Gelanoglanis pan, Calegari & Reis & Vari, 2014

Calegari, Bárbara B., Reis, Roberto E. & Vari, Richard P., 2014, Miniature catfishes of the genus Gelanoglanis (Siluriformes: Auchenipteridae): monophyly and the description of a new species from the upper rio Tapajós basin, Brazil, Neotropical Ichthyology 12 (4), pp. 699-706 : 701-703

Gelanoglanis pan , new species

Figs. 1-2 ; 4-5

Gelanoglanis cf. stroudi .—Birindelli, 2014: 535, 544 (comparative material).

Holotype. MZUSP 114669 , 24.7 mm SL, Brazil, Mato Grosso State, Itaúba, rio Teles Pires, tributary to upper rio Tapajós basin, 10°58’30”S 55°44’3”W, 1 Oct 2007, J. Birindelli & P. Hollanda-Carvalho.

Paratypes. MZUSP 96032 , 8 , 10.8 - 12.9 mm SL + 1 c&s, 20.2 mm SL; MCP 48078, 1 , 14.8 mm SL; USNM 427060, 1 , 13.8 mm SL; all collected with holotype .

Diagnosis. Gelanoglanis pan is distinguished from all congeners by the presence of an anterior middorsal fontanel situated between the anterior portions of the contralateral frontals (vs. the frontals conjoined along the entirety of their middorsal margins and the fontanel absent); by adult males having a long fleshy, tubular gonopodium extending posteriorly to a point midway along the length of the anal fin (vs. the gonopodium reaching only to, or slightly beyond, the anal-fin origin in G. travieso and G. stroudi or falling short of the anal-fin origin in G. nanonocticolus ); and by the deeper caudal-peduncle 12.1-13.5% SL (vs. 9.5-12.0% in G. stroudi , 10.2-11.6% in G. nanonocticolus , and 9.4-11.7% in G. travieso , see Rengifo et al., 2008). Gelanoglanis pan differs from G. stroudi and G. travieso by having the premaxillary teeth occupying one-half or less of the length of the premaxilla and restricted to the its more vertically expansive anterior portion (vs. the teeth distributed along most of the dentigerous margin of the premaxilla and occupying two-thirds of length of the bone); the portion of the maxilla inside the base of the maxillary barbel shorter and terminating posteriorly forward of the anterior margin of the opercle (vs. maxilla terminating posteriorly to the middle of the opercle); and by the larger orbital diameter 14.4-17.9% HL (vs. 7.2-9.3% in G. stroudi and 8.2-12.8% in G. travieso ; see Sarmento-Soares et al., 1999). Gelanoglanis pan is additionally distinguished from G. nanonocticolus by having the pectoral- and dorsal-fin spines with well-developed serrae (vs. pectoral- and dorsal-fin spines absent).

Description. Morphometric data presented in Table 1. Standard length of examined specimens 10.8 to 24.7 mm SL. Head and body overall in form of laterally compressed cylinder. Dorsal profile of head distinctly convex from tip of snout to anterior region of frontal and slightly convex from middle of head to posterior limit of head. Dorsal profile of body slightly convex to rear of dorsal-fin base; straight from terminus of dorsal-fin base to end of caudal peduncle and angling slightly dorsally at insertion of first procurrent ray. Ventral profile of head and body slightly convex from lower jaw to vertical through tip of pectoral fin; then approximately straight to caudal peduncle. Greatest body depth at dorsal-fin origin; depth progressively decreasing posteriorly to posterior portion of caudal peduncle. Greatest body width at pectoral-fin insertion and decreasing progressively posteriorly. Caudal peduncle strongly compressed.

