Tatia meesi, Sarmento-Soares & Martins-Pinheiro, 2008

Sarmento-Soares, Luisa Maria & Martins-Pinheiro, Ronaldo Fernando, 2008, A systematic revision of Tatia (Siluriformes: Auchenipteridae: Centromochlinae), Neotropical Ichthyology 6 (3), pp. 495-542 : 526-529

Tatia meesi , new species

Fig. 30-32

Holotype. INHS 99772 (44.3 mm SL), Guyana, Potaro-Siparuni: lower Potaro river (Essequibo river Drainage ), Waratuk cataract, 05º15’31.9”N 59º24’01.0”W, 26 Oct 1998, L. M. Page, M. H. Sabaj, J. M. Armbruster, M. Hardman, J. H. Knouft & W. S. Prince.

Paratypes. Guyana, Potaro-Siparuni: AUM 28140, 14 (27.3-43.1 mm SL) ; INHS 49549 , 9 , (1 CS, 43.3 mm SL) (30.3-46.6 mm SL), MBML 2046, 3 (32.2-42.6 mm SL), and MNRJ 28720 , 3 , (1 CS, 34.0- 39.5 mm SL) all collected with the holotype .

Diagnosis. Tatia meesi is uniquely distinguished from congeners by its coloration: dorsal surface of body, back and upper sides dark-brown sometimes with depigmented area around adipose fin. Cranial fontanel with two narrow openings: anterior one between mesethmoid and frontal and posterior one limited to frontal ( Fig. 31 ). The fontanel apertures are separated from each other through an orbitosphenoid suture beneath frontal. The new species also is distinguished from congeners by a combination of characteristics: nasal ossified as tube, with narrow lateral flange not sutured to mesethmoid; pectoral fin I,4; caudal-fin lobes are the same length in both adult females and males. An additional feature useful for distinguishing T. meesi has the smaller adult size, less than 50 mm SL.

Description. Measured adult specimens 39.5-46.6 mm SL; morphometric data presented in Table 10. Body slim, head slightly depressed dorso-ventrally. Head robust, outline of head in dorsal view somewhat elliptic, broader than long. Trunk from dorsal-fin base to caudal peduncle becoming gradually compressed laterally. Lateral profile of head from snout tip to opercular margin slightly convex until pectoralfin insertion. Ventral profile of head and abdomen almost straight. Ventral profile of body gently curved, concave behind anal-fin origin. Head integument thin, cranial roof visible; well-developed adipose eye lid; eye latero-dorsally located in anterior portion of head; mouth terminal, upper lip extended postero-laterally as well-developed fleshy rictal fold; snout margin rounded, in dorsal view; anterior nostril tubular, located on anterior border of snout; posterior nostril large, rounded, limited by small skin flap; transverse distance between anterior nostrils proportionally same as distance between posterior ones. Maxillary barbel short, extending close to posterior tip of postcleithral process; mental barbel short, tips not reaching pectoral-fin base, arranged in arc along ventral surface of jaw; inner mental barbel about 51.0-64.0% length of outer mentals. Postcleithral process long almost reaching vertical through middle or end of dorsal fin. Caudal peduncle moderately deep, depth about 10.4-12.3 SL.

Rostral border of cranium with mesethmoid approximately as long as broad; premaxilla underneath with synchondral articulation; elliptical cranial fontanel, with two narrow openings: anterior one between mesethmoid and frontal and posterior one limited to frontal. Fontanel apertures separated to each other by suture beneath frontal, along orbitosphenoid ( Fig. 31 ). Nasal ossified, tubular, with narrow medial flanges, not sutured to mesethmoid; autopalatine tubular, oriented obliquely to longitudinal axis of body; maxilla about same size of autopalatine; prevomer expanded anteriorly, with well developed arrow-shaped lateral processes; jaws of equal size; premaxilla and dentary narrow with two or three rows of conical teeth. First nuchal plate very short, pentagonal; second nuchal plate slightly concave along lateral margins; third nuchal plate curved, projected laterally, with broad tip. Epioccipital process very small.

Suspensorium, hyoid arch, branchial skeleton and opercular bones as in generic description. Suprapreopercle present as short canal bone. Five slender branchiostegal rays articulated with hyoid arch: three or four with anterior ceratohyal and two with posterior ceratohyal; last two flattened. Basibranchial 2 forming osseous rod with a broad cartilaginous anterior tip, separated from shorter basibranchial 3.

Five infraorbital bones in incomplete series. Infraorbital 1 thin with short ventro-lateral process; remaining infraorbitals thin, reduced to canalicular portions. Infraorbital 2 smallest, close to infraorbital 1, followed by non-ossified portion of canal below eye and two posterior ossicles much close to sphenotic, forming posterior orbital rim. Lateral line on body with ossified canal bones only close to head.

