Xyliphius sofiae Sabaj, Carvalho, and Reis, 2017

Carvalho, Tiago P., Reis, Roberto E. & Sabaj, Mark H., 2017, Description of a New Blind and Rare Species of Xyliphius (Siluriformes: Aspredinidae) from the Amazon Basin Using High-Resolution Computed Tomography, Copeia 105 (1), pp. 14-28 : 15-21

publication ID	https://doi.org/ 10.1643/CI-16-456
publication LSID	lsid:zoobank.org:pub:CE7A3E43-17E6-41EE-9A71-429640468F9B
persistent identifier	https://treatment.plazi.org/id/7AD2AC49-DD56-4C96-A21C-E51F1F88A126
taxon LSID	lsid:zoobank.org:act:7AD2AC49-DD56-4C96-A21C-E51F1F88A126
treatment provided by	Felipe
scientific name	Xyliphius sofiae Sabaj, Carvalho, and Reis
status	sp. nov.

Treatment

Xyliphius sofiae Sabaj, Carvalho, and Reis View in CoL , new species urn:lsid:zoobank.org:act:AD6D52EE-CF9D-48CA-83FD-4F0C90868920

Figure 1 View FIG , Tables 1, 2

Xyliphius sp. — Arce et al., 2013:572 [phylogeny outgroup, listed as likely undescribed species].

Holotype.— ANSP 182322, 44.1 mm SL (right pelvic fin taken for tissue), Peru, Loreto, Maynas, Río Amazonas, main channel in vicinity of Iquitos, 03843 0 21 00 S, 073812 0 14 00 W, M. Sabaj, M. Arce, A. Bullard, O. Castillo, C. DoNascimiento, et al., 13 August 2005. GenBank accession numbers (GenSeq-1): KC555831 (rag1; Arce et al., 2013), KC555965 (16S; Arce et al., 2013), KU 736764 (COI; this study), KU 736765 (Myh6; this study), KU 736766 (SH3PX3; this study).

Diagnosis.— Xyliphius sofiae is distinguished from congeners by four autapomorphies: eyes absent vs. present (though reduced); color pale, lacking pigment ( Fig. 1 View FIG ) vs. head and body darkly pigmented ( Fig. 2 View FIG ); branchiostegal rays five vs. four; unculiferous tubercles on posterior body distributed evenly vs. enlarged unculiferous tubercles typically arranged in five distinct rows from above pelvic-fin base to posterior end of caudal peduncle. In addition, the pectoral fin of X. sofiae has one ossified proximal radial vs. two in congeners (except X. magdalenae , not examined). Xyliphius sofiae is distinguished from all congeners except X. lepturus by having the snout tip elongated and narrowly rounded ( Fig. 3A, C View FIG ) vs. short and broadly rounded, often with small median notch ( Fig. 3B, D View FIG ); fifth ceratobranchial relatively narrow with two or three irregular rows of acicular teeth vs. broadly expanded with larger conical teeth; anterior limits of the branchial apertures separated by a distance smaller than length of aperture vs. greater than length of aperture; anal-fin rays modally nine vs. seven; and lateral line extending onto base of caudal-fin rays vs. finishing in hypural region.

Description.— Morphometric data summarized in Table 1. Head and body depressed. Dorsal profile rising gently from snout tip to dorsal-fin origin with shallow convexity between anterior nares and occipital region; then straight, descending gradually to end of caudal peduncle. Ventral profile more or less flat except for abrupt rise from mouth gape to snout tip. Rostrum bluntly triangular in dorsal view, lacking medial notch. Caudal peduncle long and slender, rounded in cross section.

Eyes absent. Anterior nares located dorsally about midway between snout tip and posterior rictus of mouth, enclosed by fleshy tube with posterior portion enlarged, flap-like; anterior margin of tube with two finger-like papillae projected posteriorly. Posterior nares lacking fleshy tube, aligned with posterior insertion of maxillary barbel. Rostrum overhanging inferior mouth; gape large, spanning distance between lateral contours of snout. Upper lip rugose with small flattened tubercles; lower lip with 31 elongate papillae, all unbranched; length of longest papilla about ten times its width ( Fig. 3A View FIG ).

