Tarsonemus Canestrini and Fanzago, 1876

Magowski, Wojciech Ł., 2020, Review of Tarsonemus heterosetiger Mahunka, 1974 (Acari: Heterostigmatina Tarsonemidae) - an unusual species from Central Africa warranting supraspecific recognition, Zootaxa 4790 (1), pp. 108-120 : 109-113

Genus Tarsonemus Canestrini and Fanzago, 1876

Tarsonemus (Tarsonemus) heterosetiger Mahunka, 1974

Tarsonemus (?.) heterosetiger Mahunka, 1974

Diagnosis. Pharynx broadly oval, weakly sclerotized with glandular bodies indistinct. Dorsal setae collectively elongate, slender; c 2 and e only slightly shorter than sc 2 (which are typically longest on body). Anteromedial apodeme discontinuous, broken into five short sclerotized segments. Sejugal apodeme interrupted medially, with weakly defined lateral parts. Ventral setae attenuated, but none longer than half the distance between their bases. Tegula elongate, ca. as long as wide. Leg I tarsal claw large, hooked but not sessile, stronger than claws of legs II and even more so than III. Tarsal part of Tbt I with three simple setae (pl” missing); Ta III with three simple setae (pv” missing).

Redescription. FEMALE ( Figs. 1–9 ). Gnathosoma ( Figs. 3–4 ): capsule round, weakly conical. Pharynx ( Fig. 9A ) broadly-oval in outline, with weakly sclerotized outer part (sometimes revealing very fine transverse striation), as wide as 0.4x maximum width of gnathosoma and as long as 0.65x ventral length of gnathosomal capsule. A pair of slim, elongate glandular bodies present (somewhat overly emphasised in Fig. 4 ), not protruding posteriorly beyond outline of pharyngeal structure. Palpcoxal setae (pp) slender, similar in length to su. Setae ch 1.1x as long as su. Cheliceral stylets conspicuous, almost as long as half of length of capsule, their levers moderate in size, from oval to subrectangular in shape, well pronounced, oriented transversely or obliquely across most of anterior width of capsule. Palpi short, well defined, parallel-convergent, each with one palptarsal and one (less sclerotized) adaxial processes, small palptibial claw and short palpgenual spinelike process.

Idiosomal dorsum ( Fig. 1 )—average length: 297 (SD ± 23.5), width: 165 (SD ± 8.6); length = 1.8x width; relative lengths of setae (v 1: sc 2: c 2: c 1: d: e: f: h): 1: 1.5: 1.3: 0.7: 0.7: 1.2: 0.7: 0.9. Anterior projection of prodorsal shield broadly rounded anteriorly, ca. 3.5x wider than long. Setae v 1 separated by distance between bases of 0.8x their length. Prodorsal shield (PrS) roughly semicircular in outline, on average ca. 1.5x wider than long with posterior edge weakly convex. Of prodorsal apodemes, only prodorsomedial apodeme present, in form of small indistinct line. Stigmata located posterolaterad v 1; associated tracheae without defined atria or those being fused with subsequent tracheal expansions; the latter over twice wider than distal tubes, with well pronounced transverse striation. Sensilli sc 1 typically clavate, pilose, with two larger spines apically. Pits v 2 located just posteromediad stigmata. Setae sc 2 located exactly at mid-length of prodorsal shield, exceeding posterior edge by 1/3 of their length, and displaced by distance of 0.9x their lengths. Setae c 2 ca. twice longer than c 1, and clearly longer than distance between their bases and those of c 1; the latter separated by a transverse distance of 2.3x their length, not reaching to posterior edge of its tergite. Posterior edge of tergite C weakly concave. Setae d separated by transverse distance of nearly 2.5x their length, passing markedly beyond posterior edge of tergite D. Posterolateral margin of shield D irregularly convex. Setae f clearly shorter than e and h, separated by transverse interval of 1.3x their length, and reaching with tips beyond posterior edge of idiosoma. Distance between setae e and f on each side ca. 0.7x that between f. Setae h longer than d and f, but shorter than e; distance between bases 0.8x their length. All dorsal setae slender, attenuate, either long or very long, almost entirely smooth (rarely with very few and indistinct barbs). Dorsal shielding with very fine, uniform, dimpled ornamentation; sometimes difficult to discern.

