A new species of the genus Eustigmaeus (Trombidiformes: Prostigmata: Stigmaeidae) and the first record of E. extremiorientalis in Japan Author Ikeda, Satsuki 0009-0007-9278-7590 Department of Zoology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606 - 8502, Japan satsuki.ikeda.1106@gmail.com Author Imada, Yume 0000-0003-2173-7389 Department of Zoology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606 - 8502, Japan imayume@terra.zool.kyoto-u.ac.jp Author Nakano, Takafumi 0000-0001-6107-2188 Department of Zoology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606 - 8502, Japan nakano@zoo.zool.kyoto-u.ac.jp text Zootaxa 2024 2024-11-15 5538 3 233 246 https://doi.org/10.11646/zootaxa.5538.3.2 journal article 10.11646/zootaxa.5538.3.2 1175-5326 14611671 1D9A86AF-C027-43A7-9542-700244B53F33 Eustigmaeus imadae Ikeda & Nakano sp. nov. [New Japanese name: Nezumi-no-o-maruhishi-dani] ( Figs 1–5 ) Eustigmaeus sp. 1 — Ikeda et al . (2024: 734 , fig. 4). Type material. Holotype : female , KUZ Z4780 , from moss on a wet boulder by a river, 33°36′11.3″N 135°46′02.7″E , approx. 60 m elev., Kozagawa , Higashimuro , Wakayama Prefecture , Japan , 12 October 2021 , coll. S. Ikeda [locality code 21 in Ikeda et al . (2024) ] . Paratypes : two females , KUZ Z4700 and Z4769 , from the same moss colony as the holotype . Additional material. 11 female specimens: 2 females , KUZ Z4578 and Z4763 , from moss on a wet rock in a stream, 33°52′31.5″N 134°05′46.3″E , approx. 1,360 m elev., Koyadaira , Mima , Tokushima Prefecture , Japan , 22 May 2021 , coll. S Ikeda [locality code 8 in Ikeda et al . (2024) ] ; 1 female , KUZ Z4745 , from moss on a wet rock in a stream, 33°52′37.0″N 134°06′36.4″E , approx. 1,100 m elev., Koyadaira , Mima , Tokushima Prefecture , Japan , 22 May 2021 coll. S. Ikeda [locality code 9 in Ikeda et al . (2024) ] ; 2 females , KUZ Z4546 and Z4765 , from moss on a wet boulder in a stream, 35°17′35.0″N 134°28′35.0″E , approx. 540 m elev., Wakasa , Yazu , Tottori Prefecture , Japan , 29 March 2021 coll. S. Ikeda [locality code 18 in Ikeda et al . (2024) ] ; 1 female , KUZ Z4571 , from moss on a wet boulder in a stream, 33°45′45.6″N 135°49′17.3″E , approx. 90 m elev., Kumanogawa , Shingu , Wakayama Prefecture , Japan , 11 October 2021 , coll. S. Ikeda [locality code 22 in Ikeda et al . (2024) ] ; 4 females , KUZ Z4712 , Z4713 , Z4717 , and Z4718 , from mosses on wet boulders in a stream, 35°32′40.3″N 137°23′27.1″E , approx. 590 m elev., Nakatsugawa , Gifu Prefecture , Japan , 20 April 2022 , coll. S. Ikeda [locality code 31 in Ikeda et al . (2024) ] ; 1 female , KUZ Z4655 , from moss on a wet boulder in a stream, 36°01′44.5″N 138°49′48.6″E , approx. 1,140 m elev., at Chichibu , Saitama Prefecture , Japan , 27 October 2021 , coll. S. Ikeda [locality code 36 in Ikeda et al . (2024) ]. Diagnosis. The new species resembles Eustigmaeus grandis Khaustov, 2019 and E . rotundus ( Wood, 1972 ) in having six pairs of hysterosomal setae, two pairs of callosities, and two pairs of aggenital setae. However, this species is distinguishable from the two congeners by having long rod-like dorsal idiosomal setae with hyaline sheaths (seta lengths of type series: vi 67–77, ve 123–133, sci 62–67, sce 87–95, c1 92–102, c2 60–67, d1 96–111, d2 78–93, e1 93–104, e2 76–80, f1 75–86, h1 50–56, h2 40–45) [vs. distally brush-like setae without hyaline sheath (seta lengths of type series: vi 44–48, ve 47–53, sci 38–43, sce 34–39, c1 34–43, c2 29–31, d1 41–44, d2 36–37, e1 46 –47, e2 41 –45, f1 51–53, h1 42–46, h2 27–33) for E . grandis ; slightly clavate setae with hyaline sheaths (seta lengths of type series: ve 51, sci 18, c2 24, d2 42, e1 56 , e2 46 , f1 46, h2 18, 32–37 for vi , sce , c1 , d1 , h1 ) for E . rotundus ]. Description. FEMALE ( holotype , range for type series in parentheses). Idiosomal length 470 (446–470), idiosomal width 388 (347–388). FIGURE 1. Eustigmaeus imadae sp. nov. , female, holotype (KUZ Z4780). A—prodorsal shield with focus on subcuticular reticulum; B—hysterosomal shield with focus on dimples. Scale bar = 50 μm. FIGURE 2. Eustigmaeus imadae sp. nov. , female holotype (KUZ Z4780). A—idiosomal dorsum; B—idiosomal venter. Punctation and dorsal shields reticulum are not shown. Idiosomal dorsum ( Figs 1–2 ). Two large shields almost completely cover idiosomal dorsum. Dorsal shields sclerotized; dimples amorphous and evident near margin but blurry middorsally, each dimple enclosed in faintly discernible reticulum beneath cuticular layer ( Fig. 1 ). Shield surface minutely punctate ( Fig. 1 ). Fossettes as illustrated ( Fig. 2A ). Ocelli present. Lateral margin of prodorsal and hysterosomal shields weakly sclerotized with shallow dimples. Suranal shield located ventrally, with shallow dimples enclosed in subcuticular reticulum. Dorsal setae long and rod-like with bluntly pointed tips, densely barbed in distal half, hyaline sheaths evident near tips. Lengths of dorsal setae: vi 77 (67–77), ve 133 (123–133), sci 64 (62–67), sce 95 (87–95), c1 102 (92–102), c2 67 (60–67), d1 111 (96–111), d2 93 (78–93), e1 104 (93–104), e2 80 (76–80), f1 86 (75–86), h1 56 (50–56), h2 43 (40–45). Distances between setae: vi–vi 29 (27–30), ve–ve 122 (113–122), sci–sci 215 (202–215), sce–sce 292 (273–292), vi–ve 84 (75–84), ve–sci 55 (52–56), sci–sce 53 (48–53), c1–c1 113 (112–116), d1–d1 157 (145–157), d2–d2 335 (318–335), e1–e1 160 (151–160), e2–e2 262 (251–262), f1–f1 123 (123–132), h1–h1 48 (40–48), h2–h2 112 (102–112), c1–d1 105 (97–105), c1–d2 133 (122–133), e1–d2 164 (149–164), d1–d2 92 (86–92), d1–e1 110 (99–110), d1–e2 80 (74–81), d2–e2 96 (82–96), e1–e2 71 (62–72), e1–f1 35 (35–45), h1–h2 39 (34–39). Idiosomal venter ( Fig. 2 ). Two pairs of equal-sized callosities positioned on lateral margins of idiosomal shields. Weak incision next to anterior callosity present in holotype ( Fig. 2A ) but absent in paratype . Humeral shield sparsely punctate with subcuticular reticulum. Coxisternal plates of legs minutely punctate, posterior part of leg II coxisternal plate reticulated. Endopodal plates reticulated and separated medially.Aggenital plate punctate and reticulated, with two pairs of simple aggenital setae. Anal cover with three pairs of simple pseudoanal setae, ps2 shorter than others. Lengths of setae: ag1 23 (21–23), ag2 28 (25–28), ps1 20 (18–20), ps2 11 (10–14), ps3 27 (22–27). Gnathosoma ( Fig. 3 ). Dorsal surface of chelicera punctate. Chelicera and its short movable digit 102 (94–103) and 21 (21) in length, respectively. Palpfemoral seta d barbed with bluntly pointed tip. Seta l ′ on tibia short, spinelike. The other palpal setae of femur, genu, and tibia barbed and pointed. For palptarsal setae, acm ζ, ( ul ζ), and sul ζ smooth with blunt tips, ω finger-shaped, other setae smooth and pointed. Counts of palpal setae from trochanter to tarsus: 0-3-2-3-6(1). Supracoxal seta ep short, needle-like, located dorsolaterally. Ventral surface of subcapitulum punctate. Rostrum short. Sabcapitular seta or2 smooth, thickened, and curved with a blunt tip. Setae m , n , and or1 smooth and pointed. Lengths of setae: m 22 (22–23), n 22 (19–22), or1 11 (8–11), or2 12 (12–13). Distances between subcapitular setae: m–m 30 (29–30), n–n 32 (32–35), m–n 20 (16–20). FIGURE 3. Eustigmaeus imadae sp. nov. , female. A—left palp and chelicera (paratype; KUZ Z4769); B—ventral view of subcapitulum (holotype; KUZ Z4780). Punctation is not shown. Legs ( Figs 4–5 ). Leg lengths: leg I 239 (239–240), leg II 198 (189–198), leg III 207 (189–207), leg IV 257 (250–257). Empodium with three pairs of tenant hairs. Counts of setae on leg I–IV: coxae 2 + el , 2, 2, 2; trochanters 1, 1, 2, 1; femora 6, 5, 3, 2; genua 3 + 1 k , 3 + 1 k , 1, 1; tibiae 5 + 1 φ + 1 φp , 5 + 1 φp , 5 + 1 φp , 5 + 1 φp ; tarsi 13 + 1 ω , 9 + 1 ω , 7 + 1 ω , 7 + 1 ω . Leg I ( Fig. 4A ). Supracoxal seta el short, needle-like ( Fig. 2A ). Leg setae ( ft ), ( tc ), and ( p ) of tarsus eupathid-like. Setae d of femur, d and ( l ) of genu, d of tibia barbed and bluntly pointed, and hyaline sheaths evident near tips (seta l ″ of genu barbed and pointed without hyaline sheath on left leg in KUZ Z4769). Setae ( l ) of femur barbed and bluntly pointed without hyaline sheaths. Setae v ′ of trochanter, ( v ) and bv ″ of femur, ( l ) and ( v ) of tibia, and ( pl ) and vs of tarsus barbed and pointed (seta l ′ of tibia also with hyaline sheath in KUZ Z4700). Setae ( a ) of tarsus slightly serrated or smooth, ( u ) of tarsus smooth. Solenidia ω and φ baculiform with rounded tips, φp attenuate. Seta k needle-shaped. Seta lengths: k 7 (6–7), φp 23 (21–24), φ 10 (10), ω 27 (27–31). Leg II ( Fig. 4B ). Leg setae tc ′ and p ′ of tarsus eupathid-like. Setae d and l ″ of femur, d and ( l ) of genu, d of tibia barbed and bluntly pointed, hyaline sheaths evident near tips (seta l ′ of genu barbed and bluntly pointed without hyaline sheath on left leg in KUZ Z4769, and seta l ′ of genu barbed and pointed on right leg in KUZ Z4769). Seta l ′ of femur barbed and bluntly pointed without hyaline sheath. Setae v ′ of trochanter, v ′ and bv ″ of femur, ( l ) and ( v ) of tibia, tc ″, pl ′, and vs of tarsus barbed and pointed. Setae ( a ) of tarsus slightly serrated or smooth, ( u ) of tarsus smooth. Solenidion ω baculiform with round tip, φp attenuate. Seta k needle-shaped. Seta lengths: k 6 (5–6), φp 18 (18), ω 17 (17). Leg III ( Fig. 5A ). Setae d and l ′ of femur, d of genu, d of tibia barbed and bluntly pointed, hyaline sheaths evident near tips. Seta l ′ of trochanter barbed and bluntly pointed, hyaline sheath evident near tip (without hyaline sheath in KUZ Z4769). Setae v ′ of trochanter, ev ′ of femur, ( l ) and ( v ) of tibia, ( tc ) and vs of tarsus barbed and pointed. Setae ( a ) of tarsus slightly serrated or smooth, ( u ) of tarsus smooth. Solenidion ω finger-shaped, φp attenuate. Seta lengths: φp (12), ω 6 (6). Leg IV ( Fig. 5B ). Setae d of femur, d of genu, d of tibia barbed and bluntly pointed, hyaline sheaths evident near tips. Setae v ′ of trochanter, ev ′ of femur, ( l ) and ( v ) of tibia, ( tc ) and vs of tarsus barbed and pointed. Setae ( a ) of tarsus slightly serrated or smooth, ( u ) of tarsus smooth. Solenidion ω finger-shaped, φp attenuate. Seta lengths: φp 11, ω 5 (5). Variations. (Additional material). Idiosomal length 459–488 (n = 10), idiosomal width 322–372 (n = 10). Idiosomal dorsum . On dorsal shields, amorphous dimples and subcuticular reticulum appear near margin but both disappear middorsally (KUZ Z4763). Setae lengths (n = 11): vi 65–79, ve 120–142, sci 58–72, sce 86–111, c1 96–111, c2 61–73, d1 101–114, d2 86–103, e1 93–113, e2 74–87, f1 79–87, h1 52–59, h2 40–48. Distances between setae (n = 11 unless otherwise stated): vi–vi 26–33, ve–ve 111–125, sci–sci 196–218, sce–sce 269–290, vi–ve 76–87, ve–sci 52–62, sci–sce 45–57, c1–c1 106–124, d1–d1 144–165, d2–d2 308–342 (n = 10), e1–e1 142–166 (n = 10), e2–e2 241–267 (n = 10), f1–f1 124–138 (n = 10), h1–h1 39–53 (n = 9), h2–h2 102–119 (n = 8), c1–d1 96–102 (n = 6), c1–d2 123–138, e1–d2 152–169 (n = 6), d1–d2 84–99, d1–e1 100–113, d1–e2 69–86 (n = 6), d2–e2 91–103 (n = 6), e1– e2 60–70, e1–f1 33–45, h1–h2 33–43 (n = 8). Idiosomal venter . Weak