Paralithoxus mocidade

Rapp-Py-Daniel, Lúcia, Oliveira, Andreza S., Bastos, Douglas A., Ito, Priscila Madoka M., Zuanon, Jansen & Briglia-Ferreira, Syl, 2019, A new species of Paralithoxus (Siluriformes: Loricariidae: Ancistrini) from the highlands of Serra da Mocidade, Roraima State, Brazilian Amazon, Neotropical Ichthyology 17 (4), pp. 1-13: 2-10

publication ID 10.1590/1982-0224-20190041


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scientific name

Paralithoxus mocidade

new species

Paralithoxus mocidade  , new species

( Figs. 1–4View FigView FigView FigView Fig, 8–9View FigView Fig; Tab. 1)

Holotype. INPA 54745View Materials, 50.5 mm SL, Brazil, Roraima State, Caracaraí Municipality, stream tributary to Ajarani River, Branco River basin, upstream of large waterfall, Serra da Mocidade , 01°42’52.70”N 61°48’17.64”W, 29 Jan 2016, D. A. Bastos, J. Zuanon, P. M. M. Ito and S. R. Briglia-Ferreira.GoogleMaps 

Paratypes. All from Brazil, Roraima State, Caracaraí Municipality. INPA 52422View Materials, 17View Materials, 20.6–47.2 mm SL (1 c&s, 47.2 mm SL), stream tributary to Ajarani River , Branco River basin, downstream of large waterfall, Serra da Mocidade , 01°42’50.26”N 61°48’18.65”W, 29 Jan 2016, D. A. Bastos, J. Zuanon, P. M. M. Ito and S. R. Briglia-Ferreira  . INPA 52424View Materials, 17View Materials, 15.0– 54.7 mm SL (1 c&s, 54.7 mm SL, 16 alc.)  , MNRJ 51531View Materials, 2View Materials, 23.0–26.0 mm SL  , MPEG 38600View Materials, 2View Materials, 27.0–30.0 mm SL  , MZUSP 125192View Materials, 2View Materials, 25.0–28.0 mm SL  , ANSP 206987View Materials, 2View Materials, 26.0–33.0 mm SL, all collected with holotypeGoogleMaps  .

Non-types. INPA 59028View Materials, 14View Materials, 13.8View Materials –19.0 mm SL, collected with the holotype  .

Diagnosis. Paralithoxus mocidade  differs from all congeners, except P. bovallii  , by having truncate teeth (vs. pointed to acute teeth). It differs from P. bovallii  by the truncate caudal fin (vs. caudal-fin forked). Adittionaly, P. mocidade  differs from P. pallidimaculatus  and P. surinamensis  by the presence of adipose fin (vs. absence). It differs from P. planquettei  and P. stocki  by having a more depressed and elongate body: body depth 10–13.9% of SL (vs. 15.3–16.8% in P. planquettei  and 15.7–16.9% in P. stocki  ), and body width at dorsal fin 19.3–23.0% of SL (vs. 23.3–26.5% in P. planquettei  and 24.2–25.1% in P. stocki  ); from P. raso  by the larger interorbital distance, 28.8–33 % of HL (vs. 27.1–28.6%) and larger dentaries 5.9–9.3% of HL (vs. 4.4–5.3%); from P. stocki  and P. boujardi  by the caudal fin conspicuously mottled, with alternating dark and light blotches (vs. caudal fin dark with clear distal band); and from P. jariensis  by having seven to eight plates between dorsal and adipose fins (vs. four) and 24–26 lateral median plates (vs. 23–24).

Description. Morphometrics and counts in Tab. 1. Small species of Hypostominae  , largest specimen examined 54.7 mm SL. Body very depressed and short. In lateral view, dorsal profile slightly convex from snout to dorsal-fin origin, descending almost straight to dorsal procurrent rays of caudal fin. Greatest body width at pectoral-fin origin; body of similar width between posterior base of pectoral fin and origin of pelvic fin, slightly narrowing from this point towards caudal-fin base. Caudal peduncle trapezoid in cross section. Ventral profile straight from snout to caudal-fin origin.

