Brasileirinho cavaticus, Prevorčnik, Simona, Ferreira, Rodrigo Lopes & Sket, Boris, 2012

Prevorčnik, Simona, Ferreira, Rodrigo Lopes & Sket, Boris, 2012, Brasileirinidae, a new isopod family (Crustacea: Isopoda) from the cave in Bahia (Brazil) with a discussion on its taxonomic position, Zootaxa 3452, pp. 47-65 : 49-56

publication ID	https://doi.org/ 10.5281/zenodo.211428
DOI	https://doi.org/10.5281/zenodo.6166746
persistent identifier	https://treatment.plazi.org/id/6A25347F-711F-BE50-FF32-FE21E0AE2764
treatment provided by	Plazi
scientific name	Brasileirinho cavaticus
status	sp. nov.

Treatment

Brasileirinho cavaticus View in CoL sp. nov.

( Figs 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 , 6A View FIGURE 6. A –D)

Material examined. Holotype. Male, 1.7 mm, MNRJ 22765, phreatic pond in Baixa Funda cave, Paripiranga, Bahia State, Brazil, lat: 10º42' 24.8"S, long: 37º55' 54.4"W, 400 m a.s.l., water depth 0.2 m, water temperature 26.5°C, pH 7.4, conductivity 0.21 S /m, dissolved oxygen 3.3 mg /l, leg. R.L. Ferreira, 10.01.2009. Preserved in 70% ethanol. Paratypes. Male, 1.8 mm, prepared for SEM inspection, ISLA 1452; 6 specimens (2–2.7 mm, presumably females) mounted with Hoyer’s medium on 3 slides, ISLA 1453–1455; 15 specimens (no male or ovigerous female) preserved in 70% ethanol, ISLA 1456; 3 specimens (2.3–2.5 mm, presumably females) dissected and mounted in glycerol-gelatine on slides, OBBFUL I0001–I0003; 10 specimens (no male or ovigerous female) preserved in 70% ethanol, OBBFUL I0004–I0013, all specimens same collection data as holotype. Other material. Two males, 1.9 mm and 1.6 mm, dissected and mounted in glycerol-gelatine on two slides OBBFUL I0014–I0015, locality as holotype, leg. R. L. Ferreira, May 2010; 16 males, preserved in 96% ethanol, ISLA 1507; 131 presumable females (no ovigerous), preserved in 96% ethanol, ISLA 1508–1520, locality as holotype, leg. R. L. Ferreira, May 2010.

Diagnosis. Brasileirinho species with oblong-oval body, dorsoventrally depressed, transparent-whitish ( Fig. 6 View FIGURE 6. A B–D). Head shield semicircular, approximately as long as pleotelson, eyes absent. Body length about 3 times body width; pleonites I–II much smaller than pereonites in length and width, visible dorsally, pleonites III–V as long as pereonites, pleotelson length not exceeding 1/5 of body length. Male pleopods I–II uniramous and biarticulate, distal articles almost twice as long as proximal. In pleopod I, distal article, flat and bicuspidate distally; in pleopod II, distal article elongated conical. Female pleopods I–II absent. Pleopods III–V half of length of pleonites, uniramous, circular, with longitudinal suture. Styliform uniramous uropods nearly reaching telson’s tip.

Description. Holotype and male paratype (values given in parentheses) description.

