Tympanopleura Eigenmann, 1912

Walsh, Stephen J., Ribeiro, Frank Raynner Vasconcelos & Py-Daniel, Lúcia Helena Rapp, 2015, Revision of Tympanopleura Eigenmann (Siluriformes: Auchenipteridae) with description of two new species, Neotropical Ichthyology (Neotrop. Ichthyol.) 13 (1), pp. 1-46 : 4-8

Tympanopleura Eigenmann, 1912

Tympanopleura Eigenmann, 1912: 203 . Type-species: Tympanopleura piperata Eigenmann, 1912 . Type by original designation. Gender: feminine.

Diagnosis. Tympanopleura shares the following putative synapomorphies with other members of the Auchenipterinae (sensu Ferraris, 1988) : lateral line sinusoidal and forked at the base of the caudal fin; urogenital pore of reproductively active adult males located at the distal tip of the anterior margin of the anal fin; urogenital pore of reproductively active adult females enlarged; and sexually dimorphic dorsal-fin spine. In the Auchenipterinae , Tympanopleura , Ageneiosus , Tetranematichthys , Entomocorus , Auchenipterus , Epapterus , and Pseudepapterus are distinct by the ventrolaterally positioned eyes visible in both dorsal and ventral views. Compared to species of Ageneiosus , the species of Tympanopleura have a more gently rounded anterior profile of the head ( Fig. 1 ) and less protruded upper jaw, reflected by a shorter relative preorbital distance and distinctive differences in osteology associated with the jaws and cranium as detailed below.

Tympanopleura , Ageneiosus , and Tetranematichthys share the following unique combination of characters in the Auchenipterinae : anterior fork of the mesethmoid directed anterolaterally, at an approximate angle of 45° relative to the anterior border of the bone (except in Ageneiosus inermis and A. polystictus ); nasal bifurcated with an ossified accessory lateral tube directed anteriorly; vomer rounded anteriorly, without lateral projections (also in a number of unrelated siluriforms); snout elongate, greater than horizontal eye diameter (except in T. piperata ); premaxilla variably developed posterolaterally, more elongated in species of Ageneiosus , less so in species of Tympanopleura and Tetranematichthys , where the posterior projection of the premaxilla does not reach past a plane passing through the posterior margin of the autopalatine; laminar expansion of bone on posteromedial margin of premaxilla; reduced number of teeth on posterior extremity of premaxilla; maxillary barbel very short; mandibular barbels absent in adults ( Ageneiosus and Tympanopleura ), or one pair present ( Tetranematichthys ; also in Gelanoglanis Böhlke ); tooth-bearing surface of dentary expanded near symphysis, with variable number of tooth rows (greatest in Ageneiosus , reduced in Tympanopleura ); reduction in number of bones in infraorbital series to four (also in Liosomadoras Fowler and Asterophysus Kner within the Auchenipteridae , in most doradids, and in a number of unrelated siluriforms); first infraorbital (lacrimal) bifurcated anteriorly; first infraorbital separated from neurocranium; second infraorbital flared posteriorly, funnel or trumpet shaped (tubular in Tetranematichthys ); posterior infraorbital canal ossification separated from sphenotic, with an unossified section of the infraorbital sensory canal; parurohyal with medial projection directed dorsally and articulating with or extending between hypohyals (also in Tocantinsia Mees ); osseus expansion on dorsal region of parurohyal weakly developed; anterior ceratohyal sutured to ventral hypohyal along ventromedial surface (also in Oxydoras Kner ); anteriomedial tips of first two hypobranchials concave and obliquely angled anteriomedially; medial tip of first epibranchial larger than that of second, usually covering the latter element dorsally (except T. piperata ); quadrate with enlarged dorsomedial lamina separating articular surfaces of hyomandibula and metapterygoid; bones of cephalic shield trabeculate; anterior nuchal plate absent [also in Epapterus , Pseudepapterus within the Auchenipteridae ; but see Ferraris (1988)]; long anterolateral process on sphenotic (also in some doradids and unrelated African taxa); epioccipital bifurcated distally, with a posterior laminar extension, broadly sutured with expanded parapophyses of fifth and sixth vertebrae, median branch of posterior process larger than lateral branch (also in Pseudepapterus , Trachelyichthys , and Trachelyopterus ); seventh vertebra not sutured to complex centrum (also in Pseudepapterus , Wertheimeria Steindachner within the Auchenipteridae ), or in contact with an expansion of the ventral margin ( Tetranematichthys ); posterior process of coracoid absent or rudimentary (also in Diplomystes Bleeker ); third pectoral-fin pterygiophore expanded distally and supporting several rays; postcleithral process absent, rudimentary, or only weakly developed (also in Pseudepapterus within the Auchenipteridae ); anterior margin of dorsal-fin spine of nuptial males armed with antrorse serrae of varying configuration; 2-4 pairs of dorsal-fin inclinator muscles (also in Pseudepapterus and Trachelyopterus within the Auchenipteridae , versus 1 pair in other doradoids and unrelated taxa). Most of the derived features of the neurocranium as listed above are illustrated in Figs. 2-4 .

