Two new oribatid mites from the Republic of Rwanda. Plasmobates zarae sp. n. (Acari, Plasmobatidae) and Basilobelba spasmenosi sp. n. (Acari, Basilobelbidae)

Abstract Two new species of oribatid mites, Plasmobates zarae sp. n. and Basilobelba spasmenosi sp. n. are described from the Republic of Rwanda. They can easily be differentiated from other species by a number of characters. Plasmobates zarae sp. n. is differentiated the following characters. four types of particular cerotegumental layers. Integument slightly foveate to smooth on prodorsum; foveate on notogaster; ventral region rugose to smooth.Large rostral setae inserted on protuberance, whip-shaped, with longitudinal pucker; interlamellar setae rod-shaped with triangular scales; interlamellar setae small. Medial band on prodorsum extending to anterior of central part, but not reaching rostrum. Bothridium horn-shaped; opening basally incised with rectilinear wall, internal bothridial rings dentate. Sensillus whip-like, with minute triangular scales. Variably distributed circumgastric macropores. Opisthosomal gland apophysis flat, triangular in lateral view and cylindrical in posterolateral view. Six pairs of notogastral setae, all situated posterior to opisthosomal gland level. Aggenital setae not detected; three pairs of adanal setae; two pairs of anal setae present. Nymphal scalps simple without anterior tuft or filaments, with dentate peripheral ridge. Larval scalp shaped like Chinese hat. Basilobelba spasmenosi sp. n. is characterized by the combination of the following characters: Cerotegument: thick basal layer with amorphous coat and cavities of different sizes, as well as structures resembling small cauliflowers. Setation: simple: notogastral, epimeral, genital, anal; simple long, basally barbate: le, ro setae; simple, whip-shaped: ex setae; medium length, sharpened tip with thorns on surface: in setae, leg setae; Flabellate: setae situated in ventral neotrichous zone. Thorn-like barbs and more or less parallel longitudinal grooves present on body surface of le, ro, in and leg setae. Prodorsum: rostrum finger-shaped, relative sizes of setae: le > ro > in > ex. Prodorsal cuticular surface smooth with shallow transversal furrow and two oblique furrows determining two triangular structures. Large humpbacked CSO situated anterior to and in medial line with in setal insertion, dorsal bothridial opening. Notogaster swollen, hemispheric; nine pairs of minute setae, only h1, h2, h3 easily identifiable, cuticular wart and dimple clearly visible. Humeral apophysis with longitudinal furrow dorsally. Elongate chelicera with cha, chb setae, behind them a series of scales directed dorsoventrally. Epimeral setation 3-1-3-3, adanal-aggenital neotrichy with between 8-10 setae. Nymphal scalps with very particular bean-shaped structure on either side of the decoupage zone, surrounding horn-like structure. Scalps with cuticular polyhedral reticulate to ovoid structure, often forming a cavity, either completely perforated or with a thin cuticular layer resembling an interior membrane.


Introduction
This paper is the second on material collected in Rwanda, housed at the Natural History Museum in Geneva, Switzerland. Two new species, Plasmobates zarae sp. n. and Basilobelba spasmenosi sp. n. are described. At present the family Plasmobatidae consists of four genera: Orbiculobates Grandjean, 1961;Malgachebates Fernández, Cleva, Theron, 2011;Plasmobates Grandjean, 1929 and Solenozetes Grandjean, 1931. Over the course of many years the authors have studied members of the family Plasmobatidae, principally those collected from the Afrotropic ecozone (formerly known as Ethiopian zone). This resulted in the description of the genus Malgachebates and included a summary of the principal characteristics of each genus of the family (Fernandez et al. 2011). Fernandez et al. (2013) analyzed some problematic aspects of the genus Solenozetes and presented a redefinition of the genus, as well as the description of S. makokouensis Fernandez et al., 2013. The taxonomy of the family Plasmobatidae is problematic due to succinct original descriptions lacking in detail, or in which important characteristics were neglected.
The family Basilobelbidae contains two genera: Basilobelba Balogh, 1958 and Xiphobelba Csiszár, 1961. The taxonomy of Basilobelbidae is not clear, principally relat-ing to the problematic original description of Xiphobelba (Csiszar 1961 page: 353) which indicates: "Rostrum pointed, chelicerae attenuated to a point, chela very small reduced" and "The new genus is an ally of Basilobelba Bal.1958, differing from it by the peculiar oral organs, resembling those of Eupelops". The oral organs were not illustrated, and other characteristics, such as the cerotegumental layer were neither described nor figured. Only two figures were given, one dorsal with scalps and the other dorsal without scalps. In the description of a second species of the genus, X. setosa Aoki, 1968, the chelicera are partly illustrated with the rest of the infracapitulum (Aoki 1968 p: 271, figure 14). Due to several subsequent papers, the taxonomy of Basilobelba is becoming clearer, permitting understanding of several aspects of this group.
More recently Fernandez et al. (2015) described a new species of Basilobelba (B. maidililae) from Vietnam, analysed problematic aspects of the group, and provided a comparison of species of both genera of the family.

