Ameronothrus twitter Pfingstl and Shimano, 2021

Pfingstl, Tobias, Hiruta, Shimpei F., Nemoto, Takamasa, Hagino, Wataru & Shimano, Satoshi, 2021, Ameronothrus twitter sp. nov. (Acari, Oribatida) a New Coastal Species of Oribatid Mite from Japan, Species Diversity 26 (1), pp. 93-99 : 94-98

Ameronothrus twitter Pfingstl and Shimano , sp. nov. [New Japanese name: Choshi-hamabe-dani]

( Figs 1–3 )

Type material. Holotype: adult female (length 766 µm, width 500 µm), Japan, Honshu, Choshi , 8 May 2019, coll. S. Shimano . Four paratypes: two males (length 613–625µm, width 344–369 µm) and two females (length 703–750 µm, width 438–488 µm); same data as for holotype . All type specimens preserved in ethanol, and deposited at the Collection of Arachnida, Department of Zoology, National Museum of Nature and Science, Tokyo (NMST) [collection numbers: holotype NSMT-Ac 14675 and measured four paratypes NSMT-Ac 14676–14679]. Additional two paratypes [coll. nr. 63985] are deposited in the collection of the Senckenberg Museum für Naturkunde Görlitz (SMNG).

Etymology. The specific name ‘ twitter ’ refers to the social media platform, Twitter on which this species was spotted for the first time ever. The name is treated as indeclinable.

Differential diagnosis. Colour dark brown, nearly black. Body length 613–766 µm. Notogastral cuticle with nodules, which are fused to large irregular ridges in anterior and especially posterior median notogastral areas. Prodorsal lamellar keels converging, anteriorly fused by a semicircular translamella. Sensilli short, capitate. Interlamellar and exobothridial setae absent. Labiogenal articulation complete. Primilateral setae on tarsus I present. Dorsal companion seta d on genu I, II and III and all tibiae present. Tarsal distal setae ending with a small nodule.

Description. Integument. Cuticle thin, easily deformable, showing nodular appearance. In central notogastral area, these nodules loosely distributed, but in anterior and lateral notogastral parts densely packed and mostly fused to larger irregular ridges in anterior and posterior median area of notogaster. Cerotegument densely covering whole body. Colour dark brown, nearly black in stereomicroscope.

Prodorsum ( Figs 1A , 2A ). Rostrum rounded in dorsal view, demarcated from remainder of prodorsum by transverse caudally arched ridge ct. Obvious lamellar keels (cl) converging, anteriorly fused by a semicircular translamella. Interbothridial area with larger irregular ridges. Rostral seta (ro) spiniform, long and smooth (37–60 µm). Lamellar seta (le) short, thickened, blunt and smooth (12–15 µm). Interlamellar seta (in) and exobothridial seta (ex) absent. Bothridium cup-like, orifice circular. Sensillum (ss) short (approx. 37 µm), strongly clavate, globular head with inconspicuous irregular elevations.

Gnathosoma . Palp pentamerous 0-2-1-3-9 (solenidion not included). Solenidion ω on palptarsus associated with eupathidium acm. Atelebasic rutellum. Distal part with wide paraxial tooth followed by smaller tooth merging into an undulating membranous edge. Incision between rutellar teeth stronger sclerotized. Setae a (~18 µm) and m (~23 µm) long, robust and smooth. Mentum regular, seta h setiform, robust (~30 µm). Labiogenal articulation complete. Chelicera chelate, mobile digit darker sclerotized; distinct strong interlocking teeth. Träghårds organ slender blunt lamella, slightly upward orientated. Seta cha and chb robust and finely barbed, similar in length (~46 µm).

Gastronotic region ( Figs 1A , 2A ). Oval in dorsal view, convex in lateral view; no distinct border between anterior median notogastral and prodorsal region. Ascleritic incision pgn visible along lateral humeral area. Fifteen pairs of short, thickened notogastral setae (17–23 µm), c 1–3, da, dm, dp, la, lm, lp, h 1–3, p 1–3. Notogastral lyrifissures difficult to trace due to rough cuticular surface; ia between seta c 2 and c 3; im between seta lm and lp; others could not be detected. Orifice of opisthonotal gland (gla) not traceable due to strong ornamentation.

