Hypostomus, LACEPEDE, 1803

Armbruster, Jonathan W., 2004, Phylogenetic relationships of the suckermouth armoured catfishes (Loricariidae) with emphasis on the Hypostominae and the Ancistrinae, Zoological Journal of the Linnean Society 141 (1), pp. 1-80 : 60-61

GENUS HYPOSTOMUS LACÉPÈDE, 1803 ( FIGS 39 , 40 )

Type species: Acipenser plecostomus Linnaeus, 1758

Synonyms:

Aphanotorulus Isbrücker & Nijssen, 1982 Cheiridodus Eigenmann, 1922

Cochliodon Heckel, 1854

Isorineloricaria Isbrücker, 1980

Plecostomus Gronovius, 1754

Squaliforma Isbrücker & Michels, 2001

Watawata Isbrücker & Michels, 2001

Includes:

See Appendix 4.

Diagnosis: Hypostomus is not diagnosed by any unique characteristics. Characteristics considered synapomorphic for Hypostomus are: a hatchet-shaped opercle (78: 1; Fig. 19B ), the anterior process of the pterotic-supracleithrum passing halfway through the orbit (112: 1), and a pointed cleithral process (156: 1). In addition, in several trees, the bulk of Hypostomus [except H. commersoni Valenciennes and H. boulengeri (Eigenmann and Kennedy) ] are supported by a pointed transverse process of the Weberian apparatus that is fused to the pterotic-supracleithrum (132: 1, 133: 1; Fig. 25B ).

Description: Small to large loricariids that defy a unifying description. Colour pattern varies from having a white ground colour and black spots, to brown and spotted, to black with red, gold, or white spots. Abdomen also varies in colour from white to black and may be spotted or not. Abdomen ranges from naked to completely plated (usually with plates). Caudal fin forked with the lower lobe longer than upper. Two or three predorsal plates. Five rows of plates on caudal peduncle (except H. dlouhyi Weber which has three). Body typically stout, but H. emarginatus group, H. cordovae (Günther) , H. spiniger (Hensel) , and H. spinosissimus with elongated bodies. Lateral plates keeled or not. Cheek plates evertible to c. 30∞.

Comparisons: Hypostomus is most similar to the Hemiancistrus annectens group. Externally, it is very difficult to separate from the H. annectens group, differing mainly in the lack of highly evertible cheek plates with hypertrophied odontodes in adults (cheek odontodes are present in H. spinosissimus , but they are present only in nuptial males, are not highly evertible, and are accompanied by a lengthening of nearly all of the odontodes on the body) and by usually having only one (occasionally two) row of plates between the suprapreopercle and the exposed opercle (vs. three, occasionally two). The only species of Hypostomus sympatric or potentially sympatric with the H. annectens group are members of the H. cochliodon group which have wide, spoon-shaped teeth (vs. viliform teeth) and H. spinosissimus , H. tenuicauda and H. villarsi which have a white or tan ground colour (vs. dark brown) and are elongate (vs. short); thus, most Hypostomus can be distinguished from the H. annectens group by having a distribution east of the Andes (vs. west).

Hypostomus can be distinguished from most Pterygoplichthys by the same characters as for the H. annectens group with the addition of having only seven (vs. 9–14) dorsal-fin rays; most species from all Pogonopoma and Rhinelepis by having a single, medium-sized plate posterior to the pterotic-supracleithrum (vs. many small plates); from Pseudorinelepis and Rhinelepis by usually having an adipose fin (adipose fin is also missing in H. levis of the H. cochliodon group); from all the Rhinelepini by generally having one unbranched and four branched anal-fin rays (vs. one unbranched and five branched rays) and a dorsal flap of the iris making the eye appear bilobed (vs. iris round, without flap); and from most of the Ancistrini by a lack of highly evertible cheek plates with hypertrophied odontodes ( Spectracanthicus lacks evertible cheek plates with hypertrophied odontodes and can be distinguished by having the dorsal-fin membrane attached to the preadipose plate; some Pseudancistrus lack evertible cheek plates and can be distinguished by a combination of the presence of hypertrophied odontodes along the snout and on the cheek and no plates on the abdomen).

Sexual dimorphism: Most males develop hypertrophied odontodes on the leading edge of the pectoral-fin spine and the distal tip of the spine may become swollen. Additionally, in members of the H. emarginatus clade, males develop hypertrophied odontodes on the body during the breeding season ( Armbruster & Page, 1996); these odontodes are normally best developed on the posterolateral plates, the caudal-fin spines, and the adipose-fin spine. In addition, H. spinosissimus develops hypertrophied odontodes over the entire lateral and dorsal surfaces of the body including the cheeks ( Armbruster & Page, 1996). Nuptial males of some species of the H. cochliodon group develop wider, more widely spaced odontodes on the lateral plates (the odontodes are not longer in nuptial males).

Ecology: Hypostomus are essentially ubiquitous across their range. Most species are lowland, sluggish stream- and lake-dwellers usually found associated with submerged wood; however, many species may be found among rocks in piedmont to mountain streams with moderate to swift flow. Hypostomus may be found above substrates ranging from mud and detritus, to gravel and cobbles and boulders, to sand. Many spawn in hollows dug into mud banks or within hollow logs ( Burgess, 1989).

Range: Throughout most of the range of loricariids except for drainages west of the Río Atrato.

Figures

Figure 19. Opercle, right side, mesial view. A, Hemiancistrus maracaiboensis, EBRG 2855. B, Hypostomus taphorni (Lilyestrom), ANSP 16195. C, Peckoltia sp., FMNH 70863. D, Ancistrus pirareta Müller, UMMZ 206085. Scale bars = 1 mm.

Figure 25. Weberian apparatus, ventral view. A, Acanthicus hystrix Spix and Agassiz, INHS 36803. B, Hypostomus micromaculatus Boeseman, ANSP 160774. C, Pseudacanthicus leopardus, FMNH 95554. D, Hemiancistrus maracaiboensis, EBRG 2855. Scale bars = 5 mm. In B, the transverse processes of the Weberian complex centrum (TPWA) appear to fuse into the pterotic-supracleithrum (PT) as is shown for the left (upper) side while the right (lower) side shows the TPWA as it appears after closer scrutiny.

Figure 39. Examples of the Hypostomini. A, Hypostomus ammophilus (holotype), INHS 32035, 86.0 mm SL. B, Hypostomus cochliodon, UMMZ 206338, 139.8 mm SL. Photographs by K. S. Cummings.

Figure 40. Examples of the Hypostomini. A, Hypostomus emarginatus 2, INHS 29085; 196.4 mm SL. B, Hypostomus plecostomus (type species of genus), ZMA 105.306, 111.2 mm SL. Photographs by K. S. Cummings.