Otothyropsis dialeukos, Calegari, Bárbara B., Morlis, Walter Gill & Reis, Roberto E., 2017

Calegari, Bárbara B., Morlis, Walter Gill & Reis, Roberto E., 2017, A new species of Otothyropsis (Siluriformes: Loricariidae) from the upper Río Paraná basin, Paraguay, with a discussion of the limits between Otothyropsis and Hisonotus, Zootaxa 4244 (2), pp. 231-245: 232-236

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Otothyropsis dialeukos

new species

Otothyropsis dialeukos   , new species

Fig. 1 View FIGURE 1 ; Tables 1 View TABLE 1 , 2 View TABLE 2

Holotype. MNHNP 3880 View Materials , female, 34.6 mm SL, Paraguay, Alto Paraná, Hernandarias , Arroyo Itá at Paso Itá , near to Embalse de Acaray , ca. 8 km from road between Hernandarias and Ciudad del Este, Río Paraná basin, 25°22’56.9”S 54°41’34.8”W, approx. 200 m asl, 21 January 2013, W. Gill Morlis and R. Torres. GoogleMaps  

Paratypes. All from Paraguay, MNHNP 3881, 4, 9.7–34.6 mm SL and MCP 49901, 5 + 1 cs, 9.6–35.8 mm SL, collected with the holotype   ; and MNHNP 3882, 1, 31.8 mm SL and MCP 49899, 1, 26.3 mm SL, same locality as the holotype, 16 February 2012, W. Gill Morlis and R. Torres.  

Diagnosis. Otothyropsis dialeukos   differs from congeners by its unique caudal-fin coloration pattern, composed of a brown to almost black background with roundish hyaline blotches in the middle of the outermost branched rays and a hyaline posterior border interrupted in middle rays (vs. various color patterns but never two isolated roundish hyalines blotches). The new species is also distinguished from all congeners, except O. marapoama   , by having the abdomen entirely covered by enlarged plates ( Fig. 2 View FIGURE 2 ), without naked areas (vs. abdomen almost entirely naked or with naked areas among the plates). The new species further differs from all congeners, except O. piribebuy   and O. alicula   , by the absence of a raised crest of enlarged odontodes in the posterior portion of the parieto-supraocciptal (vs. presence of such crest). Otothyropsis dialeukos   is further distinguished from O. biamnicus   , O. polyodon   , and O. alicula   by having a longer prepelvic length (40.2–44.3%, vs. 36.7–39.3%, 35.8– 39.5%, and 33.9–37.7% SL, respectively); longer pectoral-fin spine (26.7–30.9%, vs. 18.6–21.3%, 21.4–26.9%, and 16.5–20.0% SL, respectively); longer dorsal-fin spine (23.1–27.1%, vs. 19.4–22.9%, 18.2–22.0% and 19.1– 22.3% SL, respectively); and shorter caudal peduncle (31.5–34.2%, vs. 41.3–45.1%, 40.0–45.1%, and 39.9–45.4% SL, respectively). The new species differs from O. biamnicus   and O. polyodon   by having fewer plates in the median lateral series (19–20 vs. 24–25 plates in both species). Otothyropsis dialeukos   is distinguished from O. marapoama   and O. piribebuy   by having more numerous plates between the anal and the caudal fins (11–12 vs. 9– 10 plates in both). It is further distinguished from O. piribebuy   by having a higher number of premaxillary teeth (18–25 vs. 10–19), and by the larger orbital diameter (15.1–18.5, vs. 12.3–15.1% HL), and from O. marapoama   , by having a smaller cleithral width (21.5–23.4 vs. 23.8–25.8% SL).

Otothyropsis dialeukos   can be also distinguished from the species of Hisonotus   inhabiting the upper Paraná River system by the deeper caudal peduncle 9.5–11.0% SL (vs. 7.2–8.5% in H. alberti   , 7.9–9.4% in H. depressicauda   , 6.6–7.9% in H. depressinotus   , 6.9–8.3% in H. francirochai   ) and São Francisco basin (6.8–8.2% in H. vespuccii   ), or by the plated abdomen (vs. abdomen naked in H. pachysarkos   ).