Three pairs of barbels, all simple. Maxillary barbel long, reaching vertical through base of first branched dorsal-fin ray; leading edge scalloped with low, ridge-like tubercles. Mental barbels staggered, surfaces slightly rugose. Outer mental barbel long, surpassing posterior margin of scapulocoracoid bridge, and nearly twice as long as inner mental barbel. Opercular opening entirely ventral, concealed by large rounded membranous flap, and nearly reaching its counterpart anteriorly (i.e., anterior limits of opercular openings separated by distance less than length of aperture).

Skin roughened with flattened unculiferous tubercles. Largest tubercles appear as small irregular plates tightly spaced on skin covering neurocranium. Smaller, subtriangular, weakly imbricate tubercles on posterior flanks and not arranged in distinct rows. Smallest tubercles on ventral surfaces. Enlarged and slightly raised tubercles on underside of overhanging snout. Small, oblique, slit-like pore at axilla of pectoral fin. Base of caudal fin covered with skin bearing small triangular tubercles.

Based on HRXCT data, external surfaces of skull-roof bones with pitted texture, lacking bony knobs. Mesethmoid long and deep with cornua weakly projected laterally, elongate anterolateral concavity for articulation with premaxilla (completed by lateral process from ventral face), slight superficial posterolateral expansion for suture with lateral ethmoid, and elongate posterior rami enclosing nearly onethird of anterior cranial fontanel ( Figs. 4 View FIG , 5 View FIG ). Anterior face of mesethmoid with small bony tubercles directed anteroventrally; anterior margin separated by distinct anteromedial notch continuing as dorsal median furrow to midlength (notch not visible in whole specimen). Posterior portion of mesethmoid not elevated, level with anterior portion of frontals. Lateral ethmoid with large internal chamber housing olfactory bulb and large circular foramen on anterolateral face for connection between olfactory bulb and olfactory organ ( Fig. 6C, E, F View FIG ). Lateral ethmoid extended dorsoposteriorly, contributing to small portion of dorsal surface and lateral margin of neurocranium, partially enclosing anterolateral margin of frontal. Lateral ethmoid with large protruding lateral process articulating with central mesial face of autopalatine ( Figs. 4A View FIG , 5A View FIG ). Frontal moderately compact with deeply pitted surface; length about three times width; lateral margin lacking orbital concavity; contacting supraoccipital via posteriorly directed arms. Anterior cranial fontanel elongated and narrow, length about 7.5 times width; anterior third enclosed by mesethmoid, remainder by frontals. Posterior cranial fontanel similarly long and narrow, length over nine times width; enclosed mostly by frontals except posteriormost rim formed by supraoccipital. Epiphyseal bar centered along cranial fontanel with broad median suture over one-fifth as long as distance between anterior and posterior limits of fontanel. Supraoccipital compact, greatest length about 1.5 times greatest width; surface smooth anteriorly, pitted posteriorly; posterior process narrow, length nearly three times width, contacting dorsal keel of Weberian complex vertebrae. Sphenotic curved, contacting pterotic, supraoccipital, and posterior half of lateral margin of frontal; surface pitted. Pterotic expanded anteriorly as shelf contacting posterolateral portion of sphenotic; anterolateral margin concave in dorsal view; surface pitted. Pterotic expanded by lateral blade that is somewhat rounded in dorsal view. Supratemporal fossa distinct, enclosed by posterior portions of pterotic and supraoccipital at their suture. Epioccipital compact, contacting supraoccipital anteriorly, pterotic laterally, and posttemporal-supracleithrum posteriorly; dorsal face contributing to skull roof and posteromedial face contributing to posterior wall of cranium. Posttemporal-supracleithrum plate-like with pitted surface, contributing to dorsal aspect of skull; anterolateral process overlying dorsal process of cleithrum.