Mouth terminal, with margin sinuously curved. Curvature commencing dorsally at anterior margin of lip, then curving ventrally before arching to its most dorsal position along vertical passing through anterior margin of posterior naris and base of maxillary barbel; margin then curving again ventrally to rictus of mouth. Lower lip with large, fleshy rictal flap, or epidermal flange, situated ventral to region of maximum dorsal curvature of margin of upper lip. Anterior portion of lower lip fleshy and extending forward as anteriorly tapering process beyond anterior limit of dentary. Fleshy contralateral upper lips meet medially along distinct arch at midline. Snout fleshy, more so anteriorly. Maxillary barbel arising ventral of posterior naris and extending posteriorly beyond vertical through pelvic-fin origin. Maxillary barbel in juveniles and adults of both genders with rugose dorsal surface resulting from series of well-developed rounded, regularly spaced, soft papillae arranged in single discrete row along length of barbel. Single pair of well developed mental barbels extends posteriorly beyond isthmus. Posterior naris in form of elongate, ovoid, posteromedially angled opening immediately anterior to orbit.

Dentary elongate and bearing narrow band of conical teeth with slightly posteriorly recurved tips. Lateral teeth of dentary oriented somewhat posteromedially. Anterior dentary teeth distinctly longer than remaining teeth on lower jaw; occupying area of dentary covered by fleshy flap. Premaxillary teeth similar in form to those of dentary, but slightly shorter than longer anterior teeth on latter bone. Contralateral premaxillae broadly separated medially. Each premaxilla with patch of dentition limited to anterior, more vertically expanded portion of bone.

Anterior middorsal fontanel present and bordered solely by frontals, and forming somewhat longitudinally ovoid opening situated anterior of vertical through orbit. First infraorbital ossified and large. Remaining four infraorbitals represented by transparent unossified tubes surrounding segments of laterosensory canal system. Lateral line unossified, incomplete, nearly straight except for sinuous curve anteriorly; extending along midlateral surface of body from post-temporal-supracleithrum approximately to vertical through posterior limit of anal fin.

Pseudotympanum apparent in larger individuals (13.8- 24.7 mm SL) and located anterodorsally on lateral portion of body; opening situated posterior to margin of opercle and terminating posteriorly approximately at vertical through base of dorsal-fin spine. Pseudotympanum slightly horizontally elongate, with anterior portion narrower.

Dorsal-fin rays, II,5. Dorsal-fin spine robust, 5 to 7 well-developed serrae along posterior margin; posterior margin of spine not covered by skin. Bony spine continued distally as unsegmented filament approximately one-half length of spine. Pectoral-fin rays I,5. Adpressed pectoral-fin spine reaching posteriorly to vertical through middle of dorsal-fin base. Spine bearing 11 well-developed serrae along posterior margin. Adipose-fin origin located along vertical through posterior terminus of anal-fin base. Posterior margin not attached to body. Juveniles (10.8-12.4 mm SL) with long, fleshy, middorsal ridge arising at vertical through pelvic-fin origin and extending posteriorly to slightly beyond posterior terminus of anal-fin base. Fleshy ridge in juveniles gradually increasing in depth posteriorly and then abruptly terminating at rounded posterior margin. Pelvic-fin rays i,5; rays very short. Anal fin, iii,4,i. Anal fin of males with base of rays aligned at right angle to longitudinal axis of body. Anteroventral margin of fin supporting elongate gonopodium in males (see details in Sexual dimorphism). Caudal-fin rays, i,15,i; fin deeply forked. Total vertebrae, 34 (n= 2).

Color in alcohol. Ground coloration of head and body whitish to yellowish cream. Head and body with numerous discrete chromatophores; chromatophores of large size in smaller individuals. Head with tiny to small black chromatophores and very small black spots; spots more intense on dorsal surface of head, region anterior to orbit and to lesser degree on opercle. Pigmentation on opercle more prominent in juveniles. Region under orbit plus lateral and ventral surfaces of jaw with sparse black chromatophores; these more concentrated near attachment area of mental barbels. Body covered with relatively evenly spaced, tiny to small black chromatophores and very small black spots other than for ventrally. Larger individuals with chromatophores on body more concentrated below dorsal-fin base and along midlateral line of caudal peduncle. Dorsal fin with few chromatophores extending about one-third length of basal portion of each ray. Chromatophores most intense and numerous on second dorsal-fin ray. Anal, caudal, pectoral and pelvic fins hyaline to yellowish tan without any dark chromatophores. Gonopodium of males unpigmented.

