Nannoxyropsis acicula, Delapieve & A. & Reis, 2017

Delapieve, Maria Laura S., A., Pablo Lehmann & Reis, Roberto E., 2017, An appraisal of the phylogenetic relationships of Hypoptopomatini cascudinhos with description of two new genera and three new species (Siluriformes: Loricariidae), Neotropical Ichthyology 15 (4), No. e 170079, pp. 1-38 : 30-32

Nannoxyropsis acicula , new species

urn:lsid:zoobank.org:act:C05ED1D9-1707-4C90-AB18-07B7375209B5

Fig. 19

Holotype. MCP 51326, female, 27.1 mm SL, Brazil, Pará , Itaituba , Igarapé Capiteo on Transamazonic road between Comunidade 28 and Vila Rayol, 04°22’43”S 56°16’32.9”W, 24 October 2016, R. E. Reis, T. P. Carvalho & B. B. Calegari.

Paratypes. Brazil, Pará State, Rio Tapajós basin: MCP 51325, 3 23.4-24.3 mm SL + 2 tissue sample vouchers, same data as holotype. MCP 51324, 3 , 24.9-25.4 mm SL + 1 tissue sample voucher, creek tributary to rio Tapajós ca. 20 km SW of Itaituba, on road to Comunidade 28, Itaituba , 04°18’21”S 56°05’54.4”W, 24 October 2016, R. E. Reis, T. P. Carvalho & B. B. Calegari. MPEG 25249 , 23 , 20.9- 29.7 mm SL and MCP 51462, 7 , 23.4 -29.0 mm SL+ 3 c&s, 23.9-27.8 mm SL, rio Tapajós near Mamãe Anã village , Jacareacanga, approx. 05°46’S 57°23’W, 4 October 2012, N. Benone. MPEG 26488 , 38 , 22.5-33.5 mm SL and MCP 51463, 15 , 22.8-27.6 mm SL, rio Tapajós near Buburé village , Jacareacanga, 04°42’58”S 56°26’24”W, 6 January 2013, N. Benone. MZUSP 92752 , 3 , 23.2-25.7 mm SL, right margin of rio Tapajós at Pimental, 04°34’15”S 56°15’39”W, 11 November 2006, L. M. Sousa & J. L. Birindelli .

Diagnosis. Nannoxyropsis acicula is distinguished from N. ephippia by lacking preopercle latero-sensory canal (vs. sensory canal present); and by odontodes on posterior margin of the parieto-supraoccipital enlarged, forming crest (vs. odontodes not enlarged or forming crest). Nannoxyropsis acicula is further distinguished from N. ephippia by a longer head (34.8-39.4 vs. 29.4-33.5% SL); a narrower snout (width of snout measured at widest point of mouth opening 37.0-40.7 vs. 43.1-45.3% HL); a larger predorsal length (44.7-48.9 vs. 40.1-44.5% SL); a smaller dorsal interorbital distance (37.1-42.4 vs. 43.0-54.2% HL); a smaller number of plates in median series of lateral plates (20-22 vs. 23); and a smaller number of teeth on premaxilla (11-17 vs. 18-26).

Description. Proportional measurements and counts in Tabs. 2, 4. Body relatively small and slender, moderately elongated; head moderatly depressed. Dorsal profile of head and body slightly convex from snout tip to dorsal-fin origin; parieto-supraoccipital slightly elevated leaving interorbital region convex. Trunk profile descending from dorsal-fin origin to anteriormost procurrent caudal-fin ray.Body deepest at dorsal-fin origin; body shallowest at posterior portion of caudal peduncle. Body ovoid to transversely depressed in cross section, progressively compressed posterior to anal-fin base. Greatest body width at cleithrum.

Anterior margin of snout acute and triangular in dorsal view with rounded tip. Snout with slight depression anterior to each nostril. Eye large, laterally positioned, barely visible in ventral view; iris operculum absent. Compound pterotic perforate only laterally, fenestrae increasing in size posterolateral margin of bone. Pore between canal-bearing cheek plate and fourth infraorbital present. Three predorsal plates anterior to trapezoidal nuchal plate. Odontodes on dorsal and ventral margins of snout distinctly larger than other odontodes on head. Enlarged odontodes on ventral margin extending below eye. Posterior tip of parietosupraoccipital with tuft of enlarged odontodes; without other crests on dorsal surface of head. Lips rounded and covered with globular papillae. Teeth slender, bifid, with blade-like larger medial cusp and smaller lateral cusp. Plates anterior to cleithrum absent.

