Baryancistrus xanthellus,

Py-Daniel, Lúcia Rapp, Zuanon, Jansen & Oliveira, Renildo Ribeiro de, 2011, Two new ornamental loricariid catfishes of Baryancistrus from rio Xingu drainage (Siluriformes: Hypostominae), Neotropical Ichthyology 9 (2), pp. 241-252: 242-247

publication ID

http://doi.org/ 10.1590/S1679-62252011000200001

publication LSID

lsid:zoobank.org:pub:E7FAF466-BD3B-4CAF-9E40-AA86CCD6B3AE

persistent identifier

http://treatment.plazi.org/id/9E1A87D5-FF80-5D45-FF74-F9D92CCDFCC1

treatment provided by

Carolina

scientific name

Baryancistrus xanthellus
status

new species

Baryancistrus xanthellus  , new species

Figs. 1View Fig and 2View Fig

Holotype. INPA 33849, 214.2 mm SL, Brazil, Pará, Senador José Porfírio, rio Xingu in the vicinity of the cachoeira Buraco do Inferno , 03º27’07”S 51º41’53”W, 18 Mar 1997, J. Zuanon.GoogleMaps 

Paratypes. Brazil, Pará, rio Xingu : ANSP 191482View Materials, 3View Materials, 183.8View Materials  - 188.7 mm SL, MCP 45752View Materials, 2View Materials  , 191.0- 196.3 mm SL, MNRJ 37863View Materials, 2View Materials, 186.2View Materials  - 191.5 mm SL, Arroz Cru , 03º25’16”S 51º55’08”W, 1 Oct 1990, L. Rapp Py-Daniel & J. Zuanon. INPA 3942View Materials, 7View MaterialsGoogleMaps  , 78.3-184.8 mm SL (4 not measured), Furo do Tucum Seco , 1 Oct 1990, L. Rapp Py-Daniel & J. Zuanon. INPA 3955View Materials, 27View Materials  , 48.9-126.2 mm SL, 1 c&s, 82.0 mm SL, (19 not measured), INPA 3963View Materials, 3View Materials, 110.3View Materials  - 145.1 mm SL (1 not measured), Cachoeira do Kaituká , 03º33’47”S 51º51’20”W, 9 Oct 1990, L. Rapp Py-Daniel & J. Zuanon. INPA 4057View MaterialsGoogleMaps  , 1, 223.3 mm SL, Ilha de Babaquara , 03º12’43”S 52º12’12”W, 4 Oct 1990, L. Rapp Py-Daniel & J. Zuanon. INPA 4058View Materials, 1View MaterialsGoogleMaps  , 224.0 mm SL, Praia do Pedral , 03º15’16.7”S 52º13’12”W, 7 Oct 1990, L. Rapp Py-Daniel & J. Zuanon. INPA 31414View Materials, 9View MaterialsGoogleMaps  , 49.8-210.2 mm SL (4 not measured), Comunidade do Maia , 03º30’44”S 51º44’43”W, 9 Nov 2008, L. Rapp Py-Daniel & R. RGoogleMaps  . Oliveira. INPA 31423View Materials, 1View Materials  , 48.3 mm SL, Cachoeira do Landi , 03º35’01”S 51º49’21”W, 8 Nov 2008, L. Rapp Py-Daniel & R. RGoogleMaps  . Oliveira. INPA 31473View Materials, 6View Materials  , 51.2- 171.8 mm SL, (2 not measured), Arroz Cru , 03º25’20”S 51º57’22”W, 6 Nov 2008, L. Rapp Py-Daniel & R. RGoogleMaps  . Oliveira. INPA 31772View Materials, 1View Materials  , 55.3 mm SL, Ilha do Davi , 03º32’39”S 51º57’29”W, 10 Nov 2008, L. Rapp Py-Daniel & R. RGoogleMaps  . Oliveira. INPA 31799View Materials, 2View Materials  , 57.8-189.3 mm SL, Gorgulho da Rita , 03º20’14”S 52º11’18”W, 7 Nov 2008, L. Rapp Py-Daniel & R. RGoogleMaps  . Oliveira. INPA 33848View Materials  , 1, 212.8 mm SL, Cachoeira Buraco do Inferno , 03º27’07”S 51º41’53”W, 17 Mar 1997, J. Zuanon. INPA 33850View Materials, 5View MaterialsGoogleMaps  , 88.4-162.6 mm SL, 1 c&s, 88.4 mm SL, Corredeiras do Arini , 03º24’15”S 51º41’53”W, 6 Sep 1997, J. Zuanon. INPA 33851View Materials, 1View MaterialsGoogleMaps  , 65.1 mm SL, Furo do Ramiro , 03º15’21”S 