Pseudancistrus sidereus Armbruster, 2004, new species
Creators: name: Jonathan W. Armbruster
Publisher: name: Zenodo
Year: 2004
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Siluriformes
Loricariidae
Pseudancistrus
Pseudancistrus sidereus

description: Pseudancistrus sidereus new species
Fig. 3
Holotype: VENEZUELA, Amazonas, Ro Orinoco dr.: MCNG 26125, 175.6, Río Siapa from 10 to 15 km downstream, Río Casiquiare - Río Negro dr., 01.50000°, -065.71667°, ABD and F. Morillo, 20 April 1991.
Paratypes. VENEZUELA, Amazonas, Río Orinoco dr.: MCNG 48261, 1, 1CS, 149.8, AUM 37562, 1, 148.7, same data as holotype. FMNH 105294, 4, 149.5-176.7, Río Orinoco ca. 5 h above Atabapo by falca; at rocks and beach, B. Chernoff, A. and D. Machado, and J. Wheeler, 23 January 1991.
Diagnosis: Pseudancistrus sidereus is diagnosed by a unique modification of the ventral plates on the caudal peduncle. In loricariids, the plates of the ventral row on the caudal peduncle are typically bent at an approximately 90° angle to follow the contour of the body. The bend is often the site of a slight keel formed from one or more rows of slightly longer odontodes. In P. sidereus, the keel is accentuated by having the dorsal laminae of the plates strongly concave. Although some loricariids may have the dorsal laminae slightly concave, it is much more pronounced in P. sidereus.
Pseudancistrus sidereus can be separated from all other species of the Ancistrini by the presence of the keel mentioned above and by the presence of a single large white to yellow spot located at the center of the posterior lateral plates. The only species with a similar coloration are some Hypancistrus and some Panaque, both of which have far fewer than 25 teeth per jaw ramus (vs. much more than 25 teeth), some other species of Pseudancistrus which have hypertrophied odontodes along the snout in males and females (vs. no hypertrophied snout odontodes), and have the dorsal fin reaching at least the preadipose plate when depressed (vs. about two plates anterior to preadipose plate); and some Hemiancistrus and Peckoltia which generally have the spots much more diffuse (vs. borders of spots distinct) and have the dorsal fin reaching at least the preadipose plate when depressed (vs. about two plates anterior to preadipose plate).
Description. Fairly large loricariids, largest specimen 176.7 mm SL. Body elongate, fairly narrow, and dorsoventrally flattened. Head and anterior part of trunk gently sloped from snout tip to dorsal-fin origin, dorsal profile of body straight to adipose fin with slight decrease in depth, dorsal profile of caudal peduncle very concave, shallowest at posterior insertion of adipose fin. Ventral surface flat.
Head contours smooth. Slight, rounded ridge from anterolateral corner of nares, above orbit to posterior edge of pterotic-supracleithrum, dorsal margin of orbit higher than mesial portion of head. Mesethmoid slightly higher than lateral surface of head forming rounded ridge on snout, continued posterior to mesethmoid and terminating at level of posterior margin of orbits. Supraoccipital with slight posterior point medially. Following head bones supporting odontodes: frontal, infraorbitals, opercle, nasal, pterotic-supracleithrum, sphenotic, supraoccipital, and suprapreopercle.
Lips wide, fairly thin. Upper lip with wide, thin papillae. Lower lip with small papillae anteriorly, a band of larger papillae, and then smaller papillae posteriorly, papillae fading towards posterior edge. Maxillary barbel only barbel present, not reaching base of evertible cheek plates. Mouth with small, narrow buccal papilla. Iris with small dorsal flap, not reaching ventral to center of pupil.
25 plates in median series. Ventral plates forming a right angle on caudal peduncle with dorsal margin of plates concave forming a strong keel along lower portion of caudal peduncle. Dorsal plate series bent between dorsal and adipose fins to form slight ridge, ridges on two sides converging just posterior to insertion of adipose-fin spine. Inframedian plate series bent in middle from cleithrum to insertion of pelvic-fin forming slight keel. Abdomen naked except for some small, embedded plates laterally between pectoral and pelvic fins. Five rows of plates on caudal peduncle.
