Trichomycterus argos, Lezama & Triques & Santos, 2012

Lezama, Antônio Queiroz, Triques, Mauro L. & Santos, Patrícia S., 2012, Trichomycterus argos (Teleostei: Siluriformes: Trichomycteridae), a new species from the Doce River Basin, Eastern Brazil, Zootaxa 3352, pp. 60-68 : 62-65

Trichomycterus argos , new species

( Fig. 2 )

Holotype. DZUFMG 103, 95.4mm SL; Brazil: Minas Gerais State: Araponga municipality, Parque Estadual da Serra do Brigadeiro, Córrego Serra Nova, headwaters of the Rio Casca, right bank tributary of Rio Doce at the limits of Rio Doce and Rio Paraíba do Sul basins, 20°43'19''S / 42°28'43''W, 1400 m asl; P. S. Santos, 7 October 2001.

Paratypes. DZUFMG 0 58, 0 1 ex., 114.7 mm SL; DZUFMG 0 59, 14 ex., 56–116.8 mm SL; DZUFMG 0 67, 1 ex., 101 mm SL, C&S; MZUSP 106274, 3 ex., 57.4–91.8 mm SL; all collected with holotype.

Diagnosis. Trichomycterus argos differs from its congeners, excluding T. alternatus (Eigenmann) , T. brasiliensis Lütken , T. brunoi Barbosa & Costa , T. candidus (Miranda Ribeiro) , T. claudiae Barbosa & Costa , T. fuliginosus Barbosa & Costa , T. macrotrichopterus Barbosa & Costa , T. maracaya Bockmann & Sazima , T. mariamole Barbosa & Costa , T. mimonha Costa , T. mirissumba Valenciennes , T. novalimensis Barbosa & Costa , T. pantherinus Alencar & Costa , T. potschi Barbosa & Costa , T. rubiginosus Barbosa & Costa , and T. vermiculatus (Eigenmann) by the presence of six branched rays in the pectoral fin, and by having the first pectoral-fin ray prolonged as a filament. Trichomycterus argos is distinguished from T. brasiliensis by the absence of series of spots, as well as absence of confluent spots forming elongated marks or vermiculations (vs. presence of series of large [three times eye-diameter or more] spots dorsolaterally, laterally and ventrolaterally on flank in T. brasiliensis , more clearly visible in small specimens), by a transverse and straight border between the parietosupraoccipital and frontal bones ( Fig. 3 a) (vs. oblique and irregular border, in T. brasiliensis ; Fig. 3 b) and by a large foramen for the ramus lateralis accessorius facialis, visible in dorsal view, in the parietosupraoccipital bone (vs. foramen for the ramus lateralis accessorius facialis minute, at least four times smaller than in the new species, located on a ridge of the bone, and visible only in lateral view, in T. brasiliensis ; Fig. 3 b). Trichomycterus argos is distinguished from T. candidus by the presence of pelvic fins (vs. absence of pelvic fins, in T. candidus ). Trichomycterus argos differs from T. alternatus , T. maracaya and T. pantherinus by having superficial and deeper layers of small spots that seldom reach eye diameter in size (vs. consistently different color patterns in these species). Trichomycterus argos differs from T. mimonha by the shorter head width (79.1–87.6% HL vs. 93.8– 98.9 % HL, in T. mimonha ), and by having the tip of nasal barbels extending to posterior border of opercular plate of odontodes (vs. not reaching origin odontodes of interopercular plate, in T. mimonha ). Trichomycterus argos differs from T. mirissumba by the absence of stripes on the dorsum (vs. two dorsal stripes, from the nape towards dorsal-fin origin, in T. mirissumba ) as well as by the absence of confluence of dark spots bellow horizontal midline. Trichomycterus argos differs from T. vermiculatus by the absence of vermiculations, formed by fused spots on the body, and by having pelvic-fin origin placed one or two ocular diameters anterior to dorsal-fin origin (vs. pelvic-fin origin in a vertical through dorsal-fin origin, in T. vermiculatus ). Trichomycterus argos differs from T. potschi by the absence of spots fused as stripes on the lateral region of the body (vs. one or more stripes, in T. potschi ). Trichomycterus argos differes from T. brunoi , T. claudiae , T. fuliginosus , T. mariamole , T. novalimensis and T. macrotrichopterus by the absence of stripes, vermiculations or reticulations, present in these species ( Barbosa & Costa, 2010). Trichomycterus argos differs from T. rubiginosus by a wider head (head width 79.1–87.6% of head length, vs. 72.2–78.9% in T. rubiginosus ), larger eye (eye diameter 10.5–17.5% of head length, vs. 7.3–9.2 in T. rubiginosus ) and smaller anal-fin base (7.2–8.8 % of standard length, vs. 9.0–9.9 in T. rubiginosus ).

