Bongotarsonemus, Mondal & Karmakar, 2021

Mondal, Priyankar & Karmakar, Krishna, 2021, A new genus Bongotarsonemus with two new species of tarsonemid (Acari: Heterostigmata) mites discovered from the Himalayan forests of West Bengal, India, Zootaxa 5072 (6), pp. 575-591 : 577-579

Genus Bongotarsonemus gen. nov.

Type species Bongotarsonemus unicornus sp. nov. by original designation (In addition to the type species this genus also includes Bongotarsonemus bicornus sp. nov.).

Diagnosis: This new genus is best characterized as a member of tribe Tarsonemini under subfamily Tarsoneminae based on the descriptions by Lindquist (1986) and catalogue by Lin & Zhang (2002). However, this genus can be distinguished from all other genera of tribe Tarsonemini by a combination of character states (1–14) as listed below.

Adult females are distinguished by 1) setae v1 set on prominent tubercles which conspicuously extend posteriorly and sometimes contiguous with tubercles of setae sc2 delimiting a medially raised section of prodorsum; 2) one or two strong horn like projections mediad bases of setae v1; 3) longitudinal sclerotized ridges or set of elevated striae medially on raised section of prodorsum; 4) sejugal apodeme strongly developed and characterisically bipartite 5) tibial seta d setiform, sparsely barbed, always longer than tibiotarsus, reaching beyond the apex of claw on leg I 6) seta pl’’ retained on tarsus II; males are distinguished by 7) prodorsal setae sc2 nearly as long as sc1; 8) tarsus II with rod-shaped solenidion ω, longer than half the length of this segment and similarly long, spinose, blunt ended pl’’ inserted well anteriad ω; 9) tibia IV with relatively long (>18 μm) and curved solenidion φ, more than half the length of femorogenu IV, and longer than combined length of tibia and tarsus IV; both sexes can be characterized by 10) elongated muscular pharynx, fusiform, always two third the length of gnathosomal capsule 11) leg I having movable fish-hook shaped claw with relatively long shank, strongly curved apex and small ambulacrum at base; 12) leg II–III similarly long symmetrically paired claws 13) tibia I with complete sensory cluster 14) seta l’ on femur I slightly lanceolate and plumose.

The characters listed as 1–3 (single character state complex), 5, 8 and 11 are autapomorphic for Bongotarsonemus gen. nov.. Peculiar prodorsal ornamentation and conspicuously long seta d reaching beyond claw on tibiotarsus I in females, and elongated fish-hook shaped claw on leg I of both sexes make this genus remarkably unique in the tribe Tarsonemini . Also, the combination of characters viz. rod-shaped solenidion ω with similarly long bacilliform pl’’ on tarsus II of males is not known from the formerly described genera of this tribe. Though character 13 is plesiomorphic for the tribe Tarsonemini , it has been included as diagnostic character for Bongotarsonemus gen. nov. as the genus Kaliszewskia Lofego et al. 2015 (monotypic) and few species of Metatarsonemus and Tarsonemus lost one or more sensory setae from the cluster on tibia I. The character states enlisted as 4, 6, 7, 9, 10, 12 and 14 are homoplasies shared with several other genera of subfamily Tarsoneminae .

Description.

Adult of both sexes. Gnathosoma: Capsule slightly wider than long or as wide as long, sub-triangular; palpcoxal setae indiscernible. Dorsal gnathosomal setae sparsely barbed with pointed tip, and ventral gnathosomal setae smooth and setiform. Palpi directed anteriorly, slightly convergent distally, short and robust, each with two short setae and two cone shaped structures apically. Cheliceral stylets of moderate length, with swollen basal levers and a nodular projection posteriorly. Pharynx well developed, muscular, always two thirds the length of gnathosomal capsule.