Premaxilla broad and plate-like with anterior and posterior margins somewhat rounded, surface rugose; teeth absent. Premaxilla lateroventral to mesethmoid and remote from counterpart; dorsolateral margin contacting anterior wing of infraorbital 1. Maxilla long and slender, distally bifurcate for about two-thirds its length with ventrolateral arm longer than dorsomedial one. Dentary slender with symphyseal gap, forming broad arc to accommodate large gape ( Fig. 5A View FIG ). Dentary teeth conical, curved slightly inwards; arranged in two rows, outer row occupying symphyseal half of dentary length, inner row more restricted to symphyseal portion of bone ( Fig. 7A View FIG ). Coronomeckelian bone absent.

Hyomandibula with anterodorsal process contacting ventral face of sphenotic, concave anteroventral face contacting quadrate, and laterally associated with preopercle. Quadrate subtriangular, anterior condyle articulating with retroarticular and anguloarticular, not contacting ventral margin of small metapterygoid (except perhaps by cartilage). Endopterygoid squarish, located beneath and medial to posterior end of autopalatine. Autopalatine moderately compact, length about six times minimum diameter, posterior end truncate, not bifurcate. Opercle boomerang-shaped with posterior wing about twice as long as ventral one. Interopercle present, wedge shaped with dorsoposterior margin firmly attached to ventral wing of opercle ( Fig. 7A View FIG ).

Urohyal present, rounded anteriorly with three posteriorly directed wings and distinct foramen in central portion visible in dorsal view ( Fig. 7C View FIG ). Two ossified basibranchials. First hypobranchial ossified. Dorsal hypohyal absent. Ventral hypohyal triangular. Anterior ceratohyal broad with expand- ed lamina along anterolateral margin, contacting posterior ceratohyal via interdigitated suture. Interhyal present, compact, squarish, located anterodorsal to posterior portion of posterior ceratohyal. Branchiostegal rays five; outermost (fifth) with anterior half expanded, approximating size of posterior ceratohyal; fourth branchiostegal ray also with expanded basal portion; remaining branchiostegals 3–5 becoming gradually shorter and more slender, ray-like. Five ceratobranchials, all bearing short gill rakers; fifth ceratobranchial with two or three irregular rows of acicular teeth along dorsal surface of anterior half ( Fig. 8B View FIG ). Four epibranchials, third bearing distinct uncinate process ( Fig. 8 View FIG ). First and second pharyngobranchials absent or unossified; third and fourth ossified, suspending expanded tooth plate with elongate acicular teeth.

Nasal composed of two separate tubular ossifications between supraorbital sensory pores 1–2 and 2–3, respectively ( Fig. 6A View FIG ). Infraorbital 1 with anterior half curved medially, finishing dorsal to premaxilla ( Fig. 4A View FIG ); mesial limb short; lateral face notched with foramen for canal passage posteriorly ( Fig. 6A, D View FIG ). Remaining infraorbitals reduced to series of small, disjointed tubules, some with small ventrolateral ossification associated with branch for infraorbital canal pores i4–i6. Additional small canal-like ossifications situated between pores i1–i2, ventrolateral to infraorbital sensory branch 2, and dorsomedial to infraorbital 1. Infraorbital canal ( Fig. 6A View FIG ) begins with pore (i1) and enters foramen at midpoint of dorsal margin of infraorbital 1; second pore (i2) at end of branch posteromedial to pore 1. Infraorbital canal exits through foramen in posterior notch in infraorbital 1 and begets four branches ending in pores i3–i6. Preopercle-mandibular canal ( Fig. 7 View FIG ) incomplete anteriorly with one short tubular ossification ventral to posterior portion of dentary, separated by gap from second similar ossification beneath posterior portion of retroarticular. Second ossification separated by gap from disjointed series of closely set ossified tubules finishing with canal passage into preopercle. Preopercle-mandibular canal associated with hyomandibula posteriorly. Suprapreopercle present, small, bearing canal, received by notch in hyomandibula anteriorly and contacting pterotic posteriorly. Extrascapula present, small tubular ossification located between pterotic and posttemporalsupracleithum ( Fig. 4A, B View FIG ) and at ramification of postotic sensory branch 2. Lateral line complete, not associated with fourth parapophysis, exiting posterolateral corner of posttemporal-supracleithum and extending onto base of caudal-fin rays as simple ossified tubes.