Lateral aspect ( Fig. 2C ). Pedotectum I and II absent. Discidium dis between acetabulum III and IV, developed as conspicuous rounded ridge.

Podosoma and venter ( Figs 1B , 2B ). Epimeral setation 3-1-2-2, all setae setiform and smooth, seta 1b conspicuously longer (40–45µm) than others (20–25µm). Genital orifice large, rectangular with rounded corners, anteriorly broader. Six pairs of genital setae (25–30 µm) arranged in longitudinal rows along inner edge of plates, whereas fifth pair slightly laterally displaced. One pair of short, setiform aggenital setae ag. Strongly curved obvious transversal ridge between genital and anal opening. Anal valves subtriangular, but strongly rounded. Two pairs of smooth anal setae, an 1–2 (~30 µm); conspicuous oblique slightly curved ridge present posterior to seta an 1. Three pairs of spiniform adanal setae, ad 1–3 (25–30 µm), first two pairs inserted laterally and third pair posterior of anal orifice. Lyrifissure iad flanking anterior third of anal plates.

Legs ( Fig. 3 ). 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 present. Primilateral setae of tarsus I present. Tectal (tc) and iteral (it) setae as well as most other terminal tarsal setae with spoon-shaped or nodular tips (these are sometimes difficult to observe). Famulus ε 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. Formula of leg setation: I (0-4-3-5-18) (1-2-2); II (0-4-3-5- 15) (1-1-2); III (2-3-2-4-15); IV (1-2-2-4-14).

Remarks. Ameronothrus twitter sp. nov. shows a unique cuticular structure, which allows to easily distinguish it from several other members of Ameronothrus . Two Russian species, A. nidicola and A. oblongus show strongly reticulate cuticular notogastral patterns ( Sitnikova 1977), and though A. yoichi also shows a nodular notogastral cuticle, it lacks the conspicuous ridges in the anterior and posterior areas of notogaster as shown in A. twitter sp. nov. The European and North American species of Ameronothrus were classified into four groups based on morphological characters ( Schubart 1975): (1) the Ameronothrus marinus (Banks, 1896) group, including A. bilineatus (Micheal, 1888) , A. schusteri Schubart, 1970 and A. schubarti Weigmann and Schulte, 1975 , (2) the Ameronothrus maculatus (Michael, 1882) group including A. schneideri (Oudemans, 1903) , (3) the Ameronothrus lineatus (Thorell, 1871) group including A. nigrofemoratus (L. Koch, 1879) and (4) the Ameronothrus lapponicus Dalenius, 1963 group containing only this single species. Ameronothrus twitter sp. nov. can be easily distinguished from members of the A. marinus group by showing tarsal setae (tc) and (it) with nodules instead of hooks, and by adjacent solenidia ω 1 and ω 2 on tarsus II (these are clearly separated in the group). The primilateral setae (pl) on tarsus I are lacking in the A. maculatus group, but are present in A. twitter sp. nov. In the A. lineatus group the dorsal companion setae on all tibiae are lost whereas these are clearly present in A. twitter sp. nov., and finally A. lapponicus can be distinguished from the latter by its differently shaped pedipalp.

Considering the geographic proximity of A. twitter sp. nov. and A. yoichi , a close relationship of both Japanese species could be the case, but apart from cuticular similarities in the prodorsal and notogastral regions there are several striking differences, such as the reduction of dorsal companion setae, the loss of tarsal primilateral setae and the postanal position of all adanal setae in A. yoichi , contradicting such a relationship. However, Pfingstl et al. (2019) already stated that a clear assessment of phylogenetic relationships within Ameronothrus is not feasible yet due to incomplete descriptions of the Russian species and lacking molecular genetic data for nearly all taxa. A revision of the genus including morphological and molecular genetic data from all species could reveal natural relationships and provide important insights into the evolutionary history of this marine associated Holarctic group.

