Basilobelba spasmenosi, Fernandez, Nestor & Theron, Pieter, 2016

Fernandez, Nestor & Theron, Pieter, 2016, Two new oribatid mites from the Republic of Rwanda. Plasmobateszarae sp. n. (Acari, Plasmobatidae) and Basilobelbaspasmenosi sp. n. (Acari, Basilobelbidae), ZooKeys 598, pp. 1-25: 7-12

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Basilobelba spasmenosi

sp. n.

Taxon classification Animalia Sarcoptiformes Basilobelbidae

Basilobelba spasmenosi  sp. n. Figures 43-47, 48-52, 53-57, 58-62, 63-69, 70-74; Table 2


The specific epithet “spasmenosi” is derived from (Σπασμένος, Grec = broken, English), due to characteristics of scalps with cavities or perforations.

Material examined.

Holotype: Female and two paratypes (adult females):. "73/2. Kayove-Rwanda; 2100 mts.15/V/1973" Leg. P.Werner; material deposited in the Collection of the Natural History Museum of Geneva (M.H.N.G), Switzerland; preserved in 70% ethanol. Material studied for SEM: three specimens, not deposited.

Diagnosis (adult female).

Cerotegument. Thick basal layer with amorphous coat, perforations of various sizes, and structures resembling small cauliflowers. Setation. Simple: notogastral, epimeral, genital, anal; simple, long, basal barbs: le, ro setae; simple, whip-shaped: ex setae; medium length, sharpened tip with thorn-like barbs on surface: in setae, leg setae; flabellate: setae situated in ventral neotrichy zone. Thorn-like barbs and more or less parallel longitudinal grooves on body 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 delineating two triangular structures. Large humpbacked CSO situated anterior to and in medial line with in setal insertion, dorsal bothridial opening. Notogaster. Swollen, hemispheric, with nine pairs of minute setae. Only h1, h2, h3 easily identifiable. Cuticular wart and dimple clearly visible. Humeral apophysis with longitudinal furrow dorsally. Chelicera elongate, series of dorsoventrally directing scales behind setae cha, chb. Epimeral setation 3-1-3-3, adanal-aggenital neotrichy with 8-10 setae. Nymphal Scalps. Particular bean-shaped structure on either side of the decoupage zone around horn-like structure. Scalps with polyhedral reticulate to ovoid cuticular structure. Polyhedral reticulate cuticular structure often appears either completely perforated or with a thin cuticular layer resembling an interior membrane.


Measurements.SEM: total length without scalps 618-598 × 605 μm; width without scalps 310-290 × 303 μm (measurements on three specimens). Light microscopy: 660-632μm × 643 μm; width 325-315 × 320 μm (measurements on three specimens).

Shape. Elongated oval (Figures 43, 49, 53).

Colour. Specimens without cerotegument brown, slightly shiny when observed in reflected light.

Cerotegument. Present only on prodorsum, notogastral anterior zone, ventral region and legs. Thick basal layer with amorphous coat and perforations of various sizes (indicated by¿ Figure 47). Small structures on surface resembling cauliflowers (cau) of different sizes (Figures 47, 56, 59, 60).

Setation. Simple: notogastral, epimeral, genital, anal (Figures 50, 52, 54); simple, long, basal barbs: le, ro setae (Figures 48, 55); simple, whip-shaped: ex setae (Figures 43, 46); medium length, sharpened tip with thorns on surface: in setae (Figures 43, 44, 46, 58, 59, 61), leg setae. These setae are very particular, with large thorn-like barbs basally and small thorn-like barbs distally. Flabellate (Figure 56): setae situated in ventral neotrichous zone. Particular to le, ro, in and leg setae (Figure 60) is the presence of thorn-like barbs and more or less parallel longitudinal grooves on setal body (Figures 58, 59, 60).

Integument. Smooth

Prodorsum. Rostrum finger-shaped (Figures 43, 46). Rostral setae ro laterally inserted on large promontories 107 μm (96-109 μm); le setae 155 μm (151-159 μm); in setae on small promontories 46 μm (48-50 μm); ex 40 μm (38-42 μm). Relative sizes of setae: le > ro > in > ex.