Dorsal keel of Weberian complex with straight margin reaching surface of body. Parapophysis of fourth vertebra forming broad lamina partially encapsulating gas bladder ( Fig. 9C View FIG ). Posterior margin of parapophysis of fourth vertebra in complete contact with ventrally displaced parapophysis of fifth vertebrae. Parapophysis of fifth vertebra long, extending to body wall and beyond lateral limits of parapophysis of fourth vertebra. Distal margin of fifth parapophysis obliquely truncate, not distinctly expanded. No evidence of separate anterior nuchal plate. Middle nuchal plate small, posterolaterally contacting posterior nuchal plate, distant from dorsal keel of Weberian complex. Posterior nuchal plate with acute triangular wing directed anterolaterally (visible in whole specimen). Total vertebrae 36. Vertebrae 7–27 bearing horizontal transverse processes. Hemal and neural spines moderately elongate, those on posterior portion of caudal peduncle obliquely orientated. Seven pairs of ribs on vertebrae 6–12.

Dorsal fin I,4. First ray simple, slender, stiffened (not pungent), and elongated distally as flexible filament; anterior face lacking serrations, but rugose with small plate-like tubercles resembling those on body. Soft rays unbranched, distal tip surpassing intervening membrane. Last dorsal-fin ray not adnate to dorsum by membrane. Pectoral fin I,5. Rigid pectoral spine extended by thin, flexible filament. Anterior face of pectoral-fin spine lacking serrations, but rugose with flat, imbricate tubercles with irregular posterior margin (those on distal filament resemble minute serrations). Posterior face of pectoral-fin spine with eight retrorse dentations; most proximal one small and inconspicuous, remaining ones increasing gradually in size; length of largest dentations approximating width of spine shaft. Soft pectoral-fin rays branched except for last one; distal tip of ray surpassing intervening membrane. Single ossified proximal radial associated with pectoral-fin rays two and three. Dorsal wing of cleithrum with three processes: dorsal process long and narrow with posteriorly directed keel; middle process short, truncated; ventral process (posterior cleithral process) scarcely evident as distal extension of obliquely oriented cleithral bulge (portion receiving dorsal process of pectoral spine). Ventral blade of pectoral girdle with single foramen laterally displaced and posterior to contact of cleithrum and scapulocoracoid. Posterior process of scapulocoracoid slender and moderately elongate, extending posterolaterally to vertical through tip of posterior cleithral process. Pelvic fin i,6; second and third rays longest, just reaching anal-fin origin. Lateral arm of basipterygium well developed anteriorly, reaching vertical through eighth vertebrae. Anal fin iv,5. Caudal fin with ten principal rays, five in each lobe; distal margin obliquely truncate with lower lobe slightly longer than upper. Outermost principal caudal-fin rays unbranched; proximal portion expanded and covered with small, flat, imbricate tubercles. Procurrent caudal-fin rays small and difficult to visualize via radiographs, likely two dorsal procurrent rays and three ventral. Adipose fin absent.

Coloration.— Alcohol-preserved specimen pale tan to white ( Fig. 1 View FIG ). Fins hyaline except for diffuse melanophores associated with proximal portion of anal-fin rays and extremely faint dusky blotch on basal half of middle caudal fin. Live specimen tan with salmon pink flanks ( Fig. 1 View FIG ).

Distribution and habitat.— Xyliphius sofiae is known from a single locality in the Amazon River near the town of Iquitos, Peru ( Fig. 10 View FIG ). The specimen was collected using a large floating net stretched between two canoes and dragged downstream through the water column.

Etymology.— In honor of the daughter of first author on the specific epithet, for inspiring wisdom in her father.