Adult female. Idiosoma: Prodorsal shield overlapping entire gnathosoma dorsally. All dorsal setae coarsely barbed; setae v1 inserted on tubercles which conspicuously extend posteriorly and sometimes converging with tubercles of setae sc2 delimiting a medially raised portion of prodorsal shield. One or two strongly sclerotized horn like projections mediad bases of setae v1 (hereafter, mentioned as ‘anterior prodorsal horn’). Medially raised part of prodorsal shield ornamented with pair of longitudinal ridges or a set of elevated strial thickenings, extended anteriorly to base of anterior prodorsal horn(s) and posteriorly to level of insertion of sc2. Stigmata laterad of base of tubercle bearing v1; main tracheal trunks with unsclerotized atria, and without postatrial structures. Setae v2 vestigial, only pits visible near level of sc1, latter globose and spiny, inserted ventrolaterad of prodorsal shield. Seta sc2 inserted posteriad sc1. Posterior margins of tergites nearly straight to slightly convex. Distance between pair of setae f less than length of setae h; setae ps smooth, nearly as long as setae h. Venter with apodemes 1 fused to each other, may or may not fuse conspicuously with prosternal apodeme. Apodemes 2 diffusely meet with prosternal apodeme. Prosternal apodeme may be well sclerotized up to level of anterior ends of apodeme 2 or may be visible as a small sclerotized fragment between apodemes 1 and 2, then widening and fading to reach sejugal apodeme. The latter well sclerotized, but clearly interrupted medially. Coxisternal plates I and II with pair of setae 1a and 2a respectively and alveolar vestiges of setae 1b and 2b. Apodemes 3 transverse, extending from anterior end of trochanters III to nearly level of insertion of 3a with diffused proximal ends. Apodemes 4 extending convergently from insertion of setae 3b to anterior half of poststernal apodeme. Poststernal apodeme mostly distinct, bifurcate anteriorly. Anterior margin of coxisternal plates III slightly convex. Tegula as long as wide basally and rounded apically. Aggenital plate striated at lateral margin. Dorsal and ventral plates coarsely punctate.

Legs: leg I with a single, elongated, fish-hook shaped claw with small ambulacrum at base.Ambulacra of legs II and III with empodia and well-developed, symmetrically paired, elongated and strongly curved claws. Femora I and II lacking flanges or ridges. Leg IV elongate-cylindrical, with femorogenu nearly twice as long as tibiotarsus, each with two setae; v’Ti serrate. Number of setae (solenidia in parenthesis): femur, genu and fused tibia+tarsus of leg I, 4-4-6(2)+8(1); femur, genu, tibia and tarsus of leg II, 3-3-4-7(1); femorogenu, tibia and tarsus of leg III, 1+3-4-5. Legs I-III with femoral and genual setation complete, with conspicuously barbed and thickened setae on femur I (l’ and l’’), genu I (l’), femur II (l’) and genu II (l’). Tibial sensory cluster of leg I complete (2 φ + k). Tarsi II with seta pl’’ small and spinose, adjacent to ω; both setae u’ and u’’ present on tarsi II and III. Subunguinal seta s of tibiotarsus I and unguinal seta u’ of tarsi II and III stout, spinelike, undivided apically.

Adult male (known only for one species). Idiosoma: All dorsal setae coarsely barbed. Prodorsum with four pairs of setae. Setae v1 and v2 setiform with pointed tip; setae sc1 and sc2 thickened with blunt tips. Plate CD with three paired setae and cupules ia; setae c1 located posteriad c2 comparatively closer to setae d; only c2 with pointed tip. Plate EF with paired setae f and cupules im. Apodemes 1 conspicuous and fused with prosternal apodeme forming a ‘Y’ shape. Prosternal apodeme interrupted near medial end of apodemes 2. Sejugal apodeme continuous and emarginate medially where fused with prosternal apodeme. Coxisternal plates I and II each with one pair of setae and one pair of rudimental setal alveoli. Coxisternal plates III with two pairs of setae. Coxisternal plates IV lacking setae. Anterior margins of coxisternal plates III–IV fused with each other forming nearly concave border. Apodemes 4 connected to apodemes 3 anteriorly on either side and to each other medially where joining with poststernal apodeme. The latter splitting into apodemes 5 on posterior fourth of length. Both dorsal and ventral plates coarsely punctate. Genital capsule heart-shaped, as long as wide; accessory shafts swollen distally.

