Representative examples of Pseudancistrus: A. P. brevispinis NRM 32374, 49.6 mm SL, B. Pseudancistrus sp., AUM 36409, 54.4 mm SL, C. P. nigrescens AUM 35741, 133.8 mm SL, D. P. orinoco AMNH 91023, 62.5 mm SL. Photos by J.W. Armbruster.
Pseudancistrus sidereus, Photo by M.H. Sabaj
The following is an excerpt from Armbruster (2004b)
Pseudancistrus is a medium-sized genus of the Loricariidae and is a member of the tribe Ancistrini of the Hypostominae (Armbruster 2004a). The taxonomic history of Pseudancistrus is quite confused based on the fact that the evertible cheek plates found in all other members of the Ancistrini are lacking in the derived members of Pseudancistrus. Pseudancistrus was alternatively placed in the former Ancistrinae (now the Ancistrini) or a more exclusive Hypostominae (Isbrücker 1980; Fisch-Muller 2003; Schaefer 1986).
Schaefer (1986, 1987) found Pseudancistrus to be a member of the Ancistrinae (now Ancistrini) based on the derived presence of a sickle- or bar-shaped opercle in all species examined of the Ancistrini. Isbrücker et al. (1988) described Lithoxancistrus orinoco as a new genus and species based on the derived presence of large papillae located behind each dentary. Isbrücker et al. (2001) described Guyanancistrus for several species that were formerly placed in Lasiancistrus (Isbrücker 1980; Heitmans et al. 1988). The diagnosis of Guyanancistrus in Isbrücker et al. (2001) is brief, and only states that the species lack the characteristic odontodes of Lasiancistrus (apparently referring to the whiskerlike odontodes of Armbruster 2004a); and no characteristics are given to unite the species of Guyanancistrus. The species of Guyanancistrus further lack other synapomorphies for Lasiancistrus, and are not closely related to Lasiancistrus (Armbruster 2004a). Armbruster (2004a) found that the species of Pseudancistrus, Lithoxancistrus, Guyanancistrus, Hemiancistrus megacephalus, and the species described herein as P. sidereus form a well-diagnosed (decay index = 5), monophyletic clade. Armbruster (2004a) places Lithoxancistrus and Guyanancistrus into the synonymy of Pseudancistrus and transfers Hemiancistrus megacephalus to Pseudancistrus.
Lithoxancistrus Isbrücker, Nijssen, and Cala 1988
Guyanancistrus Isbrücker 2001
DIAGNOSIS AND COMPARISONS
Pseudancistrus is not diagnosed by any unique characteristics. Characteristics considered as synapomorphies for Pseudancistrus from Armbruster (2004a) are: no suture between pterotic-supracleithrum and hyomandibula (34-0, reversal), no contact of the hyomandibula with the prootic (35-1), straight, spoon-shaped anterior process of metapterygoid (58-1), nasal bone not much wider than laterosensory canal running through it (105-0), sphenotic not contacting posteriormost infraorbital externally (117-1), and a short ventral ridge on the pelvic basipterygium (172-1, lost in some species).
Pseudancistrus can be separated from the Corymbophanini and the Hypostomini by having hypertrophied odontodes on the cheek; from most of the Rhinelepini by having an adipose fin and a dorsal flap of the iris and from Pogonopoma wertheimeri by having few or no plates on the abdomen (vs. abdomen fully plated); and from the Pterygoplichthini by lacking an enlarged, respiratory stomach and by lacking or nearly lacking plates on the abdomen (vs. abdomen fully plated in adults), and from Pterygoplichthys by having seven dorsal-fin rays (vs. nine or more).
