﻿First amphibious Crinocheta (Isopoda, Oniscidea) from the Neotropics with a troglobitic status: a relictual distribution

﻿Abstract The first freshwater amphibian representative of Crinocheta (Oniscidea) from the Neotropics is described from caves within the Brazilian Cerrado biome, state of Mato Grosso do Sul. Kadiweuoniscusrebellisgen. et sp. nov. is placed in the family Philosciidae. The present work represents a significant contribution to future studies seeking to understand the ecological and evolutionary processes of Crinocheta within the Neotropical region. Moreover, it highlights the importance of biodiversity surveys in subterranean environments toward effective conservation efforts of these unique habitats and their surroundings.

Regarding the phylogeny of the group, morphological studies show Oniscidea as monophyletic, including the Sections Ligiidae, Tylidae, Mesoniscidae, Synocheta, and Crinocheta (Schmalfuss 1989;Wägele 1989;Erhard 1998;Schmidt 2008).All these authors recognized Synocheta as the sister group of Crinocheta.The last section is the most diverse, representing more than 80% of the entire suborder inhabiting various types of habitats (Schmidt 2002(Schmidt , 2003(Schmidt , 2008;;Schmalfuss 2003).Recent molecular evidence has revealed that the genus Ligia Fabricius, 1798, is closer to marine groups of isopods, which raises doubts about the monophyly of Oniscidea (Lins et al. 2017;Dimitriou et al. 2019).However, future studies with integrative approaches will be necessary to clarify the phylogenetic relationships of the group.
In the present study, a freshwater amphibian representative of Crinocheta (Philosciidae) with troglobitic status is described for the first time in the Neotropical region.Kadiweuoniscus rebellis gen.et sp.nov. is described from caves in the Brazilian Cerrado biome, state of Mato Grosso do Sul, Serra da Bodoquena karst area.

Study area
The material was collected from three limestone caves of Serra da Bodoquena karst area, located in the Bodoquena municipality, state of Mato Grosso do Sul, southwestern Brazil (Figs 1, 2).The caves occupy an area about 220 km N to S and may reach 40 km E to W, encompassing many flooded caves beside a few sparse limestone hills, located about 100 km N to W along the Paraguay Belt.The area belongs to the Corumbá (geomorphological) Group, Bocaina Formation, and it is classified as having an Aw (tropical) climate, characterized by a dry winter and humid summer (Bedek et al. 2018(Bedek et al. , 2020)).It is known for its high diversity of troglobites (Camargo and Lourenção 2007;Cordeiro et al. 2014), surpassing 34 species, many of them aquatic (Trajano et al. 2016).The native vegetation in the area consists of savanna in contact with semi-deciduous seasonal forest, within the Cerrado Biome (Galati et al. 2003;Boggiani et al. 2011).Two of the caves are located within the Serra da Bodoquena National Park (PNSB, Parque Nacional Serra da Bodoquena), a National Conservation Unit created in 2000 that covers an area of 76,481 hectares and contains numerous caves (Camargo and Lourenção 2007;Lobo 2007;Cordeiro et al. 2014).Currently, livestock is the main economic activity in the region, followed by tourism, including speleotourism.The latter has grown in economic importance for the municipalities of Bonito, Bodoquena and Jardim (Lobo 2007;Cordeiro et al. 2014).

