Hypostomus dardanelos, Zawadzki & Carvalho, 2014

Zawadzki, Cláudio H. & Carvalho, Pedro Hollanda, 2014, A new species of the Hypostomus cochliodon group (Siluriformes: Loricariidae) from the rio Aripuanã basin in Brazil, Neotropical Ichthyology 12 (1), pp. 43-51 : 44-49

Hypostomus dardanelos , new species

Figs. 1-3

Hypostomus gr. cochliodon Fernandes et al., 2013: 843 [list of species and ecology].

Holotype. INPA 37342 , 172.2 mm SL, Brazil, Mato Grosso State, município de Aripuanã, rio Madeira basin, rio Praia Grande (at its mouth to rio Aripuanã downstream cachoeira Dardanelos and Andorinhas ), 10°02’51”S 59°23’21”W, 8 Aug 2008, I. M. Fernandes.

Paratypes. All from Brazil, Mato Grosso State, município de Aripuanã, rio Aripuanã basin: MNRJ 36319 , 1 , 145.5 mm SL, rio Aripuanã , at rapids downstream cachoeira Dardanelos , 10°09’41.7”S 59°27’41.9”W, 12 Mar 2008, F. Pupo & I. Veríssimo. MNRJ 38652 , 1 , 119.8 mm SL, rio Aripuanã , left margin, 1500 m downstream Dardanelos waterfalls, 10°09’30”S 59°26’19”W, 11 Dec 2008, F. Pupo. MNRJ 38871 , 1 , 143.0 mm SL, rio Aripuanã , 500 m downstream Dardanelos waterfalls, 10°09’47”S 59°26’56”W, 28 Jul 2010, F. Pupo. MZUSP 37595 , 2 , 172.0-183.9 mm SL (larger specimen skeletonized after measuring), rio Aripuanã , Humboldt , 3 km downstream Cachoeira Grande falls, no coordinates available, 8 Nov 1976, Expedition MZUSP and INPA. MZUSP 37795 , 1 , 168.3 mm SL, rio Aripuanã , 8 Nov 1976, Expedition MZUSP and INPA. MZUSP 110798 , 2 , 135.5 - 163.7 mm SL, rio Aripuanã , 7 Jan 2004, F. A. Machado, C. M. C. Leite & F. Rosa. NUP 6758, 8, 118.8- 160.5 mm SL, collected with holotype. NUP 6759, 2, 115.5-141.2 mm SL, stream with unknown name, tributary to igarapé Guaribal, 10°06’35”S 59°26’12”W, 8 Aug 2008, I. M. Fernandes. NUP 6760, 1, 143.5 mm SL, igarapé Guaribal, tributary to rio Aripuanã , 10°06’35”S 59°26’12”W, 18-19 May 2008, I. M. Fernandes. NUP 6765, 1, 55.0 mm SL, stream with unknown name, tributary to rio Guaribal , 10°06’35”S 59°26’12”W, 18-19 May 2008, I. M. Fernandes. NUP 6775, 1, 151.8 mm SL, stream with unknown name, tributary to rio Praia Grande , 10°02’51”S 59°23’21”W, 19 May 2008, I. M. Fernandes. NUP 7098, 1, 46.0 mm SL, stream with unknown name, tributary to igarapé Praia Grande, 10°02’45”S 59°27’24”W, 5 Aug 2008, I. M. Fernandes. NUP 7130, 2, 40.0-42.7 mm SL, stream with unknown name, tributary to igarapé Praia Grande, 10°02’59”S 59°27’40”W, 5 Aug 2008, I. M. Fernandes. NUP 7192, 1, 42.0 mm SL, stream with unknown name, tributary to igarapé Rio Claro , 10°03’09”S 59°33’20”W, 6 Aug 2008, I. M. Fernandes. NUP 7474, 4, 123.0-181.0 mm SL, collected with holotype. NUP 7637, 2, 12.3-40.1 mm SL, stream with unknown name, tributary to igarapé Guaribal, 10°04’37”S 59°31’04”W, 15 May 2008, I. M. Fernandes. NUP 7694, 1, 42.0 mm SL, stream with unknown name, tributary to igarapé Guaribal, 10°06’35”S 59°26’12”W, 5 Aug 2008, I. M. Fernandes. NUP 9452, 1, 40.6 mm SL, stream with unknown name, tributary to igarapé Rio Praia Grande , 10°02’51”S 59°23’21”W, 17 May 2008, I. M. Fernandes .

Non-type specimens. NUP 14655, 1, 103.7 mm SL, Igarapé Arraia , tributary to rio Aripuanã, 10°07’15”S 59°31’42”W, 19 Jan 2013, H. P. Silva & C. H. Zawadzki . NUP 14656, 1, 66.8 mm SL, igarapé Guaribal , tributary to rio Aripuanã, 10°08’51”S 59°29’56”W, 19 Jan 2013, C. H. Zawadzki & H. P. Silva .

