New records of water mites from Southeast Asia (Acari: Hydrachnidia) with the description of two new genera and 12 new species

Twenty-one species of water mites (Acari, Hydrachnidia) were collected in 2015 during a hydrobiological survey conducted by Burkhard Scharf in Vietnam, Laos and Cambodia. Twelve taxa new to science are described, representing the families Torrenticolidae (Torrenticola laosensis n. sp.), Limnesiidae (Limnesia scharfi n. sp.), Hygrobatidae (Vietnobates oryzae n. gen., n. sp.), Pionidae (Schwoerbelia pioniformis n. gen., n. sp., Forelia gereckei n. sp.), Aturidae (Hexaxonopsis laosensis n. sp., H. cambodiensis n. sp., H. angkoriensis n. sp., Javalbia vietnamica n. sp., Sinaxonopsis laosensis n. sp.), Athienemanniidae (Africasia purpurea n. sp.) and Arrenuridae (Arrenurus contortus n. sp.).


INTRODUCTION
In April and May 2015, Burkhard Scharf (Bremen, Germany) conducted a hydrobiological survey in Vietnam, Laos and Cambodia. This paper aims to present the complete acarological results of his survey and to enlarge our knowledge of the water mite presence and distribution in SE Asia. Over the last years significant effort was done to explore water mites of Vietnam and up to now, 16 species of water mites are reported (see Table 1 and reference therein). On the other hand, the water mite fauna of Laos was known from two species of Hygrobates salamandrarum-group (H. ancistrophorus Goldschmidt & Koehler, 2007 and H. forcipifer Goldschmidt & Koehler, 2007), one species each of the genera Piona (P. allodadayi Jin, 1997) and Neumania (N. dolichotricha Jin, 1997). Finally, two species are known of the speciose genus Arrenurus: Arrenu-rus bicornicodulus Piersig, 1906 and A. corpuscularis Jin & Wiles, 1996. Up to now, no water mites are reported from Cambodia.
In this paper, descriptions of twelve new species and two genera new for science are given.
Remarks -The single female from Vietnam resembles superficially specimens tentatively included in the so-called M. macroporus (K. Viets, 1935)-complex (see , Pešić and Smit 2009, 2014b. This group includes several similar species known from SE Asia, i.e., M. angulatus (Walter, 1928) (India), M. macroporus (K. Viets, 1935) (Sumatra, Java, Borneo), M. major (K. Viets, 1935) (Java), M. longiventris (Viets, 1939) (Java, Borneo), M. tranversalis (Lundblad, 1941) (Myanmar), M. nondescripta (Cook, 1966) (India), M. minor Wiles, 1991 (Malaysia) and M. epiales Pešić & Smit, 2014b (Borneo). The specimen from our study differs in less narrower gnathosomal bay and somewhat shorter P-4 (L P-4/P-3 ratio ≈ 1.2). In this character state, it agrees with M. minor Wiles, 1991 from Malaysia, a species differing in minor idiosoma and palp dimensions and four dorsoglandularia on the dorsal plate . Understanding the taxonomic position of the species of this complex species is not possible without the application of molecular techniques (Pešić and Smit 2014b), so introducing a new species on basis of a female will create more confusion given the present state of knowledge of this species.
Diagnosis -(Female unknown). Medial margin of Cx-II/III relatively short; P-4 stout with a strong dorsomedial peg-like seta, located away from the distal edge.
