New species of water mites from Oman, with some zoogeographical notes (Acari: Hydrachnidia)

The paper deals with a collection of epigean water mites from Oman. One new genus, Omanaxonopsis, and 16 new species are described: Bharatavolzia arabica, Nilotonia bisetosa, N. longiseta, Torrenticola arabica, T. omanensis, Limnesia kochi, Protolimnesia inexspectata, Atractides arabicus, A. omanensis, Neumania indentata, Axonopsis arabica, A. balneatoris, A. omanensis, Omanaxonopsis arabica, Arrenurus dugesi and Arrenurus rectituberculatus. The zoogeographical position of Oman is discussed briefly.


INTRODUCTION
Oman, lying in the northeastern part of the Arabian peninsula, occupies an interesting position between three faunal regions, i.e. the Ethiopian (or Afrotropical), Palaearctic and Oriental realms.In the north of Oman the Al-Hajar mountains are rising to 3,000 m.In the south we find the Dhofar mountains, which continue into Yemen.In between these two mountain ranges there is a large stretch of barren desert, which acts as a zoogeographical barrier.Wallace (1876) included Oman in the Ethiopian faunal region.More recent studies show that the northern part has more affinities with the Oriental realm, and the south with the Ethiopian (or Afrotropical) realm.Brown and Gallagher (1985) studies freshwater snails of Oman, and divided these snails in three groups: Afro-Asian, African and Asian.Gerecke (2004) studied a small collection of water mites collected in groundwater of Oman.He found two genera with an Oriental distribution.One species, Tiramideopsis expansipes Cook, 1967, was found in northern Oman.From the other genus, Bharatohydracarus Cook, one species was collected in northern Oman and one in southern Oman.Interestingly, Gerecke (2004) concluded that these two species represent two phylogenetic lines.Roselaar (2006), based on a study of passerine birds, concluded that the northern part of Oman is part of the Oriental region, while the southern part belongs to the Ethiopian region.However, in land snails no relations could be found with the Oriental realm (Mordan, 1980), and also Larsen (1984), based on a study of butterflies (Lepidoptera), came to the conclusion that the influence of the Oriental region in northern Oman is small.Three papers have been published on the water mites of Oman.Smit (2003) and Gerecke (2004) dealt with hyporheic fauna exclusively.The present study is the result of a collection trip in 2008 by the senior author.Only water mites from surface waters were collected.A first paper of the material collected during this trip has been published by Pesić et al. (2009).

Male -Unknown.
Etymology -Named after the Arabian Peninsula.
Remarks -This is the fourth known species of the genus Bharatavolzia, two species are known from India (Cook, 1967), while one species is known from Iran (Schwoerbel and Sepasgosarian, 1980).Cook (1967) erected the subgenus Bharatavolziella for species without eye capsules.The new species differs from the two other known species of this subgenus in the slender gnathosoma and the presence of two heavy setae on P-4 instead of one or none.Moreover, compared to the Indian B. pallida Cook the new species has a larger anterior extension of the anteromedial dorsal plate, and compared to B. cooki Schwoerbel and Sepasgosarian from Iran the large anterolateral plate is less slender.The large posterolateral platelet of the new species is much longer than the smaller platelet posterior to it, but in B. cooki these platelets are much less different in size.