18-39 (average = 28, N=7) evertible cheek odontodes. Evertible cheek odontodes fairly short, longest reaches posterodorsal corner of opercular opening. Evertible cheek odontodes supported by plates than can be everted up to approximately 90° from the head. Hypertrophied cheek odontodes relatively weak. Single adult male with modestly hypertrophied odontodes on tip of pectoral-fin spine, females with odontodes on tip of pectoralfin spine slightly longer than those at base (Fig. 3).
All fin spines and rays supporting odontodes. Dorsal fin II7; dorsal-fin spinelet V- shaped, dorsal-fin lock functional; dorsal-fin spine elongated relative to other fin rays in some specimens making edge of fin emarginate; dorsal fin not reaching adipose fin when adpressed. Adipose fin with single median preadipose plate and fairly long curved spine. Caudal fin I14I; caudal fin forked, lower lobe longer than upper; usually six dorsal and five ventral procurrent caudal-fin spines. Pectoral fin I6; pectoral-fin spine reaching posterior insertion of pelvic fin to slightly beyond base of pelvic fin when adpressed ventral to pelvic fin. Pelvic fin I5; pelvic-fin spine reaching end of base of anal fin when adpressed. Anal fin I4; unbranched anal-fin spine ray two thirds the length of the first branched ray. First anal-fin pterygiophore not exposed to form a platelike structure.
Teeth very long and bicuspid with a longer, median lobe. 73-85 dentary teeth (median = 77, N=7). 78-93 premaxillary teeth (median = 84, N=7). Jaws very wide, dentaries forming a very oblique angle, premaxillaries forming a gentle arc.
Color. Ground color dark brown dorsally and laterally, fading to tan on ventral half of inframedian plate series, tan ventrally. Head with small white spots (possibly yellow in life), spots getting larger posteriorly. Usually 2-3 spots per plate anteriorly and one posteriorly. Ventral spots lengthening dorsoventrally on inframedian and ventral plates series until fading into ventral coloration. Ventral surface of upper lip brown. Dorsal-fin membranes hyaline or with slight spotting; dorsal-fin spine and rays with oval spots. Adipose fin with weak spots or mottled. Caudal fin distinctly lighter ventrally; spots on ventral lobe fairly large and round and spots on dorsal lobe smaller and oval. Leading edge of pectoralfin spine light; pectoral-fin spine with or without spots; small round spots centered on pectoral-fin rays; color slightly fading posteriorly on pectoral fin. Pelvic fin with larger spots fading distally, spots on both rays and membrane. Anal fin tan or mottled.
Sexual dimorphism. One potentially nuptial male examined with hypertrophied odontodes on the sides similar to Peckoltia and Panaque (Panaqolus), but shorter and sharper. Hypertrophied odontodes on pectoral-fin spine larger in the potentially nuptial male.
Range: Known from the Río Casiquiare drainage and the upper Río Orinoco drainage of Amazonas, Venezuela (Fig. 4).
Etymology: From the Latin sidereus for starry. Named because the dark background makes the white to gold spots look like stars.
Discussion
Even with the phylogeny of Armbruster (2004), it is difficult to assign basal members of the Ancistrini to genus. Many of the basal groups are without strong synapomorphies supporting the genera; however, Pseudancistrus is strongly supported by several characteristics. Although none of these characteristics are unique to Pseudancistrus, the genus is very well supported in the phylogenetic analysis with a decay value of five (Armbruster 2004).
The previous use of the lack of evertibility of cheek plates as a diagnostic characteristic in Pseudancistrus is weak. Some advanced species such as P. nigrescens appear to have little ability to evert the cheek plates while some specimens of P. barbatus appear to be able to evert the plates almost to the same degree as most other members of the Ancistrini (pers. obs.). All species of Pseudancistrus retain the modified opercle of the Ancistrini that is used as an aid to evert the cheek plates in most of the Ancistrini, and all retain hypertrophied odontodes on the cheek.