Description -Male: Idiosoma roundish; shoulder platelet elongated (shoulder/frontal platelets L ratio 2.1-2.3); frontal platelet broad (L/W ratio 0.85 -0.9); Cxgl-4 located far anteriorly, near tips of Cx-I; gnathosomal bay deep, U-shaped; medial margin of Cx-II/III relatively short; suture line of Cx-IV distinct, originating from lateral edge of genital field and extending posteriorly beyond posterior margin of genital field; genital field subrectangular, anteriorly enlarged and triangular; ejaculatory complex with small proximal chamber, carina anterior long; gnathosoma compact, rostrum truncated (Figure 2F); P-2 longer than P-4; distal margin of P-3 and P-4 medially and laterally with several pointed extensions; P-4 stout with a strong dorsomedial peglike seta, located away from the distal edge, ventral setae slender and short, not reaching the tip of P-5 ( Figures 2C-D Etymology -Named after the country where the new species was found. Remarks -The new species is characterized by the strong dorsomedial peg-like seta, located away from the distal edge of P-4. Due to the latter character, Monatractides laosensis n. sp. resembles M. (M.) koenikei (K. Viets, 1916), a species known from West Africa. The latter species can be distinguished in having three pairs of knob-like protrusions at the lateral margins of the moderately deep gnathosomal bay, a longer medial suture line of Cx-II+III and somewhat stouter palp segments, especially P-4 (see Pešić and Smit 2014a).
Distribution -Laos; known only from the locus typicus ( Figure 25A). Diagnosis -Genital field with 2-3 small setae between Ac-1 and Ac-2; separation between Ac-1 and Ac-2 smaller than half the diameter of Ac-2; IV-L-6 with two thick ventral setae.
Gnathosoma with long dorsodistal projections ( Figure 3E); P-2 ventral margin with a rounded distal protrusion, bearing a spine-like seta, not on a basal tubercle; P-4 slender, in anterior half ventrally with two setae (proximal seta shorter than distal one), each associated with a very small tubercle, and more distally one small seta ( Figures 3C-D).
Etymology -Named after Prof. Burkhard Scharf (Bremen, Germany), the collector of the mites described in this paper.
Remarks -The new species is similar to Limnesia vietnamensis Tuzovskij, 2013, described by Tuzovskij (2013a) on the basis of one female and one deutonymph from Vietnam. Both species have P-2 with a ventrodistal protrusion with a peg-like seta and a dorsum with the small posterior transverse platelet. Female L. vietnamensis differs from the new species in 1) separation between Ac-1 and Ac-2 considerably larger than half of diameter Ac-2, 2) peglike seta of P-2 longer and more slender, and (3) IV-L-6 with four short thick ventral setae (Tuzovskij 2013).

Limnesia (Limnesia) cf. rimiformis
Gnathosoma with slightly convex ventral margin and a long dorsodistal projections ( Figure 5E); P-2 ventral margin slightly bulging, peg-like seta not on a tubercle, inserted in the distal half; P-3 dorsally with three long setae; P-4 in anterior half ventrally with two long setae (proximal seta shorter than distal one), each associated with a tubercle, and more distally one small seta ( Figures 5C-D).
Distribution -A widespread species, known from India to Australia.
Morphology -Male: Integument papillate (Figure 7B). Posteromedial margin of Cx-I broadly rounded. Cx-IV with a distinct nose-like protruding medial margin. Genital plate anterior margin with a small knob-shaped medial projection projecting in a deep indentation, posterior margin deeply indented with a small protrusion in the centre of indentation; acetabula in a triangular arrangement, Ac-2 and Ac-3 on the same level ( Figure 7A). P-2 ventral margin proximally almost straight, distoventrally protruding in a long and slender projection, apically covered by a few small denticles; P-3 distally with 7-8 larger denticles covering more than half of ventral margin (Figures 7E-F); P-4 slender, ventral setae close to each other (separation 22 µm).
Distribution -Previously known only from Thailand, and here reported for the first time for Laos.
Morphology -Female: Integument finely striated. Posteromedial margin of Cx-I slightly concave; Cx-IV subtriangular in shape, with anterior and posterior margins converging to median line. Gonopore very long, genital plates short, restricted to the level of postgenital sclerite, acetabula in triangular position ( Figure 8A). P-2 ventral margin concave, distally protruding in a slightly knob-shaped projection covered by large, scattered denticles; P-3 with a few large and scattered ventral denticles in the distal part (Figures 8E-F); P-4 ventral setae separation 14 µm. Swimming hairs absent.
Remarks -The single female from Vietnam matches the general morphology of Hygrobates sinensis Uchida & Imamura, 1951 from China. However, only a single female was taken, so our record should be considered tentative until males are examined.