52º05’06”W, 15 Sep 1997, J. Zuanon. INPA 33852View MaterialsGoogleMaps  , 1, 175.2 mm SL, Ponta da Ilha da Bela Vista , 03º24’22”S 51º43’03”W, 29 Sep 1996, J. Zuanon. INPA 33941View MaterialsGoogleMaps  , 1, 110.9 mm SL, Costa Junior , 03º29’28”S 52º19’07”W, 12 Oct 1996, J. Zuanon. MPEG 19132View Materials, 2View Materials, 171.3View MaterialsGoogleMaps  -183.0 mm SL, Ilha de Babaquara , 5 Oct 1990, J. Zuanon. MZUSP 106738View Materials, 3View Materials, 173.3View Materials  - 194.7 mm SL, Ilha de Kaituká , 03º33’47”S 51º51’20”W, 8 Oct 1990, L. Rapp Py-Daniel & J. Zuanon. ZUEC 4485View Materials, 2View MaterialsGoogleMaps  , 46.6-52.5 mm SL, just above Senador José Porfirio , 02º41’7.7”S 52º00’30.9”W, 13 Sep 1997, J. Zuanon. Rio Iriri: INPA 30767View MaterialsGoogleMaps  , 1, 146.4 mm SL, ROM 88756View Materials, 2View Materials, 137.2View Materials  - 191.2 mm SL, Ilha do Curapé , 04º06’53”S 53º22’28”W, 17 Aug 2008, H. López- Fernández et al. INPA 31081View Materials, 2View Materials, 184.4View MaterialsGoogleMaps  - 207.0 mm SL, ROM 88757View Materials  , 1, 172.5 mm SL, Cachoeira Grande do Iriri , 03º51’34”S 52º41’25”W, 23 Aug 2008, H. López-Fernández et al. INPA 31095View Materials, 2View Materials, 176.6View MaterialsGoogleMaps  - 188.6 mm SL, ROM 88755View Materials, 2View Materials, 103.8View Materials  - 187.5 mm SL, above mouth of rio Novo , 04º28’11”S 53º41’38”W, 21 Aug 2008, H. López- Fernández et al. INPA 31169View MaterialsGoogleMaps  , 1, 140.8 mm SL, ROM 88754View Materials  , 1, 131.1 mm SL, Cachoeira Grande do Iriri , 03º50’35”S 52º44’03”W, 24 Aug 2008, H. López-Fernández et al. INPA 32452View Materials, 1View MaterialsGoogleMaps  , 46.3 mm SL, Barinha , 04º09’05”S 53º23’28”W, 19 Aug 2008, H. López- Fernández et alGoogleMaps  .

Diagnosis. Baryancistrus xanthellus  differs from all its congeners by having a broad light band on dorsal and caudal fin distal borders in juveniles, becoming a small dot on dorsal and caudal-fin tips in adults (vs. conspicuous band at all ages in B. chrysolomus  and light bands absent in B. demantoides  , B. beggini  , B. longipinnis  , and B. niveatus  ). It can also be distinguished from all congeners except B. niveatus  and B. longipinnis  by the presence of light spots on the whole body (vs. the presence of uniform dark coloration in Baryancistrus beggini  and B. chrysolomus  ; presence of round spots only on the anterior part of the body until the end of dorsal-fin base in B. demantoides  ; presence of inconspicuous dots on the fins and rest of the body dark colored in B. longipinnis  ). Baryancistrus xanthellus  can be further distinguished from B. demantoides  , B. longipinnis  , and B. niveatus  by having a naked abdomen (vs. partially or completely plated in these three species). Baryancistrus xanthellus  differs from B. beggini  by a larger number of mandibulary teeth (around 60) on both maxillae versus 34-36 teeth in the premaxillary and 34 teeth in the dentary in B. beggini  ). The presence of bold yellow markings in young B. xanthellus  is the reason for its popular name in the aquarium trade: “amarelinho” in Portuguese (meaning little yellow).

