Hypostomus rhantos (Siluriformes: Loricariidae), a new species from southern Venezuela.
Author
Jonathan W. Armbruster
Author
Leigh A. Tansey
Author
Nathan K. Lujan
text
Zootaxa
2007
1553
59
68
http://www.zoobank.org/urn:lsid:zoobank.org:pub:F87041AF-3B5A-4F02-9D98-886814090969
journal article
z01553p059
F87041AF-3B5A-4F02-9D98-886814090969
Hypostomus rhantos
New Species
Figs. 1-2 and 3b
Holotype
:
MCNG
55352
, 157.2 mm SL,
Venezuela
,
Amazonas,
Rio
Manapiare-Rio
Ventuari-Rio
Orinoco Drainage
,
Rio
Parucito 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,
Rio
Orinoco 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
;
ANSP
162365
, 2, 134.4-139.0,
Backwater of
Rio
Orinoco behind sand playa ca. half hour upstream from Isla Temblador
,
03°04’N
,
066°28’W
,
B. Chernoff et al.
,
10 March 1987
;
ANSP
185240
, 4, 56.8-124.5,
AUM
39273
, 3 c &s, 5, 53.5-149.7,
MCNG
55353
, 5, 52.0-154.5,
UF
164255
, 2, 54.4-145.5, Same data as holotype
;
AUM
39308
, 1, 124.0,
MCNG
55354
, 2, 94.7-99.2,
RMNH
35500
, 1, 99.0,
Rio
Manapiare, tributary of
Rio
Ventuari, 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
;
AUM
39235
, 1, 52.9,
Rio
Ventuari, 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
;
AUM
39874
, 1, 145.3,
Rio
Ventuari at mouth of
Cano
Camoni, 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
;
AUM
40070
, 1, 123.4,
Rio
Manapiare, tributary of
Rio
Ventuari, 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
;
AUM
39506
, 1, 168.7,
Rio
Ventuari 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
;
AUM
39216
, 1, 93.1,
Rio
Ventuari, mouth
,
3.99528°
,
-067.04250°
,
N.K. Lujan and O.
Leon
,
15 April 2004
;
AUM
41496
, 1, 147.5,
Rio
Manapiare at mouth of
Cano
Yutaje, tributary of
Rio
Ventuari, 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
;
AUM
41418
, 1, 164.4,
MCNG
55355
, 1, 154.5,
Rio
Ventuari, 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
;
AUM
41336
, 1, 70.2,
Cano
Guavialito, tributary of
Rio
Manapiare, tributary of
Rio
Ventuari, 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
;
AUM
41440
, 1, 66.3,
ANSP
185241
, 1, 66.9,
Cano
Guavialito, tributary of
Rio
Manapiare, tributary of
Rio
Ventuari, directly off of
Rio
Manapiare, 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
;
AUM
41496
, 1, 147.5,
Rio
Manapiare, tributary of
Rio
Ventuari, 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
;
AUM
42100
, 8, 50.6-176.4,
Rio
Orinoco, 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
;
AUM
42114
, 5, 135.6-159.1,
Rio
Orinoco, 117 km W of La Esmeralda
,
N.K. Lujan, M. Arce, T.E. Wesley et al.
,
03.28998°
,
-066.60004°
,
29 March 2005
;
AUM
42121
, 3, 115.0-126.0,
Rio
Orinoco, 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
;
AUM
42164
, 1, 195.8,
Rio
Orinoco, 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
;
AUM
42220
, 1, 136.7,
Rio
Orinoco, 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 rhantos
is unique among
Hypostomus
(except for
H. micromaculatus
) by having extremely small spots (see especially Fig. 2).
Hypostomus rhantos
is a member of the
H. plecostomus
group, but is not a member of the
H. cochliodon
subgroup (Armbruster, 2004).
Hypostomus rhantos
can be separated from the
H. emarginatus
species 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. cochliodon
species subgroup of the
H. plecostomus
group by having viliform teeth (vs. spoon-shaped).
Hypostomus rhantos
can be separated from all other members of the
H. plecostomus
group (including species of the
H. cochliodon
subgroup) except
H. micromaculatus
by having extremely small spots (greater than 15 on the first plate in the dorsal series in
H. rhantos
vs. five or fewer).
Hypostomus rhantos
can be separated from
H. micromaculatus
by 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. rhantos
have spots on the dorsal fin whereas small specimens of
H. micromaculatus
have 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
Rio
Ventuari, a tributary of the upper
Rio
Orinoco, and the mainstem upper Orinoco above Puerto Ayacucho to the
Rio
Casiquiare in Amazonas, Venezuela (Fig. 5).
Ecology:
Hypostomus rhantos
was collected in loricariid assemblages with an average of 7.2 loricariid species per site (n=16 sites). Habitats from which
H. rhantos
were 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 rhantos
were analyzed in Armbruster (2004a) but were incorrectly referred to as
H. micromaculatus
.
Hypostomus rhantos
was 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. cochliodon
subgroup,
Hypostomus plecostomus
, the potentially undescribed
Hypostomus
similar to
H. robinii
from 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
Hypostomus
are poorly resolved and need much further study.
Hypostomus rhantos
is most similar in coloration to
H. micromaculatus
from Suriname. In addition to coloration,
H. rhantos
appears 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. rhantos
and almost absent in
H. micromaculatus
) and the amount of abdominal plating (fully plated in
H. rhantos
and 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.