Dolichancistrus Isbrucker 1980
Creators: name: Ballen, Gustavo A.
name: Vari, Richard P.
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Siluriformes
Loricariidae
Dolichancistrus

description: Dolichancistrus Isbrücker, 1980
Dolichancistrus Isbrücker, 1980: 47 [type species: Pseudancistrus pediculatus Eigenmann, 1918; herein subjective synonym of Ancistrus fuesslii Steindachner, 1911. Type by original designation].
Diagnosis. Dolichancistrus is a member of the Chaetostoma group (sensu Armbruster 2004a, 2008) differentiated in that group from Leptoancistrus Meek & Hildebrand by the presence of the adipose and anal fins (vs. the absence of both fins); from Cordylancistrus and Chaetostoma (sensu Armbruster, 2004a) by the presence of pectoral-fin spines in mature males longer than those in adult females and immatures of both sexes (vs. the pectoral spines of equal length in both sexes); and from the species of Chaetostoma except for C. platyrhynchus (Fowler) in having a plated snout (vs. naked). Dolichancistrus differs from Chaetostoma platyrhynchus in having the hyperthrophied cheek odontodes evertible to more than 90º (vs. evertible only to approximately 30-40º) and in bearing hyperthrophied cheek odontodes that are distally recurved (vs. odontodes straight along their entire length). More broadly within the Ancistrini, Dolichancistrus is externally distinguishable from Acanthicus Spix & Agassiz, Leporacanthicus Isbrücker & Nijssen, Megalancistrus Isbrücker and Pseudacanthicus Bleeker in the absence of keeled plates on the lateral surface of the body vs. the presence of keeled plates); from Ancistrus Kner, Dekeyseria Rapp Py-Daniel, Lasiancistrus Regan, Lithoxus Eigenmann, Neblinichthys Ferraris, Isbrücker & Nijssen and Pseudolithoxus Isbrücker & Nijssen in possessing five series of plates on the caudal peduncle (vs. three series of plates on the caudal peduncle); from Baryancistrus Rapp Py-Daniel, Parancistrus Bleeker, and Spectracanthicus Nijssen & Isbrücker by having the dorsal-fin membrane on the posteriormost dorsal-fin ray extending along the dorsal margin of the body for only a short distance (vs. an enlarged portion of the membrane extending from the fin posteriorly to the preadipose plate); from Exastilithoxus Isbrücker & Nijssen by the absence of fimbriae on the margin of the mouth (vs. with lips bearing fimbriae); from Hopliancistrus Isbrücker & Nijssen by having long cheek odontodes that are straight for most of their length and recurve only distally (vs. short cheek odontodes which are strongly recurved from the base to the tip); from Hypancistrus Isbrücker & Nijssen and Micracanthicus Lujan & Armbruster by having the teeth on the dentary and premaxilla of approximately the same length (vs. dentary teeth longer than those on the premaxilla); from Panaque Eigenmann & Eigenmann by the presence of elongate, distally-recurved, and slender-cusped teeth on the jaws (vs. strong, spoon-shaped teeth at least in adults) and premaxillae positioned in an approximately straight line (vs. an angle between the premaxillae about 30°); from Paulasquama Armbruster & Taphorn by having the plates on the snout and the dorsal series of lateral body plates well developed (vs. weakly developed) and in having the pectoral-fin spine always reaching at least to the insertion of the pelvic fin at least in males (vs. never reaching the pelvic insertion); and from Soromonichthys Lujan & Armbruster in bearing plates over all of the snout (vs. snout without plates along on its margins and along the midline). Notwithstanding the uncertainty about the diagnosability of Hemiancistrus, Peckoltia, and Pseudancistrus (Armbruster, 2004b, 2008), Dolichancistrus is separable from those genera as currently recognized in having the medial hyperthrophied cheek odontodes thicker than the outer odontodes (vs. all the odontodes equally thick).
Description. Medium-sized loricariids, with largest examined specimen 153.7 mm SL (a male of Dolichancistrus carnegiei). Head and body strongly depressed and moderately wide. Lateral profile of anterior portion of head gently convex from tip of snout to vertical through posterior nares, then nearly straight to dorsal-fin insertion. Dorsal profile of body straight to very slightly posteroventrally angled from terminus of dorsal-fin base to insertion of dorsal caudal-fin spine. Ventral profile of head and body straight to very slightly convex to insertion of ventral caudal-fin spine.