incision next to anterior callosity present in KUZ Z4718 and Z4745, but absent in Z4765, Z4571, Z4763, and Z4655. Length of setae: ag1 16–25 (n = 5), ag2 20–29 (n = 5), ps1 15–25 (n = 6), ps2 9–13 (n = 6), ps3 21–26 (n = 6). Gnathosoma . Chelicera and its short movable digit 101–106 (n = 6) and 20–23 (n = 6) in length, respectively. Palpfemoral seta d barbed and bluntly pointed with hyaline sheath in KUZ Z4655. Palptarsal seta va slightly barbed in KUZ Z4571. Lengths of setae: m 20–23 (n = 5), n 18–25 (n = 5), or1 8 (KUZ Z4571), or2 13–14 (n = 4). Distances between subcapitular setae (n = 5): m–m 30–33, n–n 33–37, m–n 18–20. Leg . Leg lengths: leg I 235–255 (n = 6), leg II 187–214 (n = 6), leg III 206–215 (n = 5), leg IV 252–265 (n = 5). Leg I. Seta l ′ of tibia barbed and bluntly pointed, hyaline sheath evident near tip (KUZ Z4745 and Z4718). Seta l ′ of femur barbed with bluntly pointed tip, hyaline sheath evident near tip (KUZ Z4763). Seta l ″ of femur barbed and bluntly pointed, hyaline sheath evident near tip (KUZ Z4655 and Z4718). Seta lengths: k 6–8 (n = 4), φp 19–23 (n = 5), φ 10–13 (n = 6), ω 23–34 (n = 5). Leg II. Seta d of tibia barbed and bluntly pointed without hyaline sheath (KUZ Z4718 and Z4769). Seta l ′ of genu barbed and pointed (KUZ Z4571). On left leg, seta l ′ of genu barbed and pointed (KUZ Z4718). Seta l ″ of femur barbed and bluntly pointed without hyaline sheath (KUZ Z4745). On right leg, seta l ′ of tibia barbed and bluntly pointed, hyaline sheath evident near tip (KUZ Z4718). Seta lengths: k 5–6 (n = 4), φp 15–20 (n = 4), ω 14–18 (n = 5). Leg III. Seta l ′ of trochanter barbed and bluntly pointed without hyaline sheath (KUZ Z4571 and Z4718). Seta l ′ of tibia barbed and bluntly pointed, hyaline sheath evident near tip (KUZ Z4718). Seta l ′ of tibia barbed and pointed with hyaline sheath (KUZ Z4763). Seta lengths: φp 13–15 (n = 2), ω 6–8 (n = 5). Leg IV. Seta l ′ of tibia barbed and bluntly pointed without hyaline sheath (KUZ Z4718). Seta ev ′ of femur barbed with bluntly pointed tip; hyaline sheath evident near tip (KUZ Z4655). Seta lengths: φp 12–14 (n = 2), ω 4–5 (n = 5). FIGURE 4. Eustigmaeus imadae sp. nov. , female paratype (KUZ Z4700). A—left leg I, dorsal view; B—right leg II, dorsal view. FIGURE 5. Eustigmaeus imadae sp. nov. , female paratype (KUZ Z4700). A—right leg III, dorsal view; B—right leg IV, dorsal view. DNA sequences. Six sequences were determined and deposited with International Nucleotide Sequence Databases (INSD) by Ikeda et al . (2024) . INSD accession numbers LC789951 ( KUZ Z4808 ), LC789953 ( KUZ Z4816 ), LC789955 ( KUZ Z4818 ), LC789956 ( KUZ Z4819 ), LC789968 ( KUZ Z4813 ), and LC789969 ( KUZ Z4814 ) for cytochrome c oxidase subunit I (COI). Host plants. Two species of Brachytheciaceae and one species of Entodontaceae have been recorded ( Ikeda et al . 2024 ): Brachytheciaceae , Rhynchostegium riparioides and Sciuro-hypnum plumosum Entodontaceae , Entodon luridus . Etymology. The specific name is dedicated to Dr. Yume Imada, who first guided the first author in the study of Eustigmaeus . The Japanese name “Nezumi-no-o” means “mouse’s tail,” in reference to the dorsal seta’s similar appearance. Remarks. This species was collected from Shikoku Island and the Chugoku to Kanto Regions on Honshu Island, Japan . The species exhibits a broad vertical distribution (from approximately 60 to 1,360 m in elevation). Among the geographically distant collection localities, specimens show limited morphological variation and low COI genetic divergence (less than 3.1% difference in K2P, as reported by Ikeda et al . 2024 ). Leg seta shape appears to be highly variable within this species, and variability is even observed within a single population.