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Subterranean organisms provide excellent opportunities to investigate morphological evolution, especially of sensory organs and structures and their processing areas in the central nervous system. We describe the gross morphology of the brain and some cephalic sensory organs (olfactory organ, eye, semicircular canals of the inner ear) and the swim bladder (a non-sensory accessory structure) of subterranean species of pencil catfishes of the genus Ituglanis Costa and Bockmann, 1993 (Siluriformes, Trichomycteridae) and compare them with an epigean species of the genus, Ituglanis goya Datovo, Aquino and Langeani, 2016. We compared qualitatively the size of the different brain regions and sense organs of the subterranean species with those of the epigean one, searching for modifications possibly associated with living in the subterranean environment. Our findings suggest that species of Ituglanis exhibit sensory characteristics that are preadaptive for the subterranean life, as only slight modifications were observed in the brains and sense organs of the subterranean species of the genus when compared with the epigean one. Because most subterranean fish species belong to lineages putatively preadapted for subterranean life, our results, discussed in the context of available information on the brain and sense organs of other subterranean species, help identify general trends for the evolution of the brain and sensory organs of subterranean fishes in general.

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Spelaeometra Polhemus & Ferreira, 2018 (Hemiptera: Heteroptera: Hydrometridae) is a monotypic and troglobitic genus, recently described based on material collected in the state of Minas Gerais, Brazil. From specimens collected in the Gruna do Enfurnado Cave in the Serra do Ramalho karst area, municipality of Coribe, state of Bahia, Brazil, we describe Spelaeometra hypogea Cordeiro & Moreira, sp. nov. and compare it with Spelaeometra gruta Polhemus & Ferreira, 2018. The new species is diagnosed by the general body color being pale-yellow to light-brown; antennal segments I and II being subequal in length; the reduced gular lobe, not covering any labial segment; the male proctiger without apical projections; and the male paramere with convex dorsal margin after the curvature, with a narrow hook-like apex.

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In this study, the authors present a comprehensive checklist of cave-dwelling populations of Rhamdia from the Sierra de Zongolica (SdZ) in Veracruz, Mexico, including two new records, based on permanent and verifiable evidence in the form of voucher specimens. The authors use phylogenetic and phylogeographic analyses of voucher-derived comparative cytochrome b data to shed light on the evolutionary history of these populations. The results of this study, while preliminary, suggest that hypogean forms of Rhamdia from the SdZ are cave-adapted populations of the more widespread and epigean species R. laticauda.

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In this paper, we describe three new Eukoenenia species from specimens collected in limestone caves in the northern region of the Minas Gerais state, Brazil. These species present different degrees of adaptation to the subterranean habitat, with Eukoenenia magna sp. nov., with 6 blades on lateral organs and body ratios very close to other troglobitic species, being the most troglomorphic among them. This species is morphologically very similar to the Brazilian troglobites E. navi, E. eywa and E. neytiri. Eukoenenia lundi sp. nov. and Eukoenenia jequitai sp. nov. are probably closely related species due to their substantial morphological resemblance. These two species are closer to E. virgemdalapa among the Brazilian species described to date. We provide a table summarizing the main diagnostic characters of the three species herein described and those of the Brazilian congeners to facilitate morphological comparisons.

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Herein, eyeless Pseudosinella species from Brazilian caves are reviewed, including the description of 23 new species, new records plus additional notes on the descriptions of P. ambigua Zeppelini, Brito, and Lima and of P. guanhaensis Zeppelini, Brito, and Lima. We also provide an identification key to 27 eyeless species recorded from Brazil. To organize the 26 Brazilian eyeless taxa analyzed in this work, we organize them in apparently artificial groups: 11 species have one larger tooth on the unguiculus outer lamella (petterseni group); one presents unguiculus outer lamella smooth or serrated (never with a larger tooth), with 9 held prelabral chaetae undivided and the last 6 held prelabral chaetae bifurcated. The Brazilian species of eyeless Pseudosinella herein described present a remarkably conservate dorsal chaetotaxy; therefore, the main diagnostic characters are related to other features like prelabral, labral, and ventral head chaetotaxy and empodial complex morphology. In addition, our study suggests that Brazilian caves possibly shelter a great diversity of Pseudosinella taxa, several of them potentially cave dependent.

