Myrmozercon patagonicus, Trach & Khaustov, 2018

Trach, Viacheslav A. & Khaustov, Alexander A., 2018, The first record of the genus Myrmozercon Berlese (Acari: Mesostigmata: Laelapidae) in the Neotropical region and a description of a new species, Acarologia 58 (1), pp. 41-51 : 42-48

Myrmozercon patagonicus n. sp. ( Figures 1–3 )

Zoobank: 1B9CCEB5-C623-4071-9781-1C7CD68CE780

Diagnosis — Dorsal shield broadly oval, not covering entire idiosoma; hypotrichous; with 29–30 pairs of setae; cuticle around dorsal shield sclerotised and striated; soft cuticle on posterior margin of idiosoma smooth; dorsal cuticle not hypertrichous. Sternal shield entire; setae st1–st5 present; anal shield subtriangular, without anterolateral extensions, with circum-anal setae only; peritremes short; peritrematal shields well developed, fused with dorsal shield anteriorly; ventral soft cuticle hypertrichous. Fixed cheliceral digit reduced and edentate; pilus dentilis absent; movable cheliceral digit edentate; epistome triangular, smooth; chaetotaxy of palps (from trochanter to genu 1–4–6); deutosternum with 19–21 transverse rows of deutosternal denticles (8–25 denticles per row); palp coxal seta present, simple. Chaetotaxy of legs I–IV (from coxa to tibia): 2–6–14–13/15–13; 2–5–10–11–9/10; 2–5–7/8–11–9/10; 1–5–8–11–9/10; legs long, legs I and IV subequal, longer than legs II and III.

Description of female (n=4) — Dorsum ( Figure 1A ). Idiosoma oval; 921 (930 – 949) long and 809 (763–781) maximum width. Dorsal shield broadly oval; not covering entire idiosoma; 763 (763 – 791) long and 716 (707 – 735) maximum width; reticulated with distinct sigillae; hypotrichous; with 29 or 30 pairs of setae (r5 often missing) (j1, j3–j6, z1–z6, s3–s6, r3–r5, J2–J5, Z2–Z5, S2–S5) and 15 pairs of distinguishable pores; pores near base of j1 absent. Cuticle around of dorsal shield strongly sclerotised and striated; with variable number of setae (three-five pairs); posterolateral margins of cuticle curved ventrally. Soft cuticle on posterior margin of idiosoma smooth and weakly striated; with variable number of setae (three-four pairs). Almost all dorsal setae barbed in distal part; 53 – 103 (53 – 99) long.

Venter ( Figure 2 ) — Tritosternum with short, broad base and paired smooth laciniae; base of tritosternum length 19 (21 – 23), maximum width 34 (34 – 36), laciniae length 105 (103 – 113). Presternal shields fused to anterior margin of sternal shield. Sternal shield 126 (122 – 134) long midline and 176 (172 – 181) wide at narrowest level at about middle of coxae II; reticulated on anterior part and lateral margins; with three pairs of setae and two pairs of pores (iv1, iv2); pore iv1 oriented transversely, positioned posteriad seta st1, pore iv2 oriented obliquely between setae st2 and st3. Endopodal plates I–II fused with lateral margins of sternal shield alongside coxae II, endopodal III–IV connected to the latero-corner of sternal shield at anterior margin of coxae III and to parapodal platelets. Metasternal platelets absent; setae st4 and pores iv3 located on soft cuticle. Genital shield 378 (378 – 391) long and 248 (248 – 252) maximum width at level and slightly posteriorly of st5; reticulated; with setae st5. Soft cuticle at lateral margins of genital shield with one pair of pores; cuticle at posterior margin with transverse platelets (two-three pairs in different specimens). Subtriangular anal shield with smooth surface; 130 (130 – 139) long and 223 (214 – 223) maximum width; anus located in centre of shield; with circum-anal setae; pores obscure; cribrum well developed. Soft cuticle around of anal shield striated; hypertrichous; with one or two elongate irregular metapodal plates; a pair of small platelets; 22–25 pairs of setae and three-four pairs of distinguishable pores. Peritreme 139 (139 – 151) long; peritrematal shields well developed; fused to dorsal shield anteriorly; pores on peritrematal shield absent. Setae st1–st5 and about 12 pairs of setae on soft cuticle narrow and smooth; others slightly thickened and barbed (as dorsal setae); para-anal and post-anal strongly thickened and slightly barbed in distal part; measurements of setae: st1–st5 48 – 57 (44 – 57), setae on soft cuticle 44 – 80 (44 – 88), para-anal 71 (65 – 78), post-anal 84 (82 – 86).