Supraorbital bony ridge absent, with interorbital area ranging transversely from slightly convex to flat. Ridge of hypertrophied odontodes present in adults in region from anterior portion of orbit to anteroventral portion of nares; degree of development of ridge interspecifically and ontogenetically variable. Medial region from tip of snout to nares with distinct hypertrophied odontodes; odontodes usually more obvious in mature males but variably developed interspecifically. Profile of head smoothly rounded anteriorly in dorsal view other than for odontodes extending in adults along anterior and lateral margins of snout. Hypertrophied odontodes along lateral margin of snout extending posteriorly for variable distances, but never reaching plates immediately anterior to cheek plates.
Cheek with two to ten extremely hypertrophied odontodes supported by skin-covered, bony ossicles (sensu Geerinckx & Adriaens, 2006) plus several shorter albeit lengthened odontodes supported by outer exposed cheek plates. Hypertrophied cheek odontodes distally recurved with largest fully developed odontode extending posterior of base of first or second branched pectoral-fin ray. Cheek plates in two series. Dorsal series with two large plates varying in orientation, shape, and size among species. Ventral series with three or four smaller plates usually either lacking odontodes or with odontodes mostly covered by thick skin. Frontal, infraorbital, nasal, opercle, compound pterotic, sphenotic, and parieto-supraoccipital bones supporting odontodes of various sizes. Opercular odontodes present on exposed portion of opercle, with odontodes along opercular margin frequently larger than those on exposed surface of opercle. Cheek, snout and pectoral-spine odontodes surrounded basally by fleshy collar and most often with small lateral papilla as in Dekeyseria (Sabaj et al., 1999, fig. 4b). Fleshy papillae present when odontodes not fully developed. Odontodes on pectoral spine longer than associated papillae.
All series of lateral plates other than ventral series complete and extending from compound pterotic to posterior limit of caudal peduncle. Body plates without keels, but plates of ventral series with slight flexion midway along their vertical extent forming discrete angle along ventrolateral margin of caudal peduncle. Ventral plate series incomplete anteriorly with first plate located anterior of pelvic-fin insertion. Five series of plates present on caudal peduncle. Abdomen naked. First anal-fin pterygiophore not exposed to form plate-like structure.
Tip of adpressed dorsal fin extending posteriorly to terminate within area short of, to slightly beyond, anterior margin of preadipose plate. Dorsal-fin spine stiff basally, flexible distally and not extending beyond distal margin of fin. Margin of fin ranges from straight to slightly convex. Exposed margin of dorsal-fin spinelet moderately convex and variably covered by skin. Dorsal-fin spine lock functional. Adipose-fin spine of moderate length and bearing odontodes. Distal margin of caudal fin ranging from slightly emarginate to obliquely straight, with form variable both intraspecifically and ontogenetically. Ventral lobe of caudal fin longer than dorsal lobe. Anal-fin base short, usually about one-third length of second unbranched anal-fin ray. Tip of adpressed anal fin extending posteriorly to, or nearly to, vertical through adipose-fin origin. Length of pectoral-fin spine highly variable interspecifically but longer in mature males than mature females of all species. Tip of adpressed pectoral-fin spine falling between mid-length of adpressed pelvic-fin spine and point beyond tip of spine in mature males, and between insertion and tip of pelvic-fin spine in mature females. Pectoral-fin spine in mature males with hypertrophied odontodes extending along distal onefifth to one-fourth of dorsolateral surface. Single series of odontodes present on dorsal surface of pectoral-fin spine in mature specimens regardless of sex or maturity. Distal margin of pectoral fin sigmoid when fully developed in adults, with margin convex medially and gently concave distally. Tip of adpressed pelvic fin reaching posteriorly to beyond anal-fin insertion. Dorsal surface of spine usually lacking odontodes. Form of posterior margin of pelvic fin interspecifically variable. Immature individuals of both sexes with distal fin margin straight whereas larger specimens with distal margin either W-shaped or convex.
Iris operculum present. Short, fleshy flap with round margin present between anterior and posterior nares. Lips wide and fairly thick. Upper lip with multiple series of papillae. Papillae proximate to mouth opening small and rounded and preceded anteriorly first by larger papillae and then by more elongate papillae along lip margin. Lower lip with medium-sized round papillae anteriorly and smaller ones posteriorly but with skin near posterior margin of lip nearly smooth. Lip border crenate. Maxillary barbel short, separate from lower lip distally but variably fused to lip basally in some specimens and extending up to one-half distance to transverse line along posteriormost limit of lower lip. Median buccal papilla present posterior of symphysis of premaxillae in all but one species.
