Taxonomic revision of Spectracanthicus Nijssen & Isbrücker ( Loricariidae : Hypostominae : Ancistrini ) , with description of three new species

A taxonomic review of Spectracanthicus Nijssen & Isbrücker, including Oligancistrus Rapp Py-Daniel, following a phylogenetic study, is presented. Additionally to S. punctatissimus (Steindachner) and S. murinus Nijssen & Isbrücker, three new species are recognized based on the examination of 159 specimens: S. immaculatus n. sp. from rio Tapajós basin, differs from its congeners by its color pattern consisting of a dark gray body, with no dots or spots, and by having very slender teeth; Spectracanthicus tocantinensis n. sp., from the rio Tocantins drainage is distinguished by the color pattern consisting of dark brown or black body with small, yellowish dots (except in S. punctatissimus), presence of thick teeth, infraorbital 4 forming most of the posterior edge of the orbit and the large basipterigium fenestrae; and Spectracanthicus zuanoni n. sp., from the rio Xingu basin is diagnosed by its color pattern consisting of large, white spots and by the larger orbital diameter. Other characters based on osteological features are also usefull to distinguish the species. A key to the species of the genus and a brief discussion of their threats and conservation are also provided.


Introduction
The Loricariidae is the largest family within Siluriformes and includes more than 750 species, which represent about 25% of the diversity of catfishes (Reis et al., 2003;Ferraris, 2007).The family is widely distributed in the Neotropical region, from southeastern Costa Rica to northeastern Argentina (Isbrücker, 1980) and can be found in a large variety of freshwater environments.Loricariidae species are usually divided into historically unstable subfamilies, most of them apparently monophyletic (Loricariinae, Hypoptopomatinae, Lithogeninae, and Delturinae; Reis et al., 2006).However, the monophyly and composition of Hypostominae and Ancistrinae are still under scrutiny (Reis et al., 2003;Ferraris, 2007).
Spectracanthicus Nijssen & Isbrücker was established as a monotypic genus to include S. murinus from the rio Tapajós basin.Recently, the genus Oligancistrus Rapp Py-Daniel was proposed as a junior synonym of Spectracanthicus by Armbruster (2004) based in the argument of an unnecessary recognition of two monotypic closely related genera.Chamon (2012) further corroborates such hypothesis in a phylogenetic study of the Acanthicus group, which resulted in Oligancistrus as paraphyletic, given that Oligancistrus punctatissimus as well as the new species fitting the diagnosis of that genus, represented successive sister-groups of Spectracanthicus murinus further justifying the synonymy proposed by Armbruster (2004).The genus is originally distinguished from other Ancistrini by the presence of an expansion of the dorsalfin membrane connecting it to the adipose-fin spine and the presence of up to 25 teeth on premaxilla.Herein, a taxonomic revision of Spectracanthicus is presented.In addition, a brief phylogenetic discussion on the relationships and a key to the species of the genus are provided.

Spectracanthicus murinus
Diagnosis.Spectracanthicus murinus is distinguished from its congeners by the non-eversible cheek plate (vs.check plate eversible); the triangular-shaped opercle (vs.bar shaped); presence of three branched anal-fin rays (vs.four); pale (yellow in life) bars on tip of dorsal and caudal fins (vs.bars absent; except in some specimens of S. punctatissimus); the frontal forming a small portion of orbit border (less than ¼ vs. frontal forming a large portion of orbit border); the anterior process of the pterotic-supracleithrum forming the posterior margin of orbit (vs.pterotic-supracleithrum not forming posterior margin of orbit in S. immaculatus or contacting only a small area of orbit posterior margin in remaining species).Spectracanthicus Description.Morphometric and meristic data are summarized in Table 1.Dorsal profile of body slightly convex from tip of snout to vertical through dorsal-fin origin; concave, nearly straight from that point to caudal-fin origin.Ventral profile of body straight from snout tip to caudal-fin origin.Ventral surface from tip of snout to urogenital papillae lacking plates, except for few small plates at pectoral-and pelvic-fin origins.Greatest body width at pectoral girdle.Head and trunk lacking keels or ridges.Greatest body depth at dorsal-fin origin; lowest at caudal peduncle.Head wide, pointed anteriorlly; snout and cheek completely covered by numerous small plates, except for small naked area on tip of snout.Snout slightly pointed in dorsal view.Nasal L-shaped, elongate.Frontal short with a slight contact with nares anteriorly and orbit posteriorly Anterior margin of frontal short, reaching posterior margin, or half length, of nare.Parieto-supraoccipital short with posterior edge narrow, lacking crest.Sphenotic short, contacting IO6; lacking conspicuous odontodes.Orbit moderate in size (14.1-33.4% HL) placed dorsolaterally.Iris with small dorsal flap over pupil.Pteroticsupracleithrum short with few fenestrae; anterior process forming most posterior margin of orbit.Posterior area of pterotic-supracleithrum with one median sized plate.