Sexual dimorphism. Proximal radials of anal-fin of mature males fused into single compound bone. Gonopodium in mature males in form of elongate, fleshy tube that originates anterior to the anal-fin base and extends one-half length of anterior margin of anal fin. Three anterior most unbranched anal-fin rays smallest and slightly curved. Fourth and fifth anal-fin rays branched and distinctly longer than other rays, with fourth ray longest. Sixth and seventh rays branched and shorter than fourth and fifth rays but longer than three anterior most rays. Posterior most (eighth) anal-fin ray short and unbranched ( Fig. 2 ). All anal-fin pterygiophores of females separate from one another. Anal-fin rays of females with two anterior most rays shortest; remaining rays progressively longer. Anterior most anal-fin ray unsegmented and posterior most ray unbranched.

Distribution. Gelanoglanis pan is known from the type locality in the rio Teles Pires, a tributary to the upper rio Tapajós basin, Brazil ( Fig. 3 ). Gelanoglanis pan may be an additional species endemic to the upper rio Tapajós basin (see discussion in Vari & Calegari, 2014).

Etymology. The species name, pan , from the name of the Greek God of fertility and male sexuality, refers to the large gonopodium of the males of the species.

Miniaturization. Gelanoglanis pan is a miniature species underthedefinitionproposedbyWeitzman&Vari(1988)in their overview of miniaturization within South American freshwater fishes. According to that definition, miniature fishes either mature at less than 20 mm SL or do not exceed a maximum body length of 26 mm SL. Although standard length is a readily observed indicator of miniaturization, Weitzman & Vari (1988) noted that the miniaturization process generally involves a series of other less obvious reductive (paedomorphic) morphological features. Prominent among these are reductions in the degree of development of the laterosensory system on the head and body, in the number of fin rays, and of the sculpturing on the surface bones of the head.

Despite in some instances exceeding the 26 mm SL maximum originally proposed by Weitzman & Vari (1988), all species of Gelanoglanis share a number of reductive features and, thus, are considered miniatures. Reductions general across Gelanoglanis include the decrease to one ossified infraorbital, the first infraorbital; a mandibular ramus of the lateral sensory canal separate from the dentary and instead extending as a separate ossification lateral of the dentary and anguloarticular (see Fig. 4 ); the incomplete lateral line terminating posteriorly anterior to the caudal-fin base; the reduction of the mesethmoid to an elongate narrow arch; the very small premaxilla in the form of a thin plate bearing relatively few teeth anteriorly; and the reduction to 8 total anal-fin rays (vs. 9-11 in Tatia and Centromochlus ; and 12-14 in Glanidium ). Hence, Gelanoglanis pan fits the definition of a miniature both in sharing this series of developmentally truncated features with its congeners, and also in its maximum length of 24.7 mm SL.

Figures

Fig. 1. Gelanoglanis pan, MZUSP 114669, holotype, male, 24.7 mm SL; Brazil, Mato Grosso State, Itaúba, rio Teles Pires, tributary to upper rio Tapajós basin; lateral views. Scale bar = 0.5 cm.

Fig. 2. Gonopodium and osteology of the anal fin of an adult male of Gelanoglanis pan, holotype, 24.7 mm SL, MZUSP 114669, showing fusion of the proximal radials. DR = distal radials, G = gonopodium, PR = fused proximal radials, i-iii= anterior unbranched and unsegmented anal-fin rays. Scale bar = 1 mm.

Fig. 4. Lateral view of the mandibular arch of Gelanoglanis pan, MZUSP 96032, paratype, 20.2 mm SL. AA = anguloarticular, D = dentary, PM = premaxilla, LC = subdivided autogenous laterosensory canal. Scale bar = 0.5 mm.

Fig. 3. Map of southeastern Amazon basin showing location of type locality of Gelanoglanis pan, 1 = rio Tapajós, 2 = rio Teles Pires, 3 = rio Juruena.