Diagnosis. Hypostomus dardanelos is distinguished from its congeners by its unique color pattern of yellowish-brown ground color covered by well-defined dark spots of relatively equal size, evenly spaced and moderately set along the dorsal region of the body and fins, except on the ventrolateral region of the caudal peduncle, and proximal region of anal and caudal fins, which are devoid of spots (vs. without spots, with pale spots, or with moderately- or sparsely-set dark spots that are usually larger, more faded, and more remotely spaced towards posterior region of body, and with ventrolateral caudal peduncle usually bearing spots). Additionally, H. dardanelos is further distinguished from all species of Hypostomus , except those belonging to the Hypostomus cochliodon group, by having few spoon-shaped teeth, 10 to 13 (vs. more than 16 villiform teeth), dentaries angled less than 80° (vs. dentaries angled more than 80°) and by the presence of a notch between hyomandibular and the metapterygoid (vs. notch absent). The new species is further diagnosed from H. hemicochliodon Armbruster , H. kopeyaka Carvalho , Lima & Zawadzki, H. sculpodon Armbruster , H. soniae Hollanda Carvalho & Weber , and H. weberi Hollanda Carvalho , Lima & Zawadzki by possessing massive round teeth, with mesial cusp large and distinctly spoon shaped and outer cusp, if present, fused to the mesial one and scarcely noticeable (vs. clearly bicuspid teeth, although the lateral cusp is considerably smaller than mesial cusp); from H. hemicochliodon , H. kopeyaka , H. paucimaculatus Boeseman , H. sculpodon , H. waiampi Hollanda Carvalho & Weber , H. weberi by lacking a medial buccal papilla (vs. medial buccal papilla present); from H. ericae Hollanda Carvalho & Weber , H. plecostomoides , and H. pyrineusi (Miranda Ribeiro) by having strong keels in dorsal, mid-dorsal and median series of plates (vs. keels absent in H. pyrineusi and moderately-developed keels in H. ericae and H. plecostomoides ); from H. ericius Armbruster by having caudal fin usually with dark spots distally (vs. caudal fin dark blurred distally); from H. hondae by having the exposed portion of opercle inconspicuous (vs. exposed portion of opercle easily visualized); from H. macushi Armbruster & Souza by having small dark spots (vs. medium to large dark spots); from H. oculeus (Fowler) by lacking strong keel on mid-ventral series of plates (vs. having strong keels on all lateral series plates, including the mid-ventral one, see Armbruster, 2003, fig. 16); from H. pagei by having uniformly conspicuous small dark spots (vs. spots becoming faded or absent); and from H. taphorni by having both caudal-fin lobes evenly colored (vs. bicolored caudal fin with lower lobe darker).

Description. Meristic and morphometric data in Table 1 . Holotype and additional specimens in Figs. 1-3 . Dorsal profile slightly convex to straight from snout tip to interorbital area, strongly convex from interorbital area to dorsal-fin origin, and gently descending from dorsal-fin origin to first procurrent plate of caudal fin. Ventral profile almost straight from snout tip to caudal fin. Caudal peduncle slightly compressed laterally, ellipsoid in cross section. Body width at cleithral region greater than head depth. Head broad and deep, dorsally covered with dermal bones, except for small naked area on snout tip (snout tip plated in one specimen, NUP 7474, 181.0 mm SL). Median elongated bulge associated with mesethmoid terminating coequally with transversal through nares. Conspicuous ridge originating lateral to nares, passing through supraorbital, and extending to posterior portion of pterotic-supracleithrum. Supraoccipital bone with moderate to highly developed median ridge, and with relatively well-developed posterior process bordered by single wide plate. Exposed region of opercle small, not easily seen and usually with less than ten odontodes. Oral disk round, moderate in size. Lower lip not reaching transversal through gill openings, ventral surface covered with numerous small papillae decreasing in size posteriorly. Maxillary barbel moderately developed, almost equal in length to orbital diameter. Odontodes present over anterior surface of upper lip, just below snout. Medial buccal papillae absent. Maxilla straight. Jaws acutely angled, averaging less than 80° between left and right dentary rami. Teeth spoon shaped, apparently unicuspid; mesial cusp massive and round; lateral cusp extremely reduced and usually fused to mesial cusp (similar to the condition found in Hypostomus ericae ; Hollanda Carvalho & Weber, 2004: 640, fig. 4a).

