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The deep sea is the largest and one of the most extreme environments on Earth. It is estimated that 10-15% of all fish species are dwelling in the deep sea, most of which have unique morphological and physiological adaptations. Biological expeditions to sample the deep ocean off Brazil started with the British HMS Challenger Expedition (1872-1876), followed by a few fishery stations made by the

A new species of Characidium is described based on specimens obtained from the highland streams of the Serra do Mar, Atlantic Forest Biome, in Paraná State, Southern Brazil. The new species is possibly a member member of the C. lauroi group, which is diagnosed by having the isthmus unscaled, bars poorly marked, and spots on sides of body, and is composed by four additional species: C. japuhybense; C. lauroi; C. oiticicai; and C. schubarti. The new species differs from its congeners with naked isthmus, except C. helmeri, by having 15-18 principal caudal-fin rays; and 10-12 pectoral-fin rays; and from C. helmeri, by having a slender body, tip of pectoral fin not reaching origin of pelvic fin, tip of pelvic fin not reaching beyond anus, supraorbital present and well developed, and by lacking vertically elongated dashes on sides of body. The new species is known from tributaries of the rio Jordão, in the rio Iguaçu Basin, and rio Taquari, a tributary of the rio Ribeira de Iguape coastal drainage.Uma nova espécie de Characidium é descrita com base em exemplares obtidos de riachos de altitude da Serra do Mar, no bioma Mata Atlântica, do Estado do Paraná, Sul do Brasil. A nova espécie é possivelmente um membro do grupo C. lauroi, que pode ser diagnosticado por possuir o istmo sem escamas, barras pouco marcadas e pontos nos lados do corpo, e é composto por quatro espécies adicionais: C. japuhybense; C. lauroi; C. oiticicai; e C. schubarti. A nova espécie difere de seus congêneres com istmo nú, exceto C. helmeri, por possuir 15-18 raios principais na nadadeira caudal, e 10-12 raios na nadadeira peitoral; e de C. helmeri, por possuir o corpo mais alongado, pela ponta da nadadeira peitoral não alcançar a nadadeira pélvica, pela ponta da nadadeira pélvica não alcançar o ânus, pelo supraorbital presente e bem desenvolvido, e pela ausência de manchas verticalmente alongadas na porção ventral do corpo. A nova espécie é conhecida de duas drenagens, nos tributários do rio Jordão, na bacia do rio Iguaçu, e no rio Taquari, um tributário da bacia costeira do rio Ribeira de Iguape.

A new species of Characidium Reinhardt, 1867 endemic to tributaries of the upper rio Paraguaçu in the Chapada Diamantina, Bahia, Brazil, is described. The new species can be distinguished from its congeners except C. bahiense, C. bimaculatum, C. laterale, C. nana, C. nupelia, and C. xavante, by having a conspicuous peduncular blotch in addition to the basicaudal spot on the base of the middle caudal-fin rays. Among other features, the new species differs from C. bahiense, C. laterale, C. nana, C. nupelia, and C. xavante by having a complete lateral line with 32-36 perforated scales (vs. lateral line short, with 9-11 perforated scales), and from C. bimaculatum by the body pigmentation pattern, with secondary bars present (vs. absent), total bars 11-16 (vs. 10-12), peduncular blotch rounded (vs. horizontally elongated), and mature males not having a darker dorsal fin (vs. proximal third of dorsal fin darker in mature males). Characidium bimaculatum, a poorly known species from Northeastern Brazil, is redescribed.

Kali Lloyd is a very distinctive group of bathypelagic fishes with fragile bones in the cranium and recurved teeth, which are remarkably enlarged in some species. The genus has a worldwide distribution, being found in the subtropical to equatorial regions of the Atlantic, Indian, and Pacific; one species is also found in the Southern Ocean. In this taxonomic revision, seven species are considered valid, two of them described herein: K. indica; K. kerberti; K. macrodon; K. macrurus; K. parri; K. colubrina, new species; and K. falx, new species. Kali kerberti is re-evaluated as valid and the senior synonym of K. normani. A key for the species with updated maps of distribution are also given.

Pseudoscopelus Lütken is a genus of meso- and bathypelagic fishes with a worldwide distribution. The genus is the most diversified within the family Chiasmodontidae, containing 16 valid species, three of which are described herein as new: Pseudoscopelus scriptus Lütken, from the western Central and North Atlantic; P. sagamianus Tanaka, from the Eastern Pacific and Indian Ocean; P. altipinnis Parr, widely distributed in the Atlantic and Pacific Oceans; P. cephalus Fowler, only known from the type locality in the Indo-Pacific; P. obtusifrons Fowler, from the Atlantic, Indian and Pacific Oceans; P. scutatus Krefft, widely distributed in the Atlantic, Indian and Pacific Oceans; P. aphos Prokofiev and Kukuev, from the western North Atlantic; P. parini Prokofiev and Kukuev, from the western Central Pacific to Hawaiian islands; P. astronesthidens Prokofiev and Kukuev, from the North Atlantic; P. australis Prokofiev and Kukuev, widely distribution in the southern parts of the Atlantic, Indian, Pacific Oceans, and in the Southern Ocean; P. pierbartus Spitz, Quéro and Vayne, from the North Atlantic and western South Atlantic; P. bothrorrhinos Melo, Walker Jr. and Klepadlo, from the western Pacific and Indian Ocean; P. lavenbergi Melo, Walker Jr. and Klepadlo, from the western North, western Central and western South Atlantic, P. paxtoni new species, from the western South Pacific; P. cordilluminatus new species, from the Indian Ocean and eastern South Atlantic; and P. odontoglossum new species, from the Central Pacific. Herein, Pseudoscopelus stellatus is placed in synonymy of P. scriptus; P. albeolus, in synonymy of P. australis; and P. vityazi, in synonymy of P. parini. Pseudoscopelus microps is confirmed as a junior synonym of P. altipinnis. A key to the species of Pseudoscopelus is provided as well as updated diagnoses, redescriptions, areas and distribution maps, based on extensive examination of collection material and comparison with type specimens.