Description. Morphometrics and meristics in Table 1. Mediumsize loricariids, bigger specimen examined reached 224.1 mm SL. Body short and robust, deep. Profile from snout to eye strongly sloped, gently convex from eye to insertion of dorsal fin due to prominence of supraoccipital process. Profile strongly inclined from dorsal-fin insertion to caudal fin. Body deepest at region between supraoccipital and dorsal-fin insertion. Ventral surface flat and straight from snout tip to caudal-fin base. Head and eyes without crest. Anterior lateral plates gently bent; rest of body not keeled. Anterior portion of body half oval in cross section, triangular at caudal peduncle.

Head large and wide; snout round in dorsal view. Eye large and round, iris operculum not visible. Orbit slightly elevated; interorbital area almost completely flat. No ridge between eyes and nares. Supraoccipital process conspicuous, elevated and rounded posteriorly. Supraoccipital limited posteriorly by pair of large quadrangular plates, almost fused. Predorsal area reduced, with only one pair of small, separated diamond-shaped plates anterior to nuchal plate.

Baryancistrus xanthellus  Baryancistrus chrysolo mus  Measurement Holotype N Mean Range SD Holotype N Mean Range SD Standard length (mm) 214.2 62 - 46.3-224.1 - 219.0 20 - 4 7.4-219.0 - Percents of st andard length Predorsal length 43.4 62 44.7 40.2-47.8 1.4 41.3 20 42.2 39.6 -45.1 1.2 Head length 35.8 62 37.7 35.3-41.0 1.4 33.7 20 36.6 33.6 -39.5 1.6 Cleithral width 33.7 62 34.4 31.0-37.5 1.5 34.3 20 34.4 32.9 -36.5 0.8 Thorax length 25.0 62 24.3 20.9-27.3 1.3 21.7 20 24.1 21.0 -26.2 1.4 Pectoral-spine len gth 33.7 62 33.0 25.7-38.7 3.3 34.9 20 32.0 28.5 -36.1 2.2 Abdominal length 24.3 62 24.6 21.5-27.7 1.4 25.1 20 24.3 20.9 -26.7 1.6 Pelvic-spine length 24.2 62 25.9 23.1-29.3 1.4 25.1 20 25.0 23.5 -27.0 0.8 Postanal length 21.3 62 27.8 21.3-30.7 1.7 31.1 20 29.5 26.6 -31.5 1.1 Anal-fin spine length 10.8 62 10.1 7.6-13.3 0.9 10.6 19 10.6 9.1-12.0 0.7 Dorsal spine length 25.6 62 26.6 22.8-32.1 1.9 26.0 20 27.0 24.0 -29.7 1.6 Dorsal-fin base length 40.6 62 40.5 35.4-48.0 2.7 41.2 20 39.3 36.5 -43.3 2.0 Dorsal-ad ipose distance 1.3 62 1.1 0-2.7 0.9 1.6 20 1.7 0.5 -4.0 1.1 Caudal penduncle d epth 10.6 62 10.7 9.0-12.3 0.8 11.3 20 10.6 9.4-11.9 0.6 Adipose-spine length 7.8 62 7.9 6.4-9.1 0.6 8.3 20 8.2 7.1 -9.2 0.6 Adipose-caudal length 21.1 62 22.4 19.5-24.8 0.9 25.2 20 23.5 21.2 -26.1 1.1 Body depth at dorsal-fin origin 22.2 62 22.1 17.1-26.8 1.9 21.2 20 20.4 16.6 -22.9 1.8 Body width at dorsal-fin origin 31.9 62 31.9 27.7-37.1 2.0 32.4 20 30.6 27.9 -34.0 1.7 Body width at anal-fin origin 17.6 62 16.9 12.6-20.5 1.7 18.7 20 15.7 12.4 -19.3 2.1 Postdorsal length 22.8 62 23.3 19.1-25.7 1.4 26.0 20 25.5 23.4 -27.7 1.2 Anus-anal fin len gth 3.6 62 4.1 2.9-5.6 0.6 4.5 20 4.1 3.3 -5.7 0.6 Body width 36.5 62 36.1 33.3-39.3 1.3 36.3 20 36.3 35.2 -37.8 0.8 Percents of head length Orb ital diameter 15.4 62 18.4 15.1-23.4 2.3 17.3 20 21.6 17.1 -24.9 2.9 Sn out length 74.8 62 67.2 60.6-74.8 3.1 64.0 20 61.9 58.5 -66.5 2.8 Internares width 13.8 62 13.0 9.4-15.6 1.6 14.5 20 12.3 9.6-15.7 1.6 Interorbital width 37.5 62 36.0 28.0-41.4 3.9 41.8 20 36.7 31.4 -45.2 4.1 Head depth 57.6 62 56.3 46.5-66.8 4.3 63.7 20 54.0 47.1 -63.7 5.3 Dentary len gth 21.2 62 19.5 16.7-24.4 1.6 23.2 20 20.6 17.3 -24.9 2.3 Premaxillary length 21.3 62 19.3 15.9-22.6 1.4 23.7 20 19.9 16.1 -23.7 2.1 Head width 103.9 62 90.5 77.2-103.9 7.2 100.4 20 89.3 7 9.1-100.4 6.6 Eye-nostril length 16.3 62 14.7 9.1-17.8 2.2 15.5 20 13.2 10.2 -17.9 2.3 Interbranchial distance 59.6 62 56.5 51.8-60.9 2.4 58.8 20 57.7 53.6 -61.2 2.2 Teeth on premaxilla 60 62 28-72 74 20 14 -91 Teeth on dentary 64 62 25-76 81 20 22 -96 Lateral plates in middle series 24 62 23-24 24 20 24 -25 Plates between anal and caudal 10 62 9-11 10 20 10 -11 Plates between dorsal and adipose 0 62 0-2 0.5 20 0 -2 Plates predorsal 3 62 3 3 20 3

