Trichomycterus megantoni, Luis Fernández & Roberto Quispe Chuquihuamani, 2007

Luis Fernández & Roberto Quispe Chuquihuamani, 2007, A new species of Trichomycterus (Siluriformes: Trichomycteridae) from the Andean Cordillera of Perú with comments on relationships within the genus., Zootaxa 1545, pp. 49-57 : 50-55

Trichomycterus megantoni new species

(Fig. 1)

Holotype. MUSM 29631, 91.3 mm SL, Perú, Ucayali basin, Urubamba river, Santuario Nacional Machiguenga Megantoni, Quebrada Earoto, elevation 2,100 m, 11 May 2004, coll. M. Hidalgo and R. Quispe.

Paratypes. MUSM 25464, 2, 89.3-100.9 mm SL, same data as holotype. MUSM 25465, 5, 47.3-71.9 mm SL, (1 C&S 61.8 mm SL), Perú, Ucayali basin, Urubamba river, Santuario Nacional Machiguenga Megantoni, Quebrada Matzonzori, elevation 2,200 m, 10 May 2004, coll. M. Hidalgo and R. Quispe. MUSM 25466, 3, 56.3-98.6 mm SL, Perú, Ucayali basin, Urubamba river, Santuario Nacional Machiguenga Megantoni, Quebrada Matzonzori, elevation 2,200 m, May 2004, coll. M. Hidalgo and R. Quispe. MUSM 25467, 5, 79.4-91.4 mm SL, (1 C&S 71.6 mm SL), Perú, Ucayali basin, Urubamba river, Santuario Nacional Machiguenga Megantoni, Quebrada Patiti, elevation 2,200 m, 12 May 2004, coll. M. Hidalgo and R Quispe. MUSM 3115, 4, 38.5-81.9 mm SL, Perú, Cusco, Alto Urubamba basin, Paucartambo river, Quebrada Morro Leguia, km 135, 30 August 1989, coll. H. Ortega. FML 2602, 1, 79.5 mm SL, same data as holotype.

Diagnosis. Trichomycterus megantoni is readily distinguished from all other members of the subfamily Trichomycterinae from southern South America by having autapomorphic interopercle thickened integument (Fig. 2) and the presence of foramen frontal-supraoccipital reduced (Fig. 3). It is further distinguished from other congeners, with the exception of T. pseudosilvinichthys ( Fernandez & Vari) and T. yuska ( Fernandez & Schaefer) , by the unique combination of the following features: tip of the pelvic fin when depressed not reaching the anus, premaxillae rectangle, first dorsal fin pterygiophore insertion at or posterior to vertebra 19 to 21, 17 or 19 pairs of ribs on each side, and 37 to 40 vertebrae. T. megantoni can be distinguished from T. yuska and T. pseudosilvinichthys by the presence of a supraorbital canal with pore 3, and an outer tooth row with conic teeth (versus absence pore 3 and distally narrowing incisiform teeth Fernández & Schaefer, 2003; Fernández & Vari, 2004). In addition, the new species is distinguished from T. yuska by head muscles that are not hypertrophied and 17 pairs of ribs on each side (versus head and cheek musculature hypertrophied and 18 or 19 ribs Fernández & Schaefer, 2003); from T. pseudosilvinichthys by the first pectoral fin ray prolonged as thin short filament (versus first pectoral fin ray terminating at the margin of the fin Fernández & Vari, 2004).

Description. Morphometric data for holotype and paratypes given in Table 1. Elongated body, cylindrical; slightly compressed transversely in trunk region, becoming progressively more compressed towards the caudal fin. Dorsal and ventral profiles of trunk straight. Caudal peduncle profile straight. Greatest body depth at mid-trunk region, depth uniform posterior towards caudal fin. Caudal peduncle smoothly continuous with dorsal and ventral profiles of trunk. Papillae-like structures present on body. Anus located closer to anal-fin origin than to pelvic-fin insertion.

Head rectangular in dorsal view. Eyes located on dorsal surface, ovoid. Skin covering the eyes thin and transparent, separated from the surface of the eyeball; orbital rim not free. Anterior naris slightly smaller than posterior naris, surrounded medially by fleshy flap of integument and laterally by barbels. Posterior naris partially surrounded anteriorly by flap of thin skin.