Body 1.7 mm (1.6–1.9 mm) long, 2.8 (3.0–3.2) times as long as wide ( Fig. 1 View FIGURE 1 Bm); dorsoventrally depressed, with almost flat dorsum, pleon even slightly concave ( Fig. 6 View FIGURE 6. A B–D), transparent-whitish, surface seemingly smooth, but cephalon and pereonites I–VI dorsally with 4 short setae and pereonite VII and pleonites I–II with two short setae each. Head shield subtriangular, 1.7 (1.8–2.2) times as wide as long; with a short but distinct clypeus. No eye structures visible, neither on the surface, nor within tissue. Pereonites subtrapezoidal, with rounded epimeral angles, pereonite V widest. Lateral and posterolateral margins of pereonites with 4 delicate setae each. Pleon lenght only 38% (39%) of body length; pleonites I–II visible dorsally, length of each about 50% of pereonite VII length and with one seta posterolaterally; pleonite III–V length each of about pereonite VII length and with two setae posterolaterally; pleotelson length 17% (up to 20%) of body length, with one shorter and one longer seta submarginally on anterolateral ventral surface and 3 setae at posterolateral telsonic angle, longest seta length 140% (100–140%) of pleotelson length. Male genital papilla ( Fig. 4 View FIGURE 4 Plm, Fig. 4 View FIGURE 4 Pe-Plm, Fig. 5 View FIGURE 5 ) placed medially on the articulating membrane between pereonite VII and pleonite I, protected ventrally by sclerotized shield.

Antenna I (antennula)( Fig. 1 View FIGURE 1 AI) length about 23% of body length, length relations of peduncular articles 1–3 (from first to third) 1: 1.8 (1.7–1.8): 1.8 (1.7–1.8); flagellum of single article, 1.4 (from 1.2) times as long as first peduncle article, with one aesthetasc apically, aesthetasc length 90% (85–90%) of flagellum length.

Antenna II (antenna; Fig. 1 View FIGURE 1 AII) length about 47% of body length, relations of peduncular articles 1–5 (from first to fifth) 1: 1 (0.9): 1.7 (2): 5.2 (5.4): 6.4 (6); flagellum of 6 articles, its length about 134% (130–134%) of peduncular length.

Mandibles without palp and molar process (pars molaris). Right mandible ( Fig. 2 View FIGURE 2 Mdm(R)) incisor (pars incisiva) with 4 sclerotized cusps, lacinoid spine sclerotized and bifurcate, spine row reduced to a single pappose (with dense setules loosely arranged about the shaft in a seemingly random manner) robust seta. Left mandible ( Fig. 2 View FIGURE 2 Mdm(L)) similar, lacinia mobilis 4-cuspidate.

Maxilla I (maxillula; Fig. 2 View FIGURE 2 MxI) lateral lobe from lateral to medial with 4 (4–5) simple robust setae, 4 (4–5) dentate robust setae and 1 simple robust seta with one median denticule on outer side, at the inner basis of the setal row also 2 stocky simple setae, inner margin with 2 simple setae; mesial lobe distally with 1 short and 1 longer pappose robust seta and 1 sclerotized biserrate seta.

Maxilla II (maxilla; Fig. 2 View FIGURE 2 MxII) lateral and middle lobe with 6 curved pectinate robust setae each, mesial lobe from lateral to medial with 2 long sclerotized plumose setae and 6 shorter biserrate setae with 2 simple setae at the base of the row, outer margin distally with pseudochaetae.

Maxilliped ( Fig. 2 View FIGURE 2 Mxlp) with complex endite of two lobes, smaller inner lobe apically with 6 (6–8) simple setae, inner margin and submarginal surface with numerous pseudochaetae, larger outer lobe on inner margin with 3 sclerotised biserrate setae and numerous short simple setae, two pappose robust setae on apex and 5 long plumose setae on outer margin; palp of 5 articles, first article fused with maxilliped body, articles 2–3 with long simple setae at distal medial angles, article 5 smallest, with tuft of setae distally.