Collections and taxonomy
Specimens were collected by active search with the aid of tweezers and brushes, and stored in 75% ethanol; microhabitat data was also recorded.The identifications were based on morphological characters with the use of micropreparations in Hoyer's medium (Anderson 1954).The illustrations were made with the aid of a camera lucida mounted on a Zeiss Stemi SV6 stereomicroscope and Leica DMLS microscope.The final illustrations were prepared using the software GIMP v.2.8 with the method proposed by Montesanto (2015Montesanto ( , 2016)).For scanning electron microscopy (SEM), two individuals were used, one male and one female, without performing dissections.The specimens were dried using Critical Point Drying and mounted on a plastic sheet.Uncoated SEM preparations were examined using an FEI Quanta 250 (at the UFSCar).The figures were edited using GIMP v.2.8.
The material examined is deposited in the zoological collection of the Laboratório de Estudos Subterrâneos (LES), Universidade Federal de São Carlos, São Carlos, Brazil (curator: Maria E. Bichuette).
Etymology.The new genus is named after the Kadiwéu indigenous people.The Kadiwéu are known as "Indian riders", due to their horse-riding prowess, keeping in their mythology, art and rituals the way of being of a hierarchical society between masters and captives.
The family has great morphological plasticity and the representatives are mainly recognized by the 'runner-type' habitus (sensu Schmalfuss 1984), body with a dorsal surface smooth or slightly tuberculated, pereonites 1-7 with one or two lines of noduli laterales per side (sometimes present on cephalon and pleonites), antennula and antennal flagellum of three articles, mandibles with molar penicil simple or dichotomized, maxillula outer endite with outer set of teeth simple or cleft or pectinated, maxilla bilobated, maxilliped endite bearing ventral penicil or triangular seta (sometimes absent), uropod branches unequal or similar in length and inserted at same or on distinct levels, and pleopod exopods with out respiratory areas or with covered monospiracular lungs (Taiti andFerrara 1980, 1982;Ferrara et al. 1994;Araujo and Leistikow 1999;Leistikow and Araujo 2001;Leistikow 2001).

Kadiweuoniscus rebellis
Male.Pereopod 1-7 (Fig. 5A-H) gradually more elongated, without particular modifications.Genital papilla (Fig. 6A) with lanceolate ventral shield; papilla longer than ventral shield bearing two subapical orifices.Pleopod 1 (Fig. 6A) exopod ovoidal, inner margin with one small seta; endopod stout, three times longer than exopod, slightly bent outwards, apex bearing setae on inner margin.Pleopod 2 (Fig. 6E) exopod triangular, outer margin concave bearing four setae; endopod flagelliform, slightly longer than exopod.Pleopod 3 and 4 (Fig. 6C, D) exopods rhomboid, outer margin with four setae, inner margin slightly convex.Pleopod 5 (Fig. 6E) exopod rhomboid, longer than wide, distal and outer margins rounded bearing four small setae.Etymology.The new species name alludes to the resistance group from the Star Wars fiction series, the Rebel Alliance, that fights against the Empire.The Kadiwéu indigenous people were known as warriors, and they fought for Brazil in the Paraguayan War to reclaim and secure their lands in the Serra da Bodoquena region.Today, they are confined to the outskirts of the Bodoquena plateau and the Pantanal plain.The designation 'rebellis' is used as an adjective for the genus name.