Ferraris, 2006; Peixoto & Wosiacki, 2010). Additionally, nuptial male Tetranematichthys lack the characteristic sharp recurved bony hooks on the maxillary barbel present in Tympanopleura and Ageneiosus , and the swimbladder in Tetranematichthys has a large anterior chamber with posterior diverticula enlarged and fused, unlike the structure in Tympanopleura ( Birindelli et al., 2012) .

Tympanopleura and Ageneiosus are distinct from all other auchenipterids in lacking mandibular barbels as adults (but see Remarks), and, except for nuptial males, in having the maxillary barbels greatly reduced in size, filiform, and lying in a groove at the corner of the mouth above the upper lip. In nuptial males of species in these two genera, the maxillary barbel has an inner ossified core and is armed with sharp, recurved bony hooks on the anterodorsal and posterodorsal margins. Additionally, nuptial males of Tympanopleura and Ageneiosus have an elongated, sinusoidal or nearly straight dorsal-fin spine that can be hyperabducted anteriorly, and that is ornamented with prominent, sharp antrorse serrae on the anterior margin; these characters are shared to different degrees of development among genera and species in the Auchenipterini as proposed by Ferraris (1988), which includes Tympanopleura , Ageneiosus , Tetranematichthys , an Auchenipterus -group, Trachelyopterus , and Trachelyichthys .

Tympanopleura differs from Ageneiosus in having a smaller adult body size, a large cordiform gas bladder that is unencapsulated in bone, a prominent pseudotympanum, or hiatus of musculature where the gas bladder contacts the lateral body wall ( Fig. 5 ) that is readily visible externally, and parapophyses of the fourth vertebrae (=Müllerian rami) consisting of large, discoidal plates closely adpressed to windows on the anterodorsal face of the anterior chamber of the the gas bladder. Tympanopleura , with the exception of T. piperata , also differs from Ageneiosus in having paired posterior diverticula on the gas bladder (but see Remarks).

In addition to the features described above that also distinguish Tympanopleura from Ageneiosus , Tympanopleura is further distinguished from Tetranematichthys by the absence of a single pair of mandibular barbels with serrated margins or multiple fleshy, digitiform processes at their distal tips (Vari & Description. Tympanopleura comprises species of small to medium sized auchenipterids, ranging in maximum size from about 50 mm SL ( T. piperata ) to 160 mm SL ( T. rondoni ). Body widest at pectoral-fin origin, moderately to strongly compressed posteriorly. Dorsal and ventral aspects of body gently tapered posteriorly, greatest body depth at base of dorsal fin. Head moderately depressed, dorsal profile gently sloping upward to anterior margin of supraoccipital, inflected more acutely to dorsal-fin origin. Mouth inferior to nearly terminal ( T. piperata ). Eye size variable between species but relatively large (8-36% HL), displaced laterally and visible in both dorsal and ventral views, lacking circumorbital sulcus, covered with thick epidermis continuous with that on side of head. Large opercular opening, gill membranes broadly fused to isthmus. Premaxilla and dentary with relatively few irregular rows of small, unicuspid teeth; premaxilla not greatly expanded anteromedially. Salient aspects of head osteology as listed under Diagnosis.

