Hypostomus rhantos (Siluriformes: Loricariidae), a new species from southern Venezuela. Jonathan W. Armbruster Leigh A. Tansey Nathan K. Lujan Zootaxa 2007 1553 59 68 6N2WW Loricariidae Hypostomus CoL Animalia Siluriformes 60 Chordata species rhantos  Figs. 1-2 and 3b    Holotype:  MCNG55352, 157.2 mm SL, Venezuela, Amazonas, Rio Manapiare-Rio Ventuari-RioOrinoco Drainage,  RioParucito at Raudales Salomon, 2.7 km NE of San Juan de Manapiare, 05.34637°, -066.03347°, D.C. Werneke, N.K. Lujan, O. Leon,  16 April 2004.   Paratypes: 63 specimens. All collections Venezuela, Amazonas, RioOrinoco drainage:  ANSP 160774, 11, 76.7-103.5 mm SL, Morichal 26.9 km from Puerto Ayacucho, along Puerto Ayacucho - Caicara highway, B. Chernoff et al.,  15 November 1985;   ANSP162365, 2, 134.4-139.0, Backwater of RioOrinoco behind sand playa ca. half hour upstream from Isla Temblador, 03°04’N, 066°28’W, B. Chernoff et al.,  10 March 1987;   ANSP185240, 4, 56.8-124.5,  AUM39273, 3 c &s, 5, 53.5-149.7,  MCNG55353, 5, 52.0-154.5,  UF164255, 2, 54.4-145.5, Same data as holotype;   AUM39308, 1, 124.0,  MCNG55354, 2, 94.7-99.2,  RMNH35500, 1, 99.0,  RioManapiare, tributary of RioVentuari, 14.5 km NW of San Juan de Manapiare, 05.42863°, -066.13616°, N.K. Lujan, M.H. Sabaj, L.S. de Souza, and D.C. Werneke,  12 April 2004;   AUM39235, 1, 52.9,  RioVentuari, beach across the river from Picua Village, 34 km ENE of Macuruco, 104 km E of San Fernando de Atabapo, 04. 11534°, -066.76457°, M.H. Sabaj, N.K. Lujan, D.C. Werneke, L.S. de Souza, and O. Leon,  5 April 2004;   AUM39874, 1, 145.3,  RioVentuari at mouth of CanoCamoni, 145 km NNE of Macuruco, 189 km NE of San Fernando de Atabapo, 05.05588°, -066.32742°, M.H. Sabaj, N.K. Lujan, D.C. Werneke, L.S. de Souza, and O. Leon,  8 April 2004;   AUM40070, 1, 123.4,  RioManapiare, tributary of RioVentuari, 20 km NW of San Juan de Manapiare, 05.45272°, -066.17682, D.C. Werneke, N.K. Lujan, and L.S. de Souza,  12 April 2004;   AUM39506, 1, 168.7,  RioVentuari at Raudales Tencua, 56 km ESE of San Juan de Manapiare, 05.04968°, -065.62722, D.C. Werneke, N.K. Lujan, O. Leon, A. Luna, and R. Pajua, 20-  21 April 2004;   AUM39216, 1, 93.1,  RioVentuari, mouth, 3.99528°, -067.04250°, N.K. Lujan and O. Leon,  15 April 2004;   AUM41496, 1, 147.5,  RioManapiare at mouth of CanoYutaje, tributary of RioVentuari, 14 km NW of San Juan de Manapiare, 05.43667°, -066.11261°, M.H. Sabaj, L.S. de Souza, D.C. Werneke, and N.K. Lujan,  11 April 2004;   AUM41418, 1, 164.4,  MCNG55355, 1, 154.5,  RioVentuari, bedrock outcrops, 83 km ENE of Macuruco, 153 km ENE of San Fernando de Atabapo, 04.25346°, -066.34466°, N.K. Lujan, D.C. Werneke, M.H. Sabaj, L.S. de Souza, and O. Leon,  6 April 2004;   AUM41336, 1, 70.2,  CanoGuavialito, tributary of RioManapiare, tributary of RioVentuari, near Alto Guaviarito, 17.5 km NW of San Juan de Manapiare, 05.44135°, -066.16294°, L.S. de Souza, D.C. Werneke, N.K. Lujan, and M.H Sabaj,  13 April 2004;   AUM41440, 1, 66.3,  ANSP185241, 1, 66.9,  CanoGuavialito, tributary of RioManapiare, tributary of RioVentuari, directly off of RioManapiare, 17.5 km NW of San Juan de Manapiare, 05.44010°, -066.16175°, M.H. Sabaj, L.S. de Souza, D.C. Werneke, and N.K. Lujan,  13 April 2004;   AUM41496, 1, 147.5,  RioManapiare, tributary of RioVentuari, at mouth of Cano Yutaje, 14 km NW of San Juan de Manapiare, 05.43667°, -066.11261°, M.H. Sabaj, L.S. de Souza, D.C. Werneke, and N.K. Lujan,  11 