Legs: Arrangement of claws on legs I–III similar as in female. Femora I and II lacking flanges and ridges. Tarsus I with both ft’ and ft’’ setae. Legs I–III with femoral and genual setation complete, with conspicuously barbed and thickened setae on femur I (l’ and l’’), femur II (l’) and genu II (l’). Tibial sensory cluster of leg I complete (2 φ + 1 k). Arrangement of subunguinal and unguinal setae on legs I-III similar as female. Tarsus II with rod-shaped solenidion ω, longer than half the length of this segment and similarly long, spinose, blunt ended pl’’ inserted well anteriad ω. Leg IV with seta on trochanter; femorogenu without flange, concave at inner margin near anterior half; tibia separated from tarsus, with a greatly elongated tibial solenidion, more than half the length of femorogenu and a moderately long tibial tactile seta; tarsus with three setae of similar length, and with well-developed unciform terminal claw.

Etymology. The generic name Bongotarsonemus is derived from the Bengali word ‘ Bongo ’ which indicates the state of West Bengal; as a whole referring to the tarsonemid genus discovered from West Bengal.

Diagnostic remarks. Adult females of Bongotarsonemus gen. nov. resemble those of Floridotarsonemus Attiah, 1970 , Flechtmannus Moraes et al., 2002 , Kaliszewskia , some species of Tarsonemus Canestrini & Fanzago, 1876 Daidalotarsonemus De Leon, 1956 , belonging to tribe Tarsonemini and Heterotarsonemus Smiley, 1969 from tribe Hemitarsonemini in having the prosternal apodeme sclerotized only up to the level of apodemes 2, diffused and widened posteriorly to meet with the sejugal apodeme. Females of this new genus also have prodorsal setae v1 and sometimes sc2 set on strong tubercles similar to those in Daidalotarsonemus , Excelsotarsonemus Ochoa and Naskrecki, 1995 and Metatarsonemus Attiah, 1970 (only v1). However, unlike these genera, the tubercles in Bongotarsonemus delimit a raised part of prodorsal shield medially which is again uniquely ornamented as described earlier. The females also resemble Excelsotarsonemus, Rhyncotarsonemus Beer, 1954 , Daidalotarsonemus , Neotarsonemoides Kaliszewski, 1984 some species of Xenotarsonemus and Tarsonemus in having l’ on femur and genu of leg I thickened and barbed.However, the l’ on femur I is plumose, which is not known from formerly described species of Tarsoneminae . They also resemble Biscutulumnemus Lofego & Feres, 2006 (tribe not specified); some species of Floridotarsonemus , Fungitarsonemus , Tarsonemus and Neotarsonemoides from the tribe Tarsonemini in retaining pl’’ on tarsus II. The bipartite sejugal apodeme is a widespread character in Steneotarsonemini , although in Tarsonemini a few species of Hemitarsonemus Ewing, 1939 and Tarsonemus possess a medially separated sejugal apodeme similar to Bongotarsonemus gen nov. Generally, prodorsal setae sc2 visibly shorter than sc 1 in male tarsonemids but the males known from only one species of this genus possess sc2 nearly as long as sc1. The males of Xenotarsonemus Beer, 1954 and few species of Deleonia Lindquist, 1986 may resemble the new genus based on leg IV with relatively long solenidion φ but differ by fused tibiotarsus while tibia and tarsus are distinctly separated in the new genus. Adult males of this new genus share a similarity with Metatarsonemus , some species Floridotarsonemus , Fungitarsonemus Cromroy, 1958 and Tarsonemus in having enlarged solenidion ω on tarsus II, often more than half the length of tarsus. This might be a plesiomorphic character for the family Tarsonemidae as males of many tarsonemid genera have solenidion on tarsus II longer than in conspecific females.