Jaws wide transversely. Dentaries meeting at variably oblique angle ranging from nearly straight line to distinct angle with variation apparently artifact of preservation. Anterior margin of premaxilla forming nearly straight line. Dentary larger than premaxilla. Peduncles of teeth fairly long, narrow and distally recurved. Cusps asymmetrically developed with lateral tooth cusp approximately one-half length of medial cusp. Dentary teeth 30 -100 and premaxillary teeth 20-70; number of teeth on each ramus increasing ontogenetically.
Sexual dimorphism. Mature females have a greatly widened, pad-like genital papilla with some transverse flaps at the papillary opening. The aperture of the genital papilla in mature females is located proximate to, but separate from, the opening of the vent. Mature males have a distinctly-pointed genital papilla with a distal aperture. Mature males also typically demonstrate a greater degree of development of the odontodes along the margin of the snout and medial region of head from the tip of the snout to the nares, and in the area between the orbit and the nares. The pectoral-fin spines and distal odontodes on the spines are proportionally longer in mature males than in mature females. Males of all species achieve greater standard lengths than do conspecific females and also reach maturity at larger overall sizes.
Distribution. Species of Dolichancistrus are known from eastern tributaries of the río Atrato at elevations of 460 to 1380 masl, the río Cubarradó a small coastal drainage south of the Serranía de Baudó on the Pacific Ocean versant, the middle portions of the eastern río Magdalena basin along the Cordillera Oriental between approximately 500 and 2540 masl, western portions of the río Orinoco basin on the slopes and piedmont of the Cordillera Oriental from the Serranía de la Macarena to the río San Antonio in Venezuela at elevations of approximately 500 to 2500 masl and southeastern tributaries of the lago Maracaibo basin in Colombia and Venezuela. Samples with specific locality information indicate that all species are allopatrically distributed. A few samples with inexact locality data that include two species likely represent geographically complex series of specimens (see Remarks for D. carnegiei).
Generic placement of Chaetostomus setosus. Chaetostomus setosus, the first described species eventually assigned to Dolichancistrus, was proposed by Boulenger (1887: 349). This species was shifted to Pseudancistrus Bleeker by Eigenmann and Eigenmann (1890: 435), whereas Regan (1904: 3239) assigned it to the subgenus Pseudancistrus within Ancistrus Kner. Fowler (1942: 132) followed Eigenmann & Eigenmann (1890) in recognizing the species within Pseudancistrus. Isbrücker (1980: 46) first shifted the species to Lasiancistrus and then to Dolichancistrus (2001: 27) without any comment; a practice continued by subsequent authors.
Isbrücker (1980: 47) identified one putative diagnostic feature for Dolichancistrus, “the possession of very long interopercular odontodes [= hypertrophied cheek odontodes], extending much beyond the head in the adult male” (comments in brackets ours). The two or more greatly hypertrophied and distally-recurved cheek odontodes reaching distinctly beyond the pectoral-spine origin in D. atratoensis, D. carnegiei, D. cobrensis, and D. fuesslii, as well as in Leptoancistrus likely represent the cited condition. Elongation of cheek odontodes in Dolichancistrus (exclusive of Chaetostomus setosus) and Leptoancistrus also occurs in some other ancistrin genera (e.g., Acanthicus, Cordylancistrus, Hemiancistrus, and Panaque), sometimes to a degree comparable to that in Dolichancistrus and Leptoancistrus. Chaetostomus setosus, conversely, has proportionally distinctly shorter, albeit hypertrophied, cheek odontodes that fall short of, or barely reach, the pectoral-fin spine origin.
Proportionally longer pectoral-fin spines of mature males relative to mature females and immature specimens of both sexes were also proposed as diagnostic for Dolichancistrus (Armbruster, 2004: 37). Such dimorphism does indeed occur in Dolichancistrus atratoensis, D. carnegiei, D. cobrensis, D. fuesslii, and species of Leptoancistrus but is absent in Chaetostomus setosus. Sexually dimorphic pectoral spines of this type are limited to Leptoancistrus and Dolichancistrus (other than for Chaetostomus setosus) in the Ancistrini and support the hypothesis of a sister-group relationship for Dolichancistrus plus Leptoancistrus but excluding Chaetostomus setosus.
Removal of Chaetostomus setosus from Dolichancistrus is appropriate based on the phylogenetic evidence that a more restricted Dolichancistrus is the sister group to Leptoancistrus. As a side benefit, this makes Dolichancistrus readily diagnosable externally. The question is then one of the appropriate generic placement of the species. Chaetostomus setosus shares a supraoccipital dermal ridge with components of both Chaetostoma (Salcedo, 2006) and Cordylancistrus (pers. obs.) but not Dolichancistrus and Leptoancistrus. This ridge is hypothesized as derived given its absence across the remainder of the Chaetostoma group indicating that the relationship of Chaetostomus setosus lies with components of Chaetostoma or Cordylancistrus. The absence of resolution about relationships within the Chaetostoma group complicates the assignment of Chaetostomus setosus to either Chaetostoma or Cordylancistrus with the non-monophyly of Cordylancistrus in the sense of Provenzano & Milani (2006) in subsequent analyses (e.g., Armbruster, 2008) problematic. In light of those complications, we place Chaetostomus setosus as incertae sedis within the Chaetostoma group.