April 2004;   AUM42100, 8, 50.6-176.4,  RioOrinoco, beach and bedrock outcropping, 50 km E of San Fernando de Atabapo, 03.97029°, -067.25506°, N.K. Lujan, D.C. Werneke, M.H. Sabaj, M. Arce, R. Betancur, and T.E. Wesley,  2 March 2005;   AUM42114, 5, 135.6-159.1,  RioOrinoco, 117 km W of La Esmeralda, N.K. Lujan, M. Arce, T.E. Wesley et al., 03.28998°, -066.60004°,  29 March 2005;   AUM42121, 3, 115.0-126.0,  RioOrinoco, 33.9 km E of La Esmeralda, Punto Piaroa, 03.14744°, -065.85381°, N.K. Lujan, M. Arce, T.E. Wesley et al.,  28 March 2005;   AUM42164, 1, 195.8,  RioOrinoco, bedrock outcrop, 52.9 km SE of San Antonio, 102 km W of La Esmeralda, 03.10036°, -066.46277°, N.K. Lujan, D.C. Werneke, M.H. Sabaj, O. Leon, M. Arce, R Betancur, and T.E. Wesley,  4 March 2005;   AUM42220, 1, 136.7,  RioOrinoco, near Puerto Ayacucho on a beach called Playa Bagre, 05.65642°, -067.63103, N.K. Lujan, M. Arce, and T.E. Wesley,  13 April 2005.  Diagnosis: Hypostomus rhantosis unique among Hypostomus(except for H. micromaculatus) by having extremely small spots (see especially Fig. 2). Hypostomus rhantosis a member of the H. plecostomusgroup, but is not a member of the H. cochliodonsubgroup (Armbruster, 2004). Hypostomus rhantoscan be separated from the H. emarginatusspecies group by having a dark brown base color (vs. light tan), by having a small buccal papilla (vs. large), and by lacking hypertrophied odontodes on the lateral plates of nuptial males (vs. hypertrophied odontodes present); and from the H. cochliodonspecies subgroup of the H. plecostomusgroup by having viliform teeth (vs. spoon-shaped). Hypostomus rhantoscan be separated from all other members of the H. plecostomusgroup (including species of the H. cochliodonsubgroup) except H. micromaculatusby having extremely small spots (greater than 15 on the first plate in the dorsal series in H. rhantosvs. five or fewer). Hypostomus rhantoscan be separated from H. micromaculatusby having all of the spots round and evenly distributed (vs. spots longitudinally oval and restricted to rows Figs. 1-2 vs. Fig. 4), keels of lateral plates well-developed (vs. weak), a ridge present on the pterotic that is contiguous with the supraorbital ridge (vs. ridge absent, Fig. 3), and by having a fully plated abdomen (vs. abdomen partially plated or naked). In addition, smaller specimens of H. rhantoshave spots on the dorsal fin whereas small specimens of H. micromaculatushave the dorsal fin entirely dark.  Description: Morphometric data given in Table 1. Largest specimen 195.8 mm SL. Head and nape forming arch from tip of snout to origin of dorsal fin. Body depth decreasing from origin of dorsal fin to dorsal procurrent caudal spines then increasing to caudal fin. A rounded ridge present from anterodorsal corner of orbit, running ventral to nares, and ending slightly anteroventral of anterior nare. Longitudinal ridge of raised bone and slightly larger odontodes present on pterotic-supracleithrum beginning at posterodorsal corner of orbit and contiguous with supraorbital ridge. Space between orbits concave such that supraorbital ridge higher than medial surface of head. Supraoccipital convex medially with slight crest. Nares separated by flap of skin held erect in life. Dorsal, middorsal, median and midventral plate rows complete from head to caudal fin, ventral plate row begins at insertion of pelvic fin and continues to caudal fin. Lateral plates with short, median keels with