Ameronothrus retweet Pfingstl and Shimano, 2022

Pfingstl, Tobias, Hiruta, Shimpei F., Bardel-Kahr, Iris, Obae, Yuito & Shimano, Satoshi, 2022, Another mite species discovered via social media - Ameronothrus retweet sp. nov. (Acari, Oribatida) from Japanese coasts, exhibiting an interesting sexual dimorphism, International Journal of Acarology 48 (4 - 5), pp. 348-358 : 349-353

Ameronothrus retweet Pfingstl and Shimano sp. nov.

[New Japanese name: Iwado-hamabe-dani]

Type material/locality

Holotype: adult female (length 844 µm, width 444 µm); allotype: adult male (length 641 µm, width 363 µm), Japan, Honshu, Tottori prefecture, Tottori City; Fukube , Iwado , Iwado Rock Beach ; 31 March 2021, leg. OBAE Yuito. Preserved in ethanol and deposited at the Collection of Arachnida, Department of Zoology, National Museum of Nature and Science, Tokyo ( NMST). Four paratypes (2 males, 2 females) from the same sample deposited in the collections of the Senckenberg Museum für Naturkunde Görlitz ( SMNG).

Etymology

The specific name ‘ retweet ’ is given as noun in apposition. “Retweet” is used as both a verb and noun on the social media application Twitter ( twitter Inc. ) and means repost or forward a message. The present work does not represent a direct act of retweeting in a strict sense, but the species was discovered by a post as a response to the message about the discovery of A. twitter .

Differential diagnosis

The colour is dark brown, nearly black. Body length is 641–859 µm. In centrodorsal notogastral cuticle with dense granulation, lateral parts are covered with larger granules. Prodorsal lamellar keels are converging. Short clavate sensilli are present. Interlamellar and exobothridial setae are absent. Labiogenal articulation is complete. One pair of adanal setae located posteriorly of anal orifice. Remarkable sexual dimorphism is present, females with strongly folded gastronotic integument and considerably shorter epimeral, genital, and aggenital setae. Male spermatopositor conspicuously elongated, female ovipositor very short. Primilateral setae pl on tarsus I are present. Dorsal companion seta d on genu I, II, and III and all tibiae are present. Tarsal distal setae end with a small nodule. Juveniles is unknown.

Description

Measurements. Females (N = 4), length: 813–859 μm (mean 844 μm) and width: 444–475 μm (mean 456 μm); males (N = 10), length: 641–719 μm (mean 698 μm) and width: 363–413 μm (mean 390 μm).

Integument. Cuticle was thin and easily deformable. Cerotegument shows overall dense granulation. The colour is dark brown, almost black in stereomicroscope.

Prodorsum ( Figures 1 (a,c)). Rostrum is rounded in dorsal view, demarcated from remainder of prodorsum by faint transverse caudally arched ridge ct. Pair of converging lamellar keels (cl), reaches slightly beyond insertion of lamellar seta (le). Area between lamellar keels shows several irregular smaller ridges. Rostral seta (ro) spiniform is long and smooth (52–63 µm). Lamellar seta (le) is short, thickened, blunt and smooth (approx. 16 µm). Interlamellar seta (in) and exobothridial seta (ex) are absent. Bothridium is cup-like, orifice wide, and circular. Sensillum (ss) is short (approx. 25 µm), strongly clavate, globular head (diameter ca. 17 µm) ( Figures 2).

Gnathosoma. Palp pentamerous 0-2-1-3-9 (solenidion not included), trochanter very short, femur by far longest segment, genu, tibia, and tarsus of almost equal length ( Figure 3 (a)). Solenidion ω on palptarsus is loosely associated with eupathidium acm, tips close to each other. Atelebasic rutellum: Distal part with wide and darker sclerotized external tooth followed by a smaller dark sclerotized tooth merging into a series of three lobe-like projections forming an undulating membranous edge ( Figure 3 (b)). Setae a (approx. 30µm) and m (approx. 23µm) is spiniform, robust, and smooth. Mentum regular, seta h is long, setiform, robust (approx. 46µm). Labiogenal articulation is complete. Chelicera chelate, mobile digit darker sclerotized; distinct strong interlocking teeth. Träghårdhs organ (tg) has slender blunt lamella, slightly upward orientated. Seta cha and chb is robust and barbed, approximately the same length (59–63 µm) ( Figure 3 (c)). Large porous area is present on chelicera.

Gastronotic region ( Figures 1 (a, c)). Oval and slender in dorsal view, slightly convex in lateral view; no distinct border between anterior median notogastral and prodorsal region, instead large U-shaped fold extending from posterior prodorsal area into anterior gastronotic region. Centrodorsal area with dense and fine granulation, lateral and posterior edges with conspicuously larger granulation. Fifteen pairs of slightly thickened and blunt notogastral setae (15–30µm), c 1-3, da, dm, dp, la, lm, lp, h 1-3,p 1-3; seta dp shortest and setae p 1 and h 1 longest.

Dimorphic characters: Males with domed even dorsal gastronotic plate show a weak arch-like deepening in the anterior part (best seen on Figure 2). Five pairs of notogastral lyrifissures are present but difficult to trace due to rough cuticular surface; ia between seta c 2 and c 3, but closer to the latter; im between seta lm and lp; ih laterad and anterior to h 3; lyrifissures ip and ips laterally of seta p 3 and p 2, respectively. Orifice of opisthonotal gland (gla) is posterior to lyrifissure im. Females with strongly folded gastronotic plate (especially in the centrodorsal area) are largely overhanging in humeral areas so that bothridia are more or less completely covered in dorsal view. Strong folding of integument lyrifissures and orifice of opisthonotal gland is not traceable in females.