Single pair of maxillary barbels, diminutive, filiform and fleshy for most of length in all but nuptial males, lying in small groove above upper lip. Maxillary barbel of nuptial male elongated, ossified entire length; at peak development with sharp, antrorse, tooth-like hooks on dorsomedial and ventromedial surfaces. Mandibular barbels absent in adults; small juveniles occasionally with 1-2 pair of minute chin barbels that become resorbed with growth.

Lateral-line canal extending from dorsomedial margin of posttemporal midlaterally along trunk to base of caudal fin, sinusoidal, with several short dorsal and ventral rami obliquely directed posteriorly, each branch passing to the surface and ending in a small pore. Lateral-line bifurcated at base of caudal fin with a short, branched ramus extending posteriorly a short distance on each fin lobe.

Suspensorium large but not greatly elongated and oriented in moderately oblique dorso-ventral plane. Quadrate with dorsomedial lamina extending between and broadly sutured to hyomandibular and metapterygoid, the latter bone laminar, roughly quadrangular, articulating synchondrally with quadrate near posteroventral corner. Hyomandibular articulates synchondrally with sphenotic by short anterodorsal process. Suprapreopercle small, rod-like, investing short section of preopercular latero-sensory canal anteroventral to exit from pterotic. Preopercle moderately large blade, smooth on all margins, sutured anteroventrally with quadrate. Preopercular latero-sensory canal with posterior and ventral branches exiting at anteroventral corner. Small bone, presumed mesopterygoid (but see Walsh, 1990) anterior to metapterygoid, superficially contacting vomer anteromedially, medial to palatine.

Hyoid arch consisting of unpaired urohyal, and paired hypohyal, ceratohyal, interhyal, epihyal, and branchiostegal bones. Urohyal broadly rounded anteriorly, with long, laminar projection posteriorly and a vertical extension between hypohyals anteromedially. Ceratohyal sutured anteriorly to ventral ossification of the hypohyal along its ventromedial surface; posteriorly, ceratohyal articulated suturally and synchondrally with interhyal. Total of 7-10 branchiostegal rays, first 6-7 supported by ceratohyal, remaining ones supported by interhyals. Second and third basibranchials ossified. First two hypobranchials ossified, obliquely concave on anterior margin, with medial cartilaginous flange anterior to lateral edge. Five ossified epibranchials and ceratobranchials; posterior ceratobranchial pair expanded posteromedially and supporting large pharyngeal tooth plates, each with short, conical teeth. Relatively large gill rakers on medial and lateral margins of epibranchials and ceratobranchials, numbering 4-10 on epibranchial, 9-24 on ceratobranchial. Pair of relatively large oval pharyngeal tooth plates supported by infrapharyngobranchials and posterior tips of ossified third and fourth epibranchials. Anteromedial tip of first epibranchial broadly flared and overlapping medial tip of second epibranchial.

Complex centrum formed by first six vertebrae, combined with modifications of posterior neurocranium and supporting elements of dorsal fin to form Weberian apparatus, the entire complex modified to form an elastic spring apparatus. Müllerian ramus large, discoidal, apposed anterodorsally to gas bladder tunica. Gas bladder enlarged, unencapsulated in bone, cordiform or longitudinally elongated, with a pair of short posterior terminal diverticula (except T. piperata ). Large pseudotympanum formed by hiatus of epaxial musculature and lateral contact of gas bladder with body wall.

Pleural ribs 4-8, the first articulating with transverse process of sixth vertebra. Free vertebrae posterior to complex centrum 31-36. Preural (PU1) and ural (U1) centra fused. Parhypural fused with lower caudal plate formed by first and second hypurals, third and fourth hypurals fused; fusion pattern PH +1+2;3+4,5 (after Lundberg & Baskin, 1969). Caudal fin strongly forked, principal caudal-fin rays typically i,7-8,i, 16-26 upper and 14-18 lower procurrent rays.

Dorsal fin with single small spinelet, large spine, six thin branched rays, five proximal pterygiophores, entire base of fin short. Dorsal spine pungent, typically with crenulate anterior margin and series of small, sharp or conical retrorse serrae on posterior margin in juveniles, females, and nonbreeding males. Nuptial males with highly modified dorsal-fin spine, lengthened and thickened, anterior margin with sharp, antrorse serrae, typically in two rows basally, single row distally, aligned along or oblique to midsagittal plane; rear margin of spine smooth. Adipose fin small, posterior margin forming a free flap.