enlarged, dull odontodes. Keels on first two plates of dorsal row and sometimes first three plates forming line from supraoccipital to posterolateral corner of nuchal plate, not confluent with keel on dorsal plate row beginning on fourth plate. Base of caudal fin covered in elongate, roughly triangular plates. Entire ventral surface of head and body (except region around insertion of pelvic fin) covered in small platelets. Platelets on abdomen increase in number with standard length. Head covered in small plates. Frontal, nasal, sphenotic, infraorbitals, opercle, pterotic-supracleithrum, suprapreopercle, and supraoccipital supporting odontodes. Platelets that cover anteroventral corner of opercle slightly separated from opercle allowing plates to be marginally everted (angle of eversion less than 30°).  Dorsal fin moderately long, usually just barely reaching preadipose plate when depressed, consisting of small, V-shaped spinelet, fairly strong spine, and seven rays. Caudal fin forked, lower lobe longer than upper. Pectoral-fin spine strong, extending posteriorly to pelvic-fin rays when depressed ventral to pelvic fin; cleithrum with exposed process dorsal to pectoral-fin rays that tapers posteriorly to point; pectoral fin inserted on same plane as pelvic fin such that spine, when depressed parallel with body, lies on top of and in contact with pelvic fin. Pelvic-fin spine thin, flexible, reaches slightly beyond base of anal fin. Anal fin with relatively strong, unbranched first ray supporting odontodes. Adipose fin consisting of single median, unpaired preadipose plate and a stout, strong, pointed spine; adipose-fin membrane not reaching procurrent caudal-fin spines. Dorsal fin II,7, pectoral fin I,6, pelvic fin I,5, anal fin I,4, caudal fin I,14,I. Jaws weakly angled, dentaries forming angle much greater than 90°. Teeth numerous (28-45, mode 31 in premaxilla, 29-45, mode 31, in dentary, N = 48), bicuspid, median cusp moderately long, lateral cusp about one fourth length of median, stalk moderately long. Median plates 24.  Coloration: Light gray to tan when alive, becoming tan when preserved. Body densely covered with tiny spots, head spots even smaller than body spots. Spots present on all fins, generally larger than spots on body, evenly distributed on rays, spines, and membranes. Caudal fin membranes light and spotted anteriorly, fading to dark wash posteriorly. Abdomen lighter than sides, with tiny spots. Occasionally with four dorsal saddles, first below anterior dorsal-fin rays, second below and slightly behind posterior dorsal-fin rays, third below and slightly anterior to adipose-fin spine, and fourth at base of caudal peduncle; all saddles angled anteriorly, saddles one and two combine and continue to base of pelvic fin, third and fourth terminating at middle of midventral plate row. Fin spines usually lighter than rest of body. Spots relatively larger in juveniles. Juveniles with fewer spots distally on all fins, lower half of caudal fin much darker.  Range: Currently known from the RioVentuari, a tributary of the upper RioOrinoco, and the mainstem upper Orinoco above Puerto Ayacucho to the RioCasiquiare in Amazonas, Venezuela (Fig. 5).  Ecology: Hypostomus rhantoswas collected in loricariid assemblages with an average of 7.2 loricariid species per site (n=16 sites). Habitats from which H. rhantoswere collected range from consolidated lateritic rocks in flow, to bedrock cracks in flow, to branches and trunks of trees in slack water.  