Morphological Evidence for the Monophyly of the Subfamily of Parasitic Catfishes Stegophilinae (Siluriformes, Trichomycteridae) and Phylogenetic Diagnoses of Its Genera
The subfamily of Neotropical parasitic catfishes Stegophilinae (Trichomycteridae) is a remarkable group given its specialized feeding habits (lepidophagy, muciphagy, and necrophagy). Despite its biological interest, the systematics of this group has remained in an incipient state. Most genera lack a phylogenetic diagnosis, leading thus to taxonomic instability at that level. Similarly, the hypothesis of monophyly of Stegophilinae is supported by scant morphological evidence. In this study, based on a broad morphological comparative survey of representative genera and species of each subfamily of Trichomycteridae, new evidence is provided to support Stegophilinae as a monophyletic unit. Stegophilinae is herein recognized by four unique synapomorphies, three of them proposed here for the first time. Additionally, phylogenetic diagnoses are offered for all currently recognized genera (including Pareiodon), except Parastegophilus which is placed in the synonymy of Pseudostegophilus. An identification key for stegophiline genera based on external morphology is also presented. La subfamilia de bagres neotropicales parásitos Stegophilinae (Trichomycteridae) es un grupo notable dados sus hábitos alimentarios especializados (lepidofagia, mucofagia y necrofagia). A pesar de su interés biológico, la sistemática de este grupo ha permanecido en un estado incipiente. La mayoría de los géneros carece de una diagnosis filogenética, conduciendo así a inestabilidad taxonómica a ese nivel. Similarmente, la hipótesis de monofilia de Stegophilinae es soportada por evidencia morfológica escasa. En este estudio, con base en un análisis morfológico comparativo amplio de géneros y especies representativas de cada subfamilia de Trichomycteridae, se aporta evidencia nueva para soportar Stegophilinae como una unidad monofilética. Stegophilinae es reconocido por cuatro sinapomorfías únicas, tres de ellas propuestas aquí por primera vez. Adicionalmente, se ofrecen diagnosis filogenéticas para todos los géneros reconocidos actualmente (incluyendo Pareiodon), excepto Parastegophilus el cual es sinonimizado con Pseudostegophilus. Se proporciona también una clave de identificación para los géneros estegofilinos basada en caracteres de la morfología externa.
Strict consensus of five most parsimonious trees of relationships among Stegophilinae and outgroups, generated in TNT, length = 1382, consistency index (CI) = 0.44, and retention index (RI) = 0.77. Each of the most parsimonious trees has length = 1369, CI = 0.45, and RI = 0.77. Numbers above nodes indicate Bremer support values; numbers below nodes indicate bootstrap percentages. Subfamily names of Trichomycteridae in black font.
(A) Medial view of left lower jaw (slightly tilted dorsally, anterior to the right, teeth removed) of Pseudostegophilus maculatus, FMNH 58526, and medial view (anterior to the right) of left lower jaw of (B) Pareiodon microps, MBUCV-CT-1010, and (C) Scleronema sp., MBUCV-V-32674 (MBUCV-CT-931), showing the dentary portion of coronoid process (arrows), horizontally oriented (apomorphic condition) in A and B, and vertically oriented (plesiomorphic condition) in C. Abbreviations: an-ar-re, angular-articular-retroarticular compound bone; ar fac q, articular facet for quadrate; co pr, angular-articular-retroarticular portion of coronoid process; de, dentary; in pr de, internal process of dentary; me car, Meckelian cartilage; sym; mandibular symphysis. Scale bar 1 mm.
Dorsal view of anterior region of cranium (anterior facing up) of (A) Homodiaetus anisitsi, ANSP 168835, and (B) Tridentopsis pearsoni, AMNH 78075, showing the wing-like posterior projection at distal tip of premaxilla (arrow), synapomorphy of Stegophilinae. Abbreviations: au, autopalatine; fr th, free tooth row attached to soft tissues of upper lip; le, lateral ethmoid; md pm, median premaxilla; me, mesethmoid; me co, mesethmoid cornua; mx, maxilla; pm, premaxilla. Scale bars 1 mm.
Medial view of left suspensorium (anterior to the right) of (A) Pseudostegophilus maculatus, FMNH 58526, and (B) Ituglanis sp., MBUCV-V-24976 (MBUCV-CT-922), showing the posterodorsal process of the hyomandibula (arrows). Abbreviations: co ar, condyle for articulation of lower jaw; hy, hyomandibula; iop, interopercle; lo ja, lower jaw; mt, metapterygoid; op, opercle; p ar fa, posterior end of articular facet of hyomandibula for neurocranium; pop, preopercle; q, quadrate. Scale bars 1 mm.
Ventral view of posterior region of parasphenoid (anterior facing up) of (A) Acanthopoma annectens, MBUCV-CT-1005, showing the ventrolateral projection of left side (arrow), diagnostic for the genus, and (B) Homodiaetus anisitsi, ANSP 168835. Abbreviations: au, autopalatine; le, lateral ethmoid; hy, hyomandibula; orb, orbitosphenoid; par, parasphenoid; pte+sp+pro, pterosphenoid+sphenotic+prootic compound bone; vo, vomer. Scale bars 1 mm.