Guyanancistrus is not likely to be a monophyletic entity. Although only Pseudancistrus brevispinis has been examined osteologically, the species attributed to Guyanancistrus vary from P. brevispinis that lacks hypertrophied odontodes along the snout and that has fully evertible cheek plates to P. niger that develops at least small hypertrophied odontodes on the snout and that has the cheek plates very weakly evertible. No characteristics were given to diagnose the genus or separate it from any genus other than Lasiancistrus in the original description (Isbrücker et al. 2001). Lasiancistrus is a very well diagnosed genus that is not particularly closely related to Pseudancistrus (Armbruster 2004). Lasiancistrus is readily identifiable from Pseudancistrus by having whiskerlike odontodes among the hypertrophied cheek odontodes and three rows of plates on the caudal peduncle (vs. 4-5 in Pseudancistrus; Armbruster 2004).
Hemiancistrus megacephalus was transferred to Pseudancistrus by Armbruster (2004). The genus Hemiancistrus is a mix of unrelated forms, and it remains one of the largest taxonomic problems in the Ancistrini (Armbruster 2004). The type species of Hemiancistrus is H. medians, and it differs from P. megacephalus mainly in color (it is almost the inverse of the color of P. megacephalus) and by slight differences in jaw morphology. I have not examined a skeleton of H. medians, but it may also be related to Pseudancistrus because it is so similar to P. megacephalus. Because Hemiancistrus is so confused taxonomically, decisions on where H. medians fits, and any final decision on the fate of Hemiancistrus await skeletal examination of H. medians.
The type of Pseudancistrus coquenani has the enlarged papilla behind the dentary teeth that was used to diagnose Lithoxancistrus orinoco (Isbrücker et al. 1988). It is likely that P. orinoco and P. guentheri are sisters based on this characteristic. Several other loricariids have a sister group relationship between species in the upper Río Orinoco and the upper Río Caroni including the two described species of Neblinichthys and the two known species (one is undescribed) of Exastilithoxus (Provenzano et al. 1995; pers. obs.). Although this range is currently disjunct, further collecting in the rivers between the upper Río Orinoco and the upper Río Caura may yield specimens similar to P. orinoco and P. coquenani.
Isbrücker (2001) placed Pseudancistrus genisetiger and P. papariae in Lithoxancistrus without comment. These two species lack the dentary papillae used by Isbrücker et al. (1988) to diagnose Lithoxancistrus and appear to be advanced members of Pseudancistrus as the cheek plates are only weakly evertible.
Isbrücker et al. (2001) place Hypostomus guacharote Valenciennes 1840 and Chaetostomus trinitatis Günther 1864 into Guyanancistrus. The type of H. guacharote (MNHN A-9567) is clearly a Lasiancistrus (pers. obs.) as it has the whiskerlike odontodes on the cheek (Armbruster 2004). The type locality for L. guacharote, new combination, is Puerto Rico; however, this species shares characteristics with specimens of Lasiancistrus from the Lago Maracaibo basin of Venezuela (pers. obs.). No loricariids are known to naturally occur on Puerto Rico, and the island is located far to the north of the range of the Loricariidae suggesting that the locality is incorrect. Chaetostomus trinitatis was described by Günther (1864) based on specimens reported by Gill (1858) from Trinidad. No type specimens are available for the species, the description of the species is inadequate to place the species within a genus of the Ancistrini, and the only loricariids I have examined from Trinidad are Ancistrus and Hypostomus. In all likelihood, C. trinitatis is a species of Ancistrus, and the species should be referred to as Ancistrus trinitatis new combination.
description: Published as part of Jonathan W. Armbruster, 2004, Pseudancistrus sidereus, a new species from southern Venezuela (Siluriformes: Loricariidae) with a redescription of Pseudancistrus., pp. 1-15 in Zootaxa 628 on pages 8-13