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Typhloroncus guatemalensis sp. n., found in Gruta de Lanquín, a limestone cave located in the municipality of Lanquín (Alta Verapaz, Guatemala), is described. It can be distinguished from the congeneric species mainly by the presence of lanceolate ventrodistal telotarsal setae on all legs; by the chelal teeth, which exhibit a varied morphology; by the number of trichobothria (30‒32); and by its measurements. Typhloroncus guatemalensis sp. n. represents the first record for the genus in Guatemala and is considered to be troglobitic.

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The spiders of the genus Loxosceles have been reported from caves in several regions of the world. Despite their commonness in subterranean habitats, the occurrence of troglomorphic species is quite rare. A new cave-dwelling species found in the Brazilian Caatinga can be included in the restricted list of troglomorphic Loxosceles by presenting the following troglomorphic traits: eyes with reduced diameter, absence of pigment around the eyes, appendage elongation and pale coloration. Thus, the aim of this study is to describe a new highly troglomorphic species of Loxosceles from Brazil, corresponding to the first troglomorphic species from South America. Loxosceles troglobia sp. nov. belongs to the gaucho group and can be distinguished from the other species of this group mainly by the presence of the troglomorphic characteristics mentioned above and by the shape of the female spermathecae and the male palp. The morphological traits, together with the fact that the new species was found only in inner and very humid portions of two nearby caves, indicate that it is troglobitic.

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Spelaeobochica goliath sp. n., found in a limestone cave located in the municipality of Ibiracatu (Minas Gerais, Brazil), is described. It can be distinguished from the other species of the genus mainly by the slight angular shape of the anterior margin of the carapace, distal position of the trichobothrium est relative to st on the movable finger, isb in a position much nearer to level of sb than to that of esb, and by its pedipalpal measurements and proportions. It shares many morphological features with S. iuiu.

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A new species Eukoenenia amatei sp. nov. is described on the basis of a female captured in a cave in south-eastern Spain. It is characterized by the presence of a single blade on the lateral organ and the absence of a glandular complex on sternites IV and VI. Some of these characters are shared with five other species distributed in Europe, Asia, Africa and South and Central America. The new species is remarkable for the elongation of basitarsus of leg IV which is the second longest in the E. mirabilis group. Only one other species in this group, E. indalica, has similar troglomorphic characters. In addition, formulas of palp and leg chaetotaxy are provided to facilitate species comparison.

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We describe a new scorpion species in the troglomorphic genus Troglotayosicus Lourenço, 1981 from Colombia. Troglotayosicus meijdeni sp. nov. inhabits the forest leaf litter at Rivera municipality, on the western slope of the Eastern Andes. The male of the new species remains unknown; however, this species can be distinguished from other species in the genus by the female (and juvenile) morphology. The type locality of T. meijdeni sp. nov. represents the northernmost known record for a population of Troglotayosicus, further extending the known limits of distribution of this genus, and shedding more light on the distributional range of this group of scorpions in northwestern South America. With this description, the number of known species of Troglotayosicus is raised to four; three of them are endogean species living in forested areas in the Andean region of Colombia, whereas one is a hypogean species from a cave in Ecuadorian Amazonia.

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Blind and depigmented fish belonging to the species Astyanax mexicanus are outstanding models for evolutionary genetics. During their evolution in the darkness of caves, they have undergone a number of changes at the morphological, physiological, and behavioral levels, but they can still breed with their river-dwelling conspecifics. The fertile hybrids between these two morphotypes allow forward genetic approaches, from the search of quantitative trait loci to the identification of the mutations underlying the evolution of troglomorphism. We review here the past 30years of evolutionary genetics on Astyanax: from the first crosses and the discovery of convergent evolution of different Astyanax cavefish populations to the most recent evolutionary transcriptomics and genomics studies that have provided researchers with potential candidate genes to be tested using functional genetic approaches. Although significant progress has been made and some genes have been identified, cavefish have not yet fully revealed the secret of their adaptation to the absence of light. In particular, the genetic determinism of their loss of eyes seems complex and still puzzles researchers. We also discuss future research directions, including searches for the origin of cave alleles and searches for selection genome-wide, as well as the necessary but missing information on the timing of cave colonization by surface fish.