Cleithrum broadly fused to coracoid along entire anteroventral margin; coracoids broadly sutured at midline. Postcleithral process absent or reduced to a small conical projection. Pectoral fin with single pungent spine and 6-13 branched rays supported by three ossified radials, the last radial expanded posteriorly and supporting multiple rays. Anterior margin of pectoral-fin spine weakly to moderately crenulate or rugose, dorsal and ventral margins with shallow grooves to nearly smooth, posterior margin with 12-37 retrorse serrae extending along entire shaft, usually in single row, occasionally bifurcated or split into two rows proximally. Posterior margin of fin straight or slightly falcate, anterior rays longest.

Pelvic fin abdominal, with single unbranched and 6 branched rays, unbranched ray thickened. First branched ray longest, medial rays progressively shorter, distal margin of fin straight to slightly rounded.

Anal fin long, 23-42 rays. First pterygiophore typically with a small ray-like splint of bone anteriorly (occasionally two), and a single well-developed unbranched ray. Last pterygiophore with slightly expanded dorsal lamina and supporting two short-branched rays. Distal margin of fin straight to slightly convex; anterior rays longest, progressively shorter posteriorly. Anal fin sexually dimorphic; in prenuptial and nuptial males the fin forms an intromittent organ, with the first 5-6 rays thickened and elongated, and progressive development of a tube-like canal anteriorly and displacement of the urogenital pore to near the distal tip of the first fin ray.

Pigmentation on head, body, and fins relatively drab, consisting of nearly uniform brown to gray countershading and light to unpigmented areas on venter ( T. brevis , T. cryptica , T. longipinna ), or with distinctive pattern consisting of prominent large blotches, irregular spots, or stippling ( T. atronasus , T. piperata , and T. rondoni ).

Remarks on the distinction between Tympanopleura and Ageneiosus . Although Tympanopleura and Ageneiosus are distinguished from all other auchenipterids in lacking mandibular barbels, this character state requires qualification in that it applies only to adult specimens, a condition that has not been cited in the literature. Walsh (1990) found one to two pairs of minute barbels on the chins of several juvenile specimens of two species of Tympanopleura and at least three species of Ageneiosus ; barbels were described as short, fleshy, and apparently derived from superficial integument. We did not exhaustively examine all specimens used in this study for this character, but we were able to confirm the presence of chin barbels in at least a dozen specimens of T. atronasus as well as some specimens of T. piperata . Walsh (1990) described an apparent heterochronic process whereby mandibular barbels may appear early in development and are resorbed with growth, similar to a situation in some species of Pangasiidae (Karamchandani & Motwani, 1956; Fumihito, 1989). As noted by Fox (1999), the lability of barbels in siluriforms and cypriniforms necessitates that caution be exercised when making comparisons between taxa, and that phylogenetic inferences on the basis of presence or absence of barbels, their structure, number, and location may be of value, but within a framework of additional corroborative morphological characters. There is a general lack of information regarding structure and function of mandibular barbels in siluriforms (Diogo & Chardon, 2000), and a study of their embryological development and ontogenetic fate in Tympanopleura and Ageneiosus could be informative.

Species of Tympanopleura exhibit variation in the presence of a postcleithral process on the pectoral girdle. A small or rudimentary postcleithral process is typically present in T. brevis , T. cryptica , T. piperata , and T. rondoni . The postcleithral process appears to be uniformly absent in other species of Tympanopleura and in all species of Ageneiosus . The primitive condition for catfishes in general is the presence of a moderately developed, unornamented postcleithral process. However, there is considerable variation among siluriforms in size and ornamentation of the postcleithral process, and the structure has been independently reduced or lost in several lineages ( Stewart, 1986). At the opposite extreme from Tympanopleura and Ageneiosus , most other auchenipterids have a well-developed postcleithral process, and in doradids it is generally prominent and in many species conspicuously ornamented with grooves and ridges (among auchenipterids, the postcleithral process is also reduced in Tetranematichthys and Pseudepapterus hasemani ). Stewart (1986) noted a positive correlation between relative size of the postcleithral process and strength of the pectoral-fin spine and locking mechanism in pimelodids. A similar condition appears to exist in doradoids, and within Tympanopleura , those species with the most robust pectoral-fin spines ( T. brevis and T. rondoni ) have the most prominent postcleithral process, whereas the other species with weak pectoral-fin spines have the process reduced (rudimentary in T. cryptica and T. piperata ) or absent altogether. Moreover, we noted considerable variation among species of Tympanopleura in which the postcleithral process is present; in some cases specimens either exhibited or lacked the postcleithral process (even within a single lot), and occasional individuals were observed to have the process variably developed bilaterally.