Type locality for Chaetostomus setosus. Although we exclude Chaetostomus setosus from Dolichancistrus, our investigations were informative as to the likely type region of the species. Boulenger (1887: 349) remarked that the types of Chaetostomus setosus were part of “a small collection of fishes made by F. A. Simons in Colombia (locality not mentioned).” According to Hilty & Brown (1986: 37), Simons collected birds in northeastern Colombia in the late 1870s apparently in the expeditions that yielded the types of C. setosus. Simons (1881) discussed his travels through the region around the Sierra Nevada de Santa Marta, the northern portions of the lower río Magdalena basin and other lowlands west of the Serranía del Perijá. Only two samples of Chaetostomus setosus with detailed locality information were located, both from the río Cesar basin, Departamento de Cesar, west of the Serranía del Perijá (CIUA 698, 4, 51.04- 70.82 mm SL; ICNMHN 1158, 5, 27.39-72.30 mm SL). It is likely that the syntypes originated in that region.
Remarks. Dolichancistrus was purported to be externally distinguishable from other genera in having a pronounced sexual dimorphism in pectoral spine length with the spine of mature males extending beyond the tip of the pelvic fin spine versus the shorter pectoral-fin spine in mature conspecific females. Although dimorphism in pectoral-spine length is general across Dolichancistrus, only in D. cobrensis and D. fuesslii does the tip of the adpressed pectoral-fin spine reach or extend beyond the tip of the adpressed pelvic-fin spine.
Comparable sized conspecific mature males of all species of Dolichancistrus demonstrate striking variation in odontode development and it appears that males shed their hypertrophied snout odontodes seasonally. Armbruster (2004a: 41) noted that members of Dolichancistrus and Leptoancistrus often shed their hypertrophied cheek odontodes although the underlying cause and periodicity was not noted. Seasonal loss of cheek odontodes occurs elsewhere in the Loricariidae in Panaque (pers. obs.; J. W. Armbruster, pers. comm.), Rineloricaria uracantha (Moodie & Power, 1980: 144; Loricaria uracantha therein) and an apparent periodic shedding of cheek odontodes was observed in Chaetostoma, Cordylancistrus and Leptoancistrus (pers. obs.).
Key to species of Dolichancistrus
1. Buccal papilla absent at premaxillary symphysis; hypertrophied snout odontodes in mature males and females either restricted to anterolateral regions of snout margin, or weakly developed on narrow anterior region of snout in addition to anterolateral odontode patch present in some specimens …………………….....…….. D. cobrensis
1’. Buccal papilla present at premaxillary symphysis; hypertrophied snout odontodes in mature males extending along entire margin of snout and sometimes also onto medial region of head from tip of snout to nares ……….. 2
2. Anterior margin of adpressed posterior dorsal cheek plate medially contacting anterior margin of exposed portion of opercle; tip of adpressed pectoral-fin spine in mature males extending distinctly beyond tip of adpressed pelvic-fin spine and in mature females to tip of pelvic-fin spine ……......................................................................…… D.fuesslii
2’. Anterior margin of adpressed posterior dorsal cheek plate not medially contacting anterior margin of exposed portion of opercle; tip of adpressed pectoral-fin spine in mature males extending to area between middle and tip of adpressed pelvic-fin spine and in mature females reaching to area between base and middle of pelvic-fin spine …… 3
3. Anterior dorsal cheek plate ventrally triangular and distinctly smaller than posterior check plate in lateral view; length of anal-fin spine less than or nearly equal to one-third length of pelvic-fin spine ……………………............. D. atratoensis
3’. Anterior dorsal cheek plate square and approximately as large as posterior check plate in lateral view; length of anal-fin spine nearly equaling or exceeding one-half length of pelvic-fin spine ……………….......……….… D. carnegiei
description: Published as part of Ballen, Gustavo A. & Vari, Richard P., 2012, Review of the Andean armored catfishes of the genus Dolichancistrus Isbrücker (Siluriformes: Loricariidae), pp. 499-518 in Neotropical Ichthyology 10 (3) on pages 501-504, DOI: 10.1590/S1679-62252012000300003, http://zenodo.org/record/10476379