Etymology: Rhantos is Greek for sprinkled, speckled, or spotted and refers to the tiny randomly placed spots of the species.  Discussion: Specimens of Hypostomus rhantoswere analyzed in Armbruster (2004a) but were incorrectly referred to as H. micromaculatus. Hypostomus rhantoswas found to be the sister to H. robinii; however, support for this was very weak (Bremer decay index = 1), and derived from only from two homoplastic characteristics: posteromedial invagination of the fifth ceratobranchial present (character 11 state 1 from Armbruster, 2004) and a reversal to a short levator arcus palatini crest (44-1). This clade was part of a larger clade consisting of the H. cochliodonsubgroup, Hypostomus plecostomus, the potentially undescribed Hypostomussimilar to H. robiniifrom the Orinoco, and H. cordovae, with this clade being supported by a reversal to a wide posterior edge to the posterior process of the coracoid (158-0). This clade is also poorly supported with a Bremer decay index of one. Most of the relationships within Hypostomusare poorly resolved and need much further study.  Hypostomus rhantosis most similar in coloration to H. micromaculatusfrom Suriname. In addition to coloration, H. rhantosappears taller and wider than H. micromaculatus; however, we do not have enough specimens available to provide confident measurements of this. There are no species that have been described or that we have examined between the Upper Orinoco and Suriname with a similar color pattern. Given the vast distance between the two species, it would be unlikely that they would be sister species. They are different in the size of the keels (relatively well-developed in H. rhantosand almost absent in H. micromaculatus) and the amount of abdominal plating (fully plated in H. rhantosand absent or nearly so in H. micromaculatus). Although these characteristics change a lot in loricariids, they do suggest when coupled with locality data that the two species may have small spots via convergence. 923899826 2004-04-16 MCNG D. C. Werneke, N. K. Lujan, O. Leon Venezuela 5.34637 Rio Parucito at Raudales Salomon, 2.7 km NE of San Juan de Manapiare -66.03347 MCNG 55352 Amazonas, Rio Manapiare-Rio Ventuari-Rio Orinoco Drainage Holotype 923899824 1985-11-15 ANSP B. Chernoff et al. Venezuela Morichal 26.9 km from Puerto Ayacucho, along Puerto Ayacucho - Caicara highway ANSP 160774 Amazonas, Rio Orinoco drainage Paratypes 923899829 1987-03-10 ANSP B. Chernoff et al. Venezuela 3.0666666 Backwater of Rio Orinoco behind sand playa ca. half hour upstream from Isla Temblador -66.46667 ANSP 162365 Amazonas, Rio Orinoco drainage Paratypes 923899830 2004-04-16 ANSP, AUM, MCNG, UF D. C. Werneke, N. K. Lujan, O. Leon Venezuela 5.34637 Rio Parucito at Raudales Salomon, 2.7 km NE of San Juan de Manapiare -66.03347 ANSP 185240, AUM 39273, MCNG 55353, UF 164255 Amazonas, Rio Manapiare-Rio Ventuari-Rio Orinoco Drainage Paratypes 923899825 2004-04-12 AUM, MCNG, RMNH N. K. Lujan, M. H. Sabaj, L. S. de Souza, D. C. Werneke Venezuela 5.42863 Rio Manapiare, tributary of Rio Ventuari, 14.5 km NW of San Juan de Manapiare -66.13616 AUM 39308, MCNG 55354, RMNH 35500 Amazonas, Rio Orinoco drainage Paratypes 923899831 2004-04-05 AUM M. H. Sabaj, N. K. Lujan, D. C. Werneke, L. S. de Souza, O. Leon Venezuela 4.11534 Rio Ventuari, beach across the river from Picua Village, 34 km ENE of Macuruco, 104 km E of