The unique structure of the doradoid gas bladder has long been of keen interest from a taxonomic, anatomical, and functional perspective (e. g., Bridge & Haddon, 1889, 1892, 1893; Eigenmann, 1925; Chardon, 1968; Birindelli et al., 2009, 2012). Early authors considered a gas bladder greatly reduced in size and encapsulated in a bony capsule associated with the complex centrum and Weberian apparatus to be a diagnostic feature of Ageneiosus . In the original description of Ageneiosus (= Tetranematichthys ) quadrifilis, Kner (1858) illustrated the unusal globular, bipartite gas bladder of this species, which may have subsequently led to some confusion about its taxonomic relationship relative to species that were considered at the time as congeners. The taxonomic scope of an Ageneiosus group and the known morphological variation of the gas bladder by species represented therein was expanded when Eigenmann (1912) described the genus Tympanopleura , for the type species T. piperata , based on the salient feature of the “air bladder projecting into the abdominal cavity, naked laterally, the skin over it forming a large pseudotympanum”. This was further elaborated by Eigenmann & Myers (in Myers, 1928) and by Eigenmann & Allen (1942) with subsequent descriptions of the nominal species T. alta and T. nigricollis .

In a detailed comparative analysis of gas bladder morphology among auchenipterid genera, Birindelli et al. (2012) found a suite of characters of value for inference of phylogenetic relationships within the family. Most species of auchenipterids have relatively simple gas bladders, characterized as cordiform with smooth walls, internal T-shaped septa, and with the modified and expanded parapophyses of the fourth vertebrae (Müllerian rami) attached to the anterodorsal margins of the gas bladder. Together the Müllerian rami and protractor muscles form an elastic spring apparatus, a synapomorphy shared by auchenipterids and doradids (and also present in mochokids, ariids, malapterurids, and pangasiids), that is used in sound production (Fine & Ladich, 2003; Kaatz & Stewart, 2012). In their study, Birindelli et al. (2012) proposed eight characters and alternate states of each to construct a hypothesized phylogeny of the Auchenipteridae . Therein, the authors proposed an Ageneiosus group characterized by the shared presence of a gas bladder with posterior, short, thin terminal diverticula. Within their Ageneiosus group, the authors proposed two independent lineages, one consisting of species with a reduced, diminutive gas bladder and pseudotympanum, and a lineage with an unreduced gas bladder and large pseudotympanum, comprised of A. atronasus , A. brevis , and A. piperatus (herein placed in Tympanopleura ). Recognition of distinct clades represented by species with an enlarged gas bladder and pseudotympanum versus those with reduced, variably ossified gas bladders was independently corroborated by Ribeiro (2011), in combination with other characters supporting a presumably monophyletic Tympanopleura lineage.