Head short, depressed and rounded in dorsal view. Snout tip hispid, completely covered by plates. Eye moderately small, dorsally positioned; interorbital region narrow and flat. Cheek plates with up to 20 hypertrophied odontodes. Parieto-supraoccipital large, hexagonal, with process posteriorly bordered by four plates. Predorsal area with three pairs of plates, misplaced in some specimens. Nuchal plate half-moon shaped; small but conspicuous. Seven to eight plates between dorsal and adipose fins. Body almost completely plated; abdomen naked. Body plates arranged in four longitudinal series anteriorly, five series between dorsal and anal fin, and five series on caudal peduncle. All plates covered by odontodes of similar size without carinae, except for two low keels on dorsal plates between dorsal and adipose fins. Ventral series of plates largely smooth, showing large median area without odontodes, except on nuptial male. Seven plates along dorsal- fin base; low preadipose plate. Median series with 24–26 plates not carinate; mid-ventral series not forming prominent keel. First anal-fin pterygiophore exposed, located anterior to anal-fin origin.

Oral disc large, nearly circular. Mouth opening U-shaped, wider than long. Oral internal papillae absent. Maxillary barbel very short, projected anteriorly from oral disc. Lips well developed. Whole border of oral disc covered with large round papillae. Surface of upper and lower lips covered by round papillae not densely packed. Lip surface with shallow notches mostly without papillae distributed at top of premaxillae, around dentaries and on midline on lower lip.

Teeth bicuspid; crown yellow and shaft translucent ( Fig. 4View Fig). Premaxillary teeth much larger than mandibular teeth, arranged in crescent from lateral to mesial. Cusps of premaxillary teeth asymmetrical; larger cusp with straight border, truncate; internal cusp slightly larger. Dentary teeth extremely delicate, bifurcate; cusps small, worn to similar size. Premaxilla with 5–6 and dentary with up to 8 teeth.

Dorsal fin II,7, branched rays decreasing in length posteriorly; last branched ray 1/3 shorter than dorsal-fin spine. Spinelet reduced, locking mechanism not functional and with small area exposed, covered by odontodes. Pectoral fin I,6; distal tip of branched rays not surpassing insertion of pelvic fin when adpressed. Pectoral-fin spine robust, flat and slightly curved inward; spine of equal size of first branched ray. Pectoral-fin spine distal region covered with hypertrophied odontodes, mainly in mature males. Adipose fin low but conspicuous, with small membranous extension posteriorly. Pelvic fin i,5, distal tip of branched rays surpassing insertion of anal fin when adpressed. First pelvic unbranched ray leaf-like, enlarged medially; whole ray flat and covered by odontodes ( Fig. 9bView Fig). Pelvic fin larger than pectoral fin in majority of specimens; ratio between pectoral/ pelvic length with mean of 0.9 and standard deviation of 0.1. Anal fin ii,4, i,4 or i,5, branched rays coequal in length. Caudal fin i,14,i; seven branched rays on each lobe. Caudal fin almost truncate; principal rays mostly coequal in length, with lower rays slightly longer than upper lobe; all rays with small odontodes.

Color in alcohol. Body with dark olive-brown background with irregular light blotches; blotches slightly smaller and more densely organized on head than on trunk and fins. Four inconspicuous large transverse light bars on body: first on dorsal-fin origin, second large bar on posterior dorsalfin base, third anterior to adipose, and fourth on base of caudal fin. Ventral surface of body uniformly cream to beige colored. All fins with checkered pattern, alternating large dark blotches with clear ones.

Color in life. Very similar to preserved coloration, but with overall body color dark olive-brown on dorsum with light green spots on snout and cheek ( Fig. 2View Fig); thin creamy to light green vermiculations over interorbital area and posterior portion of head; clear marks on anterior portion of dorsum becoming larger and more irregular towards caudal peduncle. Ventral side of body uniformly beige.

Sexual dimorphism. Urogenital papilla small, but conspicuous on all specimens. The only externally mature male specimen was dissected and had a more melanic coloration, darkened on body and lips, losing bars and blotches along body and fins; dorsal, pectoral and pelvic fins with branched rays darkened showing light bar close to tip; caudal fin uniformly dark ( Fig. 3View Fig). Male with odontodes on cheek plates and pectoral fin more hypertrophied than on females. Mature male with fins more developed than females: pectoral spine large, strong, bearing more developed odontodes on distal half; first pelvic-fin unbranched ray strong, rounded for entire length and enlarged medially; branched rays on pelvic fin conspicuously longer than unbranched ray. Male has caudal peduncle covered with odontodes, except around anal fin, whereas females and juveniles present caudal peduncle ventrally smooth, without aligned odontodes.