Mouth moderate in size, nearly as long as wide.Lips large, covered with papillae; size of papillae decreasing towards posterior margin of lower lip; central buccal papilla absent.Upper lip folded over itself.Maxillary barbel short; base of barbel united to lips, with free tip.Lower lip not reaching anterior margin of coracoid.Medial end of premaxillary teeth series curved inwards.Premaxillae (Fig. 3) and dentary narrow and elongate.Dentary strongly curved inwards.Teeth slightly thick, well developed, with long crown and large lateral cusp; its distal edge slightly curved inward.Three to four pairs of well developed predorsal plates.Cheek plates not eversible; without associated hypertrophied odontodes (Fig. 4).
Body covered by five longitudinal series of plates supporting odontodes.Keels absent.Three to four predorsal plates; small azygous predorsal plates sometimes present between predorsal plates.Eight furcate neural spines supporting dorsal fin.
Description.Morphometric and meristic data summarized in Table 2. Dorsal profile of body slightly convex from tip of snout to vertical through dorsal-fin origin; concave nearly straight from that point to dorsal-fin origin to caudal-fin origin.Ventral profile straight from snout tip to origin of caudal fin.Ventral surface from tip of snout to urogenital papillae lacking plates, except for few small plates at pectoral and pelvic-fins origin.Greatest body width at pectoral girdle.Head and trunk     anterior margin of coracoid.Medial end of premaxillary teeth series curved inwards.Premaxillae and dentaries narrow and elongate.Dentaries strongly curved inwards.Teeth medium in size, well developed, with long crown and large lateral cusp, its distal edge slightly curved.Eversible cheek plates with associated hypertrophied odontodes and disposed as unique block connected to opercle, that can be everted to approximately 90 o from head by opercle movements (Fig. 8).Body covered by five longitudinal series of plates supporting odontodes.Keels absent.Three to four predorsal plates; some small azygous predorsal plates sometimes present.Eight neural bifid spines supporting dorsal fin.Dorsal-fin rays i,7, located posterior to neural spines of vertebral centra 6-17.Base of dorsal-fin base very long, its length equivalent to 12 dorsal plates, reaching pre-adipose plate and connected to adipose fin by thick membrane.Dorsal-fin spinelet V-shaped with lock mechanism.Pectoral and pelvic fins well developed, medial portion much expanded relative to base; distal margins rounded.Pectoral-fin rays I,6; unbranched ray covered with conspicuous odontodes.Tip of adpressed pectoral fin almost reaching vertical through medial, unbranched, pelvic-fin ray.Pelvic-fin rays i,5; pelvic-fin spine reaching vertical through anal-fin base when adpressed.Anal-fin rays i,4 located posterior to hemal spines of vertebral centra 14-17.Caudal-fin rays i,14,i, truncated; supracaudal plates.Five to six procurrent caudal-fin rays.Caudal peduncle strongly deep in lateral view.Total vertebrae 26, precaudal 8-12.Sixth rib strongly thickened, remaining ribs slender.Infraorbital with 7-8 pores.Infraorbial 4 with little contact with orbit posterior margin.Infraorbital 6 forming only postero-vental part of orbit.Lateral line pores restricted to hypural plate.
Color in alcohol.Dorsal surface of body dark brown to dark gray with numerous, yellow, variable sized dots, from tiny to small, regularly distributed along head, trunk and fins.Density of dots on body variable; pattern apparently independent of body size, however, juvenile specimens usually have fewer dots than adults.
