Ituglanis apteryx, Datovo, Aléssio, 2014

Datovo, Aléssio, 2014, A new species of Ituglanis from the Rio Xingu basin, Brazil, and the evolution of pelvic fin loss in trichomycterid catfishes (Teleostei: Siluriformes: Trichomycteridae), Zootaxa 3790 (3), pp. 466-476 : 467-471

Ituglanis apteryx , new species

(Figs. 1–2, Table 1 )

Ituglanis sp. F: Datovo & de Pinna (2014), p. 316 (list of material examined), 324 (discussion).

Holotype. MZUSP 115048, 63.4 mm SL; Brazil, Pará State, Altamira Municipality; Rio Amazonas drainage, Rio Xingu basin, Rio Iriri sub-basin, Rio Curuá, cofferdam formed during the building of the Buriti Hydroelectric Dam (PCH); 08°46'09"S 54°57'02"W; collected by J. L. O. Birindelli, L. Souza, A. L. Netto-Ferreira, M. Sabaj-Perez, N. Lujan; 21 October 2007.

Paratypes. MZUSP 96876, 7 specimens (39.1–67.2 mm SL): 2 MS (56.9 mm SL; one specimen with anterior portion of head severed); same data as holotype.

Diagnosis. Ituglanis apteryx is promptly distinguished from all congeners, except some specimens of I. parahybae , by the absence of pelvic fins, girdle, and muscles (Fig. 1; vs. presence). Pelvic structures are absent in all known individuals of I. apteryx , whereas in I. parahybae only some specimens lack pelvic elements ( Costa & Bockmann 1993; Datovo & de Pinna 2014). Ituglanis apteryx differs from I. parahybae in the following traits: presence of a supraorbital laterosensory canal with pores s1, s3, and s6 (Fig. 2; vs. entire supraorbital canal lacking); absence of a posterior cranial fontanel (Fig. 2; vs. presence); six branchiostegal rays (vs. eight); two pair of ribs (vs. six); 43–45 post-Weberian vertebrae (vs. 38); 27 predorsal post-Weberian vertebrae (vs. 22); and presence of an epural (vs. absence; Costa & Bockmann 1993; Morris et al. 2006; Sarmento-Soares et al. 2006).

Description. Morphometrics given in Table 1 ; see Fig. 1 for general external aspects. Body elongate with dorsal and ventral profiles ranging from straight to slightly convex on trunk and from straight to gently convex along caudal peduncle. Cross section of trunk at pectoral girdle nearly circular and becoming gradually more compressed posteriorly.

Head wide and depressed, with anterior margin rounded, dorsal profile straight, and ventral profile convex. Eyes situated on anterior half of head, near to posterior nostril. Orbital rim not free. Elliptical ocular capsule formed by thin and translucent skin not adhered to eyeball’s surface. Anterior nostril surrounded by tubular flap continuous with base of nasal barbel; posterior nostril opening with crescent thin flap along its anterior border only.

Mouth subterminal and slightly convex in ventral view. Lower lip with lateral fleshy folds continuous with rictal barbel base. Nasal barbel emerging from lateral region of anterior nostril and not reaching occiput. Maxillary and rictal barbels nearly of same size with tips reaching middle region of interopercular patch of odontodes. Branchial membranes thick, united to isthmus only anteriorly and forming small free fold across isthmus. Branchiostegal rays six; median most rays barely visualized through skin.

Opercular patch of odontodes rounded and dorsolaterally placed on head; 13 (1 specimen) or 16 (1 specimen) conical opercular odontodes. Interopercular patch of odontodes narrow, elongate and posteriorly curved; 20 (1 specimen) or 25 (1 specimen) conical interopercular odontodes.

Pectoral fin with first ray slightly longer than remaining rays and forming short pectoral filament; remaining rays nearly same size resulting in straight distal margin of fin. Pectoral-fin rays i,4 (both sides of 7 specimens, including holotype; one side of 1 specimen) or, rarely, i,3 (one side of 1 specimen). Anterior portion of pectoral-fin base partially covered by branchial membrane. Axillary pore present (7 specimens; holotype) or, rarely, absent (1 specimen).

Pelvic fin, girdle, and muscles absent in all examined specimens.

Dorsal fin on posterior third of body, with origin situated approximately at vertical through anal-fin origin. Dorsal fin with distal margin convex; principal rays ii,7 (6 specimens; holotype), rarely i,7 (1 specimen) or ii,6 (1 specimen); unsegmented rays iii (2 specimens); and eight basal radials (2 specimens) located between neural spines of 27th and 31st (1 specimen) or 27th and 32nd (1 specimen) post-Weberian vertebrae.

FIGURE. 1. Ituglanis apteryx , new species, holotype, MZUSP 115048, 63.4 mm SL; Brazil, Pará State, Altamira Municipality; Rio Amazonas drainage, Rio Xingu basin, Rio Iriri sub-basin, Rio Curuá.

FIGURE. 2. Dorsal cephalic musculoskeletal system of Ituglanis apteryx , paratype, MZUSP 96876, 56.9 mm SL. Dorsal view; left superficial muscles, right eyeball, and right laterosensory system not shown.