Description. Morphometrics in Table 1 View TABLE 1 and meristics in Table 2 View TABLE 2 . Body in dorsal perspective progressively tapering from operculum to end of caudal peduncle. Dorsal profile of head straight to slightly convex from snout tip to middle of parieto-supraoccipital, and straight to slightly concave from that point to dorsal-fin spinelet. Dorsal profile of body sloped and descending from origin of dorsal fin to few plates before end of caudal peduncle. Ventral profile of body relatively straight from head to tail. Greatest body width at cleithrum. Body deepest at dorsal-fin origin and shallowest right before end of caudal-fin peduncle. Trunk and caudal peduncle oval in cross-section and laterally compressed. Adipose fin absent. Head and snout rounded in dorsal view. Snout long with region anterior to nares depressed. Mid-portion of head from end of rostral plates to posterior margin of nares raised. Dorsal margin of orbit slightly elevated. Eye dorsolaterally placed. Iris operculum present. Oral disk round; lower lip relatively short, reaching midway to pectoral girdle.

Lips papillose with small fleshy ridge immediately behind dentary. Lower lip with minute papillae except for naked area at median portion of lip just posterior to dentary. Barbel short and laterally positioned, distal portion free from lip margin. Posterior border of lower lip crenulate. Tooth series in premaxilla and dentary forming overall angle of approximately 90 degrees. Teeth bifid, elongated and slender, with large blade-like medial cusp and small lateral cusp. Accessory teeth lacking on premaxilla and dentary in adult and juvenile specimens.

Body almost entirely covered by plates, except for ventral surface prior to pectoral girdle, anterior to urogenital opening, around dorsal-fin base, and region from posterior margin of median rostral plate to posterior margin of naris. Abdomen completely covered by enlarged plates ( Fig. 2 View FIGURE 2 ). Four or five large plates in lateral series of abdominal plates (n = 6), wider than long. Plates in median series of abdominal plates comparatively smaller, forming single regular series. Plates in preanal abdominal series large and irregularly distributed, somewhat quadrangular in shape. All abdominal plates bearing small odontodes, except for pair of posterior most preanal abdominal plates which bear larger odontodes on posterior border.

Head mostly smooth, lacking odontode crests; odontodes on body uniform in size and distribution, except for augmented odontodes on ventral margin of snout tip. Infraorbital sensory canal entering infraorbital series via compound pterotic. Median series of lateral plates with 19–20 plates, incomplete, ending two plates before the end of the caudal peduncle, but continuously perforated. Mid-dorsal and mid-ventral series of lateral plates with 17 and 16–18 plates, respectively, truncated posteriorly, near to caudal fin. Three irregular transverse rows of predorsal plates, in addition to nuchal plate. Cleithrum and coracoid entirely exposed on ventral surface and covered with odontodes. Arrector fossa open in restricted portion medially, covered by bone shelves from both coracoid and cleithrum laterally. Pectoral fin I,6. Pectoral-fin spine long and somewhat slender. Tip of adpressed pectoral-fin spine almost reaching to end of first pelvic-fin ray; approximately of same width along its length. Odontodes on pectoral-fin spine distributed only on lateral border of spine and slightly increasing in size gradually towards tip. Pectoral-fin branched rays becoming progressively shorter posteriorly. Pectoral-fin axillary slit present in adults and juveniles. Pelvic fin i,5. Pelvic-fin unbranched ray thick and shorter than branched rays. Interradial membrane of pelvic fin fringed distally. Dorsal fin II,7, its origin slightly posterior to vertical through end pelvic-fin base. Dorsal-fin spinelet plate-like, oval to triangular in shape. Anal-fin i,5, its unbranched ray ticker and slightly shorter than remaining branched rays. First unbranched anal-fin ray covered with odontodes; odontodes increasing in size towards ray tip. Caudal-fin I,14,I (1 specimen with I,15,I). Caudal fin weakly forked. Total vertebrae 28 (in 1 cs specimen).

Color in alcohol. Ground color of dorsal surface of head dark brown with lighter stripe in front of each nostril. Posterior process of parieto-supraoccipital and dorsal surface of trunk medium brown with dark chromatophores uniformly distributed. Inconspicuous longitudinal dark brown stripe from snout, crossing orbit and opercle, and continuing to end of caudal peduncle. Postrostral plates, opercle, and lateral portion of cleithrum light cream, with many dark chromatophores unevenly sprinkled, forming conspicuous light cream to white cheek. Ventral surface mostly pale yellow, with dark chromatophores unevenly scattered on lower surface of head, lateral portions of abdomen and more heavily concentrated on caudal peduncle. Fin membranes mostly hyaline, with series of small dark dots arranged in irregular transverse bands in all fins except caudal fin. Caudal fin with both rays and membrane mostly dark brown, with roundish hyaline blotches in middle of outermost branched rays, and hyaline posterior border disconnected in middle rays ( Fig. 1 View FIGURE 1 ).

