Ammoglanis
Ammoglanis is a genus of pencil catfishes native to South America. Taxonomy. The phylogenetic position of "A. pulex" is problematic. It seems to be closely related to "A. diaphanus" due to some derived characters of the internal anatomy, but a conclusive assessment of its relationships has not been prevented by its paedomorphic features and scarcity of study material. This generic placement seems to be well supported. The relationships of the genus "Ammoglanis" are unknown; it is thought that this genus along with undescribed forms are the sister group to a large intrafamilial clade composed of several genera and subfamilies . In the interim, this genus is included within Sarcoglanidinae. Species. There are currently five recognized species in this genus: Distribution. "A. amapaensis" originates from three different drainages of the Amazon River, the Jari, Amapari, and Araguari River. "A. diaphanus" originates from a stream tributary to the Javaés River of the Araguaia River basin in Tocantins, Brazil. "A. pulex" originates from the Paria Grande River, the Pamoni River, and Caño Garrapata of Venezuela. "A. obliquus" is only known from the Rio Preta da Eva drainage basin. Description. "Ammoglanis" species grow to about SL. "A. pulex" is among the smallest known vertebrates . "A. pulex" can be distinguished from "A. diaphanus" by a number of characteristics, including the presence of a faint pattern of eight bands formed by internal chromatophores and the lack of teeth. Ecology. "A. diaphanus" inhabits shallow, narrow, clear water, moderately swift-flowing stream and is found buried in the sand. It feeds on Diptera larvae and a cladocerans. "A. pulex" is a translucent light-pink fish that camouflages well in sand. "A. pulex" is found in sand banks near the shorelines of clear water and slightly tea-stained streams. Apparently fossorial by daylight, it is found buried in coarse  clear sand at the stream edge, in areas shaded by dense tropical rainforest. The waters are with slow current, pH varying between 5.5–6.2, and temperature between . "A. pulex" is thought to feed on microscopic fauna like protozoa, rotifers, and nematodes since it inhabits interstitial spaces among sand grains in nutrient-poor, clear-water and backwater streams.