Given the prevailing evidence provided by recent and historic investigations, we formally recognize Tympanopleura as a valid genus and restrict Ageneiosus to related species that share a reduced gas bladder and pseudotympanum, and larger maximum adult body size. Nonetheless, considerable variation exists in gas bladder morphology, especially concerning its relative size, the ossification process (where present), and development (or secondary loss) of diverticula, such that much remains to be explored. Britski (1972) and Walsh (1990) found evidence of allometric and ontogenetic changes in size and degree of ossification in some species, and there appear to be possible homoplasies in gas bladder morphology among some species of Ageneiosus and Tympanopleura . Ageneiosus pardalis , a trans-Andean species, retains a large gas bladder, and A. militaris and A. magoi have only a partially reduced gas bladder, yet these species are postulated to be related to those taxa with greatly reduced, encapsulated gas bladders ( Britski, 1972; Walsh, 1990; Ribeiro, 2011). Conversely, T. piperata , with a large gas bladder lacking diverticula, exhibits partial ossification of the tunica externa and internal longitudinal septum in adults. In summary, species of Tympanopleura are diagnosed by the shared condition of a prominent pseudotympanum ( Fig. 5 ) and a large, cordiform or slightly elongate gas bladder ( Fig. 6 ). In contrast, most species of Ageneiosus have, as adults, a greatly reduced gas bladder that is partially to fully encased in bone as a result of progressive ossification involving the complex centrum, and, possibly, ossification of the tunica itself ( Fig. 7 ).

Figures

Fig. 1. Dorsal and ventral head profiles of species of Tympanopleura: (a) T. atronasus, INHS 106400 (82.4 mm SL); (b) T. brevis, ANSP 194010 (63.3 mm SL); (c) T. cryptica, INHS 40163 (84.9 mm SL); (d) T. longipinna, MZUSP 114000 (73.0 mm SL, holotype); (e) T. piperata, ANSP 194022 (45.6 mm SL); (f) T. rondoni, ANSP 194015 (75.3 mm SL). Scale bars: a-d, f = 1 cm; e = 5 mm.

Fig. 2. Neurocranium of Tympanopleura rondoni in dorsal view, FMNH 58144 (50.3 mm SL; paratype of Ageneiosus madeirensis). Abbreviations: epo, epioccipital; epo-p, posterior process of epioccipital. fro, frontal; io, infraorbital; let, lateral ethmoid; mes, mesethmoid; mnp, median nuchal plate; nas, nasal; pal, autopalatine; pma, premaxilla; pnp, posterior nuchal plate; pto, pterotic; scl, posttemporalsupracleithrum; soc, supraoccipital; sph, sphenotic. Scale bar = 5 mm.

Fig. 3. Neurocranium of Tympanopleura atronasus in dorsal view, UF 185769 (91.0 mm SL). Abbreviations: epo, epioccipital; epo-p, posterior process of epioccipital. fro, frontal; io, infraorbital; let, lateral ethmoid; mes, mesethmoid; mnp, median nuchal plate; nas, nasal; pal, autopalatine; pma, premaxilla; pnp, posterior nuchal plate; pto, pterotic; scl, posttemporal-supracleithrum; soc, supraoccipital; sph, sphenotic. Scale bar = 5 mm.

Fig. 4. Neurocranium ofTympanopleura atronasus in ventral view, UF 185769 (91.0 mm SL). Jaw apparatus, gas bladder, and some dorsomedial cranial bones omitted. Abbreviations: boc, basioccipital; epo-p, posterior process of epioccipital; exo, exoccipital; let, lateral ethmoid; mes, mesethmoid; mr, Müllerian ramus; orb, orbitosphenoid; os, os suspensorium par, parasphenoid; pro, prootic; pto, pterotic; scl, posttemporal-supracleithrum; sph, sphenotic; tri, tripus; tsl, transcapular ligament; vom, vomer. Scale bar = 5 mm.

Fig. 5. Pseudotympanum (arrow) in Tympanopleura piperata, INHS 36738 (41.5 mm SL).

Fig. 6. Gas bladders of species of Tympanopleura in ventral view: (a) T. atronasus, INHS 106400 (79.9 mm SL); (b) T. atronasus, FMNH 93488 (107.3 mm SL); (c) T. brevis, SIUC 39913 (59.4 mm SL); (d) T. cryptica, INHS 40163 (60.5 mm SL); (e) T. longipinna, MZUSP 34417 (50.5 mm SL); (f) T. piperata, ANSP 194019 (42.5 mm SL); (g) T. rondoni. MZUSP 7862 (117.6 mm SL). Scale bars: a-e = 5 mm; f = 2 mm; g = 10 mm.

Fig. 7. Posterior neurocranium and anterior axial skeleton of Ageneiosus inermis, UMMZ 207464 (345 mm SL) in ventral view.