Male -Unknown.
Deutonymph -The nymphs collected together with the adults are provisionally assigned to the new species, IV-Leg-6 of the nymph has only one long seta.P-2 is ventrally without a seta, but the many denticles are present.
Etymology -Named for the two long setae of IV-Leg-6.
Remarks -The subgenus Dartonia has IV-Leg-6 with more than one heavy distal setae, but is also characterized by P-2 with more than eight setae and the claw of III-Leg has heavy clawlets, leading to a bidentate or tridentate appearance (Panesar, 2004).The latter two characters are absent in the new species, and therefore it is placed in the subgenus Dartiella.No other species of this subgenus has a IV-Leg-6 with two distal long setae.
Etymology -Named after the long setae on the dorsum.
Remarks -The combination of long setae of D2 and D3, the typical shape of the female pregenital sclerite and a large dorsal plate separates this species from other Nilotonia species.
Remarks -Due to a ventral projection on P-2 which curves distally, one (of 4) P-4 ventral setae long, capitulum with a long rostrum, similarly shaped ejaculatory complex and Cx-IV posteriorly extended well beyond genital field in both sexes, Torrenticola arabica n. sp., closely resembles T. semisuta (Halík, 1930), a species widespread from the Indian Himalayas to Malaysia (Wiles, 1997b;Pesić et al., 2007;Pesić and Smit, 2009).Torrenticola semisuta (for an analysis of diagnostic characters of this species see Pesić and Smit, 2009) can be distinguished from T. arabica n. sp., in the following features: Cxgl-4 located sub-apically (apically in T. arabica n. sp.), male genital field more elongated (L/W 1.23-1.25;1.05-1.13 in T. arabica n. sp.), the excretory pore and Vgl-2 slightly shifted from the line of primary sclerotization in both sexes, and the shortened male postgenital area (18.8-22% of the total idiosoma L; in T. arabica n. sp.28-29%).
Etymology -The species is named for its occurrence in Arabian Peninsula.Diagnosis -Males (female unknown).Cx-IV extended strongly posterior to genital field; P-2 long (L ratio P-2/P-4 2.5) and with strong ventral denticles distally to slightly pronounced ventral projection, P-3 with serrulate margin distally from small pointed ventral projection; capitulum with a very long rostrum; cheliceral claw relatively short (basal segment/claw ratio 12.0).
Remarks.The new species can be distinguished from other members of the subgenus Megapalpis Halbert, 1944 in the combination of the characteristic shape of the palp (P-2 very long and with ventral denticles distally to slightly pronounced ventral projection, P-3 with serrulate margin distally from small pointed ventral projection), capitulum with very long rostrum, a relatively short cheliceral claw (basal segment/claw ratio 12.0) and Cx-IV greatly extended posterior to genital field.
Remarks -The location of the Glandulae Limnesiae is unusual within the genus.Its normal location is medial of the suture line of the Cx-III and Cx-IV.Moreover, the location of the setal tubercle of P-2 is also unusual, as it is normally located in the middle of the segment.Other material -1/0/0 (1/0/0 mounted), India, Uttaranchal, Garhwal Himalayas, Dhundeshwargad stream, a tributary of Alaknanda River, viii-2006 leg.Kumar.

Limnesia (Tetralimnesia) pinguipalpis Cook, 1967
Remarks -The specimens from Oman fit the description of Limnesia pinguipalpis, described from the Oriental part of India (Maharashtra, Karnataka, Tamil Nadu -Cook, 1967).The only non-Oriental record from India comes from Garhwal Himalayas (see above).Limnesia pinguipalpis is similar to L. monodi but differs in the more extensive secondary sclerotization associated with the posterior end of the male genital field (Fig. 10B), and the ventral margin of P-2 more or less straight (Fig. 10C, 10E) vs. convexly protruding in L. monodi (see Fig. 10D).
Diagnosis -Integument with with papillae arranged in a reticulated pattern; IV-Leg-6 with a heavy terminal seta, P-4 with six small setal tubercles, claws of legs with a few small teeth.
Etymology -Named for its unexpected finding.
Discussion -The water mite subfamily Protolimnesiinae appeared to have thus far a New World distribution (Goldschmidt 2004), and its occurrence in Oman is therefeore unexpected.The similarity of the new species with previously described species of the genus is striking.This applies especially to the shape of the palp and venter.The new species from Oman is close to some South  and Central American species of the subgenus Protolimnesia with genital field reaching or surpassing the caudal margin of Cx-IV, rounded and mediumsized acetabula, and distance between the acetabula approximately equal in males, e.g.P. oculata Goldschmidt, P. setifera Cook and P. pampaensis Smit (see Goldschmidt, 2004), but differs in the indented third+ fourth coxae, the stronger terminal seta of IV-Leg-6 and reticulate pattern of the integument.

Description
General features -Dorsal integument: striated; muscle attachment plates smooth.Coxal field: mediocaudal margin of Cx-I+II with a large, slightly indented area between the laterally directed apodemes of Cx-II.Genital field: Ac in a weakly curved line.Palp: weak sexual dimorphism, P-2 ventral margin slightly convex, P-3 straight, P-4 sword seta near distal hair.I-Leg: I-Leg-5 with S-1 and -2 strongly heteromorphic and distanced, ventral seta close to insertion of S-1, curved, with blunt tip, S-2 with strongly developed dorsal projection, bluntly pointed, I-Leg-6 long and slender, only slightly narrowed from the base to the tip.
Remarks -Atractides arabicus n. sp. is unique within the genus due to the particular shape of S-2 (with a well developed dent on the outer margin of seta).In addition, the male is characterized by the anterior margin of genital field concavely indented, with rather small Ac-3 distanced from the two anterior acetabula on each side.Etymology -The species is named for its occurrence on the Arabian peninsula.