Discussion
The Serra da Bodoquena karst area exhibits taxonomic singularities among invertebrates, housing some remarkable phylogenetic relicts among peracarid crustaceans, such as Potiicoara brasiliensis Pires, 1987 (Spelaeogriphacea) and Megagidiella azul Koenemann & Holsinger, 1999 (Amphipoda) (Pires 1987;Koenemann and Holsinger 1999).To date, no records of such singularities within Isopoda, particularly Oniscidea, have been documented.Cordeiro et al. (2014) reported a low diversity of terrestrial isopods in this region.At present, the records include Circoniscus intermedius Souza & Lemos de Castro, 1991and Diploexochus carrapicho Campos-Filho, López-Orozco & Taiti (Campos-Filho et al. 2014, 2023).The discovery of a new freshwater amphibian genus highlights the taxonomic significance to both Serra da Bodoquena karst areas and the Neotropical region.Moreover, K. rebellis gen.et sp.nov.represents a significant addition to our ecological knowledge of Neotropical Philosciidae, considering its amphibious habit.It is worth noting that the majority of species within this family commonly inhabit the edaphofauna in the epigeal environment (Leistikow 2001).
Based on the phylogeny of South American Philosciidae, the genera Quintanoscia Leistikow, 2000 and Oxalaniscus were recovered as basal groups (Leistikow 2001).These two genera show typical characters of the groundpattern Oniscidea, such as a subrectangular maxilla, the maxilliped palp with prominent setal tufts and the endite with a prominent penicil (Leistikow 2000(Leistikow , 2001)).Kadiweuoniscus gen.et sp.nov. shares the first two characteristics, however, it lacks the penicil in the endite of the maxilliped, which may suggest it is basal within Philosciidae.Further investigations including molecular data are necessary to clarify the position of the new genus within the family.Our discovery marks the initial documentation of the troglobitic amphibian Crinocheta in the Neotropics, serving as a pivotal link for comprehending aspects related to the biology, ecology, morphology, distribution and evolution of Philosciidae.
The Flor da Bodoquena Cave is a vertical fracture (Fig. 2A), with the water reaching 20 m deep and extending only 150 meters.Specimens of K. rebellis gen.et sp.nov.were found in the walls of the cave.The fracture ends at the level of the sheet, where the stygobitic catfish Trichomycterus dali Rizzato, Costa, Trajano & Bichuette, 2011 is also recorded, possibly a predator of the isopods.During the rainy season, the current increases and the water level rises, oscillating between 10 and 12 m.Dispersion of the species possibly follows this oscillation.This cave is at a higher altitude compared to the other two where the species occurs (Urubu Rei and Dente de Cão, Fig. 2B-D), and may represent the source population.Urubu Rei and Dente de Cão caves have conduits with lentic waters and bottoms formed by silt, pebbles and rocky substrate (Fig. 2B, Urubu Rei Cave).In the case of Urubu Rei, the water rises drastically in the rainy season, becoming extremely lotic, which also could disperse/spread the isopods; the same is not observed for Dente Cão Cave.
Considering the species distribution, although the limestones are continuous at the surface (Fig. 2E), hydrological barriers have been formed due to fluvial incisions that, in the north plateau, have cut down to non-carbonate rocks, forming compartments corresponding to micro-basins (Cordeiro et al. 2014).The species occurs in the upper part of these compartments, and its distribution in the three caves could be explained by one colonization event and, after the regional uplifting prior to the Pliocene/Pleistocene transition, raising the area to altitudes of 1000 m, followed by the current subsidence responsible for the formation of the adjacent Pantanal Basin.The three populations may be isolated by geological processes, as suggested by Moracchioli and Trajano (2002) for P. brasiliensis.These facts, allied with the marked troglomorphisms and unique characteristics, could indicate a relictual occupation of the Serra da Bodoquena subterranean habitats.

Conservation remarks
The species occurs in caves within the boundaries of the Serra da Bodoquena National Park, and is, a priori, legally protected.However, the caves are not controlled or even inspected by governmental bodies dealing with tourism and visitors.Furthermore, their surroundings have deforested areas with livestock farming and agriculture activities (Fig. 2F), which drastically reduces the quality of the habitat.These facts make the species vulnerable in relation to its effective protection.Ecological monitoring projects can help in the understanding of the distribution and singularities of the species, which would assist in conservation efforts.The restricted distribution makes the species vulnerable and potentially endangered.
Finally, considering that specimens of the taxon described here have been collected since 2011, it is essential to emphasize the significance of scientific collections in the study of biodiversity.These collections serve as repositories of historical information about natural environments.Therefore, it becomes crucial to review the materials collected over extended periods and stored in such institutions.By doing so, we can enhance our understanding of the vast taxonomic diversity present in our ecosystems.Scientific collections play a crucial role in research, allowing the examination of specimens over time and across different locations, and safeguarding our biodiversity.Without these collections, our knowledge of the natural world and the species it harbors would be severely limited.

Figure 2 .
Figure 2. Study area: A Flor da Bodoquena Cave B Urubu Rei Cave C Dente de Cão Cave D epigean environment in Flor da Bodoquena Cave E limestones in the Serra da Bodoquena karst area F livestock and agriculture in the Serra da Bodoquena.