Cave-dwellers Diploexochus (Isopoda, Armadillidae): new species and new records of the genus from Brazil

Abstract Two new species of Diploexochus are described. Diploexochus spinatus sp. nov. from Lapa do Honorato cave, located in the municipality of Iuiu, and Diploexochus obscurus sp. nov. from Água Escura I cave, located in the municipality of Carinhanha, both in the southwest of Bahia State, northeastern Brazil. Both species are likely to occur in caves due to anthropogenic impacts in the surrounding area (such as deforestation) and/or looking for the stable microclimatic conditions found in the subterranean realm. Additionally, D. echinatus is recorded in a cave in the municipality of Rurópolis, Pará State, northern Brazil. These represent the first records of the genus for subterranean environments.

Habitat and ecological remarks.Two specimens of D. echinatus (Fig. 1) were found in a sandstone cave (Lucas cave -Fig.2) located in the municipality of Rurópolis, Pará State, northern Brazil.Paleozoic rocks covered by a dense Amazon ombrophilous rainforest represent the regional geology.The area is located in the hot tropical climate domain with annual dry period of 2 to 3 months.The annual average temperatures are above 20 ºC and the annual precipitation is around 1,754 mm (Tereso et al., 1975).Lucas cave presents a single entrance (Fig. 2A) leading to the main cave conduit (Fig. 2B,  C), which presents 365 m of horizontal projection.

New species and records of Diploexochus from Bahia, Brazil
Nauplius, 31: e2023008 The cave does not present any drainage, although the atmosphere is moist due to the external forest and climate.A big bat colony inhabits the cave, producing massive amounts of guano, which covers a considerable portion of the floor.Both specimens of D. echinatus were found in a region close to the entrance, though already aphotic, around 25 m from the entrance on a pile of stones made by ancient inhabitants of the region (unknown reason) (Fig. 2D).These organisms are quite sensitive, curling up at the slightest touch, like other armadillids (Fig. 2E).Even though the cave was meticulously inspected looking for invertebrates, only these two specimens of Diploexochus were found.In addition, other caves sampled in the region did not reveal the presence of this species.It is important to mention that this represents the first record of this species from cave environments.
Etymology.The specific epithet "spinatus" refers to the morphology of the dorsal tubercles, which in this species are like spines.
Morphological remarks.The specimens from Honorato cave showed variations in the tubercle development on the telson, being very reduced in relation to the tubercles on pleonites (in 4 specimens) or absent (in 5 specimens); while on the female from Tapera D'água cave these tubercles are as long as those on pleonites 3-5 (Fig. 6D, E).Furthermore, the female from Tapera D'água cave presents the cephalon with seven tubercles and pereonites and pleonite epimera with posterior points well-developed, curved and directed outwards, in a pattern similar to D. echinatus (Fig. 6E).
Habitat and ecological remarks.Specimens of D. spinatus sp.nov.were found in two caves in the municipality of Iuiú, a region with several caves and cave-restricted endemic species (Souza et al., 2015;Souza and Ferreira, 2018;Cardoso et al., 2020;2021).Other caves in the area were also inventoried, however specimens of D. spinatus sp.nov.were only found in these two caves.This area is located in the Caatinga domain, the only xeric biome of Brazil with xeromorphic and deciduous vegetation (Fig. 6A).Several specimens of D. spinatus sp.nov.were found in Honorato cave, a limestone cave with 150 meters of horizontal projection.This cave has a single entrance leading to a wide chamber (Fig. 6B), partially trespassed by an intermittent stream that occurs in the cave main conduit.During dry periods, only a few ponds are observed inside the cave, while during rainy periods the stream can flow, especially after strong rains.Several specimens were found from the middle  portion of the cave to the deepest chamber (Fig. 6D).In all cases, they were sheltered under rocks on the cave floor distant from the potentially flooded areas.Although three samplings have been performed in this cave (in 2008, 2012, and 2021), specimens of D. spinatus sp.nov.were only found in the last sampling event, although body remnants potentially belonging to this species were observed in 2008.It is worth mentioning that in the first two samplings, there was a forested area surrounding the cave.In the last sampling, however, this forest was no longer present, and a considerable area of exposed soil was observed.

