Baryancistrus chrysolomus, Py-Daniel & Zuanon & Oliveira, 2011

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 : 247-250

Baryancistrus chrysolomus , new species Figs. 5 and 6

Holotype. INPA 33947 , 219.0 mm SL, Brazil, Pará, Altamira, rio Xingu at Furo do Ramiro , 03º15’21”S 52º05’06”W, 15 Sep 1997, J. Zuanon.

Paratypes. Brazil, Pará, rio Xingu: INPA 28483, 3, 40.3-65.3 mm SL, 1 c&s, 58.4 mm SL, (1 not measured), Furo da Crente, 03º27’30”S 51º54’41”W, 17 Sep 1997, J. Zuanon. INPA 31408, 4, 55.6-92.2 mm SL, Comunidade do Maia, 03º30’44”S 51º44’43”W, 9 Nov 2008, L. Rapp Py-Daniel & R. R. Oliveira. INPA 31438, 9, 47.4-89.1 mm SL, 1 c&s, 74.4 mm SL, (3 not measured), Comunidade do Maia, 03º31’42”S 51º45’02”W, 9 Nov 2008, L. Rapp Py-Daniel & R. R. Oliveira. INPA 31800, 3, 53.5 mm SL (2 not measured), Coqueiro, 03º06’54”S 51º43’15”W, 5 Nov 2008, L. Diagnosis. Baryancistrus chrysolomus can be distinguished from all its congeners, except B. xanthellus , by the presence of a broad orange to yellow band along the entire distal border of dorsal and caudal fin (vs. all fins without yellow bands). Baryancistrus chrysolomus differs from B. niveatus and B. demantoides by the absence of clear dots on the body (vs. presence of clear dots on whole body in B. niveatus and in anterior part of the body in B. demantoides ). Baryancistrus chrysolomus can also be distinguished from B. longipinnis , B. demantoides and B. niveatus by having a naked abdomen (vs. partially or completely plated in these three species). Baryancistrus chrysolomus can be further distinguished from B. beggini by the larger number of mandibulary teeth (around 70) (vs. 34-36 in premaxillary and 34 in dentary in B. beggini ). Baryancistrus chrysolomus differs from B. xanthellus by the general body color; in B. chrysolomus the body is dark with very faint, almost indistinguishable light marks, vs. a conspicuously spotted coloration in B. xanthellus . Both young of B. xanthellus and B. chrysolomus have wide light bands on dorsal and caudal fins, but only B. chrysolomus retains the band in adults. Besides, both species can be distinguished by the difference on the rest of the body coloration (spotted in B. xanthellus vs. almost plain in B. chrysolomus ).

Description. Morphometrics and meristics in Table 1. Medium-size loricariids; bigger specimen examined reached 219.0 mm SL. Very similar to preceding species. 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 between supraoccipital and dorsal-fin insertion. Ventral surface flat and straight from snout tip to caudal-fin base. Snout with low vertical ridge conspicuously covered by a series of smaller plates. Anterior lateral plates gently bent; low ridge along dorsal fin until base of adipose fin. 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 present. Orbit not elevated; interorbital area flat. No ridge between eyes and nares. Supraoccipital process not elevated, almost indistinct from rest of bone, round posteriorly and elevated. Supraoccipital limited by a pair of large quadrangular plates tightly connected. Predorsal area reduced, with one pair of separated diamondshaped plates anterior to nuchal plate.

Mouth wide; lips large with small round papillae except around maxillae. Maxillary barbels slender and short. Branchial opening moderate, wider in larger specimens. Interbranchial distance large approx. 57.7% 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 or urogenital opening, larger specimens with few patches of odontodes close to pectoral fin insertion. Twenty-five perforated median plates, 24 lateral plates; four to five short oblong plates on caudal-fin base. All plates strongly sculpted with lines of odontodes more developed posteriorly. Numerous hypertrophied odontodes on evertible cheek plates, well developed in larger specimens. Ventral border of opercle with series of strong but short odontodes.

