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