Body covered with five rows of moderately spinulose dermal plates, except for region surrounding dorsal-fin base and very small areas around pectoral- and pelvic-fin insertions and at urogenital opening. Specimen NUP 7474, 181.0 mm SL with well-developed nuptial odontodes along dorsal surface of body and fin rays ( Fig. 2c ). Predorsal region with two conspicuous keels; area between keels flat. Dorsal, middorsal, and median series of plates with keels supporting sharp odontodes. Mid-ventral series lacking sharp odontodes or having moderate odontodes. Dorsal series of lateral plates with keel from first plate to area just anterior to origin of adipose fin. Mid-dorsal series of lateral plates with keels from first plate to area just posterior to adipose fin; third plate with keel oriented upward. Median series of plates with moderately-developed keels to area just below posterior dorsal-fin base. Mid-ventral series of plates with moderate keels from first to fifth or sixth plate, then slightly arched to area below adipose fin. Ventral series of plates devoid of keels; posterior two plates deflected laterally. Ventral surface of head totally covered with platelets, except for region beneath lower lip. Abdomen completely covered with minute platelets in specimens larger than 120 mm SL. Preanal plate present.

Dorsal fin II,7, its origin at vertical through midpoint between origins of pectoral and pelvic fin, or slightly posterior to that point. Dorsal-fin margin straight to slightly convex. Adipose-fin spine compressed and curved toward its base. Pectoral fin I,6, its posterior border straight. Pectoral-fin spine slightly curved posteriorly, covered with moderately developed odontodes; odontodes enlarged towards distal portion of spine and particularly in larger specimens. Specimen NUP 7474, 181.0 mm SL with strong hypertrophied odontodes on posterodorsal region of pectoral fin. Tip of adpressed pectoral fin reaching to anterior one-third of pelvic-fin spine length. Pelvic fin i,5, its posterior border slightly roundish. Adpressed pelvic-fin spine just reaching to or just surpassing anal-fin origin. Anal fin i,4, its tip reaching the fifth to sixth plate after its origin. Rays of anal fin progressively increasing in size, third branched ray usually the longest. Caudal fin i,14,i. Caudal-fin margin falcate; ventral lobe slightly longer than dorsal one.

Color in alcohol. Overall ground color of dorsal and ventral regions of body and fins yellowish-brown. Dorsal surface of head and body covered by well-defined and moderately-set dark spots except on ventrolateral region of caudal peduncle. Spots on ventral surface uncommon, observed only in two specimens as scarce and sparsely arranged. Dorsal and pectoral fins with dark spots, mainly on proximal region and along spines and first branched rays. Pelvic fin with dark spots usually grouped on median region of branched rays. Anal fin usually lacking spots. Caudal fin with few distally, but usually lacking spots proximally; distal caudal-fin spots occasionally vertically aligned in two to three bands.

Spot pattern with pronounced ontogenetic variation ( Fig. 2 ). Marks typically larger, scarce and ill-defined on smaller specimens. Patches of pigmentation gradually forming welldefined spots during ontogenic growth. Dark spots generally large, few in number and widely spaced on specimens up to 45 mm SL; spots on fins sometimes fused forming transverse bands. Spots smaller, mores numerous and set closer on specimens up to 115 mm SL. Spots better outlined at this stage, especially on head and trunk. Spots progressively more numerous on head and trunk, and better outlined, including fins, up to specimens around 180 mm SL.

Color in life. Live specimens with coloration similar to preserved ones, except for more brownish yellow coloration on body and fins ( Fig. 3 ).

Distribution. Hypostomus dardanelos is currently known from the rio Aripuanã drainage, downstream cachoeira Dardanelos ( Fig. 4 ).

Etymology. The specific epithet, dardanelos , is a noun in reference to the cachoeira Dardanelos. A noun in apposition.

Figures

Fig. 1. Hypostomus dardanelos, INPA 37342, 172.2 mm SL, holotype, Brazil, Mato Grosso State, rio Praia Grande, tributary to rio Aripuanã, rio Madeira basin. Picture horizontally reversed.

Fig. 2. Specimens of Hypostomus dardanelos showing ontogenetic variation on the color pattern and on the development of the nuptial body odontodes in c. (a) NUP 7098, paratype, 46.0 mm SL; (b) NUP 6759, paratype, 115.5 mm SL; and (c) NUP 7474, paratype, 181.0 mm SL.

Fig.3. Live specimen ofHypostomus dardanelos, MNRJ 36319, paratype, 145.5 mm SL, from the rio Aripuanã at the rapids downstream cachoeira Dardanelos, município de Aripuanã, Mato Grosso State, Brazil. Photographed immediately after capture by F. Pupo.

Fig. 4. The cachoeira Dardanelos at the município deAripuanã, Mato Grosso State, Brazil. This fall is part of a series of close waterfalls descending about 150 m from its upper to the lower levels. This natural feature is known to be a biogeographic boundary for certain groups of fishes.