Dorsal view of anterior region of mesethmoid (anterior facing up) of (A) Apomatoceros alleni, MBUCV-CT-1006, showing slender dorsal region of mesethmoid (arrow), diagnostic for the genus, and (B) Haemomaster venezuelae, MBUCV-CT-921. Abbreviations: fr, frontal; me, mesethmoid; na, nasal; pm, premaxilla; po no, posterior nostril; vo, vomer. Scale bars 1 mm.
Left lateral view of anal fin (anterior to the left) of (A) Apomatoceros alleni, MBUCV-CT-1006, containing eight fin rays of which the last five are spinous, and (B) Trichomycterus sp. (Santa Catarina), MCP 10649, containing nine fin rays. Abbreviations: pmr1-7, anal-fin proximal-middle radial 1–7; hs25-37, hemal spine of post Weberian vertebra 25–37; pr1-7, principal anal-fin ray 1–7; pro-r, procurrent anal-fin ray; sp1-5, spinous anal-fin ray 1–5. Scale bar 1 mm.
Ventral view of anterolateral region of cleithrum (anterior facing up) of (A) Haemomaster venezuelae, MBUCV-CT-921, showing process of lateral margin (arrow) diagnostic for the genus, and (B) Ochmacanthus alternus, MBUCV-CT-260. Scale bars 1 mm.
Ventral view of branchial arches (anterior facing up) of (A) Homodiaetus anisitsi, ANSP 168835, showing posterior uncinate processes in ceratobranchials 1–3 (arrows), and (B) Trichomycterus sp. (Santa Catarina), MCP 10649. Abbreviations: b2-4, basibranchial 2–4; c1-5, ceratobranchial 1–5; h1-3, hypobranchial 1–3. Scale bars 1 mm.
Ventral view of left orbitosphenoid (slightly tilted laterally, anterior to the left) of (A) Ochmacanthus flabelliferus, MBUCV-CT-1009, and (B) Homodiaetus anisitsi, MBUCV-CT-927, showing optic nerve exit through lateral fenestra between frontal and orbitosphenoid in A and through optic foramen in B. Abbreviations: f tr fa, foramen for trigeminofacial nerve; fr, frontal; le, lateral ethmoid; orb, orbitosphenoid; pte+sp+pro, pterosphenoid+sphenotic+prootic compound bone. Scale bars 0.5 mm.
Ventral view of distal region of left pectoral girdle (anterior facing up) of (A) Ochmacanthus alternus, MBUCV-CT-260, and (B) Henonemus punctatus, MBUCV-CT-1007, showing complex radial (arrows), apomorphically elongated in Ochmacanthus and plesiomorphically compact in Henonemus. Abbreviations: cl, cleithrum; me ar, mesocoracoid arch; pe r1, pectoral-fin ray 1; pr ra, proximal radial; sca, scapulocoracoid. Scale bars 1 mm.
Ventral view of left pectoral girdle of (A) Pareiodon microps, MBUCV-CT-1010, showing the cleithrum lamina with numerous foramina, diagnostic for the genus, and (B) Pseudostegophilus nemurus, ANSP 116448. Scale bars 1 mm.
Representative species of valid genera of Stegophilinae. (A) Acanthopoma annectens, MBUCV-V-32924, 85.0 mm SL. (B) Apomatoceros alleni, MBUCV-V-32923, 120.7 mm SL. (C) Henonemus punctatus, MBUCV-V-32925, 84.6 mm SL. (D) Megalocentor echthrus, MBUCV-V-32921, 63.4 mm SL. (E) Pareiodon microps, MBUCV-V-32922, 123.3 mm SL. (F) Pseudostegophilus nemurus, MBUCV-V-29512, 92.1 mm SL. (G) Haemomaster venezuelae, MBUCV-V-33968, 53.5 mm SL. (H) Homodiaetus anisitsi, MBUCV-V-32260, 31.0 mm SL. (I) Ochmacanthus flabelliferus, MBUCV-V-9981, 42.9 mm SL. (J) Schultzichthys bondi, MBUCV-V-29367, 29.0 mm SL. (K) Stegophilus septentrionalis, MBUCV-V-23328, 34.7 mm SL. Scale bars 1 cm.
Dorsal view of anterior region of head of (A) Pseudostegophilus sp. (Orinoco and Essequibo), MCNG 23327 (47.7 mm SL), and (B) Henonemus taxistigmus, MCNG 29520, showing posterior fleshy margin of posterior nostril (arrows), continuous (apomorphic condition) in A and notched (plesiomorphic condition) in B. Scale bars 1 mm.
Ventral view of left autopalatine (anterior facing up) of (A) Stegophilus insidiosus, MZUSP 39644, showing ventral process in posterior end of autopalatine (arrow) diagnostic for the genus, and (B) Ochmacanthus alternus, MBUCV-CT-260. Abbreviations: au, autopalatine; le, lateral ethmoid; lo ja, lower jaw; mt, metapterygoid; mx, maxilla; q, quadrate; vo, vomer. Scale bars 0.5 mm.
Contributor Notes
Associate Editor: G. Arratia.