Infraorbital canal discontinuous in two segments, bearing infraorbital pores 1 and 3, separated from posterior segment behind eye and bearing infraorbital pores 10 and 11. Supraorbital canal discontinuous with four pores: 1, 2, 3 and 6. Epiphyseal branch of supraorbital canal discontinuous, pair of median pores (6) posterior to eyes. Mandibulo-preopercular canal represented by reduced preopercular canal bearing a single skin surface pore. Reduced laterosensory canal of trunk, with one ossified tube; comprising three pores anteriorly (1, 2, and 3), canal terminus at vertical through the middle of pectoral fin base. Frontolachrymal tendon bone compact, cylindrical, without lateral expansion. Lachrymal-antorbital small, tube-like ossicle, less than onehalf maxilla length.

Mouth subterminal, rictus directed posteriorly. Cranium dorsally with reduced fontanel between frontals and supraoccipital (Fig. 3). Mesethmoid T-shaped, elongated; anterior margin straight; shaft slightly smaller than lateral cornua, its posterior process extending between lateral ethmoids, vomer, and anterior portions of frontals. Lateral ethmoid without lateral expansion. Premaxilla rectangular larger than maxilla. Premaxilla with four complete rows of teeth; outer row with 12 to 15 conic teeth. Maxilla enlarged, L-shaped, smaller than premaxilla. Maxilla with pair of condyles projecting between premaxilla and anterior border of palatine; its posterior process broad, short. Lower lip with prominent fleshy lobes along lateral margin, lobes situated mesial to rictal barbel base (Fig. 2). Lips and barbels covered by papillae. Palatine quadrangular, broad anteriorly with short posterior process dorsally placed to broad metapterygoid. Medially, palatine articulates with both vomer and lateral ethmoid.

Elongated barbels, tips uniramous, without distal branching. Maxillary barbels tips extending posteriorly to interopercular odontodes, but not reaching the pectoral-fin anterior margin. Nasal barbels slender, reaching posteriorly to distinctly beyond posterior border of eye. Submaxillary barbels shorter than maxillary barbels. Branchiostegal rays six or seven. Interopercle thickened integument ventrally on head (Fig. 2). Interopercular patch of odontodes anteroposteriorly elongated, with 32 to 36 odontodes. Opercular patch of odontodes small, rounded, with 11 to 15 odontodes. Dorsal-posterior process of operculum elongated.

Pectoral fin i,7-8; posterior fin margin rounded, first ray prolonged, extending beyond the fin margin as a long filament. Pectoral girdle composed of large, triangular cleithrum-coracoid and one or two triangular, ossified proximal radial. Dorsal fin vi-v,7 in cleared and stained; externally visible rays 6 branched and 1 unbranched, with remaining fin rays hidden under thick integument that overlies anterobasal portion of fin; posterior fin margin rounded, semicircular when fin erected; midway base fin to vertical through anus; rays supported internally by eight pterygiophores. All pterygiophores are of similar length, except the last one slightly shorter, square-shaped distally. Anal fin vi,5 in cleared and stained; externally visible rays 5 branched and 1 unbranched, with remaining fin rays hidden under thick integument that overlies anterobasal portion of fin; distal margin slightly rounded; fin origin posterior to vertical through three last dorsal fin rays; rays supported internally by six pterygiophores. All pterygiophores of similar length, last square-shaped distally. Pelvic fin rays i,4 plus one splint; second and third rays longest. Pelvic basipterygium bears two anterolateral and one medial processes anteriorly, plus short posterior medial process; anterior processes narrow from base to distal tip. Pelvic radials absent. Tip of adpressed pelvic fin not reaching to anus. Caudal fin with 12 or 13 principal rays (in two cleared and stained: 3+3+7, 3 rays on hypural 3, 3 rays on hypurals 4+5, and 7 on hypurals 1+2+parahypural; 2+4+7); dorsal procurrent rays 15-16, ventral procurrent rays 15-16; fin margin rounded. Caudal skeleton with neural spine of preural centrum 1 reduced, epural absent or present; hypural 3 no fused to hypurals 4 and 5; hypurals 1 and 2 fused to parhypural. Total vertebrae 37 (9 precaudal, 28 caudal vertebrae), 40 (9 precaudal, 31 caudal vertebrae). Single haemal spine present on central posterior to vertebrae 17 or 18. First dorsal-fin pterygiophore inserts posterior to vertebrae 19 or 21; first anal fin pterygiophore inserts posterior to vertebrae 23 or 24; no overlap between last dorsal and first anal pterygiophore. Sixteen or seventeen vertebrae each between last dorsal and fourteen or fifteen last anal pterygiophore and preural centrum 1, respectively. Seventeen paired ribs; first pair compact, strong; remainder slender, longer caudally.