Geographic distribution and habitat. Paralithoxus mocidade  has only been recorded from an unnamed tributary of the Ajarani River, in the area of Serra da Mocidade, Branco River basin, Caracaraí Municipality, Roraima State, Brazil ( Fig. 5View Fig). All specimens were collected up and downstream of a 20-m high waterfall located at approximately 900 m elevation. The Ajarani River at the collection site is a small fast-flowing river (up to 15 m width and 2 m depth, as measured in dry season) with clear water, low temperature (about 21.7 ºC), acidic (pH 5.5), dissolved oxygen (DO) 20.7%, and smooth rocks on the bottom ( Fig. 6View Fig). During the day, juveniles were observed grazing in the open over smooth rocks, and adults were found in narrow cracks or under rock slabs during the night. Juveniles were captured with hand-nets and adults were collected by hand while snorkeling ( Fig. 7View Fig).

Etymology. The specific epithet “mocidade” is in allusion to the type locality, in Serra da Mocidade National Park. A noum in apposition.

Conservation status. Paralithoxus mocidade  is known only from the type locality in a geographically isolated river system, which could generate concerns about its conservation status. However, the inaccessibility of the area and the fact that nearly two-thirds of the area of Serra da Mocidade are formally protected by the Serra da Mocidade National Park and Yanomami Indigenous Territory indicate that there are no imminent threats to the species, which can be categorized as Least Concern (LC) ( IUCN, 2017).

Taxonomic remarks. Paralithoxus mocidade  and P. bovallii  were recorded from the Branco River basin: P. bovallii  from the Takutu (Branco)- Essequibo drainages and P. mocidade  from the Ajarani River. Recent collections in the upper Ireng River by N. K. Lujan and J. W. Armbruster produced new specimens of P. bovallii  from the type-locality, as listed in the redescription of the species by Lujan et al. (2018). Based on this and the original description ( Regan, 1906), we conducted a morphological comparison. Both P. bovallii  and P. mocidade  share a mottled color pattern on body and fins, a similar number of teeth on the jaws (6 to 8), same tooth shape (truncate) ( Fig. 4View Fig), and similar number of plates between dorsal and adipose fins. However, these species differ in eye size, with P. mocidade  having a usually smaller eye, with orbit representing 9–12% (average 11%) vs. 11–19% (average 14.6%) in P. bovallii ( Lujan et al., 2018)  . Based on Regan’s original ratios, the orbital diameter in P. bovallii  was contained 6–7.5 times and interorbital distance 3 times in head length, whereas in P. mocidade  , the orbit is contained 8–10 times and the interorbital 3–3.5 times in head length. Besides, P. bovallii  has the pectoral fin larger than the pelvic whereas in P. mocidade  pectoral and pelvic are equal or the pelvic is slightly larger: pectoral length 23.8–28.7% (mean of 25.5%) in SL in P. mocidade  vs. 6.9–33.0% (26.2%) in P. bovallii  ; pelvic fin 25.5–30.5% (27%) in SL in P. mocidade  vs. 4.9–29% (22.8%) in P. bovallii ( Lujan et al., 2018)  .

The other species described from the Essequibo River drainage is Lithoxus lithoides  (also distributed in other drainages such as the Trombetas River, following Ferreira, 1993). Lithoxus lithoides  is extremely different from Paralithoxus mocidade  having larger eyes, larger pectoral fins (more developed in nuptial males), larger posterior membranous extension of the adipose fin, dorsal fin almost touching the adipose-fin plate, and three series of plates in the caudal peduncle. However, L. lithoides  shares with P. mocidade  the truncate teeth and membranous extension of the adipose (reduced in P. mocidade  when compared to L. lithoides  ). Some paratypes of L. lithoides  were examined and measured, and differences in orbit and caudal peduncle were highly evident between the two species: orbit diameter ranged from 19–21% of head length in L. lithoides  vs. 9.2–12.2% in P. mocidade  ; caudal peduncle depth ranged from 18.8–23% of caudal peduncle length in L. lithoides  vs. 27.6–33.5% in P. mocidade  . Besides, L. lithoides  has the premaxilla much smaller than the dentary, whereas in P. mocidade  the toothed area in both jaws is of similar size, despite difference in the size of the teeth, reinforcing the general dissimilarity between both species.

