Spinipterus acsi, Akama, Alberto & Ferraris, Carl J., 2011

Akama, Alberto & Ferraris, Carl J., 2011, Spinipterus, a new genus of small, spiny catfish (Siluriformes: Auchenipteridae) from the Peruvian Amazon, Zootaxa 2992, pp. 52-60 : 53-57

Spinipterus acsi , n. sp.

Holotype. ANSP 178209. 32 mm SL, male. Peru, Depto. Loreto, Prov. Maynas. Cano “Santa Rita” (right bank tributary of R. Nanay), 3.32 mi NW center of Iquitos. 0 3o 45’23”S, 73o17’28”W, 02/08/2001, M. Sabaj et al. ( Figures 1–3 ).

Diagnosis. The genus being monotypic, its species diagnosis is that of the genus.

Description. Morphometric data are presented in Table 1. Body robust, elongate; body depth at dorsal-fin origin 22.8 % of SL; body width at cleithrum 28.1% of SL. Lateral line complete, midlaterally situated; canal straight, with no branches; lateral line extending onto caudal-fin base, but not bifurcated.

Standard length 32 mm Predorsal length (SL) 33.1 % Prepectoral length (SL) 23.4 % Head length (SL) 24.6 % Body depth (SL) 22.8 % Body width (SL) 28.1 % Upper gill membrane distance (SL) 22.6 % Dorsal-fin base length (SL) 12.8 % Dorsal-fin spine length (SL) 12.5 % Cleithral process length 24 % Pectoral-fin spine length (SL) 23.4 % Anal-fin base (SL) 20.2 % Caudal peduncle length (SL) 14.7 % Caudal peduncle depth (SL) 12.1 % Mouth width at rictus (HL) 67.4 % Snout length (HL) 36 % Eye diameter horizontal (HL) 19.8 % Bony interorbital (HL) 58.9 % Internarial length (HL) 17.8 %

Head and nuchal region depressed; depth of body at dorsal-fin origin 83% of body width at cleithrum. Profile of head straight from snout to dorsal-fin origin. Snout length two times orbital diameter; snout margin truncate in dorsal view. Mouth terminal, dentary projecting slightly beyond upper jaw. Upper and lower lips scarcely papillose, both lips set off by grooves from tooth plates. Premaxillary tooth patch transversely elongate and rectangular, with 3 or 4 irregular villiform tooth rows. Palate without teeth. Dentary with 3 rows of teeth near symphysis, narrowing to one row posterolaterally. Skull roof clearly visible through thin skin. Mesethmoid wide, flanked by welldeveloped lacrimal. Orbital margin of skull roof circular, delimited dorsally by lateral ethmoid and anteriorly by lacrimal bones. Frontals excluded from margin of orbit. Anterior cranial fontanel circular, large, open from mesethmoid to frontals; its width equal to eye diameter. Cephalic lateral-line sensory canals narrow; canal branches not dendritic on head.

Skull roofing bones smooth dorsally, without tubercles or ridges, except along margin of cranium where a single row of well-developed spines extends dorsally or dorsolaterally along anterior margin of mesethmoid, entire surface of lacrimal, and lateral borders of sphenotic, pterotic, supracleithrum, epiotic and nuchal plates.

Anterior nostril located on snout margin, somewhat tubular and directed ventrally. Posterior nostril located closer to eye than to anterior nostril; nostril rim a thin, folded membrane, its tip directed posteriorly with narrow and oblong aperture; long axis of aperture oblique to longitudinal body axis.

Eye laterodorsal, near snout tip; middle of eye at approximately anterior one-fourth of HL; ocular rim circular, bordered anteriorly and dorsally by strong spines on margin of lacrimal and lateral ethmoid. Eye relative small: horizontal eye diameter approximately 20% HL and 3 times in interorbital distance.

Three pairs of barbels. Maxillary barbel inserted midway between verticals through anterior nostril and anterior orbital margin; barbel reaching to vertical through dorsal-fin origin. Medial mental barbel reaching only to base of lateral mental barbel. Tip of lateral mental barbel extending past base of pectoral fin.

Posterior cleithral process narrow, directed posterodorsally. Lateral surface of posterior cleithral process ornamented with strong spines, and tip with a strong hook-like spine.