Genus Vietnobates n. gen
Diagnosis -Character states of family Hygrobatidae (see Cook 1974). Dorsum and posterior venter without sclerotized muscle attachment plates. Coxae in four groups; Cx-I separated medially. Gnathosoma with a posterior anchoral process extending beyond posterior end of Cx-I+II. Glandular opening on Cx-IV near suture line of Cx-III/IV. Cx-IV posteromedial margin with short posterior projections, apodemes extending anteriorly from these projections not extending to Cxgl-IV. Genital field with three pairs of acetabula. P-2 without a ventral projection and ventral margin without denticles; P-4 lacking a medial sword seta and a dense dorsodistal setation, P-4 ventral setae at the same level, in distal third of segment. I-L-5 at distal end with a pair of thickened, pointed setae, I-L-6 not curved.
Etymology -The genus name is derived from the country of the type locality.
Remarks -The new genus resembles a number of Australiobates-like genera from Australia in the elongated anchoral process, e.g., Australiobates Lundblad, 1941, Coaustraliobates Cook, 1974, Pseudoaustraliobates Smit, 2009. Not any of these genera are known from the Oriental region. The combination of the following characters 1) gnathosoma with a posterior anchoral process exceeding posterior end of Cx-I+II, 2) Cx-IV posteromedial margin with short projections, apodemes extending anteriorly from these projections not extending to Cxgl-4, 3) P-4 ventral setae at the same level, in distal third, medial sword seta absent, and 4) I-L-5 at distal end with a pair of thickened, pointed setae, separates the new genus from all other Australiobateslike mites.
Description -Female: Integument striated; apodemes of Cx-II directed more posteriorly, Cx-IV posteromedial margin with a slightly protruding apodeme. Genital field with acetabula subtriangular in shape, in an obtuse triangle; excretory pore smooth, Vgl-1 separated from Vgl-2. P-2 ventral margin straight, distally forming a right angle, P-3 ventral margin straight or slightly concave; P-4 ventral setae at the same level ( Figures 9B-C). Basal segment of chelicera dorsally with a pointed projection ( Figure 9E). I-L-5 at distal end with a pair of thickened and pointed setae ( Figure 9D); I-L-6 straight; leg claws with a well developed claw blade with dorsal and ventral clawlets ( Figure 9F); III-L-5 with two and IV-L-5 with 3 swimming hairs, IV-L-6 with two long bristles.
Distribution -Vietnam; known from the locus typicus only.
Remarks -In addition to the type species, Unionicola hankoi Szalay, 1927, known from the Palaearctic, the subgenus includes Unionicola crenipalpis Lundblad, 1969 from Burma. The combination of a well developed cone-shaped, projections on ventral margin of P-4 (absent in U. crenipalpis) and one proximomedial serrate seta on P-2 (lacking in U. hankoi), easily separates the single deutonymph from the Mekong delta from all other species of the subgenus Majumderatax. Most probably we are dealing with an undescribed species, but since adults are not available, a final decision can not be made.
Diagnosis -Female (Male unknown): Character states of family Pionidae (see Cook 1974). Dorsum soft. All coxal setae slender, not spatulate; medial margin of Cx-III almost as long as medial margin of Cx-IV, posterior margin of Cx-IV concave, without angular projections. Genital bay very shallow, gonopore very long, genital plates broad and rounded, much smaller than gonopore, with 5 pairs of acetabula. P-3 with a very long lateral seta, P-4 with a peg-like mediodistal seta, ventral setae not associated with tubercles ( Figures 11B-C); gnathosoma with posterior anchoral process. Legs slender, swimming setae present.