Pale bars on distal tips of dorsal and caudal fins usually present.Irregular white stains rarely observed (called "mutants" specimens by local fishermen).Ventral surface ochre, lacking dots.

Geographic distribution.
The species is spread along the rio Xingu basin, near Altamira, Pará, Brazil.It occurs in sympatry with Spectracanthicus zuanoni (Fig. 5).Fishery and economical importance.Spectracanthicus punctatissimus is an important resource of ornamental fish.It is also recognized as L016 and L030 (L-number; Schraml & Schafer, 2004) by aquarists and ornamental fishermen.It is usually captured by diving with aid of a compressor, a typical way to capture ornamental fishes in Altamira, Pará.

Remarks.
There is a great variation on premaxilla and dentary teeth counts (3-25 and 8-48, respectively), which seems to be consequently related to a variability of the premaxilla and dentary length/width.Exhaustive examination of specimens were unable to correlate that variation with sexual dimorphism, ontogeny, color pattern or geographical distribution along the river.Regardless of the variation of color and teeth counts, we prefer to sustain S. punctatissimus as single species, since these characteristics are overlapped within known populations.Distal edge of teeth slightly curved inward.Eversible cheek plates with associated hypertrophied odontodes and disposed as unique block connected to opercle, that can be everted to approximately 90 o from head by opercle movements (Fig. 12).

Material
Body covered by five longitudinal series of plates supporting odontodes.Keels absent.Three to four predorsal plates; some small azygous predorsal plates sometimes present.Eight neural bifid spines supporting dorsal fin.Dorsal-fin rays i,7, located posterior to neural spines of vertebral centra 7-17.Dorsal-fin base very long, its length equivalent to 12 dorsal plates, reaching pre-adipose plate and connected to adipose fin by thick membrane.Dorsal-fin spinelet V-shaped with locking mechanism.Pectoral and pelvic fins well developed, medial portion much expanded relative to base; distal margins rounded.Pectoral-fin rays I,6; unbranched ray covered with conspicuous odontodes.Tip of adpressed pectoral fin almost reaching vertical through medial, unbranched, pelvic-fin ray.Pelvic-fin rays i,5; pelvic-fin spine reaching vertical through anal-fin base when adpressed.Anal-fin rays i,4 located posterior to hemal spines of vertebral centra 14-17.Caudal-fin rays i,14,i, truncated; supracaudal plates.Five to six procurrent caudal-fin rays.Caudal peduncle strongly deep in lateral view.Total vertebrae 26, precaudal 8-12.Sixth rib strongly thickened, remaining ribs slender.Infraorbital with 7-8 pores.Infraorbital 4 with little contact with orbit by posterior margin.Infraorbital 6 forming only postero-vental part of orbit.Lateral line pores restrict to hypural plate.
Color in alchool.Ground color evenly dark gray to dark brown without dots or spots.Ventral surface ochre to light brown without dots.Dorsal surface of body of live specimens gray.
Etymology.The specific epithet "immaculatus" derives from Latin, meaning unspotted or unstained, in allusion to the coloration pattern of the species, lacking dots or spots.An adjective.Head wide, convex dorsally; snout and cheeks completely covered by numerous small plates, except for small naked area on tip of snout.Snout slightly rounded in dorsal profile.Nasal elongated, L-shaped.Frontal short with a slight contact with nares anteriorly and orbit posteriorly.Anterior margin of frontal short, reaching posterior margin or half of length of nare.Parieto-supraoccipital short with posterior edge narrow, lacking crest.Sphenotic short, without contact with slender in relation to its congeners.The number of premaxillary teeth (less than 25 teeth on each) is directly related to the bone shape, which is narrow and elongated.Decrease of teeth counts and narrowing of the premaxillare seems to be a derived condition within the Hypostominae, since the basal species usually have larger and shorter premaxillae supporting more than 25 teeth.Shape of teeth can vary greatly among the Hypostominae and even within Spectracanthicus.In some species of the Hypostomus unicolor group, males in reproductive period acquire elongated, Fishery and economical importance.Spectracanthicus immaculatus is an important resource of ornamental fish.It is also recognized by local fishermen and aquarists as "naná" or "L363" (L-number; Schraml & Schafer, 2004;Werner et al. 2005).Like S. murinus, it is also captured by diving with help of a compressor, a typical way of capturing ornamental fishes in Itaituba and Santarém regions (Sousa & Birindelli, 2009).