Anal fin originating approximately at vertical through dorsal-fin origin. Anal fin with distal margin convex; principal rays ii,5 (6 specimens; holotype), rarely i,5 (1 specimen) or ii,4 (1 specimen); unsegmented rays ii (1 specimen) or iii (1 specimen); and six basal radials (2 specimens) located between haemal spines of 27th and 31st (1 specimen) or 28th and 32nd (1 specimen) post-Weberian vertebrae.

Caudal fin with posterior margin ranging from straight to slightly convex and rounded dorsal and ventral corners. Principal caudal-fin rays i,5 (8 specimens; holotype) on dorsal lobe and i,6 (7 specimens; holotype) or, rarely, i,5 on ventral lobe (1 specimen); procurrent rays xi (1 specimen) or xv (1 specimen) on dorsal lobe and ix (1 specimen) or xi (1 specimen) on ventral lobe. Upper caudal plate formed by one – presumably compound hypural 3+4+5 (1 specimen) – or two separate elements – presumably hypural 3 and compound hypural 4+5 (1 specimen). Lower caudal plate consisting of single element presumably formed by fusion of parhypural with hypurals 1 and 2 (2 specimens). Single elongated epural present.

Post-Weberian vertebrae 43 (1 specimen) or 45 (1 specimen). First complete haemal arch on fifth post- Weberian vertebrae (2 specimens); first complete haemal spine on 22th (1 specimen) or 24th (1 specimen) post- Weberian vertebrae. Ribs two (2 specimens).

Laterosensory canals with simple (non-dendritic) tubes ending in single pores (Fig. 2). Supraorbital canal mostly within frontal bone with pores s1, s3 and s6. Infraorbital canal consisting of posterior segment only, with branches and pores i10 and i11. Otic canal without pores and running through sphenotic-prootic-pterosphenoid.

Postotic canal traversing pterotic and posttemporo-supracleithrum, with pores po1 and po2 located anterodorsal to opercular patch of odontodes. Short lateral line proper with pores ll1 invariably present and ll2 present (both sides of 7 specimens, one side of 1 specimen) or, rarely, absent (one side of 1 specimen).

Coloration in ethanol. Unpigmented body background white to pale yellow (Fig. 1). Dark brown melanophores almost uniformly scattered on dorsolateral region of trunk in smaller specimens (less than 39.7 mm SL). Larger individuals (more than 56.9 mm SL) with melanophores more concentrated into specific regions forming irregularly shaped, nebulous spots. Most conspicuous spots arranged into two, three, or four longitudinal rows. Dorsolateral and midlateral bilaterally paired rows invariably present and running from anterior portion of trunk to caudal-fin base. Additional ventrolateral bilaterally paired row on caudal peduncle and dorsosagittal unpaired row on anterior region of body sometimes present. Spots arranged into rows occasionally coalesced in specific regions. Ventral surface of abdomen fully or mostly devoid of dark pigmentation. Proximal regions of fins with brown melanophores sometimes forming spots, especially on caudal fin. Dorsolateral and anteroventral regions of head covered with scattered brown melanophores not forming discrete spots. Barbels with scattered dark melanophores at least on their proximal portions. Dark pigmentation on membrane covering brain sometimes visible externally as a large trapezoidal dark mark on dorsoposterior region of head.

Etymology. The specific epithet derives from the Greek a, meaning without, and pteryx, meaning fin. In reference to the absence of pelvic fins in the new species.

Distribution. Ituglanis apteryx is known only from its type series collected in the reservoir formed during the building of the Buriti Hydroelectric Dam, across the Rio Curuá, Rio Iriri sub-basin, Rio Xingu basin, Rio Amazonas drainage, Brazil (Fig. 3).

FIGURE. 3. Geographic distribution of Ituglanis apteryx (red circle). Yellow lines indicate boundaries between basins of Rio Madeira (left), Rio Tapajós (center) and Rio Xingu (right). Intermittent and first-order watercourses not shown.

Tables

TABLE 1. Morphometrics of Ituglanis apteryx, new species. Range, mean, and standard deviation (SD) include holotype and paratypes.

Measurement	Holotype	Range	Mean	SD
STANDARD LENGTH (mm)	63.4	39.1–67.2	–	–
PERCENT OF STANDARD LENGTH
Total length	109.8	107.9–110.3	109.2	1,6
Predorsal length	73.3	71.0–73.3	72.3	1,7
Preanal length	71.3	71.0–71.3	71.2	0,9
Caudal peduncle length	21.0	18.9–21.0	19.8	1,5
Body depth	11.8	9.2–10.6	11.3	2,6
Caudal peduncle depth	10.6	8.0–	9.3	1,8
Dorsal-fin base length	7.6	7.1–7.7	7.5	0,4
Anal-fin base length	7.1	4.8–7.1	6.0	1,7
Head length	14.2	13.7–15.9	14.6	1,5
PERCENT OF HEAD LENGTH
Head depth	41.1	41.1–51.6	47.2	4,0
Head width	83.3	81.0–85.9	84.1	3,5
Interorbital width	22.2	22.2–23.9	23.2	1,2
Eye diameter	8.9	7.6–9.4	8.6	1,2
Snout length	34.4	30.4–34.4	32.6	2,8
Maxillary barbel length	56.7	53.1–56.7	55.1	2,5
Rictal barbel length	44.4	44.4–47.8	45.9	2,4
Nasal barbel length	50.0	50.0–53.3	51.6	2,3
Breadth of mouth	33.3	31.3–39.1	33.5	3,3