First record of the miniature catfish Malacoglanis gelatinosus Myers & Weitzman , 1966 ( Siluriformes , Trichomycteridae ) in the Orinoco river basin

Malacoglanis gelatinosus, a species of miniature catfish of the family Trichomycteridae, is only known from 4 specimens from the Amazon basin. Recently, we collected 3 specimens from the upper basin of the Meta River, a tributary of the Orinoco. This is the first record of M. gelatinosus from the Orinoco river basin, which significantly expands the known geographic distribution of this species, making it one of the most broadly distributed species within the subfamily Sarcoglanidinae. High-resolution photographs of specimens, remarks on character variation, and an updated distribution in Colombia are provided.

The Sarcoglanidinae are distributed across the Amazon basin, in upper Orinoco basin of Venezuela, and in isolated coastal rivers in eastern Brazil (Vari et al. 2009, Mattos and Lima 2010, Wosiacki et al. 2011).Except for Ammoglanis amapaensis, A. pulex, and Microcambeva ribeirae, the remaining sarcoglanidine species are only known from a few specimens and not exceeding 3 individuals for most species (Mattos et al. 2008, Wosiacki et al. 2011).This paucity of representative material in col-lections has been attributed to limited access to collecting sites and inadequate sampling techniques (Wosiacki et al. 2011).In fact, this last aspect appears to be the main factor, given the sand-dwelling habits of most species, coupled with their miniature size, translucent body, and cryptic color pattern (Wosiacki et al. 2011, Zuanon andSazima 2004).
Two monotypic genera, Sarcoglanis and Malaco glanis, were described in the same paper where Sarcoglanidinae was proposed as a new subfamily of Trichomycteridae (Myers and Weitzman 1966).Based on a single specimen, S. simplex was described from the São Gabriel rapids in the Negro River.Additional specimens have since been collected in the Branco river drainage (Sabaj 2009), as well as in the Cuao River, a tributary of the upper Orinoco (DoNascimiento, pers.obs.).Malaco glanis gelatinosus was described based on 2 specimens collected in the Orteguaza River (Fig. 1, Table 1), a tributary of the Caquetá River (Amazon basin in Colombia), and later, Stewart et al. (1987) reported M. gelatinosus from the Napo River (Amazon basin in Ecuador).Here we report the presence of M. gelatinosus in the Orinoco river basin in Colombia; this expands considerably the geographic distribution of this species, which was thought to be restricted to the western Amazon basin.

Methods
Specimens were caught using a beach seine (10 m long, 1.5 m high, and with 0.5 mm mesh) in water <1.5 m deep along the bank of a 10 m long section of the channel at each site.These specimens were collected as part of the interinstitutional project "Aplicación de criterios biológicos y ecológicos para la identificación, caracterización y establecimiento de límites funcionales de humedales en tres ventanas: Ciénaga de Zapatosa y Ciénaga de la Virgen, Complejos de Humedales de Paz de Ariporo-Hato Corozal", under the contract number  Taxonomic identification of Malacoglanis gelatino sus was based on the original description (Myers and Weitzman 1966), complementary information provided in Baskin (1973) and de Pinna (1989), and photographs of the holotype available at CAS Ichthyology Primary Types Imagebase (http://researcharchive.calacademy.org/research/ichthyology/types/index.asp).The IAvH-P specimen was measured from digital photographs taken with a Leica MC 190 HD camera attached to a Leica S8APO stereomicroscope using the Leica Application Suite v. 3.3.0.The CZUT-IC specimens were measured on the left side of specimens to the nearest 0.1 mm using digital calipers.Measurements are expressed as percentages of standard (SL) or head length (HL).Methodology and terminology for measurements and counts follow de Pinna (1992), with the addition of (1) length of first and second pectoral-fin rays, and (2) eye diameter.We collected 2 specimens of Malacoglanis gelatino sus from the Ariporo River (Fig. 3A, B), a tributary of the Casanare River, which drains into the Meta River.An additional specimen was collected in the Caño Palomas (Fig. 3C), which drains directly into the Humea River.The Meta is a western tributary of the Orinoco, which originates in the Eastern Cordillera of the northern Andes of Colombia (Fig. 1, Table 2).Our specimens were collected in rivers with sandy and muddy bottoms, moderate water flow, and high turbidity.The Chire Nuevo River had abundant leaf litter and allochthonous material on the bottom (Fig. 2).