Species of Paralithoxus  recorded from French Guiana ( P. planquettei  , P. boujardi  and P. stocki  ) share some features distinct from P. mocidade  : teeth with acute cusps and caudal fin with distinct distal light bar vs. teeth truncate and caudal fin with alternating clear and dark blotches in P. mocidade  . Besides, both P. boujardi  and P. stocki  have a larger pectoral fin (pectoral length 3.3–3.7 and 2.8–3.6 times in SL in P. boujardi  and P. stocki  respectively vs. 3.5–4.2 in P. mocidade  ) and shorter caudal peduncle (caudal peduncle length 3–3.25 and 3.5 times in SL in P. boujardi  and P. stocki  respectively vs. 3.6–4.1 in P. mocidade  ). Paralithoxus planquettei  also has a shorter pectoral fin and a deeper caudal peduncle (caudal peduncle depth 9.8–11.75% in SL vs. 7.1–8.4% in P. mocidade  ) and larger mandible (dentary length 2.5–2.8 times in interorbital distance vs. 3.6–4.9 in P. mocidade  ).

Paralithoxus jariensis  and P. raso  were originally distinguished from other Paralithoxus  species by a set of morphological features. Paralithoxus raso  has a peculiar color pattern with light large blotches similar to P. pallidimaculatus ( Silva et al., 2017)  . Both recently described species were recorded for the eastern part of the Amazon, in Pará and Amapá States. Paralithoxus jariensis  is morphometrically very similar to P. mocidade  but shows a reduction in number of plates: four plates between dorsal and adipose fin (vs. 7–8 in P. mocidade  ) and 23–24 lateral median plates (vs. 24–26 in P. mocidade  ). Paralithoxus raso  differs from P. mocidade  mainly by having a larger pectoral- fin spine (27–29% vs. 23–28% in SL in P. mocidade  ), and smaller mandibles (premaxilla 3.3–4% and dentary 4.4–5.3% in head length in P. raso  vs. 6.1–9.9% and 5.9–9.3% in head length in P. mocidade  ). In their original description, the authors also conducted a molecular analysis using sequences of the COI mitochondrial gene for most available species of Paralithoxus  ( P. planquettei  , P. bovallii  , P. pallidimaculatus  , P. boujardi  and P. stocki  ). Paralithoxus jariensis  and P. raso  came out as sister group of P. planquettei  , also from Eastern Guiana (Oyapock River).

Osteological remarks. Armbruster et al. (2018) presented a morphology-based phylogeny for Lithoxini in which synapomorphies were proposed for the genera Lithoxus  , Paralithoxus  and Avalithoxus  as a way to compare their results with the molecular phylogeny presented in Lujan et al. (2018). Most of the synapomorphies listed for Paralithoxus  were confirmed in this study with slight variation in P. mocidade  , such as: first hypobranchial angled at 45° relative to the sagittal plane, maxilla distal end enlarged, and metapterygoid weakly sutured to lateral ethmoid.

Although cited as a synapomorphy for the tribe Lithoxini ( Armbruster et al., 2018), in P. mocidade  the difference in size between the teeth on both mandibles and the distinct shape of the cusps are remarkable ( Fig. 4View Fig): cusps truncate and subequal in size on the premaxilla, and pointed and equally forked on the dentary. As cited above, truncate teeth were also observed in L. lithoides  and P. bovallii  . Lithoxus lithoides  , however, has the mesial cusp of premaxillary teeth almost three times the size of the lateral cusp. Also, the size and enlargement of the distal end of the maxilla deserves attention. In P. mocidade  , the maxilla is well developed, its length more than 50% the length of the palatine, and its distal enlargement is rather pronounced.

The suspensorium in P. mocidade  is similar to that of other Lithoxini and comparable to P. bovallii  , the closest species to P. mocidade  . However, the metapterygoid anterior processes, both the digitiform and the “spoonshaped” ( Armbruster, 2004), are much more enlarged in P. mocidade  than in P. bovallii  and other Lithoxini. The anterior opercular process is also highly enlarged, similar to Avalithoxus jantjae  ( Armbruster et al., 2018, fig. 4-A).

