Hemiancistrus guahiborum , a new suckermouth armored catfish from Southern Venezuela ( Siluriformes : Loricariidae )

Hemiancistrus guahiborum, new species, is described from the Orinoco River drainage of Venezuela. Hemiancistrus guahiborum can be separated from all other Hemiancistrus and all Peckoltia except P. braueri and P. cavatica by having an orange edge to the dorsal and caudal fins. Hemiancistrus guahiborum can be separated from Peckoltia cavatica and P. braueri by having the dorsal fin with separated light spots or uniformly colored (vs. with dark spots forming bands) and the sides either solidly colored or with tan blotches (vs. with dark dorsal saddles).


Introduction
Loricariidae is the largest family of catfishes, and its largest subfamily is the Hypostominae.Four of the tribes of the Hypostominae (Corymbophanini, Hypostomini, Pterygoplichthini, and Rhinelepini) account for just six of the 30 currently recognized genera of the subfamily, with the Ancistrini making up the 24 remaining genera (Armbruster, 2004).Most of the genera of the Ancistrini are well diagnosed, with the prominent exceptions of Hemiancistrus and Peckoltia, which are polyphyletic and without distinct diagnoses (Armbruster, 2004).This is especially problematic because many of the undescribed species of hypostomines that were discovered recently have been assigned to either Hemiancistrus or Peckoltia because they lack the derived characteristics of other ancistrin genera (see Cardoso & Lucinda, 2003;Armbruster, 2003;Armbruster & Werneke, 2005).In general, the one character that could potentially separate Hemiancistrus and Peckoltia is that Hemiancistrus typically has spots and Peckoltia typically does not, but this is hardly an adequate diagnosis.There are notable exceptions in the current taxonomy, and more work needs to be done to separate the two genera.
The western side of the Guyana Shield in Venezuela has been the subject of several major collecting expeditions in the past 20 years, and these trips have revealed a bounty of undescribed species of the Loricariidae.One such species is described herein as Hemiancistrus guahiborum (Fig. 1), which is known from several hundred specimens taken from tributaries of the upper and middle Orinoco River.Armbruster (2004) examined the osteology of H. guahiborum (identified therein as Hemiancistus sp.) and found that it formed a basal polytomy with H. micromattos (labeled as Peckoltia oligospila), P. sabaji (labeled as Peckoltia sp.big spot) and a clade consisting of all other species of Peckoltia, Acanthicus, Hypancistrus, Leporacanthicus, Megalancistrus, Panaque, Pseudacanthicus, and Spectracanthicus.

Material and Methods
Counts and measurements follow Armbruster (2003).Specimens were cleared and stained for examination of bone and cartilage following the methods of Taylor &Van Dyke (1985).Names of plate rows follow Schaefer (1997) (1985).
Comparative specimens examined are listed in Armbruster (2003Armbruster ( , 2004) ) and Armbruster & Werneke (2005).When present in materials examined first number in parentheses represents the number of specimens measured followed by the range of standard lengths of the specimens.Specimens were sampled broadly within the type series and the non-types, but given the large number of specimens available, not all specimens were measured or examined for meristics.Measured specimens have numbered points inserted into their gill openings.
The type locality was restricted to the río Ventuari because of the many specimens available from this region and to avoid any future problems from researchers that might want to split the species.Gut contents were examined by dissecting the viscera from the peritoneal cavity of one individual from each of three lots.The viscera were removed as a unit by cutting the esophagus immediately posterior to the ventral processes of the complex centrum, and the posterior intestinal tract immediately anterior to anus.Anterior 100 mm of gut was dissected to expose gut contents.