Type species -Schwoerbelia pioniformis n. sp. Jürgen Schwoerbel (1930-2002, who described one of the pionid subfamilies. Moreover, he was one of 409 Pešić V. and Smit H. Remarks -Due to the following characters: medial margin of posterior coxal plates formed jointly by Cx-III and Cx-IV, all setae on Cx-II and -III fine, not thickened, gnathosoma ventral margin posteriorly projecting in an anchoral process (in ventral view bifurcate as in Figure 11D), and P-4 with a distoventral peg-like seta, the female of new species resembles to those of genus Piona. However the single female from a stream in Vietnam is unique in P-3 with a very long lateral seta, exceeding the tip of P-5. In all known members of subfamily Pioninae Thor lateral setae on P-3 are short. The new genus resembles Huitfeldtiinae (P-3 with a very long lateral seta) which in addition to Huitfeldtia Thor, 1900 (Holarctic), includes Larri Harvey, 1996 (Australia) and Gereckea Smith & Cook, 2009 (Canada). The new genus differs in slender, not spatulate coxal setae (present in Huitfeldtia), posterior margin concave, without acute-angled apodemes, and a small peg, not a prominent spine-like mediodistal seta on P-4 (see Smith et al. 2015). In most pionid groups, characters (sexual dimorphism on leg segments) important for classification are restricted to males. However the unique features of female from Vietnam are large enough to warrant the erection of the new genus. Schwoerbelia pioniformis n. sp. (Figure 11)
Diagnosis -(Male unknown). Anterior margin of idiosoma medially concave; genital plates with 13-16 pairs of acetabula; ventral margin of P-4 without setal tubercles, with setae located close to each and a blunt, peg-like mediodistal setal; leg claw and clawlet blunt.
Etymology -Named after Reinhard Gerecke (Tübingen) in appreciation of his studies of water mites.
Remarks -Due to the similar morphology of the dorsum (three pairs of platelets), genital plates (medial margin extended anteriorly) and palp (P-4 without setal tubercles) the specimens from Laos resemble Forelia flexipoda Jin, 1995 from Guizhou, China. The latter species differs in larger dimensions of idiosoma and palps, medially projecting anterior margin of idiosoma, a very small mediodistal peg-like seta of P-4, claws of I-L pointed (Jin 1999: figure 9) and in the increased number of acetabula (26-27 pairs, from Jin 1995).
Diagnosis -Dorsal shield colour pattern consisting of a light-reddish elongated central patch; lateral margins posterior to IV-L insertions with developed triangular projection on each side of ventral shield.
Description -Dorsal and ventral shields anteriorly lightly fused; dorsal shield with seven pairs of glandularia (the seventh pair inconspicuous, flanking the excretory pore); postocularia well distanced from anterior margin; excretory pore projecting, located at the posterior end of dorsal shield; anterior portion of dorsal shield with 14-15 pairs of triangular, posteriorly-directed (hyaline?) denticles (Figures 13A,14A); dorsal shield colour as shown in Figures 15A-B; eye pigment well developed. Ventral shield oval, slightly truncate at anterior end, lateral margins rounded, with well developed triangular projection on each side ( Figures 13B,14B), posterior to the insertions of IV-L. Lateral margins of Cx-I/II with 1-3 strong, hook-like, posteriorly-directed projections; two pairs of glandularia in region between genital field and opening for insertion of IV-L, these relatively close together; a relatively long longitudinal ridge posterior to IV-L insertions. Genital field with three pairs of Ac, arranged in an arc. Palp: ventral margin of P-2 convex, distal margin of P-3 with well developed hyaline extensions, ventral margin of P-4 convexly protruding in the centre, here with two seta (one long and heavy, another long and slender) on small elevated ridges ( Figures  13C-D,14C). Legs: number of swimming setae: II-L-4, 1; II-L-5, 2-3; III-L-4, 2; III-L-5, 2-3; IV-L-4, 2; IV-L-5, 3. Female: Gonopore relatively large ( Figure  14B).
Remarks -Due to the presence of posteriorlydirected denticles on the dorsal shield, a long longitudinal ridge posterior to IV-L insertions, and lateral projections on the sides of the ventral shield, the new species most closely resembles to Hexaxonopsis rucira (Cook, 1967), from India. The latter species differs in having smaller and bluntly pointed projections on the lateral margins of the ventral shield and a more or less uniform blue colour of dorsum (Cook 1967).