Description. Morphometric data of holotype and paratypes are given in Table 1 . Body elongate, cylindrical near head and gradually becoming more compressed towards tail. Caudal peduncle strongly compressed.

Head wide and depressed. In dorsal view, small specimens with head much wider posteriorly than anteriorly, nearly triangle-shaped; large specimens with rounded head anteriorly. Smaller specimens with straight dorsal head profile, inclined upward from anterior nostril to supraoccipital posterior border; larger specimens with dorsal head profile slightly convex anteriorly, almost horizontal, from eye to supraorbital posterior border; dorsal body profile horizontal or slightly convex from supraoccipital posterior border to dorsal-fin origin, which is somewhat elevated. Dorsal-fin base profile straight and inclined downward, along base of first three rays, continuing straight and horizontal or slightly inclined downward toward end of base, then nearly straight and inclined upward to insertion of caudal fin. Ventral profile of head horizontal or slightly convex; slightly convex or straight towards origin of anal fin; anal-fin base straight and inclined upward (horizontal in small specimens), then nearly straight and inclined downward to insertion of caudal fin.

Eyes small and elliptical, uniformly covered by skin; eyes dorsally on head, at middle or slightly at head anterior region, the former condition more common in large and medium-sized specimens, and the latter in small specimens. Mouth sub-terminal, with two fleshy lobes posterolaterally to inferior lip and medially to origin of rictal barbels. Branchial openings wide, with thick branchial membranes, anteriorly united to isthmus at a vertical through posterior edge of eyes. Opercle small and round, with 20–22 conical and thick odontodes. Interopercle oblique, ranging from two to three times longer than opercle, with 38–41 conical and thick odontodes, arranged in three series.

Anterior nostrils surrounded by a fleshy skin fold medially and one nasal barbel laterally. Posterior nostrils antero-posteriorly elongated, surrounded anteriorly by a fleshy skin fold. Tip of nasal barbels reaching posterior border of opercular plate of odontodes. Tip of maxillary barbells extending to end of pectoral-fin base. Tip of rictal barbels reaching origin of pectoral fin. Barbels laminated and wide basally, gradually narrowing towards tip, thread-like.

Anal and urogenital openings below anterior half of dorsal-fin base. Integument thick at base of all fins. Dorsal-fin rays i+7 (13*), ii+7 (6) or ii+6 (1); two unsegmented rays in C&S specimen; distal margin convex; origin nearly at two thirds of the standard length. Pectoral-fin rays i+6; distal margin convex; origin nearly at vertical by end of opercular plate of odontodes; first ray nearly an ocular diameter longer than others. Pelvic-fin rays i+4 (pelvic splint visible in C&S specimen); distal margin convex; origin from one to two ocular diameters in front of dorsal-fin origin and equidistant to tip of snout and end of caudal fin, or nearer to last one; distal margin surpassing anus and reaching one or two ocular diameters in front of anal-fin origin, being generally more anterior in large specimens than in small ones. Anal-fin rays i+5 (7*) or ii+5 (13); three unsegmented rays in C&S specimen; distal margin convex; origin at same vertical or slightly anterior to end of dorsal-fin base. Caudal-fin rays i+5; i+6; distal margin rounded or truncate.

Coloration. Body and head background color cream, in small specimens, and dark brown dorsally to cream ventrally on flanks, in adults. Head and body with spots of superficial chromatophores that seldom reach eye diameter in size, coarse dorsally, progressively more sparse ventrally, to the level of pectoral and pelvic-fin insertions, not forming vermiculations. Smaller spots of deeper chromatophores present, from dorsum to level of pectoral and pelvic-fin insertions, over head and body, with nearly same concentration over its range of distribution, not forming vermiculations. Below level of pectoral and pelvic-fin insertions, spots very few and sparse, or absent over the greater part of this region; presence of a mid-ventral line of chromatophores, from anterior part of the isthmus towards level of the pelvic-fin origin, forming, in some cases, a narrow continuous stripe, rarely absent. Opercular membrane border with line of concentrated chromatophores.