Idiosomal venter ( Fig. 2 ): apodemes 1 hardly discernible (or indiscernible), separate from anteromedian apodeme. The latter also weakly defined, made of several (up to 5) small linear separate segments (some with knotlike extensions), without conjunction with apodemes 2 and sejugal apodeme. Sejugal apodeme consisting of two separated lateral segments, each somewhat more sclerotized near midline of idiosoma, less so towards margins, bent, but not broken laterally. Posterolateral areas of propodosomal plate with dense striation anteriad lateral parts of sejugal apodeme. Margin of ventral propodosomal plate between trochanters I and II weakly angular on each side, nearly straight. Setae 1a located in a distance slightly larger than their length. Apodemes 2 weakly sclerotized, not connecting with anteromedial apodeme. Setae 2a located at midlength of apodemes 2 on each side, separated by distance of ca. 3x their lengths. Apodemes 3 weakly sclerotized, extending laterally and anteromedially of anterior extremities of trochanters III; apodemes 4 extending somewhat posteriad bases of setae 3b, uniting with posteromedial apodeme by a medial diffused area. Posteromedial apodeme with anterior bifurcation, discontinuous past medial node. Setae 3a separated by distance of ca. 3x their length. Setae 3b subequal to 3a, separated by distance as that between 3a. Anterior edge of ventral metapodosomal plate weakly concave. Tegula ( Figs. 9b, c, d ) weakly elongate with rounded posterior extremity, from subtriangular to U-shaped in outline, about as long as wide. Posterior margin of aggenital plate convex, with slightly concave mid segment. Bases of setae ps separated by distance of ca. 0.7x their lengths.All ventral setae (compared to dorsal ones) short, slender, attenuate and smooth. Ventral plates with ornamentation similar to that of dorsum.

Legs ( Figs. 5–8 ). Setal counts I: 4-4-6(2 φ)+8(1 ω); II: 3-3-4-6(1 ω); III: 1+3-4-4. Proportions of free segments of legs (I: II: III: IV): 1.0: 1.3: 1.4: 0.9. Leg I: tarsal claw ( Figs. 10 a-c) with somewhat swollen base, hooked, inserted directly at apex of pretarsal stalk; the latter atypically strong, with terminal pad rudimentary or absent. Subunguinal seta s prominent, stubby, bluntly pointed, similar to u’ of tarsi II and III. Unguinal setae u’ (on tarsus I) and u” (as on tarsi I-III) indiscernible, most probably absent. Tibiotarsus short, ca. 1.7x as long as wide at the base. All four tarsal eupathidia near equal in length. Eupathidia p” and p’ located apically, tc’ subapically and tc” in distal 0.3x length of segment. All three simple tarsal setae (pv’, pv” and pl’) slender, pointed. Solenidion ω nearly rod-like, with head fusiform, narrow, striated, with pronounced pointed tip, longer than Ta II ω. Solenidion φ 2 twice shorter than φ 1, both with weakly striated heads; φ 1 unusually prominent, slightly bigger than ω, and with more swollen and bluntly ended head. Famulus k as long as φ 1. Seta Ge l’ stiff, tapering, intermediate in length, seta Ge l” longest of genuals, pointed. Femoral seta d short, lanceolate; remaining femorals slender, pointed. Leg II: claws on pretarsus strong, hook-like, only slightly weaker than claw I. Seta u’ spine-like, strong, blunt. Solenidion Ta II ω similar in shape to that of leg I but shorter; spine-like seta pl” prominent, blunt, much stronger than and located distally to solenidion. Seta tc” (the longest) less than 2x longer than tc’ (shortest on segment), reaching beyond tip of empodium. Tibial seta v” unusually elongate, almost equal to d; v’ and l’ clearly shorter. Seta Ge l’ stiff, pointed, ca. as long as slender v’; l” notably longer than tarsal tc”, and being longest seta on leg II. Femur without a lobe; seta d stiff, pointed; setae Fe l’ and v” simple, attenuate. Leg III: tarsal claws slimmer than those of leg II. Seta u’ similar to Ta I s and Ta II u’. Tarsal seta tc” over 2x longer than attenuate pv’ and tc’. Genual v’ attenuate, long; both genual v” and femoral l” unusually elongate, the latter being only little shorter than tarsal tc”. Leg IV: free segments of leg IV slightly shorter than femorogenu and tibia III. Femorogenu over 2x longer than tibiotarsus. Genual seta v’ subequal in length but stouter than femoral seta. Tibial v’ slightly shorter than free segments of leg IV, tapering, stiff, pointed. Seta Ta tc” ca. 2.3x as long as whole leg IV. All simple setae on legs smooth.

Measurements (holotype given first followed by a spread among 2 paratypes and 2 non-types from HMNH in parentheses)—body and tagmata: length of body: 280 (275–334); length of idiosoma: 280 (275–333); width of idiosoma: 160 (156–178); length of gnathosoma: 30 (35–37); width of gnathosoma: 33 (31–34); length of pharynx: 22 (22–23); width of pharynx: 13 (11–13); ch: 18 (16–17); su: 16 (14–16). Dorsum–length of PrS: 106 (106–112); width of PrS: 156 (156–163); distance between stigmata: 57 (59–63). Lengths of setae: v 1: 52 (51–54); sc 1: 20 (20– 22); sc 2: 75 (76–80); c 2: 65 (68–70); c 1: 29(?) (32–38); d: 38 (32–44); e: 61 (58–64); f: 34 (34–45); h: 52 (46–51). Distances between setae: v 1 -v 1: 41 (41–44); sc 1 -sc 1: 58 (55–62); sc 2 -sc 2: 73 (70–76); c 2 -c 2: 142 (141–150); c 1 -c 1: 80 (74–80); c 1 -c 2: 45 (43–45); d -d: 88 (84–94); e -e: 115 (112–120); e -f: 34 (35–37); f -f: 51 (47–54); h -h: 40 (37–40). Venter-lengths of setae: 1a: 9 (10–11); 2a: 13 (11–14); 3a: 14 (11–16); 3b: 14 (13–15); ps: 25 (20–24). Distances between setae: 1a -1a: 12 (11–15); 2a -2a: 36 (34–40); 3a -3a: 42 (39–44); 3b -3b: 42 (39–43); ps -ps: 16 (14–15). Length of PrP: 97 (97–105); width of PrP: 136 (130–136); ap. 1–1: 22 (20–23); ap. 2– 2: 63 (65–68). Length of tegula: 12 (13–14); width of tegula: 13 (12–13). Leg segments and leg setae (lengths): Tbt I: 28 (25–26); ω I: 9 (7–9); φ 1: 10 (10–11); φ 2: 5 (4–5); k: 10 (9–10); ω II: 6 (6–7); pl” II: 9 (8–9); FeGe IV: 34 (31–35); Tbt IV: 16 (14–16); Fe v’: 19 (18–20); Ge v’: 16 (15–18); Tb v’: 42 (43–51); Ta tc”: 111 (100–106).

