New species of Brachystomellidae and characterization of Micronella porcus (Denis, 1933) from Brazil

Abstract Three new species of Brachystomellidae from high altitude fields of southeast Brazil are described and illustrated and additions made to the description of Micronella porcus (Denis, 1933). The new species are Neorganella rotundatae sp. n., the second for the genus, Micronella itacaman sp. n. and Micronella longisensilla sp. n. Diagnosis of the genera have been extended. An identification key to the genus Micronella Arlé, 1959 is provided.


Introduction
The cosmopolitan family Brachystomellidae is, currently, comprised of 18 genera and 130 species (Bellinger et al. 2013). However, more than half (i.e. 10) the genera are monospecific and with restricted distributions.
Both Micronella species were briefly described, without any mention to dorsal body and also the furcal area chaetotaxy, which contains a set of chaetae that can be of taxonomic importance. Nevertheless, the analysis of Brachystomellidae made by Najt et al. (2005), which includes information on M. porcus, the following characterization of Brazilian specimens of M. porcus and of other two new species allow the expansion of the diagnosis of the genus.
Concerning Neorganella Rapoport & Rubio, 1963, the only species of the genus N. nothofagutalis Rapoport & Rubio, 1963 was described based on a single specimen from a mountain called "El Roble", of about 2,000 m a.s.l. and 50km from the Pacific Ocean. In 1967, Massoud synonymized Neorganella with Folsomiella and this remained until recently, when Najt et al. (2005), in an analysis of Brachystomellidae, revalidated the genus Neorganella.
As for the first two species of Micronella, there is no reference to head and most of the dorsal body chaetotaxy, regardless of the drawing of Abd III-VI in the original description, which is not elucidative. Nevertheless, the genus is well established among the Brachystomellidae, due to the presence of a reduced furca without mucro. The analysis of Najt et al. (2005) and the description of N. rotundatae sp. n. supports the genus and allows the expansion of its diagnosis. Arlé, 1959 http://species-id.net/wiki/Micronella Syn. Brachystomella Agren, 1903 ad. part. Salmonella Stach 1949 ad. part. Denis, 1933. Diagnosis. Pigmentation absent. Antennae shorter than head diagonal. Ant IV with dorsolateral microsensillum and round subapical organite; apical vesicle simple. Eyes absent. PAO with 6-15 vesicles. Maxilla typical of Brachystomella, with 5-7 teeth. Unguis tooth present or absent; tenent hair acuminated. Ventral tube with 3+3 chaetae. Furcal area delimited by a circular region of primary granulation of the tegument and a set of six chaetae within it. Table 1 summarizes the main characters of the species of the genus. Ratio head diagonal: antenna = 1:0.63. Ant I with 7 chaetae. Ant II with 12 chaetae. Ant III and IV fused dorsally, ventral separation marked. Sensory organ of Ant III with two small club shaped sensilla, the mid-ventral one with a bilobed apex; two longer and subcylindrical guard sensilla; ventral microsensillum present (Figs 1-2). All dorsal chaetae of Ant I-III are serrated, ventral chaetae smooth and longer than those from dorsal  side (10-13 μm dorsal; 13-15 μm ventral). Ant IV with simple apical bulb and five sensilla, three weakly differentiated from ordinary chaetae; dorsolateral microsensillum present; subapical organite round; with about 30 ventral chaetae (Fig. 2).
Etymology. "Itakamã" (pronounced itakaman) means "high stone" or "rocky mountain" in the indigenous language Tupi, spoken by the Brazilian natives, reference to the three highest mountain plateaus of southeast Brazil, where the species was found.
Discussion. The new species, Micronella itacaman sp. n., is well characterized in the genus, as all the species share euedaphic characters such as absence of eyes and furca, but with PAO. It can be distinguished from its congeners by characters such as serrated chaetae on body and five sensilla on Ant IV. In relation to number of vesicles on PAO and ratio of ordinary chaetae: sensilla, the new species is most similar to M. porcus, as they have 6-8 vesicles and a ratio of ordinary chaetae: sensilla of approximately 1:1.  Type locality. Brasil, Rio de Janeiro, Teresópolis municipality, Parque Nacional da Serra dos Órgãos (ICMBio), 22°27'38"S, 43°1'45"W, leaf litter and soil of "campos de altitude", 2,100 m a.s.l.

Micronella longisensilla
Description. Habitus typical of the genus. Body length of holotype: 0.62 mm; body length range of paratypes: 0.40-0.75 mm. Color in ethanol: white, no pigmentation.
Ratio head diagonal: antenna = 1:0,.66. Ant I with 7 chaetae. Ant II with 11 chaetae. Ant III and IV fused dorsally, ventral separation marked. Sensory organ of Ant III with two cloverleaf-shaped sensilla partially covered by a fold of the integument; two longer and subcylindrical guard sensilla, the dorsal one is shorter but greatly enlarged in its width, in relation to the ventral one; ventral microsensillum present . Ant IV with simple apical bulb and four sensilla; dorsolateral microsensillum present; subapical organite round; with about 30 ventral chaetae (Fig. 16).
Etymology. In a reference to the size of the sensilla in relation to ordinary chaetae on body of the new species.
Discussion. The new species, Micronella longisensilla sp. n., is well characterized in the genus (see Table 1). It differs from its congeners in relation to the ratio of ordinary chaetae: sensilla, that is 1:2, only four sensilla on Ant IV, a PAO with 12-13 vesicles, the Ant III organ with two cloverleaf-shaped sensilla under a fold of the tegument and the dorsal guard sensilla which is greatly enlarged in its width, in relation to the ventral one. Ratio head diagonal: antenna = 1:0.57. Ant I with 7 chaetae. Ant II with 12 chaetae. Ant III and IV fused dorsally, ventral separation marked. Sensory organ of Ant III with two club-shaped sensilla; two longer and subcylindrical guard sensilla, the dorsal is stouter than ventral guard sensilla; ventral microsensillum present (Figs 29-31). Ant IV with simple apical bulb and six slender sensilla; dorsolateral microsensillum present; subapical organite round; with about 30 ventral chaetae (Fig. 30).
Etymology. The Latin word rotundatae means roundish, spherical, referring to dens shape of the new species.
Discussion. The new species N. rotundatae sp. n. is well characterized in the genus, mainly due to the facts that it shares a reduced furca without mucro, dens with 3+3 chaetae, and the presence of tenaculum with the other species N. nothofagutalis Rapoport & Rubio, 1963 (according to original description and after Najt et al. 2005). The new species differs from its congener by the presence of 10-12 vesicles on PAO, while N. nothofagutalis has only 4 vesicles. It is also noteworthy that Neorganella rotundatae sp. n. presents a reduction in the number of chaetae on Tita of legs I-III, being 18, 18, 17, respectively, while N. nothofagutalis has 19, 19, 18 (see Najt et al. 2005).