonym of H. landoni), Lasiancistrus. The H. annectens group differs from all but H. landoni by having a fully plated abdomen (vs. completely unplated); from Ancistrus and most Chaetostoma by having a fully plated snout margin (vs. snout naked); from Chaetostoma by having less than 50 teeth (vs. > 50); from H. landoni by having a deeply forked caudal fin with six or more rows of small black spots (vs. emarginate with less then five rows of large black spots), and by usually having one to three (occasionally up to eight) elongated odontodes on the cheek (vs. more than 10); from Lasiancistrus by lacking long, extremely thin, whiskerlike odontodes on cheek and by having 5 rows of plates on caudal peduncle (vs. 3); and from the subgenus Leptoancistrus of Chaetostoma by having anal and adipose fins.

Note: Hypostomus spinosissimus and Hemiancistrus landoni occur in the Gulf of Guayaquil basin outside the known range of the H. annectens group, but further collecting could reveal areas of sympatry.  Juvenile H. landoni are very difficult to separate from H. annectens; however, H. annectens has a much more deeply forked caudal fin (the caudal fin is only slightly emarginate in H. landoni) and there are more columns of spots on the caudal fin of H. annectens (6+ vs. 5 or fewer) and the spots are much smaller.

Based on observations and collection data of specimens, species of the H. annectens group generally prefer sluggish streams, swamps, and lakes (including Lago Maracaibo).  Also reported to be found over rocks in flowing water in Panama and Costa Rica (Hildebrand, 1938; Bussing, 1987; pers. obs.).  The enlarged stomach is used for air breathing; H. panamensis was used in the air-breathing experiments of Gee (1976). H. panamensis greater than 50 mm SL tend to live in deep water during the day, but move into shallower water (< 20 cm) at night in the río Frijoles, Panama (Power, 1984).  Kramer and Bryant (1995) determined that the diet of H. panamensis is 100% detritus (plant matter).

Species of the H. annectens group occur west of the Andes in Colombia, Costa Rica, Ecuador, Panama, and the Maracaibo basin of Venezuela (Fig. 4).  Dahl (1962, 1971) reports that H. wilsoni can be found in the río Magdalena basin (lower río Magdalena, río Cauca, and río San Jorge) and the río Sinú, but does not give precise localities and I have only examined ana single very small specimen from the río Magdalena.  The drawing of H. wilsoni provided by Dahl (1971) has the small spots and the deep body more characteristic of H. maracaiboensis and Dahlís identifications should be considered tentative.  Bussing (1987) provides the distribution of H. aspidolepis (referred to as Hypostomus panamensis) in Costa Rica; the H. annectens group ranges into the río Coto and the río Térraba which is further into Central America than any other loricariid (Rineloricaria ranges only into the río Coto and no other loricariids are present in Costa Rica).  Hildebrand (1938) suggests that the H. annectens group ranges throughout Panama but is absent from the río Bayano basin; however, I have examined a collection from the río Bayano (USNM 293619).

Armbruster, J.W. 1997. Phylogenetic relationships of the sucker-mouth armored catfishes (Loricariidae) with particular emphasis on the Ancistrinae, Hypostominae, and Neoplecostominae. Unpubl. Ph.D. dissertation. University of Illinois, Urbana-Champaign. 409 pp.

Armbruster, J.W. 1998a. Phylogenetic relationships of the suckermouth armored catfishes of the Rhinelepis group (Loricariidae: Hypostominae). Copeia 1998:620-636.

Armbruster, J.W. 1998b. Modifications of the digestive tract for holding air in loricariid and scoloplacid catfishes. Copeia 1998:663-675.

Armbruster, J.W. and L.M. Page.  1996.  Redescription of Aphanotorulus (Teleostei: Loricariidae) with description of one new species, A. ammophilus, from the río Orinoco basin.  Copeia 1996:379-389.

Bussing, W.A.  1987.  Peces de las aguas continentales de Costa Rica.  Universidad de Costa Rica, pub.  271 pp.

Dahl, G.  1963.  Parte primera, la ictiofauna del río San Jorge.  In G. Dahl, F. Medem, and A. Ramos Henao, eds., pp. 17-52, "El "Bocachico", contribución al estudio de su biología y de su ambiente".  Departmento Pesca de la Corporacion, Autonoma Regional de los Valles del Magdalena y del Sinú - C. V. M.  144 pp.

Dahl, G.  1971.  Los pesces del norte de Colombia.  Ministerio de Agricultura, Instituto de Desarrollo de los Recursos naturales renovables.  391 pp.

Hildebrand. S.F.  1938.  A new catalogue of the fresh-water fishes of Panama.  Field Mus. Nat. Hist. (zool. ser.), Publ. 425, 22:219?359.

Isbrücker, I.J.H.  1980.  Classification and catalogue of the mailed Loricariidae (Pisces, Siluriformes).  Versl. Techn. Gegevens, Univ. van Amsterdam No. 22, 181 pp.

Kramer, D.L. and M.J. Bryant.  1995.  Intestine length in the fishes of a tropical stream: 2. Relationships to diet - the long and short of a convoluted issue.  Env. Biol. Fish. 42:129-141.

Power, M.E.  1984.  Depth distributions of armored catfish: predator-induced resource avoidance.  Ecology 65:523?528.