Description
General features -Dorsal integument: striated; muscle attachment plates: sexual dimorphism in the dorsal area.Genital field: Ac in triangular arrangement.Palp: weak sexual dimorphism, P-3 ventral margin with one seta, P-4 sword seta enlarged, inserted on level of the distoventral hair, P-5 without cheeks.I-Leg: setae S-1 and -2 inserted on the same level, distally truncate; leg claws with dorsal clawlet.
Remarks -Due to the presence of dorsal shield and the ventral surface covered by an extended shield including coxae, Vgl-3 and -4, excretory pore and genital field in the male, and gnathosoma with elongated rostrum, the new species is similar to Atractides yukii Cook, 1967 (India).From the latter it can be distinguished in the following features: gnathosomal rostrum more slender and pointed, P-3 ventral margins with one seta, sword seta on P-4 enlarged, not hair-like, setae S-1 and -2 inserted on the same level and presence of dorsal leg clawlets.
Etymology -Named for the indented sixth segment of the fourth leg of the male.
Remarks -The shape and chaetotaxy of the fourth leg is not found in any other Neumania species.The female is not characteristic, and very likely not separable from related species (e.g.N. ambigua Piersig).
Diagnosis -Colour pattern consisting of a light yellowish central area; dorsal shield with an weakly defined ridge on each side extending anterolaterally to the region of the anterior muscle scars; second, third and fourth legs with swimming setae (III-Leg-5 with 4 swimming setae; IV-Leg-5 with 3 swimming setae).
Etymology -The species is named for its occurrence in Oman.
Remarks -Due to the presence of two pairs of glandularia lying between the genital field and insertions of the fourth legs and similar shape of the palp, Axonopsis omanensis n. sp.resembles A. guadaramensis Valdecasas, 1981, a species described originally from Sierra de Guadarrama (Central Spain, Valdecasas 1981), and later recorded from Greece (Pesić and Gerecke, 2003).The new species resembles specimens from Greece also in the presence and distribution of swimming setae on the legs.However in A. guadaramensis, according to Valdecasas (1981), all legs are without swimming setae.Most probably, the specimens from Greece therefore represent a species new to science.
The new species from Oman differs from specimens from Greece in its characteristic colour pattern (compare Figs. 28A and B) and the ridge on each side of the dorsal shield in the region of the anterior muscle scars being less prominent (this ridge more prominent in the specimens from Greece).A further difference is found in the well delineated suture line visible between genital field and ventral shield in the male specimen from Greece.
(Figures 22A-E Diagnosis -Two pairs of glandularia lying between the genital field and insertions of the fourth legs, the posterior pair closely approaching the genital field in the male; P-4 club-shaped, with a pair of hair like setae on its ventral margin; relatively large gonopore in female; II-leg-5 with two swimming setae, III-Leg-5 with two swimming setae, IV-Leg-5 with three swimming setae.
Male -similar to female, except in shape of the genital field (Fig. 23A); dorsal shield L 372, W 309; ventral shield L 372, W 378; capitular bay L 111; the posterior pair of glandularia lying between the genital field and insertions of the fourth legs closely approaching the genital field; width between most lateral pair of acetabula 112; gonopore W 23; palp (Fig. 23B): total L 214, dL and %L (in parentheses): P-1, 36 (16.8);P-2, 49 (22.9);P-3, 28 (13.1);P-4, 78 (36.4);P-5, 23 (10.7);L P-2/P-4 ratio 0.63.Legs: L of I- 32,57,67,63;66,63,75,88,78; number of swimming setae of the legs as in the female.Remarks -Due to the presence of two pairs of glandularia lying between the genital field and insertions of the fourth legs and swimming setae on the second, third and fourth legs, Axonopsis arabica n. sp., resembles A. omanensis n. sp.from which it can be distinguished in the following features: P-4 club-shaped, not distally tapering, presence of a hair-like, not heavy seta on the ventral side of P-4, female gonopore relatively large and the posterior pair of glandularia lying between the genital field and insertions of the fourth legs shifted closely to the genital field in the male.
Etymology -The species is named for its occurrence in Arabian Peninsula.Diagnosis -Idiosoma slender (L/W about 1.5 in both sexes) with subparallel lateral margins; IV-Leg-6 strongly inflated distally (L/H 2.7-2.8), with concave dorsal margin in its proximal part.
Etymology -balneator (lat.)= 'Bader'.Named after Dr Carl Bader who made the first contribution to the knowledge of the water mite fauna of the Arabian peninsula.
Remarks -The new species resembles Axonopsis vietsi Motaş and Tanasachi, 1947, a hyporheobiontic species known from the Central Europe and the Mediterranean area (Pesić and Gerecke, 2003).Axonopsis balneatoris n. sp., can be distinguished from A. vietsi by the more slender idiosoma with subparallel lateral margins.A further difference is found in the shape of IV-Leg-6 which is less elevated distally and with a straight dorsal margin in A. vietsi (Gerecke pers. comm.).Distribution -Oman.