Materials and methods
Specimens studied by means of light microscopy were macerated in lactic acid, and observed in the same medium using the open-mount technique (cavity slide and cover slip) as described by Grandjean (1949) and Krantz and Walter (2009). Drawings were made using a Zeiss GFL (Germany) compound microscope equipped with a drawing tube.
Specimens were also studied under a Scanning Electron Microscope (SEM). Specimens preserved in ethanol were carefully rinsed by sucking them several times into a Pasteur pipette, after which they were transferred to buffered glutaraldehyde (2.5%) in Sörensen phosphate buffer: pH 7.4; 0.1 m for two hours. After postfixation for 2hr. in buffered 2% OsO 4 solution and being rinsed in buffer solution; all specimens were dehydrated in a series of graded ethanol and dried in a critical point apparatus. After mounting on Al-stubs with double sided sticky tape, specimens were gold coated in a sputter apparatus (Alberti and Fernandez 1988, 1990a, 1990bAlberti et al. 1991Alberti et al. , 1997Alberti et al. , 2007Fernandez et al. 1991). SEM micrographs were taken using a SEM FEI-Quanta Feg 250; with 10 Kv and working distance (WD) variable.
Measurements: total length (tip of rostrum to posterior edge of notogaster); width (widest part of notogaster) in micrometers (μm). Leg setation was studied using standard, polarized and phase contrast microscopes are provisional, due to the fact that only adult specimens were available for study. Setal formulae of the legs include the number of solenidia (in parentheses); tarsal setal formulae include the famulus (ε). For Plasmobates zarae we added SEM images of leg setae as detail in order to clarify a number of particularities.

Morphological terminology
Morphological terms and abbreviations used herein are those developed by F. Grandjean (1928-1974) (cf. Travé and Vachon 1975. For the setae types Evans (1992); ornamentation of cuticular surfaces Murley (1951, ex: Evans op.cit) were used. Some specific morphological characters have never been described before in detail, and hence no terminology or abbreviations exist. For the sake of clarity we include the following in the text and on the figures: bean-shaped structure (h.sc); macropores (mp); medial band extension (m.b); polyhedral reticulate to ovoid structure (s.r.s); promontories of podocephalic canal (a.o.g); thin cuticular layer (t.c.l).
Prodorsum: medial band extension on central part towards anterior, not extending to rostrum. Interlamellar setae inserted on large protuberances, lamellar setae small, rostral setae large, with longitudinal cuticular puckers, inserted on protuberances. Large horn-shaped bothridium, directing laterally, rectilinear wall with basally incised opening. Internal bothridial rings dentate. Whip-shaped sensillus with minute, triangular scales; exostigmatal seta small. Rostrum medially incised, posterior of incision rounded. Notogaster: fovea situated in smooth zone with circumgastrically distributed macropores on fovea margins or inside fovea. Opisthosomal gland apophysis flat, triangular in lateral view, cylindrical in posterolateral view. Six pairs of notogastral setae, all situated posterior to level of opistosomal gland. Lateral region: opening of podocephalic canal on large promontories.
Notogaster. Circumgastrically distributed macropores (mp) of varying diameter (0.3-1 μm) situated in small foveae on smooth zone, either on periphery or internally to foveated notogastral pattern (Figures 1, 2). In dorsal view anterior zone mp clearly visible (Figure 1), but those located near gla need to be observed in lateral or posterior views ( Figure 2) due to notogastral shape, in order to obtain the best impression of their distribution.
Remarks. SEM is vital in order to observe aspects such as: 1) dorsal seta d associated with solenidium hardly discernible (detailed drawings are included to facilitate understanding) 2) clavate shape of small solenidia is problematic, as doubt regarding the exact shape remains if using only optical microscopy 3) the position of dorsal seta d relative to j 1 and j 2 on tibia II differs from Solenozetes makokouensis and Malgachebates peyrierasi. Changed angles of observation and rotation of specimens in SEM clarified the situation. 4) accessories available in SEM facilitated measurements of minute triangular scales of the sensillus with great precision 5) protuberances situated around the opening of the lateral gland also had to be observed from different angles. See Discussion for comparison with congeners.  Table 2 Etymology. The specific epithet "spasmenosi" is derived from (Σπασμένος, Grec = broken, English), due to characteristics of scalps with cavities or perforations.
Colour. Specimens without cerotegument brown, slightly shiny when observed in reflected light.
Notogaster. Swollen, hemispheric (Figure 53), bearing four-layered exuviae (larval, protonymphal, deutonymphal and tritonymphal) stacked to resemble a low tower (Figure 43), fixed anteriorly and posteriorly by particular structures (See Scalps). Dorsosejugal furrow large, rectilinear, well delimited ( Figure 44). After removal of exuviae, glabrous notogastral surface becomes visible (Figure 53), bearing nine pairs of minute setae ( Figure 52). Only h 1 , h 2 , h 3 setae easily identifiable (h 2 and h 3 always in very close proximity to each other), h 1 setae identified by relative position to lyrifissures (See Discussion). Unidentified setae indicated by * (Figure 52). Lyrifissures ih and ips identified as pores, other lyrifissures probably present but difficult to identify due to ornamentation. Anterior notogastral zone (Figures 43, 44) bearing cuticular wart (ve) hooking arched tritonymphal buckle (co.bu) by coaptation. Depression in posterior zone (Figure 53, dimple (f) indicated by rounded dotted zone) housing the us zone of tritonymphal horn by coaptation. (Figure 69 indicated by us and ¿). SEM observations of this small depression is necessary from different angles, hence it is indicated by a rounded zone (See Scalps). Humeral apophysis easily discernible, with dorsal longitudinal furrow ( Figure 43).
Lateral region. Only pedotectum I present ( Figure 49); Pd I large lamina; the border can be followed a short distance to ex setae; h.ap clearly discernible as a structure with longitudinal furrow (Figure 43).
Nymphal Scalps. Limited number of specimens and the necessity of dissection impeded comprehensive study of scalps, for this reason our study was limited to deutonymphal and tritonymphal scalps. Observed particularities: Very particular beanshaped structures are found on either side of the decoupage zone around the horn-like structure (Figures 63, 64, 65, 66).
Scalps present polyhedral reticulate to ovoid cuticular structure (s.r.s), most visible on internal side ( Figure 69) but also on entire scalp (Figures 63-69). Internally scalps present a very thin cuticular layer (t.c.l) (Figure 69) covering polygonal-ovoid structures. The s.r.s often appearing either completely perforated or with a thin cuticular      layer (t.c.l) resembling an interior membrane (Figures 63,65,66,67). In Figure 64 the s.r.s is clearly visible due to transparency, also internally, on both sides of the decoupage zone around the horn. The complexity of these perforated areas is yet more interesting as the polyhedral reticular structure, when not perforated, is more or less rounded, surrounded by a polyhedral structure (Figure 67, 68).
Tritonymphal scalps (Figures 43, 45, 66, 69). Basque beret-shaped ( Figure 66) tritonymphal scalp fixed to the adult by two structures, one situated anteriorly and the other posteriorly. Heart-shaped structure (tritonymphal buckle) in anterior part affixing scalp to adult notogaster. Tritonymphal buckle consisting of two loops (a) ( Figures  43, 44), curving outwards then inwards forming a heart-shaped structure, continuing to meet in the plane of symmetry forming a thong-like structure (n) (Figure 44 Deutonymphal scalps (Figures 43, 63, 64, 65). Tritonymphal and deutonymphal scalps differ greatly (Figures 66 and 63). No buckles for adherence observed in anterior zone of deutonymphal scalps, and posterior zone (Figures 63, 64) with horn-like structure fixing the protonynphal scalp found on a mobile strip (le) consisting of a section of deutonymphal scalp (See Grandjean 1959). Horn-like structure composed of a style   (Figure 64). In common with the tritonymphal scalp, a bean-shaped structure (h.sc) is observed. Only posterior setae h 1 , h 2 , h 3 , p 1 are visible. Remarks. The remarkable perforated structures are not observed in other congeners. At present we are studying another species from Rwanda with bean-shaped structures on scalps, similar to those in Basilobelba spasmenosi sp. n.