Dorsal fin I,5, dorsal-fin spine with 9-11 antrorse serrations along entire anterior margin, posterior margin smooth. Pectoral fin I,4, pectoral-fin spine with 15-18 antrorse serrations along anterior margin; 10-11 retrorse serrations along posterior margin; serrations along both margins progressively larger toward spine tip. Pelvic-fin i,5, margin rounded. Adipose fin small, origin on vertical through end of anal-fin base. Anal fin iii,7; anal-fin pterygiophores in eight rod-like proximal radials and seven cartilaginous distal radials. Caudal fin deeply forked, lobes with pointed tips, 8+9 principal rays, 5-8 upper procurrent, 5-6 lower procurrent rays. Pleural ribs 9 attached to consecutive vertebrae. Post-Weberian vertebrae 34 (n=2).

Color in alcohol. Dorsal surface of body, back and upper sides dark-brown sometimes with depigmented area around adipose fin. Lips and anterior nostril whitish. Head pigmentation pale, with posterior nuchal plates lighter. Lower sides and ventral surfaces whitish. Dorsal spine dark, subsequent rays darker only on its bases. Paired, anal and adipose fins unpigmented. Caudal-fin base with chromatophores becoming progressively more widely spaced, with hyaline lobes and tips.

Sexual dimorphism. Based on examination of gonads, T. meesi attains sexual maturity above 39.5 mm SL. A genital papilla is not evident in females. The genital papilla of mature male is visible, with a short deferent duct. Adult male anal fin ( Fig. 32 ) is strongly modified with a pointed tip. First unbranched anal-fin ray thickened. Second unbranched ray with a sharp tip curved towards the third unbranched ray, but not prolonged until the fin tip ( Fig. 32 , uii). Third unbranched ray is the longest one, forming a narrow fin tip, with distal segments gently curved ( Fig. 32 , uiii). First, second and third branched anal-fin rays are progressively shorter and curved towards the fin tip. Posterior branched rays normally developed; last ray not reduced ( Fig. 32 , b 7 ). The caudal fin lobes have about same length in both adult males and females.

Distribution. Known only from type locality in the Essequibo basin, Guyana ( Fig. 6 ).

Etymology. The specific name honors Dr. Gerloff F. Mees, for his significant contributions to our knowledge of the genus

Tatia , especially with regards to the species of the Guyana shield.

Remarks. The Waratuk cataract, the type locality of T. meesi , consists of rapidly flowing water over huge boulders. At the base of the cataract is a large pool and backwater area with a substrate of sand, gravel and rubble over bedrock give shelter to some catfish species, including the tiny T. meesi (L. Page, pers. comm.).

Among Tatia , subdivided fontanel apertures, with two openings separated to each other by orbitosphenoid suture is observed only in T. meesi . Dissection of alcoholic specimens confirmed the presence of an anterior and posterior fontanel. The orbitosphenoid is the place for origin of the facial mandibular muscle adductor arcus palatini. Tatia meesi has some features that are uncommon within the genus such as a tubular nasal bone and caudal-fin lobes of equal size in both males and females. It shares with T. gyrina a low number of canalicular infraorbitals and a low number of branchiostegal rays. It is distinct from T. intermedia , the only congener inhabiting the Essequibo basin, due to a cranial fontanel with two openings (vs. single opening in T. intermedia ); nasal tubular, rod-like, not sutured to mesethmoid (vs. with lateral bony flanges, sutured to mesethmoid in T. intermedia ); adult specimens small sized, less than 50 mm SL (vs. large adult size, more than 50 mm SL).

The color pattern, consisting of small chromatophores concentrated mainly on dorsolateral part of body in T. meesi , resembles superficially the pattern in T. boemia . In T. meesi , however, the caudal fin is hyaline vs. with small spots in T. boemia .

Figures

Fig. 30. Tatia meesi. (a) holotype, INHS 99772, male, 44.3 mm SL. (b) paratype, INHS 49549, female, 46.6 mm SL, Essequibo river, Guyana.

Fig. 31. Neurocranium of Tatia meesi, new species, INHS 49549, paratype, 43.3 mm SL. Dorsal view.Abbreviations: ep, epioccipital; fo, single cranial fontanel, fr, frontal; le, lateral ethmoid; me, mesethmoid; na, nasal; n1, first nuchal plate, n2; second nuchal plate; n3, third nuchal plate; pe, posterior epioccipital process; ps, posttemporal-supracleithrum; pt, pterotic; so, supraoccipital; sp, sphenotic. Scale bar = 1 mm.

Fig. 32. Male modified anal fin of Tatia meesi, INHS 49549, paratype, 43.3 mm SL. Left side lateral view.Abbreviations: b7, branched seventh ray; dd, deferent duct; ui, unbranched first ray; uii, unbranched second ray; uiii, unbranched third ray. Scale bar = 1 mm.

Fig. 7. Tatia aulopygia, (a) INPA 11080, male, 104.6 mm SL, Guaporé river, Amazonas State, Brazil. (b) ZMA 114.280, young female, 46.3 mm SL, Humaitá,Amazonas State, Brazil.

Fig. 6. Drainage map of northern South America illustrating the geographic distribution of the species of Tatia. Symbols may represent more than one locality. Base map by Marilyn Weitzman.