Brasileirinho sergipanus, Cardoso & Bento & Ferreira, 2025

Brasileirinho sergipanus sp. nov.

Figures 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6

Material examined. Holotype: Male (in slide) ( ISLA 96959), Brazil , Sergipe state, municipality of Lagarto, Toca da Fumaça cave (10.99365° S, 37.70289° W), 10/VIII/2013, leg. R. L. Ferreira. GoogleMaps

Paratypes: 1 immature male ( ISLA 96856) , 1 female ( ISLA 96880) , 1 immature male ( ISLA 96881 in slide) , 1 female ( ISLA 96885 in slide) , 1 male ( ISLA 96884) , 1 immature male, 6 females ( ISLA 96882) , 4 females ( ISLA 96883) , 2 immature males, 3 females ( ISLA 96884), same data as holotype GoogleMaps .

Diagnosis: Head shield subtrapezoidal, wider than pleotelson; pleonite 1 reduced, smaller than pleonite 2; pleonite 2 slightly wider than pleonite 3; pleotelson about half width of pereonite 7; male pleopod 1 simple, tapering, apex acute; male pleopod 2 proximal part rectangular, distal part long, flagelliform; pleopods 3–5 not sexually dimorphic, similar, endopodites rounded; female pleopods 1 and 2 absent; uropods shorter than pleotelson apex, uniramous.

Description: Maximum body length of 2 mm, three times as long as wide; dorsoventrally depressed ( Fig. 1A,B View FIGURE 1 ), transparent-whitish, surface smooth.

Head shield subtriangular, wider than long, wider than pleotelson; clypeus short ( Fig. 2A View FIGURE 2 ). Eyes absent. Pereonites subtrapezoidal, with rounded posterior margins, lateral margin with two setae each, pereonite 4 widest ( Figs 1A,B View FIGURE 1 ; 2B View FIGURE 2 ). Pleon length about 40% of body length; pleonites 1 and 2 visible dorsally, pleonite 1 reduced, smaller than pleonite 2, pleonite 2 slightly wider than pleonite 3, pleonites 1 and 3 length about 60% and 90% of pereonite 7 length, respectively. Pleotelson ( Figs 1B View FIGURE 1 ; 2B View FIGURE 2 ) length 15% (12%) of body length, about half width of pereonite 7; wider than long, with two setae medially on dorsal surface, and two setae on anterolateral ventral surface, apex with six setae, longest seta shorter than pleotelson length ( Figs 1A,B View FIGURE 1 ; 2B View FIGURE 2 ).

Antennula ( Fig. 2A,C View FIGURE 2 ) shorter than peduncle of antenna; peduncle of three articles, flagellum of one article with one aesthetasc. Antenna ( Fig. 2A,D View FIGURE 2 ) long, about 60% of body length, reaching pereonite 7; peduncle of five articles; flagellum with seven to eleven articles. Mandibles ( Fig. 2E–G View FIGURE 2 ) without palp and pars molaris, lacinia mobilis with denticulate apex, one pappose robust seta, right incisor with four teeth, left incisor with five teeth. Maxillula ( Fig. 2H View FIGURE 2 ) endite with one inner simple seta and two plumose setae; exite with one trifid seta, four robust serrate setae and four robust simple setae. Maxilla ( Fig. 2I View FIGURE 2 ) endite with two long inner serrate setae and apex with four plumose setae, plus one serrate seta; exite medial and lateral rami with five serrate setae each. Maxilliped ( Fig. 2J View FIGURE 2 ) endite apex with one robust pappose seta and five long plumose setae on inner margin; ventral face with four pappose setae; palp of five articles, first article fused with maxilliped body, articles with long simple setae, article 5 smallest, with tuft of setae distally.

Pereopod 1 ( Fig. 3A View FIGURE 3 ) ambulatory, ischium, merus and carpus with one serrate seta each on inner margin; merus with two long serrate setae on outer margin; carpus short (reminiscent of subchelae), shorter than propodus; propodus with three serrate setae on inner margin; distal margin of propodus and dactylus with pectinate scales; unguis finely serrate. Pereopods 2–7 ( Fig. 3B–G View FIGURE 3 ) progressively long, pereopod 7 ( Figs 1C View FIGURE 1 ; 3G View FIGURE 3 ) 1.5 times longer than pereopod 1, 50% of body length; ischium, merus carpus with one serrate seta each on inner margin, outer margin with one or two serrate setae; carpus as long as propodus; propodus one short serrate seta on inner margin; distal margin of propodus and dactylus with pectinate scales; unguis finely serrate. Pleopods 1 and 2 sexually dimorphic. Pleopods 3–5 ( Figs 1D,E View FIGURE 1 , 4A–C View FIGURE 4 ) not sexually dimorphic, similar in size, reduced, endopodites rounded. Uropods ( Figs 1B View FIGURE 1 ; 2B View FIGURE 2 ) inserted laterally, shorter than pleotelson apex, uniramous, styliform, with acute apex, length about 30% of pleotelson length; lateral margin with three sets of setae.

Females ( Figs 1D View FIGURE 1 , 4A View FIGURE 4 ): Body length of 2 mm. Pleotelson ( Figs 1B View FIGURE 1 , 4A View FIGURE 4 ) length 12% of body length. Antennal flagellum with 11 articles ( Fig. 1B View FIGURE 1 ). Pleopods 1 and 2 absent, respiratory pleopods 3–5 ( Figs 1B View FIGURE 1 , 4A View FIGURE 4 ) similar in size, reduced, endopodites rounded.