San Fernando de Atabapo -66.76457 AUM 39235 Amazonas, Rio Orinoco drainage Paratype 923899823 2004-04-08 AUM M. H. Sabaj, N. K. Lujan, D. C. Werneke, L. S. de Souza, O. Leon Venezuela 5.05588 Rio Ventuari at mouth of Cano Camoni, 145 km NNE of Macuruco, 189 km NE of San Fernando de Atabapo -66.32742 AUM 39874 Amazonas, Rio Orinoco drainage Paratype 923899839 2004-04-12 AUM D. C. Werneke, N. K. Lujan, L. S. de Souza Venezuela 5.45272 Rio Manapiare, tributary of Rio Ventuari, 20 km NW of San Juan de Manapiare -66.17682 AUM 40070 Amazonas, Rio Orinoco drainage Paratype 923899833 2004-04-21 AUM D. C. Werneke, N. K. Lujan, O. Leon, A. Luna, R. Pajua Venezuela 5.04968 Rio Ventuari at Raudales Tencua, 56 km ESE of San Juan de Manapiare -65.62722 AUM 39506 Amazonas, Rio Orinoco drainage Paratype 923899836 2004-04-15 AUM N. K. Lujan, O. Leon Venezuela 3.99528 Rio Ventuari, mouth -67.0425 AUM 39216 Amazonas, Rio Orinoco drainage Paratype 923899838 2004-04-11 AUM M. H. Sabaj, L. S. de Souza, D. C. Werneke, N. K. Lujan Venezuela 5.43667 Rio Manapiare at mouth of Cano Yutaje, tributary of Rio Ventuari, 14 km NW of San Juan de Manapiare -66.11261 AUM 41496 Amazonas, Rio Orinoco drainage Paratype 923899832 2004-04-06 AUM, MCNG N. K. Lujan, D. C. Werneke, M. H. Sabaj, L. S. de Souza, O. Leon Venezuela 4.25346 Rio Ventuari, bedrock outcrops, 83 km ENE of Macuruco, 153 km ENE of San Fernando de Atabapo -66.34466 AUM 41418, MCNG 55355 Amazonas, Rio Orinoco drainage Paratypes 923899841 2004-04-13 AUM L. S. de Souza, D. C. Werneke, N. K. Lujan, M. H Sabaj Venezuela 5.44135 Cano Guavialito, tributary of Rio Manapiare, tributary of Rio Ventuari, near Alto Guaviarito, 17.5 km NW of San Juan de Manapiare -66.16294 AUM 41336 Amazonas, Rio Orinoco drainage Paratype 923899834 2004-04-13 AUM, ANSP M. H. Sabaj, L. S. de Souza, D. C. Werneke, N. K. Lujan Venezuela 5.44010 Cano Guavialito, tributary of Rio Manapiare, tributary of Rio Ventuari, directly off of Rio Manapiare, 17.5 km NW of San Juan de Manapiare -66.16175 AUM 41440, ANSP 185241 Amazonas, Rio Orinoco drainage Paratypes 923899827 2004-04-11 AUM M. H. Sabaj, L. S. de Souza, D. C. Werneke, N. K. Lujan Venezuela 5.43667 Rio Manapiare, tributary of Rio Ventuari, at mouth of Cano Yutaje, 14 km NW of San Juan de Manapiare -66.11261 AUM 41496 Amazonas, Rio Orinoco drainage Paratype 923899840 2005-03-02 AUM N. K. Lujan, D. C. Werneke, M. H. Sabaj, M. Arce, R. Betancur, T. E. Wesley Venezuela 3.97029 Rio Orinoco, beach and bedrock outcropping, 50 km E of San Fernando de Atabapo -67.25506 AUM 42100 Amazonas, Rio Orinoco drainage Paratypes 923899837 2005-03-29 AUM N. K. Lujan, M. Arce, T. E. Wesley et al. Venezuela 3.28998 Rio Orinoco, 117 km W of La Esmeralda -66.60004 AUM 42114 Amazonas, Rio Orinoco drainage Paratypes 923899828 2005-03-28 AUM N. K. Lujan, M. Arce, T. E. Wesley et al. Venezuela 3.14744 Rio Orinoco, 33.9 km E of La Esmeralda, Punto Piaroa -65.85381 AUM 42121 Amazonas, Rio Orinoco drainage Paratypes 923899842 2005-03-04 AUM N. K. Lujan, D. C. Werneke, M. H. Sabaj, O. Leon, M. Arce, R Betancur, T. E. Wesley Venezuela 3.10036 Rio Orinoco, bedrock outcrop, 52.9 km SE of San Antonio, 102 km W of La Esmeralda -66.46277 AUM 42164 Amazonas, Rio Orinoco drainage Paratype 923899835 2005-04-13 AUM N. K. Lujan, M. Arce, T. E. Wesley Venezuela 5.65642 Rio Orinoco, near Puerto Ayacucho on a beach called Playa Bagre -67.63103 AUM 42220 Amazonas, Rio Orinoco drainage Paratype