Lateral aspect. Pedotectum I and II are absent. Discidium between acetabulum III and IV is developed as rounded ridge.

Podosoma and venter ( Figures 1 (b), 2(b)). Epimeral setation 3-1-2-2, all setae are setiform and smooth, seta 1b is conspicuously longer than others. Genital orifice is large, rectangular, anterior edges more rounded. Six pairs of spiniform genital setae arranged in longitudinal rows, first and last pair longest. One pair of setiform aggenital setae ag. Anal valves triangular but strongly rounded. Outer part of preanal organ is rectangular with rounded edges, inner part is shaped like a transverse bar. Two pairs of anal setae, an 1-2 (28–32µm) insert close to median border. Three pairs of adanal setae, ad 1-3 (39–42µm), ad 3-2 are located laterally and ad 1 posteriorly of anal orifice. Lyrifissure iad flanking anterior third of anal plates.

Dimorphic characters: Males with more even ventral plate show only faint ridges or folds. Epimeral, genital, and aggenital setae conspicuously are longer than in female. Epimeral setae 1a, 2a, 3a (8–13µm), 1b (ca. 63µm), 3b (ca. 47µm), 4a (31µm), 4b (45µm); genital setae (25–55µm) and aggenital seta (31µm). Females with strongly folded ventral plate (see Figure 2) and shorter epimeral, genital and aggenital setae. Setae 1a, 2a, 3a (8–10µm), 1b (ca. 26 µm), 3b and 4b (ca. 22µm), 4a (16µm); genital setae (19– 31µm) and aggenital seta (ca. 20µm).

Legs. Ambulacrum tridactylous, median claw broad and strong, lateral claws weaker developed and dorsally slightly dentate. Extensive brachytracheae with slit-like stigmata on dorsal paraxial face of all femora and tracheal sacculi ventrally on all tibiae and dorsally on trochanter III and IV. Dorsal companion setae d associated with solenidia on genu I, II, III, and all tibiae are present. Primilateral setae of tarsus I present. Tectal (tc) and iteral (it) setae as well as most other terminal tarsal setae are with spoon-shaped or nodular tips (difficult to observe) ( Figure 4). Famulus on tarsus I rod-like, blunt and next to solenidion ω 1, solenidion ω 2 shorter. Solenidia ω 1 and ω 2 on tarsus II adjacent. For Chaetome and solenidia, see Table 1 .

Dimorphic characters: Legs of females are shorter than their body width, while legs of males are considerably longer than body width and therefore males possess relatively longer legs than females.

Reproductive organs. Male spermatopositor elongated consisting of a proximal and a distal smooth tube, latter is fitted in the former when retracted. Distal part is three lobes containing darker sclerotized plates. Posterior lobe bearing setae εε and c, lateral lobes bearing setae ε 1, 1,a and b ( Figure 5 (a)). Female ovipositor, very short, tube-like structure strongly plicated, allowing strong increase of diameter. Three short terminal lobes are present, posterior lobe bearing setae εε and c, lateral lobes bearing setae ε 1, 1,a and b ( Figure 5 (b)), k setae is absent.

Remarks

The new species A. retweet sp. n. can be easily distinguished from all congeners by its conspicuous sexual dimorphism, with males showing a completely different notogastral surface structure. Apart from this dimorphism, A. retweet sp. n. differs distinctly from A. bilineatus , A. marinus and A. schneideri in the presence of a sensillum (vs. absence) and from A. nigrofemoratus by the presence of 3 claws (vs. 1 claw). Ameronothrus maculatus possesses only one pair of anal setae (instead of two in A. retweet sp. n.), A. lineatus lacks the dorsal setae on all tibiae (these are present in A. retweet sp. n.), and A. schusteri and A. schubarti show an incomplete labiogenal articulation (vs. complete). Ameronothrus lapponicus and the Russian A. dubinini , A. oblongus , and A. nidicola show different femoral surface patterns (either reticulate or smooth versus granular in A. retweet sp. n.), and the Japanese A. yoichi and A. twitter exhibit strongly nodular notogastral integuments (vs. granular and folded in A. retweet sp. n.). These are just the most important distinctive characters, a detailed comparison of diagnostic traits of all Ameronothrus species is given in Table 2 .

Genetic data

Mitochondrial COI as well as nuclear 18S rRNA sequence data ( Table 3 ) confirm all investigated dimorphic Ameronothrus specimens as a single distinct species and thus support their description as new species Ameronothrus retweet sp. n. A maximum likelihood tree and a Bayesian inference tree based on nuclear 18S rRNA produced identical topologies, whereas node support was higher in the latter and thus only this tree is shown ( Figure 6). All Ameronothrus species are closely related and form a monophyletic clade. Interestingly, the two A. maculatus specimens, one from the North Sea coast of Germany and the other from the coast of Portugal, are placed as separate taxa. Paraquanothrus grahami (GenBank synonym Aquanothrus sp. ) and Halozetes capensis , which are supposed by most authors as members of Ameronothridae , are placed in apparent paraphyletic positions ( Figure 6). Marine-associated Fortuyniidae and Selenoribatidae are given as monophyletic families representing sister groups in the phylogenetic tree.