Measurements
Remarks -The combination of posteriorly directed denticles on the dorsal shield, a short longitudinal ridge posterior to IV-L insertions, and absence of the lateral projections on the sides of the ventral shield, makes the new species most similar to Hexaxonopsis paxillatus (Uchida & Imamura, 1951), a species described by Uchida and Imamura (1951) from central China. The latter species can be separated in different arrangement of dorsal glandularia and the two pairs of glandularia located between genital field and insertions of the IV-L are more closely approached to each other. In the original description Uchida and Imamura (1951) did not mention the colour pattern. Moreover, at the illustrated figure of gnathosoma of A. paxillatus enlarged posterior setae which are so characteristic of the present new species are completely missing (see Uchida and Imamura 1951, figure 8d).
Distribution -Cambodia; known only from the locus typicus ( Figure 25D).  six pairs of small glandularia (the sixth pair inconspicuous, flanking the excretory pore); postocularia well distanced from anterior margin; excretory pore projecting, located at the posterior end of dorsal shield ( Figure 18A); dorsal shield colour indistinct ( Figure 18E); eye pigment well developed. Ventral shield oval, slightly truncate at anterior end, lateral margins with well developed triangular projection on each side ( Figure 18B) posterior to IV-L insertions. Lateral margins of Cx-I/II with several, blunt and posteriorly-directed projections; two pairs of glandularia (posterior one visible as a pair of distinct pores and could be interpreted as the remnants of a second pair of glandularia) located between insertions of the IV-L and genital field. Genital field with three pairs of Ac, arranged in an arc. Palp: ventral margin of P-2 convex, distal margin of P-3 with well developed hyaline extensions, middle of ventral side of P-4 expanded, bearing relatively long and heavy seta ( Figure 18C-D). Legs: numbers of swimming setae: II-L-5, 2; III-L-4, 2; III-L-5, 3; IV-L-4, 2; IV-L-5, 3.
Etymology -Named after the country where the new species was collected.
Remarks -The new species resembles Hexaxonopsis bharatensis Cook, 1967 from India, due to the absence of a longitudinal ridge posterior to IV-L insertions, the lack of posteriorly-directed denticles on the dorsal shield and the similar morphology of palp. The latter species can be distinguished from A. angkoriensis n. sp. by the lacking projections on the lateral margin of the ventral shield, the sharppointed hook-like extensions of the coxae and the characteristic colour pattern of the dorsum consisting of a central elongated blue patch (Cook 1967).
Diagnosis -Anterior lateroglandularia fused with dorsal shield; postocularia lying much closer and at the same level of glandularia pair; genital field with four pairs of acetabula; I-L-6 distally strongly tapering.
Description -Male: Idiosoma egg-shaped. Posterior margin of the dorsal shield forming an indistinct cauda. Dorsal shield flanked by three pairs of lateroglandularia in posterior half of the dorsal furrow, anterior lateroglandularia fused with dorsal shield ( Figure 19A): postocularia at the same level of glandularia pair; A2 fused with dorsal shield. Genital field with four pairs of acetabula ( Figure  19B). Genital field fused with ventral shield, suture lines indistinct. Palp slender, P-2 ventral margin straight, P-3 ventral margin concave, P-4 with convex dorsal and almost straight ventral margins bearing two fine ventral setae (one of them elongated) . Glandularia (Vgl-4) flanking genital field on enlarged platelets in posterolateral indentations of the ventral shield. Excretory pore on a transverse oval platelet immediately posterior to genital field. Legs: I-L-6 distally strongly tapering; swimming setae absent.
Remarks -Due to the presence of four pairs of acetabula the new Javalbia species from Vietnam should be assigned to the subgenus Javalbicula K.O. Viets, 1974. This subgenus includes three species, i.e. J. lata K. O. Viets & Böttger, 1974 (South Africa), J. turcica Esen, Pešić & Erman, 2011 (Turkey) and J. ovata Kim & Chung, 1996 (Korea). Recently, Smit (2016) proposes to synonymize Javalbicula with Javalbiopsis Cook, and to transfer the two four-acetabulate species having the excretory pore on a separate platelet (i.e., J. ovata and J. siamis Smit, 2016) to Javalbia s.s. The new species from this study can be separated from J. ovata in I-L-6 distally strongly tapering (equally narrowed in J. ovata, see Kim and Chung 1996). Javalbia siamis from Thailand differs from the species from our study in freelying anterolateral dorsal glandularia and the postocularia distanced and posteromedially from the nearest pair of dorsal glandularia (Smit 2016).
