Description of a New Blind and Rare Species of Xyliphius (Siluriformes: Aspredinidae) from the Amazon Basin Using High-Resolution Computed Tomography
Xyliphius sofiae,
new species, is described based on a unique specimen exhibiting four autapomorphies: eyes absent vs. present (though reduced); color pale, lacking pigment vs. head and body darkly pigmented; branchiostegal rays five vs. four; and unculiferous tubercles on posterior body distributed evenly vs. enlarged unculiferous tubercles typically arranged in five distinct rows above pelvic-fin base to posterior end of caudal peduncle. In addition, the pectoral fin of
X. sofiae,
new species, has one ossified proximal radial vs. two in congeners (except
X. magdalenae
, not examined).
Xyliphius sofiae,
new species, differs from all congeners except
X. lepturus
by snout tip elongated and narrowly rounded vs. short and broadly rounded, often with small median notch; fifth ceratobranchial relatively narrow with elongate acicular teeth vs. broadly expanded, leaf-shaped, with shorter and broader, conical teeth; anterior limits of branchial apertures separated by distance less 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. Based on the single specimen collected in the main channel of the Río Amazonas near Iquitos, Peru, we describe the osteology of
X. sofiae,
new species, using a non-invasive technique: high-resolution X-ray computed tomography (HRXCT). We consider
Xyliphius lombarderoi
Risso and Risso, 1964, a species based on a unique holotype that is now lost, to be a subjective junior synonym of
X. barbatus
Alonso de Arámburu and Arámburu, 1962. Variable characteristics are summarized for the seven species of
Xyliphius
treated here as valid, and their distributions are plotted based on a comprehensive review of museum specimens.
Se describe la especie nueva
Xyliphius sofiae
basado en un único ejemplar que exhibe cuatro autoapomorfias: ojos ausentes vs. presente (aunque muy reducidos); color pálido, ausencia de pigmento vs. cabeza y cuerpo con pigmentación oscura; cinco radios branquiostegales vs. cuatro; y tubérculos en la parte posterior del cuerpo distribuidos uniformemente vs. tubérculos dispuestas típicamente en cinco filas visibles sobre la región entre la base de la aleta pélvica hasta el pedúnculo caudal. Además, la aleta pectoral de
X. sofiae
tiene un radial proximal osificado vs dos en sus otros congéneres (no observado en
X. magdalenae
).
Xyliphius sofiae
se diferencia de todos sus congéneres, excepto
X. lepturus,
por la punta del hocico alargado y estrechamente redondeada vs. corto y ampliamente redondeado, a menudo con una pequeña muesca mediana; quinto ceratobranquial relativamente estrecho con los dientes aciculares alargados vs. ampliamente expandidos, en forma de hoja, con dientes cónicos y más amplios; límites anteriores de las aberturas branquiales separadas por la distancia menor que la longitud de la abertura vs. mayor que la longitud de la abertura; los radios de la aleta anal de forma modal nueve vs. siete y la linea lateral extendiendose posteriormente hasta la aleta caudal vs. linea lateral extendiendose posteriormente hasta los hipurales. El único espécimen de
X. sofiae
depositado en colecciones de museos fue colectado en el canal principal del Río Amazonas cerca de Iquitos, Peru y describimos su osteología utilizando técnicas no invasivas: tomografía computarizada en alta resolución.
Xyliphius lombarderoi
Risso and Risso, 1964, especie descrita solamente basado en el holotipo que está perdido, es considerado como sinónimo junior de
X. barbatus
Alonso de Arámburu y Arámburu, 1962. Se resumen características variables de las siete especies de
Xyliphius
tratadas aquí como válidos, y sus distribuciones se representan gráficamente basadas en una extensiva revisión de especímenes en museos.
Holotype of Xyliphius sofiae, ANSP 182322, 44.1 mm SL, Río Amazonas in vicinity of Iquitos, Loreto, Peru. (A–C) Alcohol preserved (scale bar = 5 mm). (D) Live. Photos by M. Sabaj.
Lateral view of select species of Xyliphius. (A) X. barbatus, MLP 6798, holotype, 92.0 mm SL. (B) X. lepturus, ANSP 128941, 94.5 mm SL. (C) X. magdalenae, CZUT-IC 1288, 75 mm SL. (D) X. melanopterus, FMNH 99495, 120.4 mm SL. (E) X. kryptos, MCNG 27310, 112.0 mm SL. Photos by M. Sabaj (A), T. Carvalho (B, E), J. Garcia-Melo (C), and A. Thomaz (D).
Ventral view of head. (A) Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL. (B) X. melanopterus, FMNH 99495, 120.4 mm SL. (C) X. lepturus, ANSP 128941, 94.5 mm SL. (D) X. barbatus, MLP 6798, 92.0 mm SL. Photos by M. Sabaj.
