Stenolicmus, Wosiacki, Wolmar Benjamin, Coutinho, Daniel Pires & Montag, Luciano Fogaça De Assis, 2011

Wosiacki, Wolmar Benjamin, Coutinho, Daniel Pires & Montag, Luciano Fogaça De Assis, 2011, Description of a new species of sand-dwelling catfish of the genus Stenolicmus (Siluriformes; Trichomycteridae), Zootaxa 2752, pp. 62-68 : 63-68

Stenolicmus ix, new species

Figs. 1–3 ; Tab. 1

Holotype: MPEG 15101, 19.0mm SL, Brazil, Pará State, Alenquer Municipality, unnamed igarapé tributary of Igarapé Curuá, tributary of the left margin of the Rio Amazonas, 0°9'47.6''S and 55º11'1.2''W, L. F. A. Montag, D. P. Coutinho and W. B. Mota.

Diagnosis. Stenolicmus ix can be distinguished from S. sarmientoi by the length of the nasal barbels, reaching the base of the first opercular odontodes (vs. reaching anterior margin of eyes); length of maxillary barbels reaching posterior margin of opercular odontode plate (vs. reaching posterior margin of interopercular odontode plate); seven well-developed opercular odontodes (vs. six); seven well-developed interopercular odontodes (vs. five or six); pelvic fin rays, i+4 (vs. iv); color pattern of posterior region of trunk composed of agglomerated chromatophores forming circular patches twice the diameter of the eye (vs. without circular patches twice the diameter of the eye); large eyes with 11.8% HL (vs. 6%); caudal peduncle depth, 11.6% SL (vs. 8.5–9.5%); absence of dark bar at the base of the caudal fin (vs. presence of dark bar); head length, 17.9% SL (vs. 14.9–15.1%); and unbranched rays of caudal fin long, reaching distal margin of fin (vs. rays short, not reaching half the length of caudal fin).

Description. Morphometric data are provided in Table 1. Overall shape of body similar to that of S. sarmientoi (see de Pinna and Starnes, 1990, Fig. 1 ). Body elongate, head wider than trunk in dorsal view. Body slightly depressed at pectoral-fin insertion, gradually taller and more compressed posteriorly. Caudal peduncle gently tapering to caudal fin. Dorsal profile of head straight, gently convex from occipital to dorsal-fin origin, concave at dorsal-fin base. Dorsal profile of caudal peduncle straight; low cutaneous fold from close to last dorsal-fin ray to continuous caudal-fin base. Ventral profile of head convex, pectoral-fin girdle concave, body convex to anal-fin origin, anal-fin base concave. Ventral profile of caudal peduncle straight; low cutaneous fold from close of last dorsal-fin ray to continuous caudal-fin base.

Head small, depressed, less deep than body, its dorsal surface flat. Branchial membranes united to isthmus, gill openings not constricted. Eyes small but well-defined margins, with distinct lenses and covered by thin transparent integument, located dorsolaterally on head. Posterior naris round, with similar diameter of eyes, located midway between these and anterior naris, and surrounded only anteriorly by low rim of integument. Anterior naris surrounded by short tube of integument, continuous posterolaterally with nasal barbel. Mouth subterminal, upper jaw slightly longer than lower, corners only slightly curved posteriorly. Upper lip continuous with remainder of dorsal surface of head, its anterior border abruptly thinner, forming a narrow fold. Lower lip narrow, limited by rictal barbel bases, scattered papiles over surfaces, cutaneous fold as discreet lobes at corners. Snout with flat lateral expansion along area between eye and maxillary barbel base.

Holotype

mm %

Standard length 19.0

Total length 23.1

SL Body depth 3.2 16.8 Predosal length 12.8 67.4 Preanal length 13.1 68.9 Prepelvic length 10.5 55.3 Caudal peduncle depth 2.2 11.6 Caudal peduncle length 4.2 22.1 Head length 3.4 17.9 Pectoral-fin length 4.0 21.1 Pelvic-fin length 1.8 9.5 Dorsal-fin base length 1.9 10.0 Anal-fin base length 1.9 10.0 HL Head width 3.4 100.0 Interobital 0.9 26.5 Eye diameter 0.4 11.8 Maxillary barbel length 2.4 70.6 Nasal barbel length 2.0 58.8 Rictal barbel length 1.8 52.9 Breadth of mouth 1.4 41.2 All barbels with visible internal cores and similar to each other in general aspect. When completely extended, maxillary barbel reaching posterior margin of opercular patch of odontodes, rictal barbel to posterior margin of interopercular patch of odontodes, and nasal barbel to posterior margin of opercular patch of odontodes. Maxillary barbel with very broad base by enlarged maxilla, visible by transmitted light. Internal core of maxillary barbel thick and slightly darker than surrounding tissues. Rictal barbel shortest, narrow, completely overlain and partly surrounded by base of maxillary barbel. Nasal barbel thinnest. Internal cores of rictal and nasal barbels not as conspicuous as that of maxillary barbel.