Remarks.In Spectracanthicus immaculatus, teeth are extremely Description.Morphometric and meristic data are summarized in Table 4. Dorsal profile of body slightly convex from tip of snout to vertical through of dorsal fin; concave, nearly straight from that point to caudal-fin origin.Ventral profile straight from snout tip to origin of caudal fin.Ventral surface from tip of snout to urogenital papillae lacking plates, except for few small plates at pectoral and pelvic-fin origins.Body deep and robust even at caudal peduncle.Head and trunk lacking keels or ridges.Greatest body depth at dorsal-fin origin; lowest at caudal peduncle.
Head wide, convex dorsally; snout and cheeks completely covered by numerous small plates, except for small naked area on tip of snout.Snout slightly rounded in dorsal profile.Nasal elongated, L-shaped.Frontal short with a slight contact with nares anteriorly and orbit posteriorly.Anterior margin of frontal short, reaching posterior margin or half of length of nare.Parieto-supraoccipital short with posterior edge narrow, lacking crest.Sphenotic short, without contact with IO6, lacking conspicuous odontodes.Orbit moderate in size (15.4-20.3%HL), placed dorsolaterally in head.Iris with small dorsal flap over pupil.Pterotic-supracleithrum short with few fenestrae; anterior process forming most posterior margin of orbit.Posterior area of pterotic-supracleithrum with one plate.
Mouth moderate in size, nearly as long as wide.Lips large, covered with papillae; size of papillae decreasing towards posterior margin of lower lip; central buccal papilla absent.Upper lip folded over itself.Maxillary barbel short; base of barbel united to lips with free tip.Lower lip not reaching anterior margin of coracoid.Medial end of premaxillary teeth series almost straight.Premaxillae and dentaries narrow and elongate.Dentaries strongly curved inwards.Teeth medium in size, well developed, slender, with long crown and large lateral cusp.Distal edge of teeth slightly curved inward inward.Eversible cheek plates with associated hypertrophied odontodes and disposed as unique block connected to opercle, that can be everted to approximately 90 o from head by opercle movements (Fig. 12).
Body covered by five longitudinal series of plates supporting odontodes.Keels absent.Three to four predorsal plates; some small azygous predorsal plates sometimes present.Eight neural bifid spines supporting dorsal fin.Dorsal-fin rays i,7, located posterior to neural spines of vertebral centra 6-17.Dorsal-fin base very long, its length equivalent to 12 dorsal plates, reaching pre-adipose plate and connected to adipose fin by thick membrane.Dorsal-fin spinelet V-shaped with locking mechanism.Pectoral and pelvic fins well developed, medial portion much expanded relative to its base; distal margins rounded.Pectoral-fin rays I,6; unbranched ray covered with slender and unicuspid teeth, which returns to its normal shape, shorter, thicker and with a small cuspid, after this period (Armbruster, 1997).However, this condition in S. immaculatus is not related to sexual dimorphism.On the other hand, in S. murinus the teeth are very short and thick, while the teeth have a regular size and density in the remaining species.

Spectracanthicus tocantinensis, new species
Fig. 13 Holotype.MZUSP 110989, 49.5  Diagnosis.Spectracanthicus tocantinensis can be diagnosed from its congeners by the infraorbital 4 forming most of the posterior edge of the orbit (vs.IO4 forming a minute portion of orbital rim) and by the large basipterigium fenestrae (vs.medium or small-sized basipterigium fenestrae) (Fig. 11).It can be further distinguished from S. immaculatus and S. zuanoni by its color pattern, consisting of small, yellowish dots, and by the presence of thick teeth (vs.dots lacking in S. immaculatus and large, white spots in S. zuanoni; and slender teeth).It is additionally distinguished from S. zuanoni by the lower number of dentary teeth (8-16 vs.19-43).Spectracanthicus tocantinensis differs from S. murinus by the presence of a bar-shaped, eversible opercle with conspicuous odontodes (vs.triangle shaped opercle not eversible, without conspicuous odontodes) and by the presence of four unbranched anal-fin Color in alcohol.Dorsal surface of body and fins dark brown with small to median-sized yellowish dots regularly distributed along head, trunk and fins.Body dots sparced and usually fewer in juveniles.Ventral surface light tan without dots.