Hemiancistrus guahiborum, new species
Figs.   Description.Member of Hypostominae, Ancistrini as diagnosed by Armbruster (2004).Morphometrics in Table 1.Medium-sized loricariids, largest specimen 125.5 mm SL.Body stout.Head sloped at 45° angle to point above anterior portion of eye.Nape ascending slightly to insertion of dorsal fin.Dorsal slope decreasing to insertion of dorsal procurrent caudal rays then ascending to caudal fin.Body depth greatest below anterior insertion of dorsal fin.Ventral profile flat to caudal fin.Caudal peduncle triangular in cross section with dorsal surface slightly rounded.Body widest at insertion of pectoral fins, narrowest at insertion of caudal fin.Snout rounded.
Lips covered with short, wide papillae.Lower lip wide, upper lip narrow.Maxillary barbel only barbel present, reaching one third of distance to gill opening.Iris with small dorsal flap.
Dorsal fin II,7; dorsal-fin spinelet V-shaped, dorsal-fin locking mechanism present, dorsal fin free from adipose fin, distal margin of dorsal fin reaching insertion of adipose spine when adpressed.Adipose fin with single preadipose plate and moderately long spine.Caudal fin i,14,i; caudal fin forked, lower lobe longer than upper, dorsal and ventral procurrent caudal rays four to five (mode four).Pectoral fin I,6; pectoral-fin spine reaching beyond insertion of pelvic-fin spine when adpressed ventral to pelvic fin.Pelvic fin I,5; adpressed pelvic-fin spine extending beyond base of anal fin.Anal fin I,4; anal-fin spine slightly shorter than first ray.
Color in Life.Base color of head and body mottled gray and tan, with dermal plates outlined with dark gray.Pattern irregular and varies among individuals, but between and behind eyes tan spots are smaller and rounded.Behind dorsal fin, upper half of flank gray with irregular tan blotches, lower half of flank mostly tan.Lips tan.Eye light reddish-brown.Dorsal fin with smoky charcoal membranes, spine gray on anterior margin but tan laterally, not spotted; rays with series of gray and tan blotches, more or less aligned to form alternating rows with three or four gray blotches of each contrasting color; fin edged with very thin margin of brick red or orange, wider on first three or four rays.Adipose fin tan with distal gray edge.Caudal-fin rays dark gray, membranes in between transparent, basal plate on base of fin gray; distal margin edged with orange, widest on upper rays.Pectoral fin spine gray, rays tan, sometimes spotted.Pelvic-fin spine and rays tan on distal two thirds of fin, dark gray on distal third.Abdomen tan to cream.

Color in alcohol.
Base color brown or gray (Figs.1-2).Small faint light gray-tan spots on head, becoming larger and more irregularly shaped on body.Sizes of spots vary between individuals and absent in some specimens.Dorsal-fin spine lacking spots.Dorsal-fin rays and membranes typically with spots, spots on dorsal-fin membranes difficult to discern in some specimens.Adipose-fin spine with only one or two spots if present, membrane dusky.Caudal fin dusky, occasionally with lighter narrow bands in some specimens.Pec-

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toral and pelvic fins sometimes with spots dorsally, rays and membranes lacking spots dusky.Anal fin dusky near insertion, fading distally.Lips, barbels, and throat tan.Small embedded plates below pectoral girdle gold.Venter behind pectoral girdle to anus translucent white, internal musculature and organs visible through skin.Venter behind anus tan with scattered melanophores.
Etymology.Named for the Guahibo, a tribe of people inhabiting parts of southern Venezuela and western Colombia for the help some members of the tribe provided in collecting specimens in the upper río Ventuari.
Gut Morphology and Ecology.Gastrointestinal tract brown with yellow fat deposits loosely attached to intestinal wall with viscera packed tightly into peritoneal cavity.Esophagus turns 90° to right upon entering the peritoneal cavity, extends short distance (~10 mm in specimens examined), then turns 90° to posterior before transitioning into stomach.Stomach extends straight to posterior for two thirds of total stomach length then turns 180° to right for final one third.Length of stomach 15 mm.Volume of stomach highly variable.From stomach, intestines turn 90° to left, crossing dorsally over esophagus, then turn 90° to posterior, continuing towards anus.Proximal and distal portions of intestine spiral clockwise in parallel, with coils accruing ventral to stomach.Total length of intestines plus stomach ranged from 15-18 times SL.External diameter of intestines ranged from 1.0-1.5 mm.Hemiancistrus guahiborum were most frequently encountered in cracks and interstitial spaces of granitic and lateritic rocks in flow.Gut contents of all individuals consisted largely of small grained (<0.001mm diameter) mineral matrix.Identifiable organic material embedded in the gut matrix of three individuals surveyed was limited to midge larvae (Chironomidae, n=3), a fly pupa (Diptera, n=1), an unidentified insect exoskeleton (n=1), and a shed tooth (n=1).

Discussion
Hemiancistrus guahiborum is one of the most common ancistrins in the upper Orinoco River basin.It is found in both granitic and lateritic rocky habitats with flow, where it was caught in abundance.Hemiancistrus guahiborum feeds by scraping periphyton and ingesting both the sediment matrix deposited from the water column, and attached algae and benthic macroinvertebrates.Other loricariids commonly collected with H. guahiborum were Hypostomus squalinus, Hemiancistrus subviridis, Peckoltia sabaji, and P. aff vittata.Although the range of H. guahiborum encompasses a region where loricariids are intensively harvested for the ornamental fish trade and it is one of the most abundant loricariids in the area, it is not commonly exported.Despite its often quite at-tractive appearance when alive, it is typically passed over by fishermen seeking the more strikingly colored species with which it is sympatric.
. The following are abbreviations used in the text: D = distance, Dia = diameter, , dr = drainage, L = length, W = width, SL = standard length.Museum acronyms follow Leviton et al.