Pereopods do not display serial gradation of orientation: pereopods I–IV oriented forward, pereopods V–VII oriented backward. Pereopod I ( Fig. 3 View FIGURE 3 PeI) ambulatory, but reminiscent of subchelae due to extremely short carpus (article 5) and somewhat widened propodus (article 6); lateral coxal plate large, completely fused with pereonite I; pereopod length 31% (28–31%) of body length, length relations of articles from basis (article 2) to dactylus (article 7) 1: 0.22 (0.22–0.24): 0.39 (0.38): 0.22 (0.21–0.22): 0.67 (0.65–0.67): 0.33 (0.32–0.36), unguis length 50% (50–57%) of dactylus length; superior distal angle of merus (article 4) with 2 long setae with hairy apical transverse cutting (sensu Messana et al. 2002), inferior margins of basis, ischium (article 3) and merus with one finely serrate seta each, inferodistal angle of carpus with one apically plumose seta with whip-shaped median hair, inferior margin of propodus with 3 biserrate setae, secondary unguis finely serrate. Pereopods II–VII ( Fig. 3 View FIGURE 3 PeII, Fig. 3 View FIGURE 3 PeVII) ambulatory, mutually similar in shape and setation, increasing in length; coxae ( Fig. 3 View FIGURE 3 C, Fig. 3 View FIGURE 3 C–Pe) expanded laterally into flattened lateral coxal plates (completely fused dorsally with their respective pereonites) and inwardly over sternum, as sternal coxal plates; inferior margins of articles from basis to propodus with one finely serrate seta, on carpus additionally one longer apically plumose seta with whip-shaped median hair, superior distal angles of merus and carpus with two long setae with hairy apical transverse cutting and with one long seta with hairy apical transverse cutting and one long penicillate seta, respectively, superior margin of propodus with longer finely serrate seta and shorter simple seta, superior margin of dactylus with short simple seta; unguis and secondary unguis with acute apices, latter finely serrate. Pereopod II length 41% (38–41%) of body length, length relations of articles from basis (article 2) to dactylus (article 7) 1: 0.14: 0.48: 0.67: 0.62: 0.29 and 1: 0.14–0.15: 0.46–0.49: 0.65–0.70: 0.61–0.65: 0.27–0.29 in holotype and other males, respectively, unguis length 67% (66–68%) of dactylus length. Pereopod VII length 50% (48–52%) of body length, length relations of articles from basis (article 2) to dactylus (article 7) 1: 0.23: 0.50: 0.86: 0.82: 0.36 and 1: 0.22–0.26: 0.51–0.52: 0.83–0.86: 0.81–0.84: 0.34–0.37 in holotype and male paratypes, respectively, unguis length 63% (60–64%) of dactylus length.

Pleopods I–II uniramous, unipartite, modified for copulatory purposes, with identical ventral and dorsal ( Fig. 4 View FIGURE 4 PlpI(d), Fig. 4 View FIGURE 4 PlpII(d)) sides. Pleopod I ( Fig. 4 View FIGURE 4 Plm, Fig. 5 View FIGURE 5 B) protopodite subrectangular, its width about 78% of its length, subrectangular ramus (supossedly exopodite) length about 130% of protopodite length, thick lamellar, vaulted, with acute lateroapical and obtuse medioapical angles. Pleopod II ( Fig. 4 View FIGURE 4 Plm, Fig. 5 View FIGURE 5 B) protopodite obtusely subtrapezoidal, ramus (suposedly endopodite) about twice as long as protopodite, elongated conical and slightly spindle shaped.

Pleopods III–V ( Fig. 4 View FIGURE 4 Plm, Fig. 4 View FIGURE 4 Plf, Fig. 4 View FIGURE 4 PlpIII, Fig. 5 View FIGURE 5 A) not sexually dimorphic, mutually similar, presumably without or with extremely reduced exopodites, endopodites ellipsoid, tumescent, about 1.25 times as long as wide, with a longitudinal suture. The origin of the subtriangular structures (“scales”) at the basis of each pleopod remains unclear due to the indistinguishable protopodite, hidden in the »vault« formed underneath the distal border of the pleonite. As articulations between structures are vague it is only presumed that structures in question could be exceptionally reduced exopodites.

Uropods ( Fig. 1 View FIGURE 1 Bm, Fig. 1 View FIGURE 1 U(v)) inserted laterally, slightly surpassing pleotelson apex, uniramous, with no visible suture lines, styliform, with acute apex, their length about 50% of pleotelson length; lateral margin with 2 setae, their length about 80% of uropod length, ventral and dorsal surfaces distally with 3 and 5 (4 and 5) shorter setae, respectively.