Counts

Mouth wide; lips large, covered with small round papillae except on area around maxillae. Maxillary barbel thick and short. Branchial opening moderate, wider in larger specimens. Interbranchial distance approx. 56.5% in head length.

Head and body completely covered by large plates dorsally, except dorsal-fin base. Ventral surface largely unplated from snout to anal fin; in larger specimens, presence of two or three minute round plates close to insertion of pectoral spine or urogenital opening. Twenty-two perforated median plates, 23 lateral plates; four oblong plates on caudalfin base. All plates marked with lines of odontodes. Numerous hypertrophied odontodes only on evertible cheek plates, well developed in larger specimens with largest odontode reaching posterior end of first lateral plate. Ventral border of opercle with series of strong but short odontodes on probably mature males.

Dorsal fin II,7; spinelet present and dorsal-fin locking mechanism functional. Dorsal fin long and low, reaching adipose spine on small specimens when adpressed. Dorsalfin posterior membrane covering four plates immediately behind last dorsal-fin ray, but not reaching preadipose plate. Adipose fin large and with posterior membrane slightly developed. One single plate separating dorsal from preadipose plate. Caudal fin i,14,i, emarginated. Pectoral fin I,6, large, reaching well beyond posterior end of pelvic-fin base when adpressed. Pectoral fin covered by large odontodes on (possibly mature) males. Pelvic fin i,5 reaching posterior end of anal fin base when adpressed. Anal fin i,4, very reduced. All simple first rays covered by numerous short odontodes on their free surface.

Teeth long and deeply cuspidate. Cusps round and similar in larger specimens with vertical divide between cusps; in smaller specimens cusps are largely asymmetrical, with internal cups larger. Premaxilla and dentary of similar size and disposed in parallel to anterior border of snout. Modal number of premaxillary teeth 32; dentary teeth mode 46 (range of number of mandibulary teeth in Table 1). Buccal papilla long and digitiform.