Opercular patch of odontodes large, roundish, with seven odontodes surrounded by fleshy rim of integument. Interopercular patch of odontodes roundish, slightly longer than deep, with seven odontodes surrounded by rim of integument.

Pores po1-2 (postotic sensory pores 1 and 2) representing limits of latero-sensory system of skull. Lateral line nearly absent, pores ll1-2, lateral line sensory branches 1 (supracleithral sensory branch) and 2 represent a short oblique branch dorso-posterior to base of pectoral fin.

Pectoral fin long, narrow, originating immediately posterior to posterior margin of branchial membrane, at vertical through posterior margin of opercular patch of odontodes; pectoral-fin rays i+4; first ray unbranched, segmented, longer, thicker, prolonged as a filament 1/3 of its length; remaining rays branching once, becoming gradually shorter, and thinner. Axillary gland small, restricted to area dorso-posterior to base of pectoral fin, its small pore located immediately dorsal to pectoral-fin base. Pelvic-fin rays i+4, all segmented, first largest, rays gradually decreasing mesially; fin smaller than others, origin slightly in front of anal and uro-genital openings, margin reaching area close anal-fin origin; bases of contralateral fins not in contact. Dorsal fin elongated, with rounded posterior profile, posteriorly placed, its origin located on 67.4% SL; dorsal-fin rays i+6, first, second and third longest, branched rays with incipient branching at tips. Anal-fin rays ii+4, segmented rays, first and second longest, branched rays branching once; origin located on 68.9% SL, adjacent to posterior margin of anus, continuous with integument surrounding vent, similar shape and size of dorsal fin. Caudal fin large and round, continuous with remainder of caudal peduncle; caudal-fin rays i+5/5+i, middle two rays longest, branched rays branching only once. Procurrent caudal-fin rays at least eight dorsally and ventrally forming large part of caudal peduncle depth and merging gradually into principal caudal rays. Exact number difficult to determine in alcohol preserved specimen. Five branchiostegal rays visible by transparency.

Pigmentation in alcohol. Background color cream, slightly darker dorsally. Dorsum and flanks partially covered with irregularly distributed black chromatophores, slightly more concentrated dorsally, gradually scarce ventrally through flanks, until no pigmentation on belly. Dark chromatophores equally scattered on caudal peduncle with same concentration as in flank. Melanophores, similar to few defined stars, concentrated, forming poorly defined blotches dorso-laterally more concentrated on upper half of body on trunk and caudal peduncle. Caudal peduncle with several series of dotted lines of small chromatophores, posteriorly oblique, over myosepta, toward dorsal and ventral profiles, forming poorly defined stripes.

Dorsal head partially covered by small chromatophores, smaller than dorsal region of trunk, mostly concentrated in regions between nostrils, snout, upper lip, maxillary barbel bases, interorbital and supraoccipital. Eyes black, sharp edges. Small area lateral to eyes without chromatophores. Few minute melanophores on cheek region and surrounding opercular and interopercular patches of odontodes. Ventral portion of head white, with few chromatophores on corners of lower lip closer to rictal barbel base. Dorsal and pectoral fins with few minute chromatophores at bases. No pigmentation over anal and pelvic fins. Caudal fin with few minute chromatophores at base, a small blotch between bases of two middle-rays.

Habitat and ecological notes. The specimen of Stenolicnus ix was collected in the headwaters of the Rio Curuá, from a lotic area about 5m wide and less than a meter deep. A large amount of leaf litter was present on the river bed, and the margins were dominated by amphibious vegetation ( Fig. 4 ). Fifteen species of fishes, including Characiformes, Siluriformes and Perciformes occur syntopically with Stenolicnus ix.

Distribution. Stenolicnus ix is known only from the type locality in the lower Amazon basin at the igarapé Curuá, Alenquer, Pará State, Brazil ( Fig. 5).

Etymology. The specific epithet, ix, refers to the Mayan word "Ix", term used to describe the jaguar ( Panthera onca ). The name refers to the color pattern of grouped patches scattered from the flanks to the dorsum, unique among its congeners and similar to the jaguar. Name in apposition. Gender masculine.