Malacoglanis gelatinosus Myers and Weitzman, 1966
Identification.Our specimens of Malacoglanis gela tinosus (Fig. 2) are in agreement with the characters provided in the diagnosis and original description of this species (Myers and Weitzman 1966), as well as with photographs of the holotype.Our specimens generally agree in all morphometric and meristic characters of the original description, which was based on the holotype and a single paratype, but as can be expected from so few specimens, some of our counts show a broader range of variation (Table 2).In addition to those meristics reported by Myers and Weitzman (1966), we provide some additional meristics and complete morphometric data from our specimens (Tables 2, 3).Myers and Weizman (1966) provided a very accurate and detailed description of Malacoglanis gelatinosus that con- forms to the current standards of taxonomic descriptions of fishes.Although these authors described and illustrated the pattern of sensory pores of the lateral line system, they did not identify the homology of individual pores or their correspondence to the lateral line canals.A standardized nomenclature and terminology for laterosensory pores in loricarioid catfishes was proposed later by Arratia and Huaquin (1995) and Schaefer and Aquino (2000).In this sense, M. gelatinosus has 2 supraorbital sensory pores: s3 placed behind the posterior nostril and a single median s6, anterior to the nape.The infraorbital canal is represented by only 1 pore, which corresponds to the posteriormost section of the canal.The preopercular canal has 1 sensory pore, at the lateral margin of neurocranium.The postotic canal has a single pterotic branch with its terminal pore situated also at the margin of the cranium.The lateral line canal on the trunk is short, consisting of only 2 sensory pores.The presence of a single sensory pore s6 was proposed as a synapomorphy (among others) supporting the sister-group relationship of Malacoglanis and Sarcoglanis (Costa and Bockmann 1994).

Discussion
Sarcoglanis simplex and Malacoglanis gelatinosus show the broadest geographic distribution recorded for any sarcoglanidine species, with both encompassing 2 main rivers systems, the Amazon and the Orinoco.In contrast, most sarcoglanidines are only known from their type localities in a single river (i.e.Ammoglanis diaphanus, Microcambeva barbata.M. draco, Stenolic mus ix, and S. sarmientoi).The distribution range of S. simplex spans the Negro drainage (Amazon basin) and the upper basin of the Orinoco (both systems connected by the Casiquiare canal) (Winemiller and Willis 2011), a common distribution pattern in other groups of fishes (Winemiller et al. 2008).In contrast, M. gelatinosus has a disjunct distribution in the upper Caquetá and Meta rivers in Colombia.There are two other species belonging to different families of catfishes that also exhibit a similar distribution pattern: Centromochlus altae Fowler, 1945 (Auchenipteridae) (DoNascimiento pers.obs.) and Chaetostoma platyrhynchus (Fowler, 1943) (Loricariidae) (Ballen et al. 2016).Further investigations to detect other species with similar disjunct distributions in the Caquetá and Meta rivers are required to assess this biogeographic pattern and test hypotheses of past connections between these Andean tributaries of the Amazon and Orinoco rivers.(Myers and Weitzman 1966).*Median fin-rays counts follow Datovo et al. (2016).ander von Humboldt, and FEDEPALMA for funding the projects.Special thanks are due to Cristhian C. Conde-Saldaña who prepared the map.This manuscript was enriched and improved by the helpful comments from G. Echevarría and the anonymous reviewers.

Table 2 .
Meristic characters of specimens of Malacoglanis gelatinosus collected in the Orinoco river basin contrasted to values from the original description