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Rhamdiopsis krugi, a new troglobitic heptapterid catfish, is described from the caves of Chapada Diamantina, State of Bahia, northeastern Brazil. This species, although frequently cited in the scientific literature along the last seventeen years, remained undescribed largely due to its uncertain phylogenetic affinities. The generic assignment of R. krugi was clouded largely by its high number of unusual morphological features (some related to cave life), for instance: absence of eyes and body pigmentation; presence of a widely exposed pseudotympanum; posterior border of the anterior branch and anterior margin of the arborescent portion of the posterior branch of the transverse process of fourth vertebra joined; dorsal hypural plate commonly with seven rays; ventral caudal plate usually with six rays; dorsal and ventral caudal-fin lobes typically with six branched fin rays each; 38-39 vertebrae; anal fin with 14-17 rays; and lateral line very short. Rhamdiopsis krugi can be easily distinguished from its congeners, R. microcephala and R. moreirai, by its troglomorphic features and by the presence of a shorter lateral line, fewer vertebrae and anal-fin rays, pattern of branching of caudal-fin rays, and several attributes of skeletal system. The affinities of this new species are discussed in light of current phylogenetic knowledge of the family Heptapteridae. Incongruent derived characters do not allow selection of a particular hypothesis of sister group relationships among species of Rhamdiopsis. The occurrence of R. krugi in the rio Paraguaçu basin is possibly due to an event of hydrological capture from a section of the middle portion of the rio São Francisco basin, caused by tectonic events. The semi-arid region where R. krugi presently lives was probably covered by a wide forested area during a humid cycle in Quaternary. A summary of natural history and ecology data of R. krugi, as well as notes on its conservation, are provided. We also offer comments on the morphological plasticity of R. krugi.

Rhamdiopsis krugi, um novo bagre heptapterídeo troglóbio, é descrito de cavernas da Chapada Diamantina, Estado da Bahia, nordeste do Brasil. Esta espécie, embora frequentemente citada na literatura ao longo dos últimos dezessete anos, não foi descrita antes em função das suas afinidades filogenéticas incertas. A posição genérica de R. krugi foi obscurecida principalmente pelo seu alto número de caracteres morfológicos incomuns (parte deles relacionada à vida nas cavernas), como por exemplo: ausência de olhos e de pigmentação corporal; presença de um pseudotímpano amplamente exposto; borda posterior do ramo anterior e margem anterior da porção arborescente do ramo posterior do processo transverso da quarta vértebra conectados um ao outro; placa hipural dorsal normalmente com sete raios; placa caudal ventral usualmente com seis raios; lobos dorsal e ventral da nadadeira caudal tipicamente com seis raios ramificados cada; 38-39 vértebras; nadadeira anal com 14-17 raios; e linha lateral muito curta. Rhamdiopsis krugi pode ser facilmente distinguida de seus congêneres, R. microcephala e R. moreirai, por seus caracteres troglomórficos e pela presença de uma linha lateral mais curta, menos vértebras e raios na nadadeira anal, padrão de ramificação dos raios da nadadeira caudal e vários atributos do sistema esquelético. As afinidades desta nova espécie são discutidas à luz do conhecimento atual sobre a filogenia da família Heptapteridae. Caracteres derivados incongruentes não permitem optar por uma hipótese particular de relação de grupo-irmão entre as espécies de Rhamdiopsis. A ocorrência de R. krugi na bacia do rio Paraguaçu é devida, possivelmente, a um evento de captura hidrológica de uma seção da porção média da bacia do rio São Francisco, ocasionada por eventos tectônicos. A região semi-árida onde R. krugi atualmente vive estava provavelmente coberta por uma ampla floresta durante um ciclo úmido no Quaternário. Um sumário das informações sobre a história natural e ecologia de R. krugi, assim como observações sobre sua conservação, são apresentadas. Apresentamos também comentários sobre a plasticidade morfológica de R. krugi.