Immature males ( Figs 1E View FIGURE 1 , 4B View FIGURE 4 ): Body length of 2 mm. Antennal flagellum with eight articles ( Fig. 2A View FIGURE 2 ). Pereopods with no modification. Genital papilla ( Fig. 1E View FIGURE 1 ) as one lobe on articulating membrane between pereonite 7 and pleonite 1. Pleopod 1 ( Figs 1E View FIGURE 1 , 4B View FIGURE 4 ) reduced, not reaching pleopod 2, simple, apex acute. Pleopod 2 ( Figs 1E View FIGURE 1 , 4B View FIGURE 4 ) protopodite trapezoidal apparently fused with sternite, distal part about twice as long as protopodite, apex tapering.

Mature male: Body length of 1.5 mm. Antennal flagellum with 10 articles ( Fig. 2D View FIGURE 2 ). Pereopods absent. Genital papilla ( Fig. 4C View FIGURE 4 ) as one lobe on articulating membrane between pereonite 7 and pleonite 1. Pleopod 1 ( Fig. 4C View FIGURE 4 ) simple, tapering with apex acute. Pleopod 2 ( Fig. 4C View FIGURE 4 ) protopodite rectangular, anterior margin as wide as distal margin, apparently fused with sternite; distal part flagelliform, long, surpassing pleonite 3. Pleotelson ( Fig. 4C View FIGURE 4 ) with two distal setae longer than pleotelson length.

Etymology. The new species name ‘ sergipanus ’ is a noun in apposition to the state where the species is found, Sergipe. The word comes from the Tupi language and means river of crabs.

Habitat. Specimens of B. sergipanus sp. nov. were exclusively found in the Toca da Fumaça cave, which is inserted within Cretaceous limestone of the Canudos Geological Formation. Positioned near the border between the states of Sergipe and Bahia, it is located approximately 40 km in a straight line from the Baixa Funda cave, which is the type-locality of B. cavaticus ( Fig. 5 View FIGURE 5 ). However, it is noteworthy that the Toca da Fumaça cave is positioned at a significantly lower altitude, approximately 150 meters above sea level, in contrast to Baixa Funda cave, which is located at an elevation of 395 meters above sea level.

The Toca da Fumaça cave extends for approximately 200 meters. This cave possesses a single entrance, which is vertical and located at the base of a sinkhole ( Fig. 6A,B View FIGURE 6 ). The cave displays a marked verticalization, characterized by numerous inclined passageways leading to chambers of varying dimensions. In the innermost regions of the cave, the phreatic level forms a lake that spans in the deepest cave conduit, which provides a habitat for the newly discovered species B. sergipanus sp. nov. ( Fig. 6E,F View FIGURE 6 ). Although the lake covers a considerable area, it is relatively shallow, with a maximum depth of 1.5 meters. However, as our cave exploration was conducted during a single survey, we cannot assert that the lake maintains this constant configuration. Much like the observed fluctuations in the phreatic level at the Baixa Funda cave, which can vary significantly throughout the year, it is likely that the phreatic level in the Toca da Fumaça cave also experiences seasonal variations. At the lake’s bottom, a fine sediment is present, seemingly resulting from the amalgamation of inorganic sediments and bat guano. This sediment serves as a vital organic resource for the invertebrate inhabitants. Other organisms observed in this habitat include earthworms (Oligochaeta) and copepods.

In contrast to their relatives, who were predominantly observed at the bottom of the pond, specimens of B. sergipanus sp. nov. were found moving along the submerged walls within the cave, generally in proximity to the lake’s surface. Notably, specimens were not sighted in the sediment at the lake’s bottom (which was deeper when compared to the pond observed in the Baixa Funda cave). It is worth noting that specimens of B. cavaticus were observed in the shallower regions of the pond within the Baixa Funda cave. This suggests that both species may not thrive in deeper areas within the phreatic level, a pattern also observed in other aquatic and semiaquatic isopods in Brazil ( Silva et al. 2018). However, it is crucial to emphasize that only a limited portion of the habitat for was accessed during this study. Therefore, further investigations are highly recommended to gain a more comprehensive understanding of the actual distribution the species.

Significant environmental damage has been evident both in the immediate vicinity of the Fumaça cave and within its interior. Despite being situated within the limits of the Brazilian Atlantic Forest, the cave's surroundings have been transformed into pasturelands through deforestation, resulting in the loss of its original vegetation. Additionally, local inhabitants used to burn tires inside the cave in an attempt to reduce bat populations, as they erroneously believed that bats were detrimental to their cattle. This regrettable practice left numerous tires behind, with some remaining unburned, in the first and second cave chambers ( Fig. 6C,D View FIGURE 6 ). Thankfully, this practice appears to have ceased, as a substantial bat colony (inhabited by Pteronotus bats) was encountered during our samplings in 2013. It is important to note, however, that although we have not revisited the cave since our samplings, a different group of researchers engaged in fossil investigations in 2022. They reported that the cave’s condition, particularly concerning the tires, has remained unchanged (pers. comm. from Mario Dantas). Unfortunately, this team did not explore the cave’s deepest sections, including the phreatic level. While the tire burning took place primarily in the more external chambers, relatively distant from the phreatic level, the potential impacts on the population of B. sergipanus sp. nov. cannot be ruled out. Given our single visit to the cave, we cannot guarantee the preservation or protection of this population.