Dorsal fin inserted near anterior one-third of SL. Fin composed of seven fin elements: spinelet, spine and five soft, branched rays. Dorsal-fin spine strong, shorter than first branched ray; spine with three anterior rows of developed serrations running along long axis of spine, with serrations oriented perpendicular to spine axis; posterior margin of spine with single row of nearly-imperceptible serrations. Dorsal midline of body posterior of dorsal fin with groove posterior to, and same length as, dorsal-fin base.

Adipose fin elongate, with thick base, with free posterior lobe. Anterior extent of fin somewhat posterior of dorsal-fin medial groove, but difficult to determine precisely, because it gradually merges with body.

Pectoral fin inserted at vertical through middle of predorsal distance. Fin composed of seven fin elements: spine and six soft, branched rays. First soft ray longest, but shorter than pectoral-fin spine; no low fleshy membrane along medial margin of inner ray. Pectoral-fin spine stout; posterior margin with retrorse, unicuspid, well-developed serrations; anterior margin with three rows of strong serrations. Anterior row of serrations antrorse; anterodorsal and anteroventral serrations perpendicular to long axis of spine.

Pelvic fin inserted near vertical through middle of SL; fin with 5 soft rays on left side and 6 on right side; first ray simple, all others branched. Adducted fin reaches to base of anal fin.

Anal-fin base short, with slightly-convex distal margin; fin with 4 unbranched rays and 16 branched rays. Anal-fin origin posterior of middle of SL.

Caudal fin obliquely convex, with dorsal rays slightly more elongated than ventral rays; principal caudal-fin rays i,7,9,i. Dorsal and ventral fin folds present anterior of caudal fin, but with few procurrent rays preceding principal rays.

Sexual dimorphism. The holotype is a young adult male in which the urogenital tube is beginning to elongate, but is not yet extended along the entire length of the anterior anal-fin margin. Typically in auchenipterids, secondary sexually-dimorphic characters of the fins, barbels, and epidermis do not appear until the urogenital tube is fully, or nearly fully, extended to the distal margin of the anal fin. In the holotype of Spinipterus acsi , the dorsal-fin spine and the maxillary barbel show no evidence of being unusually elongated or ossified, and there is no indication of epidermal modifications. The unusual array of spines found on the margin of the cranium and on the fin spines of Spinipterus acsi might be external sexual characters that have developed at a comparatively early stage. However, in the absence of more fully-mature males, or females, that would allow us to better interpret the significance of these features in the ontogenetic development of males, we consider the presence of spines around the periphery of the cranium and the serrations on the fin spines instead to be a novel characteristic of the species.

Size. The length of the only known individual of this species is 29 mm SL. As noted above, the holotype is already showing signs of transforming into an adult male, which suggests that the maximum size of the species is not substantially larger than the size of this individual. If this is the case, then Spinipterus acsi is one of the smallest species of the subfamily Auchenipterinae , but its small size is probably not related to miniaturization (as defined by Weitzman & Vari, 1988); note that small size in the family was already registered for Gelanoglanis species ( Böhlke, 1980).

Color pattern. Body heavily pigmented with dorsum, head, and lateral body surfaces dorsal of lateral line dark brown. Dorsolateral surface of body covered with nearly-rectangular spots of different sizes and erratic distribution. Ventral of lateral line, body becoming lighter ventrally, but covered with large dark chromatophores; abdomen white.

Dorsal and pectoral fins darkly pigmented; anal fin pigmented basally, pale distally; pelvic fin pale; most of caudal fin covered with large dark chromatophores, but pale distally.

Head darker than body, at least dorsally. Margin of lower jaw heavily pigmented, becoming lighter posteriorly; no chromatophores posterior of branchiostegal rays. Maxillary barbels pigmented; mental barbels without dark chromatophores, except for base of outer mental barbel.

Etymology. Name from ACSI , the acronym of the All Catfishes Species Inventory, a project that is supported by the Planetary Biodiversity Inventory Program of the National Science Foundation.

Distribution. Known only from the type locality, at Caño Santa Rita, a tributary of the Nanay River, Amazon River basin, Peru.

Figures

FIGURE 1. Spinipterus acsi, lateral view, holotype, ANSP 178209, 32 mm SL.

FIGURE 2. Pectoral-fin spine of Spinipterus acsi. A. Anterior view. B. Schematic illustration of cross section of spine. 1. Anterior row of serrations. 2. Posterior row of serrations. 3. Anterodorsal row of serrations. 4. Anteroventral row of serrations.

FIGURE 3. Head of Spinipterus acsi in anterodorsal view.