The branchial apparatus in P. mocidade  has a strong hyoid arch, and strongly pointed, villiform teeth on both pharyngeal plates (upper and lower), a condition already registered by Armbruster (2004) for L. lithoides  and P. bovallii  . Paralithoxus mocidade  has only one basibranchial (BB) ( Fig. 8View Fig), ossified and very elongate, almost filling the whole mesial extension of the branchial apparatus; the other basibranchial is a cartilaginous mass connected to the fourth and fifth ceratobranchials. The ordinary siluriform condition is the absence of the first basibranchial ( Arratia, 2003), second (BB2) ossified, and third (BB3) reduced, ossified or not ( Schaefer, 2003). Most loricariids show the generalized siluriform condition. In Paralithoxus mocidade  , the long ossified BB can be explained by the fusion of BB2 and BB3 (very elongate BB) or BB2 lost ( Armbruster, 2004 – for L. lithoides  and P. bovallii  ). This condition was also observed in Exastilithoxus fimbriatus  and other members of Lithoxini ( Armbruster et al., 2018).

Paralithoxus mocidade  has a highly reduced accessory flange of the first ceratobranchial (CB1) ( Fig. 8View Fig) (approximately 1/5 of the ceratobranchial properly). Most Hypostominae  have a well-developed CB1 accessory flange ( Schaefer, 1987; Armbruster, 2004), an extra sheet of thin bone originating on the same point of the ceratobranchial, of similar size and, usually, bearing a row of branchial filaments. Lithogenes  and astroblepids lack this accessory flange. The condition in P. mocidade  has been already cited for P. bovalli  , L. lithoides  , and some other non-hypostomines ( Armbruster, 2004) and it was also observed in Exastilithoxus fimbriatus  .

Finally, the pectoral girdle in P. mocidade  has a conspicuous small hornlike process ( Fig. 9aView Fig) on the anterior surface of the cleithrum. Lithoxus lithoides  and P. bovallii  have a short and dense bony crest at the same point, but in P. mocidade  this crest comes forward as a small, blunt, cylindrical process, inclined towards the lateral sides of the body, with an extra blue-stained tissue coming off its extremity that could be a tendon or a thin cartilage. This condition is quite unusual, and it was not observed in E. fimbriatus  , but it has been observed in one specimen of Hypostomus gymnorhynchus  .

Tab. 1. Morphometrics, meristics and ratios of Paralithoxus mocidade.

  Holotype Mean (N=7) SD Min Max
Standard length 50.49     38.35 55.2
Percents in standard length
Predorsal length 44.6 44.9 2.0 42.0 48.3
Head length 34.5 34.1 1.4 32.1 36.2
Head depth 14.1 12.1 1.0 10.8 14.1
Head width 30.7 30.0 1.6 27.3 32.6
Body depth at dorsal fin origin 13.9 11.6 1.2 10.0 13.9
Body width at dorsal origin 23.0 20.6 1.7 19.3 23.0
Body width at anal origin 15.3 12.4 1.6 10.2 15.3
Snout length 17.9 18.4 1.0 17.2 20.6
Orbit diameter 3.6 3.8 0.3 3.2 4.4
Interorbital width 10.4 10.7 0.5 10.2 11.7
Dorsal-fin base length 20.0 18.8 1.4 15.8 21.1
Interdorsal distance 23.6 22.2 2.2 18.2 24.8
Caudal peduncle length 25.9 25.7 1.1 24.5 27.9
Caudal peduncle depth 7.5 7.9 0.4 7.1 8.4
Dorsal-fin spine length 21.5 22.0 1.6 20.6 24.5
Pectoral-fin spine length 27.9 25.5 1.9 23.8 28.7
Pelvic-fin spine length 27.0 27.8 1.8 25.5 30.5
Anal-fin first ray length 11.5 9.8 1.8 7.6 13.6
Adipose-fin spine length 7.3 6.8 1.1 4.9 8.1
Lower lip width 25.2 25.3 1.3 23.5 27.4
Lower lip length 10.2 10.3 0.7 9.5 11.4
Dentary length 2.6 2.6 0.3 2.1 3.2
Premaxillary length 2.7 2.6 0.4 2.2 3.2
Percents in head length
Head depth 40.8 35.6 3.1 30.1 40.8
Head width 89.1 88.0 4.2 80.4 96.1
Interorbital 30.3 31.4 1.4 28.8 33.1
Orbit diameter 10.3 11.1 1.0 9.2 12.2
Pectoral length 80.9 74.4 5.6 66.9 84.9
Pelvic length 78.4 81.4 5.6 74.8 93.6
Snout length 52.1 53.8 1.8 51.6 56.8
Premaxillary length 7.8 7.7 1.1 6.1 9.9