Coloration in alcohol: T. megantoni exhibits a pattern of distinct, albeit faint, marmoration formed by patches of small dark chromatophores (Fig. 1). Darkly pigmented on the dorsal surfaces of the head and trunk and all but ventral most portion of the caudal peduncle. The ventral surfaces of head and trunk range from lightly pigmented to hyaline (Fig. 2). All barbels are pigmented at least to some degree and opercular and interopercular odontodes and oral dentition unpigmented. Dorsal, anal, and pectoral fins show irregular dark pigmentation present on rays and membranes. Caudal fin with membranes irregularly darker than those of other unpaired fins. Pelvic fin ranging from lightly pigmented to hyaline.

Ecology. Trichomycterus megantoni was collected in mountain rivers and streams that were generally 0.5- 12 m wide and 0.3-1.5 m deep, with clear waters running over sandy, and rock-pebble substrates, at elevations of approximately 1,360-2,200 m. The water temperature ranged between 12-16 °C, and the speeds of the current were moderate during the dry season. The environmental characteristics were similar to those observed for other Trichomycterus species in streams of Chile (Arratia, 1983a) and in streams of northwestern Argentina(Fernandez & Vari, 2002).

Distribution. Trichomycterus megantoni has been collected at several localities from southeastern Perú at the Santuario Nacional Machiguenga Megantoni: Quebrada Earoto, elevation 2,100 m, Quebrada Matzonzori, elevation 2,200 m, Quebrada Patiti, elevation 2,200 m, and Quebrada Morro Leguia, km 135, in Paucartambo, Cusco. The region is characterized by torrential hydrological conditions associated with abundant summer rains between January and March and by a dry season between May and November.

Etymology. The specific name, megantoni, is in reference to Santuario Nacional Machiguenga Megantoni, where the type locality is situated.

Discussion. Two probable autapomorphies were identified for T. megantoni . None of these can be definitely ascertained as unique within Trichomycterinae at this time, because some species are too rare to have their internal anatomy examined. The most peculiar features of T. megantoni are the interopercle thickened integument (Fig. 2) and frontal-supraoccipital foramen reduced (Fig. 3).

The interopercle thickened integument ventrally on head, like an interopercular lobe of T. megantoni (Fig. 2) is unique among trichomycterines and possibly among trichomycterids. The condition differs from other species ( Fernández, 1999: Fig. 49C, 133B), where the interopercle lobe is absent and from basal trichomycterids such as the Copionodontinae (de Pinna, 1992: Fig. 2B) and Trichogeninae.

The most conspicuous feature in the skull of T. megantoni (Fig. 3) is the reduction of the frontal-supraoccipital foramen (=parietosupraoccipital Arratia, 1998). The plesiomorphic condition for the trichomycterids and catfishes in general is to have open cranial fontanels (de Pinna & Bristki, 1991). The cranial foramen of basal trichomycterids and other catfishes primitively extends though frontal and supraoccipital (Baskin, 1973; de Pinna & Britski, 1991; de Pinna, 1989a: Fig. 24B, 1993, 1998; Arratia & Menu-Marque, 1984: Fig. 3A, 12A-B; Fernández, 1999: Fig. 136A-C; Bockmann & Sazima, 2004: Fig. 5). The only other member of the Trichomycteridae with similar reductions of the foramen in the skull is Ituglanis (Costa & Bockmann, 1993: Fig. 3A, 1994; de Pinna, 1998; Bichuette & Trajano, 2004: Fig. 2, 5, 8). However, Ituglanis has a cranial foramen reduced to a small round orifice. Elsewhere in trichomycterids, an extreme condition like foramen absent is found in Stegophilinae (Baskin, 1973: Fig. 18, 26) and Glanapteryginae (de Pinna, 1989b: Fig. 5). The closed fontanels of stegophilines are certainly derived within the family, even though they are not exclusive to them (de Pinna & Britski, 1991). Such case of frontal-supraoccipital foramen reduced, however, must be interpreted as homoplastic according to the current understanding of the trichomycterid phylogeny.