Etymology.The specific epithet "tocantinensis" is in allusion to the type locality of the new species, the rio Tocantins.An adjective.
conspicuous odontodes.Tip of adpressed pectoral fin almost reaching vertical through medial, unbranched, pelvic-fin ray.Pelvic-fin rays i,5; pelvic-fin spine reaching vertical through anal-fin base when adpressed.Anal-fin rays i,4 located posterior to hemal spines of vertebral centra 14-17.Caudalfin rays i,14,i, truncated; seven supracaudal plates.Description.Morphometric and meristic data summarized in Table 5. Dorsal profile of body slightly convex from tip of snout to vertical through of dorsal fin; concave, nearly straight vs. up to 25.7% in S. punctatissimus, 20.3% in S. tocantinensis, 16.2% in S. immaculatus).It further differs from S. murinus by the rounded dorsal view of the snout, the bar-shaped, eversible opercle with conspicuous odontodes, and the presence of four unbranched anal-fin rays (vs.snout slightly pointed; opercle triangle-shaped, not eversible, lacking conspicuous odontodes; three anal-fin unbranched rays).From S. tocantinensis it differs everted to approximately 90 o from head by opercle movements.Body covered by five longitudinal series of plates supporting odontodes.Keels absent.Three to four predorsal plates; some small azygous predorsal plates sometimes present.Eight neural bifid spines supporting dorsal fin.Dorsalfin rays i,7, located posterior to neural spines of vertebral centra 6-17.Dorsal-fin base very long, its length equivalent to 12 dorsal plates, reaching pre-adipose plate and connected to adipose fin by thick membrane.Dorsal-fin spinelet V-shaped with lock mechanism.Pectoral and pelvic fins well developed, medial portion much expanded relative to base; distal margins rounded.Pectoral-fin rays i,6; unbranched ray covered with conspicuous odontodes.Tip of adpressed pectoral fin almost reaching vertical through medial, unbranched, pelvic-fin ray.Pelvic-fin rays i,5; pelvic-fin spine reaching vertical through anal-fin base when adpressed.Anal-fin rays i,4 located posterior to hemal spines of vertebral centra 15-17.Caudal-fin rays i,14,i, truncated; supracaudal plates.Five to six procurrent caudal-fin rays.Caudal peduncle strongly deep in lateral view.Total vertebrae 26, precaudal 8-12.Sixth rib strongly thickened, remaining ribs slender.Infraorbital with 7-8 pores.Infraorbital 4 with little contact with orbit by posterior margin.Infraorbital 6 formed just postero-vental part of orbit.Lateral line pores restrict to hypural plate.
Color in alcohol.Dorsal surface of body and fins evenly brown covered by large white spots.Spots more frequent and conspicuous in dorsal and caudal fins than in pectoral, pelvic and anal fins.Some specimens, especially juveniles, can present overlapped spots forming smudges.Head poorly spotted, some individuals can present vermicular bands near snout region.Abdomen region ochre without spots.
from that point to caudal-fin origin.Ventral profile straight from snout tip to origin of caudal fin.Ventral surface from tip of snout to urogenital papillae lacking plates, except for few small plates at pectoral and pelvic-fins origins.Body deep and robust even at caudal peduncle.Head and trunk lacking keels or ridges.Greatest body depth at dorsal-fin origin; lowest at caudal peduncle.
Head wide, convex dorsally; snout and cheeks completely covered by numerous small plates, except for small naked area on tip of snout.Snout slightly rounded in dorsal profile.Nasal elongated, L-shaped.Frontal short with a slight contact with nares anteriorly and orbit posteriorly.Anterior margin of frontal short, reaching posterior margin or half of length of nare.Parieto-supraoccipital short with posterior edge narrow, lacking crest.Sphenotic short, without contact with IO6, lacking conspicuous odontodes.Orbit enlarged (16.6-29.2%HL), placed dorsolaterally in head.Iris with small dorsal flap over pupil.Pterotic-supracleithrum short with few fenestrae; anterior process forming most posterior margin of orbit.Posterior area of pterotic-supracleithrum with one plate.