Distribution -Vietnam; known only from the locus typicus.
Description -Male: Idiosoma colourless; dorsal and ventral shield present; dorsal shield formed by a large posterior plate bearing six pairs of glandularia (Dgl-2-4, and Lgl-2-4) and one pair of anterior platelets bearing the lateral eyes, postocularia, A2 and Dgl-1 ( Figure 20A); excretory pore projecting, located at the posterior end of dorsal shield; dorsal shield colour indistinct, eye pigment well developed. Ventral shield ( Figure 20B) oval, slightly truncate at anterior end; tips of Cx-I not extending beyond frontal margin. Cx-IV with distinct medial, posterior and lateral suture lines, medial suture line straight, suture line Cx-III/IV developed only laterally, ending medial to IV-L insertions and not reaching the medial line; genital field triangular, gonopore elongated, acetabula numerous (approximately 30 pairs of acetabula, but due to rugosity of idiosoma some of these not visible in ventral view) and extend in parallel to the coxal plate margin as indistinct strips from the gonopore to the posterolateral idiosoma edge.
Legs: ventral margin of I-L-6 and II-L-6 with small denticles and a dense hair-like setae ( Figures  21A-B); III-L-4 with dorsal and ventral margins diverging from base to tip, distal margin bearing two sword setae and two strong simple setae; III-L-5 slightly curved, distally with one strong sword seta, slightly set off from distal margin, and several slender simple setae; III-L-6 not bearing modified setae, claws modified and heteromorphic as illustrated in Figure 21C (inset); IV-L-4 with dorsal and ventral margins diverging from base to tip, in the enlarged distal half a group of strong, variously modified setae, one strong bifurcated ( Figure 21D, arrow), two strong sword setae, and two simple slender setae; IV-L-5 ventral margin almost straight, distally not remarkably thicker distally than proximally, distally in addition to one strong sword seta, slightly set off from distal margin, one pennate and two slender simple setae; IV-L-6 slightly curved, anteriorly slightly enlarged, posteriorly with three strong, laterally flattened setae; claws of I-III legs with a dorsal and ventral clawlets ( Figure 21A inset).
Recently, Smit (2016) described, based on a single female, the second species Sinaxonopsis siamicus from Thailand, a species clearly differing in Lgl-2 not on large posterior dorsal shield, a different configuration of Dgl-1 and A2 and comparatively more stouter palp.

Family
Diagnosis -(Male unknown). Dorsal colour pattern consisting of anterior and two posterolateral deep purple patches; Cx-IV with a short longitudinal ridge posterior to IV-L insertions; IV-L-4/5 each with one strong distal pennate seta.
Etymology -The name refers to the characteristic colour of the new species.
Remarks -The characteristic colour pattern on the dorsal shield easily separates the new species from all other members of the genus. Other diagnostic features of the new species include Cx-IV with lateral ridges posterior to IV-L insertion, and the presence of one strong pennate seta on IV-L-4/5 each.
Distribution -Laos; only known from the locus typicus ( Figure 25A). Diagnosis -Petiole consisting of hyaline appendages; posterior dorsal margin with a pair of double-lobed hyaline membranes; genital plates reversed wing-shaped, broadening laterally; gonopore very narrow.
Etymology -Named for the complicated structure of the appendages.
Remarks -The shape of the genital plates is very unusual, and thus far found in the subgenus Rhinophoracarus Viets, 1916 and in a small number of other subgenera. However, members of Rhinophoracarus have a very long petiole, very unlike the hyaline petiole of the new species. Due to the presence of a hyaline petiole and hyaline appendages assignment to Micruracarus seems most appropriate.