Gnathosoma — Second cheliceral segment 139 (139 – 143) long; fixed cheliceral digit reduced and edentate; pilus dentilis absent; antiaxial and dorsal lyrifissures, cheliceral seta and arthrodial process distinct; movable cheliceral digit edentate ( Figure 1B ). Epistome triangular, smooth ( Figure 1C ). Palp 151 (147 – 155) long; numbers of setae on palp trochanter-genu: 1, 4, 6, tibia and tarsus about 23; setae aciculate and smooth; apotele two-tined, located on palp tarsus ( Figure 1D ). Subcapitulum 181 (181 – 193) maximum width. Deutosternum with 19–21 transverse rows of deutosternal denticles (8–25 denticles per row); marginal line of deutosternal groove weakly discernible anteriad setae h2 and h3. Corniculi short, broad, irregular shape, weakly sclerotised. Internal malae pointed and smooth, not projecting beyond tips of corniculi; labrum projecting somewhat beyond tips of internal malae. Hypostomal and palp coxal setae smooth; measurements of setae: h1 21 (21 – 23), h2 27 (27 – 29), h3 48 (44 – 46), pc 44 (40 – 44).

Legs ( Figures 3 A–D) — Lengths: I 1051 (1051 – 1097), II 716 (707 – 735), III 884 (865 – 893), IV 1042 (1042 – 1079). Number setae on some leg segments abnormal for Laelapidae (on femora I–IV, genua III–IV, and, sometimes, genu I and tibiae III–IV). Some leg segments with variable setation. Chaetotaxy of holotype: leg I: coxa 2, trochanter 6 (1 0/1 1/2 1), femur 14 (2 3/2 2/3 2), genu 14 (2 3/3 3/1 2), tibia 13 (2 3/2 3/1 2); leg II: coxa 2, trochanter 5 (1 0/1 0/2 1), femur 10 (2 2/1 2/2 1), genu 11 (2 3/1 2/1 2), tibia 10 (2 2/1 2/1 2), tarsus 18 (3 3/2 1/1 3/2 3); leg III: coxa 2, trochanter 5 (1 0/1 0/2 1), femur left 7 (1 2/1 2/1 0), femur right 8 (1 2/2 2/1 0), genu 11 (2 2/1 3/1 2), tibia left 10 (2 1/1 3/1 2), tibia right 9 (2 1/1 2/1 2), tarsus 18 (3 3/2 1/1 3/2 3); leg IV: coxa 1, trochanter 5 (1 0/1 0/2 1), femur 8 (1 2/1 2/2 0), genu 11 (2 2/1 3/1 2), tibia 10 (2 1/1 3/1 2), tarsus 18 (3 3/2 1/1 3/2 3). In paratypes genu I with 13 (2 3/2 3/1 2; av3 lacking), 14 (2 3/3 3/1 2) or 15 setae (2 3/3 3/2 2; added pv2); tibia II with 10 (2 2/1 2/1 2) or 9 setae (1 2/1 2/1 2; al1 lacking); femur III with 7 setae (1 2/1 2/1 0; av1 lacking); tibia with 9 (2 1/1 2/1 2) or 10 (2 1/1 3/1 2; pd3 added) setae; tibia IV with 10 (2 1/1 3/1 2) or 9 setae (2 1/1 2/1 2; pd2 lacking). All setae smooth; some thickened. Pretarsi I–IV similar in shape; claws apparently absent; ambulacral pads well-developed.

Genital structures — Insemination ducts opening between bases of coxae III and IV. Tubuli sclerotised; slightly curved; 2–3 in diameter ( Figure 2 ). Sacculus is indiscernible.

Type material — Female holotype, slide No 30–10–2015 /01, Chile, Patagonia, vicinity of Puerto Natales , on Camponotus sp. collected from rotten log of Nothofagus sp., 51°56’55.2”S, 72°23’24.8”W, 30 October 2015, A.A. Khaustov coll.; paratypes: 3 females, same data.

Etymology — The name of a new species refers to its distribution in Patagonia.

Differential diagnosis — According to the presence of palpcoxal setae and setae st4, anal shield without anterolateral extensions, absence of hypotrichous leg setation and long legs, Myrmozercon patagonicus n. sp. belongs to the group of species referred to as Myrmozercon “ sensu lato ” by Joharchi et al. (2015).

By the hypotrichous dorsal shield, hypertrichous ventral soft cuticle and by its large size, M. patagonicus n. sp. is similar to M. antennophoroides ( Berlese, 1904) , M. beardae Shaw and Seeman, 2009 , M. hunteri Joharchi, Babaeian and Seeman, 2015 and M. rotundiscutum Rosario and Hunter, 1988 .