HRXCT model of skull and anterior body of Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL. (A) Dorsal view. (B) Lateral view of left side.
ang: anguloarticular; at: antorbital tubule; br: branchiostegal rays; cl: cleithrum; co: scapulocoracoid; cv: complex vertebrae; den: dentary; en: endopterygoid; epo: epioccipital; ex: extrascapular; fr: frontal; hyo: hyomandibula; ih: interhyal; io1: infraorbital 1; iop: interopercle; iot: infraorbital tubules; lal: lateral line tubules; let: lateral ethmoid; mc: mandibular canal tubules; mes: mesethmoid; met: metapterygoid; mnp: middle nuchal plate; mx: maxilla; na: nasal; op: opercle; pal: autopalatine; pch: posterior ceratohyal; pfr: pectoral-fin rays; pmx: premaxilla; po: preopercle; ps: pectoral-fin spine; pto: pterotic; pv5: parapophysis of vertebra five; qu: quadrate; rad: pectoral-fin radial; rb6: rib six; ret: retroarticular; sc: posttemporal-supracleithrum; soc: supraoccipital; spo: sphenotic; sup: suprapreopercle; v6: vertebrae six. Scale bar = 2 mm.
HRXCT model of skull and anterior body of Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL. (A) Ventral view. (B) Mesial view of left side. ach: anterior ceratohyal; bb: basibranchials; bo: basioccipital; br: branchiostegal rays; cl: cleithrum; co: scapulocoracoid; cv: complex vertebrae; den: dentary; epo: epioccipital; exo: exoccipital; fr: frontal; let: lateral ethmoid; mc: mandibular canal tubules; mes: mesethmoid; mnp: middle nuchal plate; mx: maxilla; orb: orbitosphenoid; pal: autopalatine; pas: parasphenoid; pch: posterior ceratohyal; pfr: pectoral-fin rays; pmx: premaxilla; pro: prootic; ps: pectoral-fin spine; pte: pterosphenoid; pto: pterotic; rad: pectoral-fin radial; ret: retroarticular; sc: posttemporal-supracleithrum; soc: supraoccipital; spo: sphenotic; tr: tripus; uh: urohyal; v5: vertebrae five; vh: ventral hypohyal. Scale bar = 2 mm.
HRXCT model of select bones in Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL. Bones associated with the anterior cephalic canals of the lateral line system (anterior is left) in dorsal (A) and lateral (B) views. Entire lateral ethmoid (anterior is left) in ventral (C) and frontal (D) view. (E) Partial lateral ethmoid in dorsal view cut to about half of its depth (anterior is left). (F) Partial lateral ethmoid in frontal view cut to about vertical through origin of lateral process. at: antorbital tubule; i1–i6: infraorbital branches one to six; io1: infraorbital one; iot: infraorbital tubules; lp: lateral process of lateral ethmoid; na: nasal; obc: olfactory bulb chamber; s1–s3: supraorbital branches one to three. Scale bar = 2 mm.
HRXCT model of suspensorium plus lower jaw (A) and hyoid arch (B–C) of Xyliphius sofiae, ANSP 182322, 44.1 mm SL. ach: anterior ceratohyal; ang: anguloarticular; br: branchiostegal rays; den: dentary; en: endopterygoid; hyo: hyomandibula; ih: interhyal; iop: interopercle; mc: mandibular canal tubules; met: metapterygoid; op: opercle; pch: posterior ceratohyal; pop: preopercle; qu: quadrate; ret: retroarticular; sup: suprapreopercle; uh: urohyal; vh: ventral hypohyal. Scale bar = 2 mm.
HRXCT model of branchial arches (A–B, left side, dorsal view, anterior up), and 5th ceratobranchial of cleared and stained specimens (left side, dorsal view, anterior up). (A) Xyliphius sofiae, ANSP 182322, holotype, 44.1 mm SL (scale bar = 2 mm). (B) Unobscured dorsal view of 5th ceratobranchial in ANSP 182322 (scale bar = 1 mm). (C) Xyliphius lepturus, FMNH 99488, 72.1 mm SL (scale bar = 1 mm). (D) Xyliphius melanopterus, FMNH 99493, 81.9 mm SL (scale bar = 1 mm). bb: basibranchial; cb: ceratobranchial; cb5: ceratobranchial five; eb: epibranchial; hb: hypobranchial; pb: pharyngobranchial; tp: tooth patch.
Ventral view of Weberian complex in select species of Xyliphius (anterior is top). (A) X. lepturus, FMNH 99488, 72.1 mm SL. (B) X. melanopterus, FMNH 99493, 81.9 mm SL. (C) Xyliphius sofiae, ANSP 182322, 44.1 mm SL. cv: complex vertebra; gbc: gas bladder chamber (line points to portion encapsulated by bone in B); hc: hemal canal; in: intercalarium; lal: lateral line tubules; pcv: parapophysis complex vertebra; pv5: parapophysis vertebra five; r6: rib 6; sc: scaphium; tr: tripus; v6: vertebra six. Scale bar = 2 mm.
Distributions of valid species of Xyliphius based on museum specimens and literature accounts (Alonso de Arámburu and Arámburu, 1962; Orcés, 1962; Taphorn and Marrero, 1993; Maldonado-Ocampo et al., 2005; Figueiredo and Britto, 2010; Ohara and Zuanon, 2013). Black triangles = X. kryptos; white triangles = X. magdalenae; white circles = X. melanopterus; black circles = X. lepturus; star = X. sofiae; black squares = X. barbatus; white diamonds = X. anachoretes; circles half black, half white mark localities where X. melanopterus and X. lepturus were collected together.
Contributor Notes
Associate Editor: W. L. Smith.