From an ecological point of view, we do not know much about this species, but aggregating individuals (a colony: Fig. 4C ) of A. twitter sp. nov. were observed in a crack of a wharf on the 5 May, 2019 which was a quite cool day at the fishing port ( Fig. 4A, B ). On an earlier visit, on 2 May they were observed leaving the crack during warmer daytime ( Fig. 4D, E ). However, from the 6 May temperatures rose considerably and no aggregating individuals were found on the following sampling day, on the 8 May. Aoki and Ohkubo (1974) reported colonies of Phauloppia adjecta Aoki and Ohkubo, 1974 found under bark in winter time and referred to this behavior as winter time aggregation. Ameronothrus twitter sp. nov. may also show aggregation behavior as protection against cold temperatures, but further observations are necessary. Presently, we only found this species on manmade concrete structures, but its original habitat may be coastal rocks. Several Ameronothrus species are known to live mainly in the sediment-free rock littoral ( Schulte et al. 1975) and the same may apply to A. twitter sp. nov. Natural rocks and concrete structures are very similar substrates and lichen and algae are growing on both therefore, they are more or less equal habitats.

The accidental discovery of this species with the help of social media is quite unique and represents a rather unusual case. TN, who is not a scientist, came to the wharf of the fishing port for fishing in his leisure time, but could not catch any fish at all. As one of his other hobbies is taking photographs of small arthropods, he randomly photographed some specimens that crossed his path this day and later uploaded it on twitter. SS checked the tweet with the photographs and video of oribatid mites and realized they probably belong to a new Ameronothrus species (Supplements 1 and 2).

Therefore, SS immediately went to Choshi-Gaikou and contacted TN via Twitter for guidance helping him to find the exact location where the photos were taken. SS found the colony and after examination in the lab it was clear this is a new species.

However, a handful of new species have already been discovered with the use social media (e.g., Wintertorn et al. 2012; Jaume-Schinkel et al. 2020), and one fungus species, namely Troglomyces twitteri Santam., Enghoff & Reboleira , was even the first to be found via twitter and named after it ( Santamaria et al. 2020). All these cases show that social media platforms and citizen science can provide additional tools in biodiversity research. Moreover, in the future the increasing interplay between research and social media platforms will play an important role, but also a challenge for science and the dissemination of knowledge.

Figures

Fig. 1. Ameronothrus twitter Pfingstl and Shimano, sp. nov., adult female. A, Dorsal view, legs omitted; B, ventral view, mouthparts and legs distal segments omitted.Scale bar valid for both depictions.

Fig. 2. Ameronothrus twitter Pfingstl and Shimano, sp. nov., stereomicroscopic photographs of adult female. A, Dorsal view; B, ventral view; C, lateral view.

Fig. 3. Ameronothrus twitter Pfingstl and Shimano, sp. nov., adult legs. A, Right leg I dorsal view; B, left leg II dorso-lateral view of antiaxial aspect; C, left leg III antiaxial view; D, left leg IV antiaxial view. Scale bar valid for all legs.

Fig. 4. Ameronothrus twitter Pfingstl and Shimano, sp. nov., collecting place and macro photography images (A and B taken by SS; C, D and E original photographs shared on Twitter by TN). A, Collecting place on the wharf of the fishing port (Choshi-Gaikou), Chiba, Japan, arrow pointing to exact location of mites; B, location of a colony in a crack between a car chock and the wharf, arrow pointing to the exact location of the colony; C, a colony of A. twitter Pfingstl and Shimano, sp. nov. in the colder day (11:23am), 5 May 2019 (https://twitter.com/ yatsume_project/status/1124999187626483717?s=20); D (https://twitter.com/yatsume_project/status/1123890470285918209?s=20) and E, moving individuals of A. twitter Pfingstl and Shimano, sp. nov. in the warmer day (11:57am), 2 May 2019.