Description of female. Almost identical to males, except mainly larger, up to 2.7 mm long. Body 3–3.5 times as long as wide ( Fig. 1 View FIGURE 1 Bf), pleotelson ( Fig. 4 View FIGURE 4 Pltf) with almost straigth posterolateral and posterior margins, its length 16–19% of body length, longer submarginal seta length 60–150% of pleotelson length.

Antenna I length 19–21% of body length, length relations of peduncular articles 1–3 (from first to third) 1: 1.7–2: 1.8–2; flagellum 1.2–1.4 times as long as first peduncle article, aesthetasc length only 64–76% of flagellum length. Antenna II length 39–42% of body length, relations of peduncular articles 1–5 (from first to fifth) 1: 1–1.1: 1.7–2: 5.7–6: 6–6.2; flagellum of 5–6 articles, its length 130–140% of antenna length.

Mouthparts (mandibles: Fig. 2 View FIGURE 2 Md(L), Fig. 2 View FIGURE 2 Md(R)) as in males.

Pereopods somewhat shorter than in males, pereopod I, II and VII lengths 24–29%, 32–36% and 42–46% of body length, respectively; length relations of articles from basis to dactylus, as in males.

Pleopods I and II absent ( Fig. 4 View FIGURE 4 Plf), pleopods III–V as in males.

Uropods ( Fig. 1 View FIGURE 1 Bf, Fig. 4 View FIGURE 4 Pltf) as in males.

Etymology. Brasileirinho is a small Brazilian in Portuguese. The animal is less than 3 mm long. Latin word ' cavaticus ' meaning living in a cave, refers to its troglobiotic status.

Habitat, ecology and behavior. The Baixa Funda cave is located in the municipal district of Paripiranga, NE of Bahia. A single, 50 m long rectilinear conduit descends gently from the entrance towards a small pond at the cave’s far end. In January 2010, the length and the width of the pond were about 5 and 1.5 m, respectively. However, water level variation of more than a meter could be inferred from the “tide marks” on the conduit walls. In May 2010, the level of the pond was about 30 cm lower, and water parameters were: temperature, 26.5°C; pH, 7.4; conductivity, 0.21 S /m; dissolved oxygen, 3.3 mg /l.

While some specimens were assembled on a submerged guano patch ( Fig. 6A View FIGURE 6. A ), countless specimens were walking around in the observable area of the pond. On both occasions, the population consisted of few thousands of individuals. During the first collection the majority of specimens were observed assembling on the bottom of the pond. Nevertheless, due to the extremely fine sediments which would be easily disturbed the sampling and observing were confined to the pond margin. The deepest part of the pond remained uninspected.

The individuals were roaming the bottom, stopping randomly. At times they entered small cracks present in the substrate, but they were not observed to bury themselves into the fine sediment. No specimen was caught swimming. Moreover, individuals that accidentally fell off the brush during collection were passively sinking down to the bottom, demonstrating clearly their swimming inability.

No agonistic behavior was observed. As the population density was high, specimens were found to bump into each other frequently, changing their direction consequently. Some smaller individuals (maybe immature) were observed to walk over larger individuals. Specimens were exhibiting no phototactic behavior, neither positive, nor the negative.

The observed sex ratio was highly biased in Brasileirinho ; in the January sample we’ve only got 2 males (4%) for 49 females while in the May sample, 16 males (12%) for 131 females have been found. There were no signs of gravidity in the females: neither visible eggs within the body nor developed oostegites in any of 180 sampled female specimens.

There were no apparent predators in the pond, which could explain high population density, as well as the absence of agonistic or cryptobiotic behavior in Brasileirinho . The only cohabitants in the pond seem to be oligochaetes, copepods and bathynellaceans. The only visible food resource present at the bottom of the lake was guano and brasileirinhos apparently fed on it. Almost all specimens had their intestine filled with a dark-colored content.