Within the Ancistrini, Pseudacanthicus can be separated from Ancistrus, Dekeyseria, Exastilithoxus, Hopliancistrus, Lasiancistrus, most Lithoxus, Neblinichthys, and Pseudolithoxus by having 4-5 plate rows on the caudal peduncle (vs. 3); from most Baryancistrus, Spectracanthicus, and Parancistrus by not having a membranous connection of the posterior end of the dorsal fin with the adipose fin; from some Hemiancistrus, Hypancistrus, Panaque, and Peckoltia by having 10+ odontodes on the opercle (vs. usually 0, but up to 10, odontodes); from Acanthicus, Leporacanthicus, Megalancistrus, and Pseudacanthicus by lacking hypertrophied keel odontodes on the lateral plates; from Ancistrus and Chaetostoma by having plates on the edge of the snout; and from Chaetostoma, Cordylancistrus, Dolichancistrus, and Leptoancistrus by having the spinelet and the nuchal plate of the dorsal fin supporting odontodes (vs. skin covering the spinelet and nuchal plate in all but adult male Dolichancistrus).
Member of subfamily Hypostominae, tribe Ancistrini as diagnosed by Armbruster (2004a). Small to large loricariids. Ventral surface from anus to head largely naked in adults. Lateral plates unkeeled except ventral plate bent to form keel-like ridge on caudal peduncle, inframedian plate row bent from pectoral-spine insertion to above pelvic fin forming ridge, and dorsal plate row bent, forming ridge from insertion of dorsal-fin spine to posterior end of adipose-fin spine (ridges on either side converging at posterior end of adipose-fin spine). Cheek plates with numerous hypertrophied odontodes, longest odontode reaching almost to posterior edge of cleithral process; cheek odontodes and supporting plates evertible at an angle greater than 75¡ from head primitively although advanced species may not have evertible cheek plates, 15-60 evertible cheek odontodes. Frontal, infraorbitals, nasal, opercle, preopercle (in some species), pterotic-supracleithrum, and suprapreopercle supporting odontodes.
Caudal fin emarginate to forked, lower lobe longer than upper. Lower surface flat. Head moderate in length with horizontal distance between anterior of eye and tip of snout long. Head dorsoventrally flattened. Body depth increasing slowly, in broad arc from tip of snout to insertion of dorsal fin. Body depth decreases very little to dorsal procurrent caudal-fin spines; body depth increases slightly from posterior adipose-fin insertion to insertion of upper caudal-fin spine. Dorsal surface of head between eyes moderately concave. Supraoccipital crest not raised, posterior edge of supraoccipital rounded. Eye large (Table 1) with well-developed dorsal flap of iris. Gill opening restricted.
Dorsal-fin spine short (table 1); dorsal fin reaching posterior edge of preadipose plate when depressed in all species except Pseudancistrus sidereus where the dorsal fin does not reach preadipose plate. Depressed pectoral-fin spine reaching beyond base of pelvic-fin rays; depressed pelvic-fin spine typically reaching anterior insertion of anal fin (sometimes slightly beyond). Dorsal fin II7, caudal fin I14I, anal fin I4-5, pectoral fin I6, pelvic fin I5.
Lips papillose, forming oval disk about as wide as head. Maxillary barbel short, thin, and pointed. Buccal papilla short, narrow. Teeth long, thin with pointed cusps, lateral cusp about half length of medial cusp, 45-89 dentary teeth, 38-94 premaxillary teeth.
Color: Generally dark gray, lighter on abdomen. Some species with light spots or blotches on the sides. Some species with the body mottled gray or brown. Fins generally colored as sides, but some species with bands in the caudal fin, or with orange to red edging on the dorsal and/or caudal fins.
Sexual Dimorphism: Most species with hypertrophied odontodes along the snout in both males and females, but males generally with longer snout odontodes. Pseudancistrus sidereus may have hypertrophied odontodes on the lateral plates (see description below). Some specimens with hypertrophied odontodes on tip of pectoral spine, but it is unknown if these are dimorphic.
Pseudancistrus barbatus head showing hypertrophied odontodes along snout. Photo by M.H. Sabaj
Found in swift flow among gravel, cobble, and
Found around the
Guyana Shield in the Guyanas, Venezuela, and Brazil. Also found in northeastern
Brazil in the Rio Jaguaribe and Rio Grande do Norte.
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