Discussion
The taxonomy of the genus Plasmobates in the Afrotropic ecozone is very complex. Species of the genus Plasmobates Grandjean, 1929 recorded in this region are: P. africanus Balogh, 1958;P. foveolatus Ermilov et al., 2010;P. machadoi Balogh, 1958;P. minor Balogh, 1958;and P. zarae sp. n. Subías (2015) considers P. africanus Balogh, 1958;P. machadoi Balogh, 1958 andP. minor Balogh, 1958 as "sp. inq.", without providing reasons. We analyzed the work of Balogh (1958), but found it impossible to identify the cited species. A comprehensive search in the available collection from this ecozone failed to provide specimens with the characters in the provided text. One comparable species from the region is P. foveolatus Ermilov et al., 2010, but the study lacks SEM micrographs, and is not detailed enough to provide a conclusive comparison.
In our opinion the following characteristics permit easy differentiation of species of Plasmobates from other congeners, not only those from the Afrotropic ecozone: the cerotegumental layer, shape and insertion type of ro and in setae, sensillus with scales, promontories of podocephalic canal, distribution of macropores, type of lateral gland, number and distribution of notogastral setae, positions of setae d of tibia I and particular setae found on tibia II.
The taxonomy of Basilobelba Balogh, 1958 andXiphobelba Csiszár, 1961 were discussed in preceding work (Fernandez et al. 2015). B. spasmenosi sp. n. presents all characteristics of the genus and also displays very interesting particularities, permitting easy differentiation from other congeners, such as: shape and characteristics of cerotegumental layer, lamellar and rostral setae, prodorsum, rostrum and CSO, infracapitulum, notogastral setae, nymphal scalps with perforated areas and particular distribution of leg setae. The distribution of notogastral setae is especially particular as all nine setae are situated on the posterior notogastral zone.