Prodorsal cuticular surface smooth with a shallow transversal furrow situated anterior to in setal insertion (Figure 46 indicated by 5). Two oblique furrows (Figure 46 indicated by a) delimiting two triangular structures (Figure 46 indicated by *). Large humpbacked CSO situated in front of and in medial line with in setal insertion (Figures 43, 46, 53). More or less parallel le setae with criss-crossing tips (Figure 46). Two oblique furrows and two triangular structures conspicuous in dorsal view of prodorsum.

Ovoid bothridial opening dorsally (Figures 43, 48, 53); in medial zone ovoid loop directing anteriorly and slightly obliquely (Figure 61 indicated by¿). Sensillus long, setiform, generally directing backward, both sides barbate (Figure 61).

Frontal view. Beak-shaped rostral margin (Figure 57). Large humpbacked CSO clearly visible, slightly anterior to interlamelar setal insertion.

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 h1, h2, h3 setae easily identifiable (h2 and h3 always in very close proximity to each other), h1 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).

Ventral region. Subcapitulum diarthric, cerotegumental layer observed only behind h setal insertions (Figure 55). Subcapitular setae faintly barbate on either side, sharply tipped. Setae differing greatly in shape (see Figure 55): a (42 μm ± 3 μm) simple, sharply tipped; m (55 μm ± 3 μm); h (48μm ± 3 μm). Chelicera (Figure 51) elongate, with cha, chb setae. Series of dorsoventrally directing scales posterior to cha, chb setae; the largest is found dorsally, appears darker, followed by small transparent scales. Small movable digit (Figure 51) (see Discussion).

Epimeres I, II typical morphology, ventrosejugal furrow easily discernible, other epimeres not visible. Epimeral setation 3-1-3-3 (Figures 49, 54). Aggenital and adanal setae difficult to identify due to adanal-aggenital neotrichy. Neotrichy originates laterally to anal opening, is very prominent on posterior zone, number of setae varies between 8-10 (See Discussion).

Legs (Figures 70-74, Table 2). Leg shape similar to Basilobelba retiarius  (Grandjean, 1959), moniliform with bulbous segments and large peduncles (Figures 70-74), femoral peduncles being largest. Tarsi particularly shaped, narrower between bulb and claw on legs I-IV. Cerotegumental layer covering segments but only basal zone of setae (Figure 60).

Setal formulae: I(1-6-4-5-20-1) (1-2-2); II(1-2-4-4-14-1) (1-1-2); III(2- 3-3-4-12-1) (1-1-0); IV(1-3-2-4-10-1) (0-1-0). Setae d present on all femurs, genua and tibiae. On tibia I (Figure 70) seta d is small and hardly discernible (Figure 73), situated on the same promontory as solenidion φ 2. On all other tibiae (II, III, IV) (Figures 71, 72, 74),genua and femurs setae d large and barbate (Figures 70, 71, 72, 74).

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 bean-shaped 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) in order to receive the wart (ve) (Figures 53). The ve is a round-ovoid structure (Figure 62) situated on the adult cuticular surface, functioning like a snap button, fixing the anterior part of the scalp to the adult cuticle. Depression (f) on the posterior adult cuticular surface (Figure 53) is indicated by a dotted round zone with f in centre. Observing f is difficult, necessitating changes in angle of observation. Zone f functions by coaptation with the interior part (su) (Figure 69 indicated by ¿) (i.e. the inner curving part of the horn-like structure). Small polyhedral structures (poly) are present (Figure 69 indicated by poly and¿) with similar characteristics to Basilobelba maidililae  Fernandez et al., 2015 but obtaining high resolution SEM images was impossible due to a technical problem. Setae h1, h2, h3, p1 clearly visible; setae lp, lm only visible in some instances, due to the cerotegumental layer impeding observation (Figure 65). Horn-like structure on posterior scalp border (Figure 64, 65) aiding in hooking the deutonymphal scalp.

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 (s) and a stylet (st) (Figure 64). In common with the tritonymphal scalp, a bean-shaped structure ( is observed. Only posterior setae h1, h2, h3, p1 are visible.


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.