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RESUMO

Rhamdiopsis krugi, a new troglobitic heptapterid catfish, is described from the caves of Chapada Diamantina, State of Bahia, northeastern Brazil. This species, although frequently cited in the scientific literature along the last seventeen years, remained undescribed largely due to its uncertain phylogenetic affinities. The generic assignment of R. krugi was clouded largely by its high number of unusual morphological features (some related to cave life), for instance: absence of eyes and body pigmentation; presence of a widely exposed pseudotympanum; posterior border of the anterior branch and anterior margin of the arborescent portion of the posterior branch of the transverse process of fourth vertebra joined; dorsal hypural plate commonly with seven rays; ventral caudal plate usually with six rays; dorsal and ventral caudal-fin lobes typically with six branched fin rays each; 38-39 vertebrae; anal fin with 14-17 rays; and lateral line very short. Rhamdiopsis krugi can be easily distinguished from its congeners, R. microcephala and R. moreirai, by its troglomorphic features and by the presence of a shorter lateral line, fewer vertebrae and anal-fin rays, pattern of branching of caudal-fin rays, and several attributes of skeletal system. The affinities of this new species are discussed in light of current phylogenetic knowledge of the family Heptapteridae. Incongruent derived characters do not allow selection of a particular hypothesis of sister group relationships among species of Rhamdiopsis. The occurrence of R. krugi in the rio Paraguaçu basin is possibly due to an event of hydrological capture from a section of the middle portion of the rio São Francisco basin, caused by tectonic events. The semi-arid region where R. krugi presently lives was probably covered by a wide forested area during a humid cycle in Quaternary. A summary of natural history and ecology data of R. krugi, as well as notes on its conservation, are provided. We also offer comments on the morphological plasticity of R. krugi.(AU)

Rhamdiopsis krugi, um novo bagre heptapterídeo troglóbio, é descrito de cavernas da Chapada Diamantina, Estado da Bahia, nordeste do Brasil. Esta espécie, embora frequentemente citada na literatura ao longo dos últimos dezessete anos, não foi descrita antes em função das suas afinidades filogenéticas incertas. A posição genérica de R. krugi foi obscurecida principalmente pelo seu alto número de caracteres morfológicos incomuns (parte deles relacionada à vida nas cavernas), como por exemplo: ausência de olhos e de pigmentação corporal; presença de um pseudotímpano amplamente exposto; borda posterior do ramo anterior e margem anterior da porção arborescente do ramo posterior do processo transverso da quarta vértebra conectados um ao outro; placa hipural dorsal normalmente com sete raios; placa caudal ventral usualmente com seis raios; lobos dorsal e ventral da nadadeira caudal tipicamente com seis raios ramificados cada; 38-39 vértebras; nadadeira anal com 14-17 raios; e linha lateral muito curta. Rhamdiopsis krugi pode ser facilmente distinguida de seus congêneres, R. microcephala e R. moreirai, por seus caracteres troglomórficos e pela presença de uma linha lateral mais curta, menos vértebras e raios na nadadeira anal, padrão de ramificação dos raios da nadadeira caudal e vários atributos do sistema esquelético. As afinidades desta nova espécie são discutidas à luz do conhecimento atual sobre a filogenia da família Heptapteridae. Caracteres derivados incongruentes não permitem optar por uma hipótese particular de relação de grupo-irmão entre as espécies de Rhamdiopsis. A ocorrência de R. krugi na bacia do rio Paraguaçu é devida, possivelmente, a um evento de captura hidrológica de uma seção da porção média da bacia do rio São Francisco, ocasionada por eventos tectônicos. A região semi-árida onde R. krugi atualmente vive estava provavelmente coberta por uma ampla floresta durante um ciclo úmido no Quaternário. Um sumário das informações sobre a história natural e ecologia de R. krugi, assim como observações sobre sua conservação, são apresentadas. Apresentamos também comentários sobre a plasticidade morfológica de R. krugi.(AU)

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