Color in life. Overall body color dark brown at dorsum and sides, paler on abdomen. Numerous bright, similar-sized yellow spots over head, body, dorsal, adipose, and caudal fins, and on dorsal surface of pectoral and pelvic fins. Yellow spots almost size of pupil in juveniles, becoming proportionally smaller, more numerous and somewhat paler in adults. Young specimens with wide yellow band on distal third of caudal and dorsal fin; dorsal-fin band larger anteriorly, becoming gradually slender posteriorly. In adults, bands on fins become reduced to spots on anterior distal ends of dorsal and caudal fins ( Fig. 2View Fig). Considerable variation in density and size of spots.

Color in alcohol. Similar to pattern described for living specimens but with ground color brown to dark olive and white to cream markings ( Fig. 1View Fig).

Distribution. This species has been recorded from the area called Volta Grande do rio Xingu, an area immediately above Belo Monte falls, and from rio Iriri, the larger tributary of rio Xingu ( Figs. 3View Fig and 4aView Fig).

Etymology. From the Greek xanthellus  , yellow, in allusion to the bright color of the specimens. A noun in apposition.

Popular name. Known in the aquarium trade as “amarelinho” (= little yellow) and “cascudo pepita-de-ouro” (in Portuguese), or L018 and L085; and golden nugget pleco or Iriri golden nugget pleco (in English), or L177.

Ecological notes. Baryancistrus xanthellus  is one of the most common species observed in the rapids of rio Xingu in the area known as “Volta Grande do Xingu” near the town of Altamira, Pará State ( Fig. 4aView Fig). Young specimens of B. xanthellus  occur in groups of several individuals under flat rocks at the bottom of shallow rapid stretches. Other loricariid species found sintopically are Ancistrus  spp., Oligancistrus punctatissimus  , and an undescribed species of Oligancistrus  , young individuals of Baryancistrus aff. niveatus  , Parancistrus nudiventris  , and Pseudancistrus  sp. Adult specimens occupy larger spaces among and under submerged boulders, together with large specimens of Baryancistrus aff. niveatus  , Scobinancistrus aureatus  , and S. cf. pariolispos  , and Hypostomus  spp. The diet of three examined specimens of B. xanthellus  was composed mainly of algae, especially diatoms and loose filaments of clorophyceans such as Spirogyra  , which are commonly found associated with fine sediments and sand grains in the long

Rapp Py-Daniel & R. R. Oliveira. INPA 33844View Materials, 1, 166.2 mm SL, Viracebo do Arroz Cru , 03º25’16”S 51º55’08”W, 7 Oct 1996, J. Zuanon. INPA 33845View Materials, 2View Materials, 207.6View Materials - 207.8 mm SL, same data as holotype. INPA 33846View Materials, 1, 191.7 mm SL, MPEG 19133View Materials, 1, 142.7 mm SL, Furo do Ramiro , 03º15’21”S 52º05’06”W, 12 Sep 1997, J. Zuanon. MZUSP 106739View Materials, 1, 184.2 mm SL, Furo do Ramiro , 03º15’21”S 52º05’06”W, 6 Oct 1996, J. Zuanon. ZUEC 4484View Materials, 1View Materials, 69.5 mm SL, Furo de Ramiro , 03º15’21”S 52º05’06”W, 13 September 1997, J. Zuanon. Rio Curuá: MZUSP 97226View Materials, 8View Materials, 45.5-182.4 mm SL, rio Iriri drainage, 08º19’07”S 55º05’23”W, 22 Oct 2007, J. L. Birindelli et alGoogleMaps  .

intestines of loricariids (intestinal length up to 16 times the body length; Zuanon, 1999). Occasional bryozoans and chironomid larvae were also found. Underwater observations indicate that the food is scraped from the surface of submerged rocks by gently combing the periphyton cover with the numerous and tightly spaced teeth (JZ, pers. obs.).

INPA

Instituto Nacional de Pesquisas da Amazonia

SL

University of Sierra Leone, Njala University College

MCP

Pontificia Universidade Catolica do Rio Grande do Sul

R

Departamento de Geologia, Universidad de Chile

ROM

Royal Ontario Museum