Sexual dimorphism. Sexual dimorphism characterized by the possession of a small, conical urogenital papilla immediately posterior to the anal opening in males, which also possess a fleshy flap along the dorsal margin of the first pelvic-fin ray. In addition, males have longer first unbranched pelvic-fin ray (18.8–20.0 vs. 15.2–17.0% SL in females). As usual in Otothyropsis   species, males have markedly wider nares than females (13.1–13.3 vs. 7.5–9.4% HL in females), and smaller internareal width (8.1–8.4 vs. 9.2–10.7% HL in females).

Distribution. Otothyropsis dialeukos   is known only from its type locality, the Arroyo Itá, a tributary to the Embalse de Acaray, upper Río Paraná basin in Paraguay ( Fig. 3 View FIGURE 3 ).

Etymology. From the Greek dialeukos   , meaning marked with white, in reference to the white or light cream color of the cheek. A noun in apposition.

TABLE 1. Morphometric data for Otothyropsis dialeukos. Holotype (Hol) and five paratypes; ranges include holotype. SD = standard deviation.

Character Hol N Low High Mean SD
Standard length (mm) 34.6 6 26.3 35.8 31.8 -
% SL            
Head length 35.3 6 33.8 35.4 34.8 0.6
Predorsal length 46.3 6 44.2 48.7 45.6 1.7
Postdorsal length 44.9 6 40.9 44.9 42.8 1.4
Prepectoral length 26.6 6 26.6 27.8 27.1 0.5
Prepelvic length 42.9 6 40.2 44.3 42.3 1.4
Preanal length 62.4 6 58.1 63.2 61.5 2.0
Cleithral width 23.4 6 21.5 23.4 22.7 0.8
Snout-opercle distance 26.6 6 26.5 27.8 27.1 0.5
Pectoral-pelvic-fins distance 17.5 6 14.5 17.5 16.2 1.2
Pelvic-anal-fins distance 21.3 6 19.0 22.0 20.6 1.1
Dorsal-fin spine length 24.9 6 23.1 27.1 24.7 1.4
Dorsal-fin base length 12.3 6 11.4 12.8 12.2 0.5
Pectoral-fin spine length 29.8 6 26.7 30.9 29.2 1.8
First pelvic-fin unbranched ray length 17.0 6 15.2 20.0 17.2 1.8
First anal-fin unbranched ray length 17.4 6 13.4 18.3 16.6 1.8
Caudal-peduncle length 34.2 6 31.5 34.2 32.6 1.0
Caudal-peduncle depth 11.1 6 9.6 11.1 10.4 0.5
Caudal-peduncle width 4.1 6 3.6 5.5 4.5 0.8
Body depth at dorsal-fin origin 17.6 6 14.2 17.6 16.1 1.2
Body width at dorsal-fin origin 19.5 6 16.9 19.5 18.2 1.1
% HL            
Head depth 40.3 6 38.4 45.9 42.4 2.7
Snout length 52.0 6 50.3 53.7 52.1 1.2
Orbital diameter 15.3 6 15.1 18.5 16.7 1.4
Interorbital distance 40.4 6 38.2 41.3 40.0 1.1
Internareal width 10.7 6 8.1 10.7 9.4 1.0
Nares diameter 7.7 6 7.5 13.3 10.0 2.6
Prenasal length 37.4 6 35.2 38.8 37.5 1.3
Suborbital depth 16.4 6 14.6 17.1 15.9 0.9
Barbel length 10.6 6 7.0 10.6 9.0 1.7

TABLE 2. Meristic data for Otothyropsis dialeukos. Holotype included in range. n = number of specimens.

Character n Holotype Range
Right premaxillary teeth 6 19 18-25
Left premaxillary teeth 6 19 18-24
Right dentary teeth 6 17 15-20
Left dentary teeth 6 17 14-21
Plates in dorsal lateral series 6 20 18-20
Plates in mid-dorsal lateral series 6 17 17
Plates in median lateral series 6 20 19-20
Plates in mid-ventral lateral series 6 18 16-18
Plates in ventral lateral series 6 19 17-19
Plates between anal and caudal fins 6 11 11-12
Plates at dorsal-fin base 6 5 5
Plates at anal-fin base 6 2 2-3
Predorsal plates 6 3 3

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