MALE and LARVA unknown.

Examined material ( Fig. 11 ). The holotype female labeled “ Ghana No. 398. Kwadaso 1969. IX. 15. ”; two female paratypes mounted on separate slides: one with data same as holotype, and second labeled “ Ghana No. 383. Kwadaso 1969. VII. 27. ”. Other material: two non-type adult female specimens mounted on separate slides: one labeled “ Ghana No. 359. Kwadaso 1969. V. 23. ”, and another one “ Ghana No. 318. Kwadaso 1969. III. 3. ” (referred in the present text as “1st-” and “2nd non-type specimen” respectively). All examined material was collected (leg.) by S. Endrődi—Younga .

Type depositions. Holotype adult female, two paratype females and two non-type females are deposited in the Hungarian Museum of Natural History ( HMNH, Budapest, Hungary). One paratype (not seen) is stored at the Muséum d’histoire naturelle de Genève ( MHNG), Geneva, Switzerland (Dr. P. Schwendinger 2020, pers. comm.). It is labelled “ Ghana, No. 383, Kwadaso, 1969.VII.28, leg. Endrody-Younga ”.

Differential diagnosis. The morphology of T. heterosetiger is congruent with the diagnosis of the subgenus Tarsonemus by having: the pharynx enlarged with lateral walls sclerotized, with its width less than one-third of width of gnathosomal capsule; sensilli sc 1 capitate; and the anterior protrusion of the propodosomal plate short, slightly concave. Leg setation is typical as in the majority of Tarsonemus subgenus species, i.e. tibiotarsus I with three simple tarsal setae, femur I with four setae, femur II with three setae, and tibia I sensory cluster complete (lack of seta pv” on tarsus III is not unusual in many Tarsonemus species); general layout of ventral apodemes (with no major reductions in sejugal and posteromedial apodemes) and ventral podosomal setae moderately short (notably 2a, 3a and 3b being much shorter than half distance between their bases).

Females of T. heterosetiger match closely those of T. smithi Ewing, 1939 (according to Kaliszewski, 1992) by the characters listed above, and additionally by a lack of sclerotized postatrial sacs along the tracheae, and slender, pointed dorsal opisthosomal setae. However, they differ from the latter species by having the prodorsal setae v 1 slen- der, pointed (stiff and blunt in T. smithi ); setae e and h nearly 2x longer than c 1 (e and h shorter than c 1 in T. smithi ) and claw I strong, hooked, swollen at the base (claw I moderate, weakly bent and uniformly thin in T. smithi ).

Figures

FIGURE 1. Tarsonemus heterosetiger female dorsum.

FIGURE 2. Tarsonemus heterosetiger female venter.

FIGURES 3–4. Tarsonemus heterosetiger female gnathosoma: 3—dorsum, 4—venter.

FIGURES 5–8. Tarsonemus heterosetiger female legs: 5—leg I (a—whole leg, dorsal aspect, b—apical part of tibiotarsus, ventral aspect), 6—leg II (dorsal aspect, a—whole leg, b—apical part of paratype tarsus), 7—leg III (ventral aspect), 8—leg IV (ventral aspect).

FIGURE 9. Details of female structures, Tarsonemus heterosetiger: a—pharynx (ex sample 318), b, c, d—posterior region of metapodosomal plate (ex samples 398, 383, 318 respectively). Scale bars are 10 μm.

FIGURE 10. Female empodium I with claw in various aspects: a, b, c—Tarsonemus heterosetiger ex samples 398, 383 (both paratypes) 318 (non-type) respectively, d, e—Suctarsonemus litteratus (Mahunka, 1973) non-type female, f—Tarsonemus fusa- rii Cooreman, 1941. Scale bar is 10 μm.

FIGURE 11. Tarsonemus heterosetiger, microscopic slides with examined material: a—holotype, b—paratype 1, c—paratype 2, d—non-type 1, e—non-type 2.