Mouth moderate in size, nearly as long as wide.Lips large, covered with papillae; size of papillae decreasing towards posterior margin of lower lip; central buccal papilla absent.Upper lip folded over itself.Maxillary barbel short; base of barbel united to lips with free tip.Lower lip not reaching anterior margin of coracoid.Medial end of premaxillary teeth series almost straight.Premaxillae and dentaries narrow and elongate.Dentaries strongly curved inwards.Teeth medium size, well developed, slender, with long crown and large lateral cusp.Distal edge of teeth slightly curved inward.Eversible cheek plates with associated hypertrophied odontodes and disposed as unique block connected to opercle, that can be L354 (L-number; Schraml & Schafer, 2004) by aquarists and local fishermen.As in Itaituba and Santarém, at rio Tapajós, Altamira is also known for its ornamental fishery activities.
Ecological notes.Spectracanthicus zuanoni is a nocturnal species that feeds on algae and other food items off periphyton by grazing over rock bottom.According to Zuanon (1999) and Rapp Py-Daniel & Zuanon (2005), Spectracanthicus zuanoni is a moderate reophilic species that is found in rock-bottom areas subjected to backwater and strong currents.Specimens were found individually or in groups of three, under shelter boulders (adults) and spaces beneath rocks (juveniles), up to 2m deep.The juveniles share the shelters with other loricariids such as Ancistrus sp., A. ranunculus, Baryancistrus xanthellus, Spectracanthicus punctatissimus, Hopliancistrus tricornis, Parancistrus nudiventris, Peckoltia vittata, and Pseudancistrus aff.barbatus.Isbrücker (1980) and Schaefer (1986Schaefer ( , 1987) ) diagnosed the Ancistrini (sensu Armbruster, 2004) according to the presence of evertible cheek plate, usually bearing hypertrophied odontodes, a feature also present in Pterygoplichthyini.However, according to Armbruster (2004), the Pterygoplichthyini are distinguished from Ancistrini the by the presence of a connective tissue covering the stomach.Characters like the eversible cheek plates and presence of four umbranched anal-fin rays, present in most of Ancistrini taxa, are both absent in Spectracanthicus murinus, due to reversion.

Discussion
The most evident character that distinguishes Spectracanthicus from other loricariids is the membranous connection between dorsal and adipose fins.Although such feature is present in other loricariid genera (i.e., Baryancistrus and Parancistrus), other characters readily distinguish these from Spectracanthicus: the mesial wall of the metapterygoid being much taller than the lateral; the spoon-shaped anterior process of the metapterygoid; and the presence of a deep pouch on the lateral ethmoid (Armbruster, 2004).Chamon (2012) proposed four additional synapomorphies supporting the monophyly of the genus: the presence of a cartilaginous second basibranchial; the pointed distal margin of the Weberian apparatus transverse process; the short hypurapophysis; and a great hiatus between the inferior hypural lobe and last hemal spine.All synapomorphies proposed in the aforementioned studies were observed in all species of Spectracanthicus recognized herein.In addition to these features, all species of Spectracanthicus (except S. immaculatus) share the contact between sphenotic and IO6; the elongate anterior metapterygoid process; and the enlogate lateropterygium, not surpassing the vertical through the anterolateral process of the basipterygia.Geographic distribution.Spectracanthicus zuanoni is known from the rio Xingu basin, near Altamira and Belo Monte, Pará State, Brazil (Fig. 5).
Etymology.The specific epithet is in honor to Jansen Zuanon (INPA) due to his contribution to the knowledge of Neotropical Ichthyology.Jansen Zuanon was also the first ichthyologist who collected and identified this species as a new one.