Dorsal fin II,7; spinelet present and locking mechanism functional. Dorsal fin long and low, reaching adipose spine when adpressed. Dorsal-fin posterior membrane covering next three to four plates, but not reaching preadipose plate. Adipose fin large with posterior membrane well developed. Only one plate separating dorsal fin from preadipose plate. Caudal fin i,14,i, emarginate. Pectoral fin I,6, large, reaching well beyond posterior end of pelvic-fin base when adpressed. Pectoral fin covered by large odontodes in males. Pelvic fin i,5 reaching posterior end of anal fin base when adpressed. Anal fin i,4. All simple first rays covered by numerous short odontodes on their free surface.

Teeth long and deeply cuspidate. Cusps largely asymmetrical; internal cusp larger. Premaxilar and dentary bones of similar size and disposed parallel to anterior snout border. Maximum of 91 teeth on premaxillary and 96 on dentary. Modal number of premaxillary teeth 30; dentary teeth mode 34 (range of number of mandibulary teeth in Table 1). Buccal papilla short and digitiform.

Color in life. Body dark brown to olive at dorsum and sides, paler ventrally. Very faint pale spots over body, hardly visible on fins. Juveniles with whitish orange band on distal fourth of caudal and dorsal fins, narrower in adults ( Fig. 6 ).

Color in alcohol. Similar to pattern of living specimens but opaque brown to dark olive ground color and almost indistinguishable pale marks. Bands on fins creamy ( Fig. 5 ).

Distribution. Known from rio Xingu, in the area called Volta Grande do rio Xingu, immediately above Belo Monte falls and below Belo Monte village, and from rio Curuá, rio Iriri, the larger tributary of rio Xingu ( Figs. 3 and 4b ).

Etymology. From the Greek chryso, meaning orange or yellow and loma meaning border, in allusion to the colored band at the border of the dorsal and caudal fins. A noun in apposition.

Popular name. This species is commonly known in the Brazilian aquarium trade as “aba laranja”, (orange border), “cascudo Magnum”, (large pleco), or L047. In English, this fish receives the name of mango pleco.

Ecological notes. Baryancistrus chrysolomus seems to be much rarer than B. xanthellus in the rapid stretches of “Volta Grande” of the rio Xingu ( Fig. 4b ). Differently from the preceding species, young specimens of B. xanthellus occur in marginal areas of the rapids, near the river banks, usually just one or two individuals. The individuals were found under rocks in places with slow to moderate flowing water, usually with sediment accumulation over the rocks and river bottom. Other loricariid species found in the same habitat were Peckoltia vittata and young individuals of Hypostomus spp. Adult B. chrysolomus were collected under large flat rocks settled directly on the river bottom, in places with considerable amounts of fine sediments. The diet of B. chrysolomus (only two specimens analyzed) is very similar to that described for B. xanthellus and was composed by loose algae (mainly diatoms) and occasional invertebrate larvae associated with fine sediments and sand grains. The combination of the type of food items detected, the presence of fine sediments in the gut, a very long (up to 20 times the body length) and coiled intestine, and tooth number and arrangement, also suggest a periphyton-combing feeding strategy for this species.

Figures

Fig. 5. Baryancistrus chrysolomus, INPA 33845, holotype, 219.0 mm SL in lateral, dorsal, and ventral views (photos RRO). Brazil, Pará, Altamira, rio Xingu at Furo do Ramiro.

Fig. 6. Lateral view of live specimens of Baryancistrus chrysolomus, (above) adult, MZUSP 97226, paratype, 127.7 mm SL (photo M. Sabaj-Pérez), Brazil, Pará, rio Curuá, rio Iriri drainage; (below) juvenile, INPA 31408, paratype, 80.2 mm SL (photos RRO), Brazil, Pará, rio Xingu, Comunidade do Maia.

Fig. 3. Map of lower rio Xingu area, showing the collecting sites of Baryancistrus xanthellus (triangles) and Baryancistrus chrysolomus (squares). Black solid symbols indicate holotypes localities.

Fig. 4. Rio Xingu: (a) Cachoeira Buraco do Inferno, type locality of Baryancistrus xanthellus, and specimen hidden in crevice in detail and (b) Furo do Ramiro, type locality of B. chrysolomus, and specimen hidden in crevice in detail (underwater photos Henrique Anatole).