As the comparative morphology suggests, Bongotarsonemus gen. nov. shares most of its morphological traits with Tarsonemus , the most speciose genus of the family Tarsonemidae . Compared to other genera, Tarsonemus does not include species with derived character states as noted by Lindquist (1986) and Lofego et al. (2019). However, morphologically remote species have been affiliated to this extensive assemblage, previously nested inside four subgenera viz. Tarsonemus s. str.; Chaetotarsonemus Beer & Nucifora, 1965 , Metatarsonemus Attiah, 1970 and Floridotarsonemus Attiah, 1970 with latest inclusion of Schaarschmidtia Magowski, 2010 ( Lindquist, 1986; Lin & Zhang, 2002; Magowski, 2010). Such taxonomic conundrums within this genus have very recently been addressed by elevating several subgenera of Tarsonemus to generic rank with the discovery of a greater number of species and a better understanding of the derived characters. Lofego et al. (2019) established Metatarsonemus as evolutionarily independent from Tarsonemus and reinstated it with a set of apomorphies in females viz. the presence of several coxisternal fissures often overlapping apodemes and sclerotized ridges flanking tegula. Later, Mondal & Karmakar (2021c) and Mondal et al. (2021a) confirmed those apomorphies with the description of five more species and enlisting eight nominal species of Metatarsonemus worldwide. The subgenus Floridotarsonemus with five nominal species has been seperated as a genus by a set of apomorphies in males viz. femorogenu IV with a concave arc at posterior base, possessing a triangular to keel-shaped flange at inner margin and tarsus IV with a flattened blade-like claw (Ochoa, 1991; Mondal & Karmakar, 2021a). Subgenus Chaetotarsonemus (monotypic) can be categorized by reduced, setiform bothridial setae sc 1 in adult females and broadly rounded flange on leg IV of adult males. These characters are homoplasies shared with the genus Steneotarsonemus in the tribe Steneotarsonemini , three genera of Tarsonemellini and insect parasitic species of subfamily Acarapinae which makes its insertion as a subgenus of Tarsonemus very problematical but requires further investigation with a greater number of species. Bothridial setae are also vestigial in another monotypic genus Flechtmanus belonging to tribe Tarsonemini . This homoplastic character may have evolved due to adaptation to a confined habitat in which well developed bothridial organs might not be required ( Lindquist, 1986). However this hypothesis often becomes contradictory as bothridial setae are well developed in many tarsonemid species which live in confined spaces either parasitizing other invertebrates or feeding within plant parts ( Moraes et al. 2002). Differentially, subgenus Schaarschmidtia with 17 nominal species is diagnosed by several characters such as leg setal reduction, pharyngeal width to gnathosomal width ratio, glandular bodies posterior to pharynx, subcircular to tongue-shaped tegula, tripartite sejugal apodeme and elongated tibia IV in adult males which defines the group as a coherent assemblage within the genus Tarsonemus and different from the subgenus Tarsonemus s. str. However, many of these characters such as the shape of tegula, reduction of leg seta in females and elongated tibia IV in males are sporadically present in several species of the subfamily Tarsoneminae . Some derived morphological traits in this group might be an outcome of their association with subcortical coleopteran insects but those certainly can not be considered as robust apomorphies to create a generic concept for Schaarschmidtia . However, the set of unique apomorphies noted in the ‘diagnosis’ presents Bongotarsonemus gen. nov. as a cohesive group with precisely defined morphological patterns that distinguish the genus from Tarsonemus . The phylogenetic relationship of this new genus with other genera of Tarsoneminae is difficult to resolve at such an early stage. Nevertheless, the most acceptable hypothesis might be that Bongotarsonemus evolved as a derived group within the tribe Tarsonemini with immediate kin taxa proposed as Tarsonemus and Xenotarsonemus based on the above discussion and the probable phylogenetic position of Tarsonemus suggested by Lindquist (1986). Considering the dorsal ornamentation of female and leg chaetotaxy of both sexes, the new genus could be a sister group of the genera complex Metatarsonemus + Daidalotarsonemus + Ceratotarsonemus + Excelsotarsonemus as suggested by Lofego et al. (2019).