In T. megantoni , the first dorsal fin pterygiophore inserts posteriorly to the 19-21 vertebrae. A similar position 21 or more is present in T. yuska , T. pseudosilvinichthys , T. catamarcensis , T. areolatus , T. chiltoni , T. vittatus , plus T. chapmani and T. romeroi from Colombia and T. gabrieli from Brazil ( Fernández & Schaefer, 2003). This shape is quite distinct from the position 9 or 10 in basal trichomycterids, such as Copionodontinae (11 or 12; de Pinna, 1992) and the nematogenids, sister group to Trichomycteridae. In most trichomycterids, the first dorsal fin pterygiophore is associated with vertebra 15 (de Pinna, 1992). Other members of the subfamily have a derived condition of the position (19 or more), indicating that the occurrences in Hatcheria and Silvinichthys are homoplastic.

The high number of vertebrae observed in T. megantoni (37-40) is shared by T. yuska (38-39), T. pseudosilvinichthys (37-40), T. catamarcensis (37-39), T. ramosus (38-39), T. vittatus (41), T. chiltoni (42), and T. areolatus (37-39) ( Fernández & Schaefer, 2003). Basal trichomycterids, such as Copionodon , have vertebrae 35 to 37 (de Pinna, 1992), and most Trichomycterus species show 37 or less total vertebrae. However T. ramosus , T. areolatus , T. chiltoni , T. vittatus , and most Trichomycterus have 6 to 7 precaudal vertebrae, while T. megantoni , T. yuska , T. pseudosilvinichthys , T. catamarcensis have 8 to 11.

Based on this small sampling of derived character states, it appears that T. megantoni is more closely related to T. yuska , T. pseudosilvinichthys , T. catamarcensis , and the genera Silvinichthys and Hatcheria than to other Trichomycterus species and Trichomycterinae. As discussed by de Pinna (1989), such proposals of a close relationship between subsets of taxa now included in the patently non-monophyletic genus Trichomycterus to other, non-trichomycterine taxa such as those mentioned above, should not necessarily be viewed as unreasonable. On the contrary, they are an expected consequence of an objective taxonomic fragmentation of the Trichomycterinae that will likely follow upon future resolution of phylogenetic relationships within the Trichomycteridae.

Comparisons. At present, sixteen Trichomycterus species are distributed in the Andean drainages of Perú, Bolivia, and northern Chile: T. dispar (Tschudi) , T. punctulatus (Cuvier & Valenciennes) , T. taczanowskii (Steindachner) , T. oroyae (Eigenmann & Eigenmann) , T. quechuourus (Steindachner) , T. atochae (Allen) , T. weyrauchi (Fowler) , T. chaberti (Durand) , T. duellmani (Arratia & Menu-Marque) , T. tiraquae (Fowler) , T. rivulatus (Cuvier & Valenciennes) , T. laucaensis (Arratia) , T. barbouri (Eigenmann) , T. fassli (Steindachner) , T. vittatus (Regan) , and T. chungaraensis (Arratia) . The unique morphology of the interopercle thickened ventrally separates T. megantoni from those sixteen species. T. megantoni is further distinguished from T. rivulatus , T. laucaensis , T. chungaraensis (Arratia, 1983b), T. atochae , T. oroyae , T. quechuourus , T. tiraquae , T. duellmani , T. weyrauchi by having the first pectoral ray prolonged, extending beyond fin margin as long filament, tip of adpressed pelvic fin not reaching to anus (versus first pectoral ray not extending beyond fin margin, tip of adpressed pelvic fin reaching the anus; Eigenmann, 1918; Fernández, 2000a, 2001); from T. punctulatus , T. dispar , T. barbouri , T. fassli , T. vittatus by head rectangular (versus triangular); from T. taczanowskii , T. chaberti by spotted body (versus unspotted Eigenmann, 1918).