The first records of the subfamily Euthyadinae K. Viets, 1931 (Acari, Hydrachnidia, Hydryphantidae) from China with description of one new species

The first records of subfamily Euthyadinae K. Viets, 1931 are presented from China. Two species are reported from Anhui Province P. R. China, i


Introduction
Hydryphantidae Piersig, 1896 is a large group of water mites consisting of 13 subfamilies (Smit 2020).A study based on molecular data confirmed the viewpoints of previous acarologists that this family is of paraphyletic origin (Dabert et al. 2016).However, their phylogenetic relationship is still unclear.Therefore, the development of more species resources and intensive research are particularly important.
During a field survey of water mites from Anhui Province, a new species of Trichothyas, i.e.T. (Neothyas) zhangae Li, Jin & Guo sp.nov.and the first record of Trichothyas (Lundbladia) feuerborni (K.Viets, 1929) were discovered, which are the first records of the subfamily Euthyadinae K. Viets, 1931 for the Chinese fauna.Detailed structures are illustrated and photographed with the help of optical microscope and SEM (scanning electron microscope).

Material and methods
The collection, preservation of water mites and preparation of slides follows Gu et al. (2021).Specimens were examined and illustrated under a Leica DM3000 microscope.In the illustrations, short curved lines on platelets indicate the muscle attachment scars.All photographs and illustrations were edited with Adobe Photoshop CS6.All measurements were made with a Nikon Ni-E (with Nikon DS-Ri2 camera) and are given in μm, and measuring methods can be found in Figure 1.The treatments of SEM (scanning electron microscope) refer to Li et al. (2022).
The terminology and abbreviations used were updated from Jin (1997) and Gerecke (2020 The type series were deposited in the Institute of Entomology, Guizhou University, Guiyang, P. R.China (GUGC).
Diagnosis -Male.All dorsal plates widely separated; FS inverse isosceles trapezoid approximately; posterior edge of D 2 close to posterior edge of FS; middle margin of ACG with two rows of densely feathered setae; C 2 both rounded under optical microscope and SEM; trapezoidal PS with indentation at the frontal margin, GF touching third pair of acetabula, Gp extending to frontal margin of third acetabula; a round CP located anterior to V 3 ; a pair of V 1 separated; P-4 terminal with a seta-liked protrusion; I-L-3 bearing two strong dorsal peg setae on one side.
Description -Male (n=5).Integument papillae bluntly pointed, interspaces with fine lineation (Figure 2A).In dorsal view: apical angles of Cx-I and Cx-II visible in dorsal view; all dorsal plates widely separated; FS inverse isosceles trapezoid approximately, with median eye, O 2 and five muscle attachments; posterior edge of D 2 close to posterior edge of FS; ACP with a muscle attachment in the middle; PCP with a pair of muscle attachment; all LP with a muscle attachment, LP 1 and 4 triangle, LP 2 and 3 trapezoidal (Figures 3A, 4A).In ventral view: middle margin of ACG with two rows of densely feathered setae (Figure 2B); C 2 both rounded under optical microscope and SEM (Figures 2C, 4B); trapezoidal PS with indentation at the frontal margin (Figure 4B), three pairs of acetabula arranged in two rows and closed (Figure 2D), GF touching third pair of acetabula, Gp relatively long, extending to frontal margin of  third acetabula, a round CP located anterior to V 3 , a pair of V 1 separated (Figures 3B, 4B).In lateral view: except L 1 and L 4 , four sclerotized plates with varying shapes near the body axis and separated from each other (Figures 3C, 4C).In frontal view: A 1 fused with a triangular plate, lateral eyes attached to O 1 platelets (Figures 3D, 4D).In rear view: V 4 separated with LP 4 (Figures 3E, 4E).
Due to a similar genital field structure (especially PS) and the position of the dorsal sclerites we assigned the males from Anhui to T. (L.) feuerborni (K.Viets, 1929).There are some small differences, however, between the specimens from Java and China.The posterior margin of Cx-IV is convex in the male from Java, but straight in the male from Anhui.Moreover, the plate lateral to L 2 is divided in the male from Java, but complete in the male from Anhui.Possibly, larval parasitism on tipulids dipterans allow populations to keep gene flow over wide areas with their aerial drifting hosts (Mitchell 1953).Distribution -Java (K.Viets 1935); Subfamily and Genus are new records for China (this study).
Material examined -Holotype: adult male, Mount Huangshan World Geopark, Anhui Province, P. Etymology -This new species is named after Dr Xu Zhang (P.R. China) in appreciation of providing the specimens and her brilliant contribution on water mites taxonomy.
Diagnosis -All dorsal plates separated; D 2 slightly behind posterior edge of FS; middle margin of ACG with two rows of feathered setae; C 2 rounded under SEM, but with sclerotization beneath integument under optical microscope; PCG widely separated; genital field with three pairs of acetabula, GF extended from the middle of Ac-1 to Ac-3, Gp relatively long, extending to frontal margin of third acetabula; a round CP bigger than V 3 ; EP with sclerotized extension; a pair of V 1 separated; P-4 terminal with a seta-liked protrusion; I-L-3 without two strong dorsal peg setae.Male.PS trapezoidal.Female.PS triangular.Description -Male (n=5).Integument papillae bluntly pointed, interspaces with fine lineation (Figure 9A).In dorsal view: apical angles of Cx-I and Cx-II visible in dorsal view; all dorsal plates separated; FS inverse isosceles trapezoid, with median eye, O 2 and five muscle attachments; D 2 slightly behind posterior edge of FS; ACP with a muscle attachment in the middle; PCP with a pair of muscle attachment; all LP with a muscle attachment, LP 1 and 4 triangle, LP 2 and 3 trapezoidal (Figure 10A).In ventral view: middle margin of ACG with two rows of feathered setae most dense near the base of ACG (Figure 11A-B); C 2 rounded under SEM, but with sclerotization beneath integument under optical microscope (Figures 9B, 10B); PCG widely separated (Figure 10B); genital field with three pairs of acetabula, PS trapezoidal, GF extended from the middle of Ac-1 to Ac-3, Gp relatively long, extending to frontal margin of third acetabula (Figure 10B); a round CP bigger than V 3 ; EP with sclerotized extension; a pair of V 1 separated (Figure 10B).In lateral view: except L 1 and L 4 , four sclerotized plates with varying shapes near the body axis close to each other (Figure 10C).In frontal view: A 1 fused with a triangular plate, lateral eyes attached to O 1 platelets (Figure 10D).In rear view: V 4 close to LP 4 but not fused (Figure 10E).Gnathosomal base long and slender (Figure 9C).Chelicera base relatively long; chela with teeth on one side (Figure 9D).Palp five-segmented (Figure 12A, C); P-1 short, with two feathered setae; P-2 with three dorsal and two lateral feathered setae; P-3 with two dorsal feathered setae; P-4 terminal with three setae and a seta-liked protrusion (Figure 12B, D); venter of P-5 with a mini seta on one side (Figure 12B, D).
Legs robust: I-L-3 without two strong dorsal peg setae.Female (n=3).Similar to the male except larger idiosoma and PS wider (Figures 11C-D    Remarks -Previously, only one species of the subgenus Neothyas was known, i.e.Trichothyas (Neothyas) hygropetrica Lundblad, 1941 from Indonesia (Table 1).Unfortunately, the female T. (N.) hygropetrica was not described by Lundblad (1941).Therefore, only males of the two species are compared here.Trichothyas zhangae sp.nov.from Anhui differs from T. hygropetrica in the following characters:

Discussion
There are quite a number of similarities in some genera of Euthyadinae K. Viets, 1931, especially Almuerzothyas Goldschmidt & Gerecke, 2003, Dacothyas Motas, 1959, Heterothyas Lundblad, 1941, Javathyas K. Viets, 1929, and Trichothyas K. Viets, 1926.These genera have a similar idiosomal plate pattern, palps, gnathosoma and legs.But their relationship is much confused.Cook (1974) discussed the four genera, and called them Trichothyas-like mites.Later on, another similar genus, i.e.Almuerzothyas Goldschmidt & Gerecke, 2003 was described from Costa Rica by Goldschmidt & Gerecke (2003).So far, a total of five genera, five subgenera and 26 species (subspecies) are recorded in Trichothyas-like group (Table 1).When Cook (1974) and Smit (2020) wrote the key to the genera and subgenera of Euthyadinae, Trichothyas was divided into two parts to differentiate from other Trichothyaslike genera.This obvious contradiction inevitably raises doubts about the rationality of the taxonomy.Adults of Almuerzothyas has five important characteristics: (1) idiosomal plates relatively small and widely separated; (2) a single small V 1 (rarely a fused pair) posterior to excretory pore; (3) genital field of males separated into anterior and posterior parts, and with genital flaps reduced to fragments behind Ac-2; (4) CP long and slender; (5) I-L-3 of males bearing two strong dorsal peg-like setae on outer side (Goldschmidt & Gerecke 2003; I.M. Smith & Cook 2009).Adults of Dacothyas has four important characteristics: (1) idiosomal plates adjacent to each other; (2) genital field with four pairs of acetabula; (3) genital field of males separated into anterior and posterior parts and with genital flaps reduced to fragments; (4) first leg of male highly modified, I-L-3 with a large seta (Cook 1974; Oezkan & Bader 1988; Smit 2020).Adults of Heterothyas have four important characteristics: (1) genital field with numerous acetabula; (2) genital field of males separated into anterior and posterior parts and with genital flaps reduced behind second acetabular group; (3) CP much wider than long; (4) I-L-3 of males with two heavy setae (Smit 2020).Adults of Javathyas has two important characteristics: (1) genital field of males separated into anterior and posterior parts, and with genital flaps reduced to fragments; (2) first leg of male highly modified, I-L-3 with a large seta (K.Viets 1935; Cook 1967, 1974; Smit 2009, 2020; Gerecke 2020).
However, these characteristics (the space between the idiosomal plates, the number of acetabula, the shape of CP, and the modification of male first leg) can also be found in Trichothyas.Therefore, the above characteristics are more like the result of independent species evolution, rather than the differences to distinguish the genera these species presented from Trichothyas.
On the other hand, all males of the four Trichothyas-like genera have a divided genital field, but only Trichothyas has a slight indication of separation.This characteristic indicates that Trichothyas-like genera seem to have a completed independent evolution.In summary, there may be three possibilities for the taxonomy of this enigmatic group: (1) four Trichothyas-like genera belong to Trichothyas; or: (2) four Trichothyas-like genera merge into an independent genus as a sister group of Trichothyas; or: (3) Trichothyas is a paraphyletic group, and its subgenera should be independent genera.Traditional morphological research is clearly no longer sufficient, and molecular data should be utilized as soon as possible to solve this problem.

Table 1
List of global Trichothyas-like species.