Median series of lateral plates complete with lateral line continuous. Odontodes on head and trunk pointed, uniform in size and shape and conspicuously aligned; odontodes on caudal peduncle slightly larger. Odontodes on ventral surface of body smaller and scattered, not arranged in lines. Body covered by plates, except area around anus, region overlying lateral opening of swimbladder capsule, area between lower lip and pectoral girdle, and area around fin bases. Ventral portions of cleithrum and coracoid completely exposed and supporting odontodes. Abdomen covered by 2-6 (mean

4) transversely elongate lateral abdominal plates; middle

abdominal plates 1-6 (mean 4). Single, large preanal plate between pelvic fins. Anal tube slightly right turned. Total vertebrae 26; ribs 3, beginning on tenth vertebral centrum, in addition to large rib on sixth centrum.

Dorsal fin I,7, its origin at vertical through middle of pelvic fin. Dorsal-fin spinelet absent. Pectoral fin I,6, with small axillary slit in skin behind fin insertion. Pectoral-fin spine with small serrae composed of retrorse, conical, acute teeth along posterior margin, one per ray segment. Serrae more conspicuous in younger specimens, absent in larger. Pectoral fin reaching to vertical through posterior third of pelvic-fin unbranched ray. Adipose fin absent. Pelvic fin i,5, short, with robust thickened first ray shorter than two first branched rays. Odontodes on pelvic-fin unbranched ray turned and strongly pointing mesially. Anal fin i,5; first analfin pterygiophore exposed in front of unbranched fin ray. Caudal fin i,14,i, forked, upper and lower lobes equal.

Color in alcohol. Ground color of dorsal surface of head and

body tan to light brown. Dark brown melanophores on head more densely concentrated on compound pterotic, parietosupraoccipital, frontals, postrostral plates, and anterior surface of upper lip. Longitudinal dark brown lateral stripe on midlateral surface of head and body; stripe beginning laterally on snout tip, crossing eye, and continuing to end of caudal peduncle. Brown melanophores arranged in four or five inconspicuous dorsal saddle-like blotches; one anterior to dorsal fin, one on posterior portion of dorsal fin, two or three at caudal peduncle. Ventral surface of body mostly unpigmented except for ventral portion of snout plates, canal-bearing cheek plate, and lateral portions of caudal peduncle. Dorsal and pectoral fins with 5-6 dark brown spots, continued as 3-4 irregular bands on branched rays. Pelvic fin with 1-2 and anal fin with 2-3 such spots. Caudal fin with dark brown spot at base and 5-7 bands of brown melanophores on unbranched and branched rays. Interradial membrane of all fins unpigmented.

Sexual dimorphism. Males have a small urogenital papilla behind the anal tube. One mature male has a pelvic-fin contact organ, composed of a row of slightly enlarged odontodes on the dorsal surface of the first pelvic-fin branched rays. Those odontodes are approximately twice the size of other odontodes on the dorsal surface of the pelvic fin.

Distribution and habitat. Nannoxyropsis acicula is known from tributaries to the lower rio Tapajós in Brazil ( Fig. 16). Collecting localities near Itaituba are clear to blackwater creeks with moderate water current, the bottom is composed of stones, gravel and mud or clay in parts, and there are moderate amounts of marginal vegetation. Dissolved oxygen at locality of lot MCP 51324 was 2.2 mg /l at the collecting event.

Etymology. From the Latim acicula , meaning needle, pin, in reference to the narrowness of the snout compared to N. ephippia . A noun in apposition.

Conservation status. Nannoxyropsis acicula is relatively frequent and abundant in the tributaries of the middle rio Tapajós, with an EOO of approximately 1,800 km 2. As the population is not fragmented, continuing decline cannot be inferred, and no eminent threats are detected, N. acicula can be categorized as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2016).