Myrmozercon patagonicus n. sp. differs from M. antennophoroides by the shape of its body (oval in M. patagonicus n. sp., obovoid in M. antennophoroides ), shape of the genital shield (rounded posteriorly in M. patagonicus n. sp., with notch in M. antennophoroides ), size and shape of the anal shield (large and subtriangular M in. patagonicus n. sp., small and indistinct in M. antennophoroides ).

It differs from M. beardae by the number and shape of setae on dorsal shield (29–33 pairs of mainly barbed setae in M. patagonicus n. sp., 23–25 pairs of smooth setae in M. beardae ), presence of setae st4 and st5 (absent in M. beardae ), shape of setae on soft ventral cuticle (simple or barbed in M. patagonicus n. sp., simple or spinose in M. beardae ), shape of the anal shield (anus located in centre of shield in M. patagonicus n. sp., in posterior part of shield in M. beardae ), number setae on palps (trochanter with one seta, genu with six setae in M. patagonicus n. sp., trochanter with two setae, genu with four-five setae in M. beardae ), presence of only one seta on coxa IV (two setae in M. beardae ).

The new species is also very similar to M. hunteri in the number of setae on dorsal shield, shape of anal shield, thickened circum-anal setae and chaetotaxy of palps. M. patagonicus n. sp. differs from M. hunteri by hypotrichous dorsal cuticle (hypertrichous in M. hunteri ), fusion of dorsal shield with peritrematal shields (free M in. hunteri ), shape of circum-anal and leg setae (pointed in M. patagonicus n. sp., blunt in M. hunteri ), and shape of palpcoxal setae (simple in M. patagonicus n. sp., two-tined in M. hunteri ).

Myrmozercon patagonicus n. sp. is distinguished from M. rotundiscutum in having 29–30 pairs of setae on the dorsal shield (27 pairs in M. rotundiscutum ), hypotrichous dorsal cuticle (hypertrichous in M. rotundiscutum ), dorsal shield fused with peritrematal shields (free and weakly developed peritrematal shields in M. rotundiscutum ), having 19–21 transverse rows of deutosternal denticles on deutosternum (11 in M. rotundiscutum ) and six setae on palp genu (five in M. rotundiscutum ).

Myrmozercon patagonicus n. sp. also differs from all congeners by the number setae on leg segments. The presence of 14 setae on femur I is also known in M. burwelli Shaw and Seeman, 2009 , M. hunteri and M. rotundiscutum ; the presence of 14 or 15 setae on genu I is unknown in other species. The presence of 10 setae on femur II is known in M. beardae , M. iainkayi Walter, 2003 , M. iranicus Babaeian and Nemati, 2014 , and M. rotundiscutum . Seven setae on femur III occur in M. cyrusi Ghafarian and Joharchi, 2013 , and M. hunteri and most specimens of M. patagonicus n. sp., but presence of eight setae on femur III is unknown in other species of Myrmozercon . The new species has 11 setae on genu III (as M. burwelli and M. rotundiscutum ) and 9–10 setae on tibia III (nine setae in M. beardae , M. burwelli , M. iainkayi and M. crinitus Joharchi, 2013 ; 10 setae in M. hunteri and M. rotundiscutum ). The presence of eight setae on femur III is also known in M. brevipes Berlese, 1902 and M. iainkayi , and 11 setae on genu IV is known in M. beardae and M. burwelli . Unfortunately, leg chaetotaxy described in detail only for 16 species of Myrmozercon .

Joharchi and Moradi (2013) presented a key to 13 species of Myrmozercon occurring in the Palaearctic Region and Joharchi et al. (2015) provided a key to the 18 species of Myrmozercon that are well-described; they also briefly diagnosed the remaining species. The following key to non-Palaearctic species of the genus Myrmozercon is based on keys of Walter (2003), Shaw and Seeman (2009) and Joharchi et al. (2015) and published descriptions and illustrations.

Figures

Figure 1 Myrmozercon patagonicusn. sp., female: A – idiosoma, dorsal view; B – chelicera; C – gnathotectum; D – subcapitulum and palp. Scale bar: A 200 μm, B–D 100 μm.

Figure 2 Myrmozercon patagonicusn. sp., female: idiosoma, ventral view. Scale bar 200 μm.

Figure 3: Myrmozercon patagonicusn. sp., female: A – leg I; B – leg II; C – leg III; D – leg IV; from the right side of the body; ventral aspect. Scale bar 200 μm.