Fishery and economical importance.Spectracanthicus zuanoni is also recognized as "acari bola branca", L020 and direct decrease of stocks by fishing.Among fish species that are endangered, only a small number of these have commercial interest as ornamental.In relation to rio Xingu ichthyofauna, it is forbidden to capture some species for ornamental purpose when the decline of these populations is remarkable, for instance Hypancistrus zebra that was considered endangered according to Normative Instruction MMA 05/2004 of the Brazilian Goverment.
For the majority of the ornamental loricariid fish species from Amazon basin, the most imminent danger is the construction of dams.In the case of rio Xingu, the project of Belo Monte Dam includes a major barrage located 40 km downstream from the city of Altamira (Volta Grande region), forming the reservoir Xingu.As a consequence, areas of the River with current water will give rise to a large lake of standing water.Fish that live in this type of environment are not adapted to slow flowing waters or lenthic environments which are low in oxygen.Furthermore, dozens fish species that exist only at the Volta Grande may disappear, because while the region is a lotic environment, it will not keep sufficient flow to maintain such species (L.M. Sousa, pers. comm.).The Xingu Spectracanthicus species are widely distributed along the rio Xingu and have several subpopulations.In this case, some of these subpopulations may be greatly reduced or even become locally extinct, but the species as a whole will probably not be extinguished, since it will remain in little or non-impacted areas where the water reaming is current.The same scenario may be expected to occur with S. zuanoni, even though its subpopulations are smaller than S. puctatissimus.
The construction of a complex of five dams at rio Tapajós and rio Jamaxim is already scheduled: São Luiz do Tapajós and Jatobá, on rio Tapajós; and Cachoeira dos Patos, Jamanxim and Cachoeira do Caí on the rio Jamanxim (Fernandes et al., 2010).Regarding S. murinus, which has relatively high abundance in the region of Itaituba, such impacts can directly affect the population due to habitat loss.However, as the species has a wide distribution along the rio Tapajós, some subpopulations will probably not be impacted by habitat loss, being restricted to regions where the environment remains lotic.Concerning S. immaculatus, although it has little representation in scientific collections, it is abundant at the region and this fact can be explaned by the lack of specific capture effort.
In rio Tocantins, the Tucuruí Dam construction was completed in 1981 and, as in others dams, the change from a lotic to a lenthic habitat was considered a major environmental interference, because of the effects to the aquatic ecosystem in general.The formation of the lake resulted on major changes in the fish fauna of the rio Tocantins, promoted by disruption of migratory routes and the disappearance of some species (Mérona et al., 2010).Although Spectracanthicus tocantinensis is mentioned in several web sites of ornamental fish as Spectracanthicus sp.
Although species of Spectracanthicus can be distinguished from each other based on morphological features, they can be promptly diagnosed from each other by their color pattern.In fact, the color pattern is a very useful source of characters allowing the identification of loricariid fishes, but some intraspecific variation is often common, (as with other characters sources) and must be considered.Such plasticity has rendered fishermen and aquarists to recognize specimens, falling into that variation, as different species.Specimens of Spectracanthicus puntatissimus, for instance, are recognized under different L numbers (Schraml & Schaefer, 2004) according to the amount and size of the spots, and its occurrence along the rio Xingu: L016 (specimens from Altamira); L030 (specimens from Belo Monte); and L353 (specimens from the rio Iriri).Some other characters referring to the shape of the snout and teeth number are also employed to justify the recognition of these specimens as different species, but these differences are not constant in each subpopulation.A similar scenario can be observed for S. zuanoni, with different subpopulations along the rio Iriri (L354).It is not uncommon, thought, to find further variations on the color pattern of all aforementioned subpopulations, which hinders the recognition of populations as independent species within the genus.