Discussion. Based on the single available individual of S. ix, it was only possible to conduct the observation and analysis of its external anatomy and color pattern but not of its internal structure. Thus, the three synapomorphies proposed for Sarcoglanidinae (see Costa, 1994) cannot be observed in S. ix. In contrast, the presence of several characters proposed by de Pinna and Starnes (1990) as diagnostic of Stenolicmus justify the inclusion of the new species in the genus. The diagnostic characters for Stenolicmus present in the S. ix are: (1) elongated body, HL 17.9%; (2) absence of frontal and parietal fontanels; analysis of the skull roof of S. ix under a stereoscopic microscope showed absence of fontanels, with no visible trace of this structure even when pressuring the tegument with a utility needle in the sagittal line, indicating that the frontal bones are completely fused together and to the supraoccipital, which also shows no evidence of a fontanel; (3) opercular and interopercular odontode plates are well developed with seven major odontodes each; and (4) eight dorsal and ventral procurrent rays, visible with transmitted light, a number consistent with that present in S. sarmientoi but differing from all remaining genera of the subfamily. Conversely, the three following additional diagnostic features proposed by de Pinna and Starnes (1990) for Stenolicmus were not analyzed, because these are minute osteological structures that can only be seen in clear and stained specimens: posterior process of dorsal expansion of quadrate straight and narrow, pointed; absence of metapterygoid; and expanded distal half of maxilla.

Eight dorsal and ventral procurrent rays were visible under transmitted light, a number consistent with that seen in S. sarmientoi but different from other genera of the subfamily. De Pinna and Starnes (1990) proposed in the diagnosis of Stenolicmus sarmientoi that the caudal peduncle is tall, however, its measurement of 8.5–9.5% SL, agrees with the proportions in other species of Sarcoglanidinae (de Pinna, 1989; Costa, 1994; de Pinna and Winemiller, 2000). In contrast, S. ix does have a distinctly tall peduncle (11.6% SL) when compared to other members of Sarcoglanidinae .

Most of species of Sarcoglanidinae , except for S. ix and Microcambeva riberae , have a pale or translucent color pattern, with only minute chromatophores sparsely scattered over the body, usually more concentrated dorsally on the body but not forming visible patches with a diameter similar or larger than the eye. In contrast, the patches present in S. ix and M. riberae have a distinct pattern. In S. ix, the patches are large, poorly defined, with a diameter equal to or, twice the diameter of the eye and irregularly distributed over the body, more concentrated in the dorsal region. In M. riberae , there are conspicuous dark patches, but smaller than the diameter of the eye, arranged in series of 9–13 patches along the midline of the flanks and in two series of patches along the dorsolateral and dorsal midline portions. Costa (1994) hypothesized that the more densely pigmented pattern observed in S. sarmientoi is a reversal within Sarcoglanidinae , a pattern that is evidently shared with S. ix. Thus, considering the proposal of Costa (1994), it is more parsimonious to interpret the color patterns observed in M. riberae and in the species of Stenolicmus as independent reversals.

The distribution of species of the genus, apparently, is not limited to the physical and chemical conditions of the rivers, since S. sarmientoi occurs in whitewater of the Río Matos, tributary of the Río Apero, Mamoré system ( Bolivia), and S. ix occurs in clearwater, also recorded for species of Typhlobelus and Pygidianops ( Schaefer et al., 2005) , both Glanapteriginae.

The individual of S. ix was collected with a sieve by scraping sand and leaf litter from the river bed. It is not possible, though, to assert the type of environment used by S. ix, because no observations were made of the species in its natural habitat. However, we can suggest a sand-dwelling behavior for this species, considering where it was collected and the fact that most species of Glanapteryginae and Sarcoglanidinae are associated with sandy environments ( Schaefer et al., 2005).

Figures

FIGURE 1. Left lateral view of Stenolicmus ix, holotype, MPEG 15101, 19.0 mm SL.

FIGURE 2. Drawing of left lateral view of Stenolicmus ix, holotype, MPEG 15101, 19.0 mm SL.

FIGURE 3. Dorsal view of head of Stenolicmus ix, holotype, MPEG 15101. Bar = 1 mm.

FIGURE 4. Type-locality of Stenolicmus ix, an unnamed stream, tributary of Igarapé Curuá, right bank tributary of the Rio Amazonas, 0 ° 9 ' 47.6 '' S and 55 º 11 ' 1.2 '' W.