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.

UNASSIGNED: Troglocoelotes Zhao & S. Li, 2019 is the only known genus of Coelotinae of which all species have deep morphological adaptations to the subterranean environment, such as depigmentation of body, degenerated or absent eyes and, frequently, with attenuated bodies and/or appendages. Four species of Troglocoelotes have been reported from Guizhou Province, China.
UNASSIGNED: A new funnel-web spider of the genus Troglocoelotes is described and illustrated on the basis of a single female specimen from Tongren City, Guizhou: Troglocoelotessinanensis sp. nov. Additionally, photos of the collection site and a distribution map are also provided.

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.

Caves have long been recognized as a window into the mechanisms of diversification and convergent evolution, due to the unique conditions of isolation and life in the dark. These lead to adaptations and reduce dispersal and gene flow, resulting in high levels of speciation and endemism. The Israeli cave arachnofauna remains poorly known, but likely represents a rich assemblage. In a recent survey, we found troglophilic funnel-web spiders of the genus Tegenaria in 26 caves, present mostly at the cave entrance ecological zone. In addition, we identified at least 14 caves inhabited by troglobitic Tegenaria, which are present mostly in the twilight and dark ecological zones. Ten of the caves, located in the north and center of Israel, are inhabited by both troglophilic and troglobitic Tegenaria. These spiders bear superficial phenotypic similarities but differ in the levels of eye reduction and pigmentation. To test whether these taxa constitute separate species, as well as understand their relationships to epigean counterparts, we conducted a broad geographic sampling of cave-dwelling Tegenaria in Israel and Palestine, using morphological and molecular evidence. Counterintuitively, our results show that the troglobitic Tegenaria we studied are distantly related to the troglophilic Tegenaria found at each of the cave entrances we sampled. Moreover, seven new troglobitic species can be identified based on genetic differences, eye reduction level, and features of the female and male genitalia. Our COI analysis suggest that the Israeli troglobitic Tegenaria species are more closely related to eastern-Mediterranean congeners than to the local sympatric troglophile Tegenaria species, suggesting a complex biogeographic history.

Throughout most of the kingdom Animalia, evolutionary transitions from surface life to a life permanently bound to caves and other subterranean habitats have occurred innumerous times. Not so in tetrapods, where a mere 14 cave-obligate species-all plethodontid and proteid salamanders-are known. We discuss why cave tetrapods are so exceptional and why only salamanders have made the transition. Their evolution follows predictable and convergent, albeit independent pathways. Among the many known changes associated with transitions to subterranean life, eye degeneration, starvation resistance, and longevity are especially relevant to human biomedical research. Recently, sequences of salamander genomes have become available opening up genomic research for cave tetrapods. We discuss new genomic methods that can spur our understanding of the evolutionary mechanisms behind convergent phenotypic change, the relative roles of selective and neutral evolution, cryptic species diversity, and data relevant for conservation such as effective population size and demography.

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.

A new species of Cryptops Leach, 1814, C. speleorex sp. nov., is described from Movile Cave, Dobrogea, Romania. The cave is remarkable for its unique ecosystem entirely dependent on methane- and sulfur-oxidising bacteria. Until now, the cave was thought to be inhabited by the epigean species C. anomalans, which is widespread in Europe. Despite its resemblance to C. anomalans, the new species is well-defined morphologically and molecularly based on two mitochondrial (cytochrome c oxidase subunit I COI and 16S rDNA) and one nuclear (28S rDNA) markers. Cryptops speleorex sp. nov. shows a number of troglomorphic traits such as a generally large body and elongated appendages and spiracles, higher number of coxal pores and saw teeth on the tibia of the ultimate leg. With this record, the number of endemic species known from the Movile Cave reaches 35, which ranks it as one of the most species-rich caves in the world.

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.

Freshwater gammarids are known to colonise occasionally sinking-cave streams, providing contrasting morphological, life-history and ecophysiological adaptations compared to their surface conspecifics. In this study, a subterranean and a surface population of the species Gammarus balcanicus was surveyed for one year in a sinking-cave stream from the Western Carpathians (Romania). The results showed that the cave-dwelling population comprised individuals that were significantly larger compared to their surface conspecifics, had larger body-size at sexual maturity and that the females produced fewer, but larger eggs, compared to the population situated outside the cave. The trophic position and the omnivory were significantly higher for the cave-dwelling compared to surface population and the elemental imbalance for C:P molar ratios lower, but similar for C:N. However, the subterranean population did not present troglomorphic characters or longer lifespan as known for other cave-surface paired crustaceans. This, together with the rather extensive hydrological connection of the habitats, suggests active gene-flow between populations and similar response to seasonality for body-size distributions, indicating that the observed ecophysiological and life-history differences are rather the consequence of phenotypic plasticity than the result of genetic adaptation.

We provide a comparative population genetic study of the elusive amphibian, Proteus anguinus, by comparing the genetic diversity and divergence among 4 cave populations (96 individuals) sampled in the Dinaric Karst of Croatia. We developed 10 variable microsatellite markers using pyrosequencing and applied them to the 4 selected populations belonging to 4 different cave systems. The results showed strong genetic differentiation between the 4 caves corroborating with previous findings suggesting that Proteus might comprise several unrecognized taxa. Our results confirmed that gene flow should be high within the caves, whereas it is low between hydrographic systems since geological periods. Finally, we conclude that the high genetic subdivision suggests the necessity of treating the 4 studied Proteus populations as evolutionary significant units.