All species studied in the present contribution have commercial interest as ornamental fish.The ornamental fish exploration has been a common practice in the rio Xingu and rio Tapajós regions for the last 30 years.These activities have become economically profitable within some communities of these regions and, in many cases, constitute the entire source of income for several families.According to Rapp Py-Daniel & Zuanon (2005) and Camargo et al. (2011) this practice has become most frequent in Altamira since end of the1980's, when gold prospectors that lost their jobs began to collect loricariids fish.The capture of attractive species for the ornamental fish trade was possible with the adaptation of old techniques employed in gold prospect at great depths (up to 15 meters), such as the use of air compressors, diving masks and lanterns.From this period several loricariid species have become known worldwide.Presently, the Xingu and Tapajós drainages together constitute one of the largest sources of ornamental fish of the family Loricariidae.In the rio Xingu the ornamental fishery activities is very intense, especially at Altamira, Senador José Porfírio, Belo Monte, Vitória do Xingu, and Porto de Moz (Camargo et al., 2011;L. M. Sousa, pers. comm.).On the other hand, at rio Tapajós the ornamental fish activities are concentrated at Santarém and Itaituba (Sousa & Birindelli, 2009).In the rio Tocantins, the ornamental fishery is also a common practice concentrated at Marabá region.
According to Andrews (1990) two of the major ways in which the market for ornamental fish can affect natural populations are the introduction of exotic species and the L086, LDA014, their representation in scientific collections is relatively low and the last samples were collected in 1984.This decrease of sampling at Tucuruí and Cametá regions may be related to deficient collection effort for ornamental fisheries.Furthermore, the species seems to occur in abundance at Marabá region, where it is commercialized for several regions in the country (H.Anatole, pers. comm.)Given the current scenario of investment in hydropower energy in the Brazilian Amazon, it can be stated that fish species that are directly dependent on rapid waters with high oxygen content are in threat.Obviously, species with a wide distribution along certains Amazonian rivers or in several drainages will be safe.On the other hand, species that are naturally rare, usually restricted to specific habitats and localities, may suffer a drastic population decline and even become extinct.

Table 1 .
Morphometric and meristic data of Spectracanthicus murinus.Values are given as percents of standard length or head length.SD = standard deviation.

Table 2 .
Morphometric and meristic data of Spectracanthicus punctatissimus.Values are given as percents of standard length or head length.SD = standard deviation.
M. Sousa & J. L. Birindelli.Paratypes.MZUSP 92617, 11, 38.2-82.2mmSL(1 c&s, 81.2 mm SL), Brazil, Pará, rio Tapajós near Itaituba and Pimental, approximately 4°16'46.56"S55°59'5.77"W,8Nov 2006, L. M. Sousa & J. L. Birindelli.Diagnosis.Spectracanthicus immaculatus can be distinguished from all congeners by its color pattern consisting of a dark gray body, without dots or spots, and by having very slender teeth (vs.with small to mid-sized yellowish dots in S. punctatissimus, S. murinus, and S. tocantinensis; and large white spots in S. zuanoni).to vertical through of dorsal fin; concave, nearly straight from that point to caudal-fin origin.Ventral profile straight from snout tip to origin of caudal fin.Ventral surface from tip of snout to urogenital papillae lacking plates, except for few small plates at pectoral and pelvic-fins origins.Body deep and robust even at caudal peduncle.Head and trunk lacking keels or ridges.Greatest body depth at dorsal-fin origin; lowest at caudal peduncle.
IO6, lacking conspicuous odontodes.Orbit moderate in size (13.6-16.2%HL),placed dorsolaterally in head.Iris with small dorsal flap over pupil.Pterotic-supracleithrum short with few fenestrae; anterior process forming most posterior margin of orbit.Posterior area of pterotic-supracleithrum with one plate.Mouth moderate in size, nearly as long as wide.Lips large, covered with papillae; size of papillae decreasing towards posterior margin of lower lip; central buccal papilla absent.Upper lip folded over itself.Maxillary barbel short; base of barbel united to lips with free tip.Lower lip not reaching anterior margin of coracoid.Medial end of premaxillary teeth series almost straight.Premaxillae and dentaries narrow and elongate.Dentaries strongly curved inwards.Teeth medium in size, well developed, slender, with long crown and large lateral cusp.

Table 3 .
Morphometric and meristic data of Spectracanthicus immaculatus.Values are given as percents of standard length or head length.SD = standard deviation.

Table 4 .
Morphometric and meristic data of Spectracanthicus tocantinensis.Values are given as percents of standard length or head length.SD = standard deviation.

Table 5 .
Morphometric and meristic data of Spectracanthicus zuanoni.Values are given as percents of standard length or head length.SD = standard deviation.