Chromatophores present on rays and ray-borders all through length of fins. Bases of dorsal, caudal and dorsal side of pectoral fin with superficial and deep spots. Fin membranes hyaline distally, exception in large specimens with dorsal, anal and caudal fins presenting clear brown background color, with dark roundish marks proximally, and hyaline membrane distally (only dorsal fin pigmented distally on membrane). Medial area of fins variably pigmented or hyaline. Barbels pigmented on each edge, becoming lighter towards tip; rictal barbels slightly lighter than others.

Etymology. The epithet “argos” (Gr.), meaning “a hundred-eyed monster” ( Brown, 1956: 312), refers to the eye-spotted color pattern of the new species, not forming vermiculations.

Biological data. Sampling for study of habitat use was conducted between October 2001 and September 2002 at Serra Nova stream and two of its tributaries, in the same area where the holotype was collected, in a region of the Parque Estadual da Serra do Brigadeiro called Fazenda da Neblina. The local climate presents two well defined seasons, one predominantly mesothermic (Köppen’s “Cwb” climate classification) with annual mean temperature of 15°C, with possible occurrence of minimum temperatures below 0°C. Mean annual precipitation is 1,500 mm, with the dry season extending from July to August.

Twenty funnel traps with double entrances were installed monthly in each stream. The height of the water column was measured, and each trap was used for 72 hours/month. The 49 specimens of Trichomycterus collected throughout the study period (SL between 4 and 17 mm) occupied habitats with depth and temperature varying from 13 to 44 cm and from 14 to 19°C. A larger number of specimens (15) was collected in July 2002, possibly a reflection of the lower water flow which did not promote the downstream flow of specimens. Twenty nine of the 49 specimens belong to T. alternatus , a clearly different species than T. argos , on the basis of body color pattern and other features.

Predation of tadpoles of Scinax gr. catharinae by specimens of T. argos was observed under laboratory conditions.

Figures

FIGURE 2. Holotype of Trichomycterus argos, DZUFMG 103, 95.4 mm SL, in dorsal (1), lateral (2), and ventral (3) views.

FIGURE 3. Dorsal views of the cranium and Weberian complex of a) Trichomycterus argos (DZUFMG 0 67, 101 mm SL, paratype) and b) Trichomycterus brasiliensis (DZUFMG 0 64, 102, 1 mm SL). Abbreviations: AP, autopalatine; EP, epioccipital; FF, frontal fontanels; FR, frontal; IO, tendon-bone infraorbital; LE, lateral ethmoid; ME, mesethmoid; MX, maxilla; PM, premaxilla; PS, posttemporosupracleithrum; PT, pterotic; RF, foramen for the ramus lateralis accessorius facialis; SC, cephalic sensory canal; SO, tendon-bone supraorbital; SPP, sphenotic-prootic-pterosphenoid compound bone; SU, parietosupraoccipital; WC, Weberian capsule. Scale bar = 1 cm.

Tables

TABLE 1. Morphometric data for holotype and paratypes (n=19) of Trichomycterus argos, new species.

	Holotype	Range	Mean
Standard length (mm)	95.4	56.0–116.8	83.9
Total length (mm)	109.5	65.1–134.9	97.1
Head length (mm)	20,3	12.6–26.3	18.6
Percentages of standard length
Total length	114.8	114.8–118	116.0
Body depth	13.8	12.8–17.5	15.9
Caudal peduncle length	20.4	19.2–22.7	21.0
Caudal peduncle depth	15.8	14.6–17.5	16.3
Predorsal length	63.1	60.9–65.9	64.0
Preanal length	72.0	70.1–73.7	71.5
Prepelvic length	58.7	55.4–76.6	60.3
Dorsal fin base length	10.9	8.7–11.2	10.0
Anal fin base length	8.4	7.2–8.8	8.1
Dorsal-caudal length	37.3	34.5–39.2	36.6
Pelvic-caudal length	42.7	40.1–43.6	41.8
Head length	21.3	20.8–23.3	22.3
Percentages of head length
Head width	85.2	79.1–87.6	84.3
Head depth	55.2	47.2–60.2	53.0
Interorbital width	26.6	24.6–29.4	26.9
Internasal width	19.2	16.4–20.6	18.9
Snout length	40.9	37.4–46.9	42.0
Eye diameter	13.3	10.5–17.5	9.7
Mouth width	44.3	32.8–47.4	39.2