New species and records of Diploexochus from Bahia, Brazil
Nauplius, 31: e2023008 The presence of living specimens of D. spinatus sp.nov.only in the last sampling may have occurred due to their migration from the external area to the cave environment, seeking more suitable habitat.Considering that the species lacks any troglomorphic traits, it is likely that it exhibits external populations and their occurrence in caves may be related to the presence of impacts (such as deforestation) in the epigean environments.A single specimen was observed in Tapera D'água cave, located around 11.5 km away from Honorato cave.This cave presents around 300 meters of horizontal projection, trespassed by a stream.The single specimen (Fig. 6E) was also found under a rock on the cave floor, in a chamber located in the deep portion of the cave (Fig. 6C), far from the potentially flooded areas.The surrounding area of this cave is more preserved, although there are signs of human impacts in the past (like deforested areas and some abandoned water reservoirs).In this sense, several suitable habitats seem to exist for the species in the cave surroundings.
Habitat and ecological remarks.Specimens of D. obscurus sp.nov.were found in a limestone cave (Água Escura I cave) located in the region of "Serra do Ramalho", northeastern Brazil.This area has hundreds of caves and several cave-restricted species (e.g., Baptista and Giupponi, 2002;Kamimura and Ferreira, 2018;Hellmann et al., 2020).Although many other caves in the area were also inventoried, specimens of D. obscurus sp.nov.were only found in this cave.Although this cave is peripheral to the main subterranean drainage in the area, it can be considered part of the Água Clara cave system, which comprises the richest hotspot of subterranean biodiversity in South America (Souza-Silva et al., 2021).The Água Escura I cave presents a single entrance, located at the base of a limestone outcrop (Fig. 10A).The cave presents two main conduits (one intercepting the other), which were extremely dry during the samplings (Fig. 10C).However, the cave conduits are located at a lower level when compared to the surface, so that the water from floods can enter the cave, submerging part of its chambers during strong rains (Fig. 10B).According to Köppen's climate classification system, the local climate is "Aw", with dry winter and an average annual rainfall of 640 mm 3 (Alvares et al., 2013).Only four specimens of D. obscurus sp.nov.were found in the cave (Fig. 10D, E), all sheltered under big rocks, in which microhabitats still retained some moist content on the subjacent floor (Fig. 10C).The cave surroundings are severely impacted (Fig. 10A), mainly by deforestation and fires, although cattle and goat breeding were also observed.As mentioned for D. spinatus sp.nov., the cave is likely being used by D. obscurus sp.nov.as a refuge, considering the highly impacted area surrounding the cave.

DISCUSSION
The disposition of tubercles has shown to be a strong character that varies among Diploexochus species, along with the shape of the male pleopod exopod, the proportion of the uropod exopod, and the shape of the telson.The number and topology of pereonite tubercles differ in the new species in relation to D. echinatus, which shows 15 tubercles on pereonites 2-6; and 13 tubercles on pereonite 7. Diploexochus spinatus sp.nov.presents 13 tubercles in two rows on pereonites 2-6 and 11 tubercles on pereonite 7; while D. obscurus sp.nov.presents 13 tubercles on pereonite 2, and 11 tubercles on pereonites 3-7.Regarding the pleonites, each species shows a different pattern.In D. echinatus there are four tubercles on pleonites 3 and 4 and two paramedian tubercles on pleonite 5 and telson; in D. spinatus sp.nov.there are two paramedian tubercles on pleonites 3-5, with some species showing tubercles on the telson; and in D. obscurus sp.nov.there are four tubercles on pleonite 3, and two paramedian tubercles on pleonites 4 and 5 and telson.
The shape of the male pleopod 1 exopod in D. spinatus sp.nov. is similar to D. echinatus.In comparison with D. echinatus, the uropod exopods and endopods in D. spinatus sp.nov.and D. obscurus sp.nov.are minute.In proportion, in D. spinatus sp.nov. the endopod is around twice as long as the exopod, similar to D. echinatus, while in D. obscurus sp.nov. the endopod is around threefold longer than the exopod.Lastly, the distal part of the telson in D. echinatus is quadrangular with the dorsum slightly depressed, and the distal margin concave, while in both new species it is rectangular with the distal margin straight.
Although several species have been described as belonging to the genus Diploexochus, all of them ended up being reallocated into other genera.Accordingly, almost two centuries after the description of the genus, two new species are described, which not only contributes to the taxonomy of this group but also points to potential discoveries.Furthermore, the occurrence of the herein described species in a semiarid biome, quite distinct from the moist Amazon region where D. echinatus is found, demonstrates the great adaptive plasticity of the species in this genus.Finally, it is important to highlight the increase in threats to Brazilian speleological heritage.Even considering caves as possible peripheral habitats of the herein described species, the high degree of alterations in the external environments may have forced their populations to migrate into the caves.In turn, such subterranean habitats are under unprecedented threat due to recent changes in laws regarding the protection of Brazilian speleological heritage (Ferreira et al., 2022).Thus, although little is known about the real distribution of these new species, it is worrying that they may already be threatened.

Figure 2 .
Figure 2. Lucas cave, Rurópolis, Pará State, Brazil.A, Surrounding area; B, main cave conduit; C, cave conduit; D, live specimen of Diploexochus echinatus in lateral view; E, live specimen of Diploexochus echinatus showing the ability to roll into a ball.

Figure 10 .
Figure 10.A, Karstic area surrounding Água Escura I cave; B, entrance of Água Escura I cave; C, conduit where the specimens were found; D, live specimen of Diploexochus obscurus sp.nov. in lateral view; E, live specimen of Diploexochus obscurus sp.nov. in dorsal view.