Omanaxonopsis gen. nov.
Diagnosis -Characters of the Aturidae and the subfamily Axonopsinae.Dorsal and ventral shields anteriorly fused; dorsal shield with four pairs of glandularia and a pair of postocularia; no ridge on each side extending anteriorly from area of insertion of fourth coxae; lateral margins of ventral shield with an irregular truncate projection on each side located considerably posterior to the insertions of the fourth leg; one pair of glandularia lying between the genital field and insertions of the fourth legs; genital field with 5-6 pairs of acetabula, acetabular plates fused with the ventral shield; leg claws with dorsal and ventral clawlets.
Remarks -The new genus appears to be close to Axonopsis Piersig, but differs from it in the genital field with 5-6 pairs of acetabula, lateral margins of ventral shield with an irregular truncate projection on each side and leg claws with dorsal and ventral clawlets.

Male -Unknown.
Etymology -Named for its occurrence on the Arabian peninsula.Diagnosis -Male: cauda short; pygal lobes distinct; hyaline membrane with pointed angles; petiole rounded posteriorly; ligulate process of petiole rounded, lying well distanced from posterior margin of petiole.Female: Genital plates short, tapering laterally, sloping towards posterolateral idiosoma margin.
Remarks -Two Arrenurus species having also a petiole with a row of ventral teeth differ as follows: A. glenifferensis Lundblad, 1941 from southern Africa has a long cauda and a triangular ligulate process, A. denticulatus Motaş, 1927 from the Western Palaearctic has also a long cauda and a more angular-shaped petiole and ligulate process.The assignment of the female is uncertain, as two types of the females were collected on the type locality.
The most common of these have been assigned to the new species, the less common to A. ortali Smit (see below).Moreover, the females here assigned to A. ortali Smit share with males of the same number and arrangement of medial setae on P-2.

Description
Male -Described in Smit et al. (2000).The male from Oman is slightly larger than the types (given in parentheses): Idiosoma 1089 (1038-1057) long and 664 (660-669) wide.Following the original description the petiole should have grooves, but in fact these are short, stiff curved setae.
Remarks -The female was not known before (but see note at the preceding species).Previously known from the Sinai (Israel, nowadays Egypt) and the Negev (Israel) (Smit et al. 2000).Diagnosis -Male with a large rectangular hump near posterior margin, between pygal lobes; dorsal furrow very short.Female with laterally widened genital plates.
Etymology -Named after the rectangular posterodorsal hump of the male.Remarks -The very short dorsal furrow of the male, resulting in the almost absence of a dorsal shield, is quite unusual.Complete absence of a dorsal shield is also found within the genus Thorophoracarus Viets.Cook (1974) postulated the hypotheses that Thorophoracarus has arisen several times from divergent Arrenurus stock.The male of the new species, with hardly a dorsal furrow, could support this hypotheses.The female shares some characters with other Brevicaudaturus species, like the long bowed genital plates and the shape of the posterior idiosoma margin.It is most close to A. moorei Green, 1974 from Cameroon, an insufficiently described species, only known from the female sex.The female of the new species differs from A. moorei in the laterally widened and shorter genital plates (not widened and longer in A. moorei).

ZOOGEOGRAPHICAL NOTES
With the results presented we can conclude that the water mite fauna of the Arabian peninsula is incompletely known.Of the 23 species reported in this paper, only 7 were known to science (30%), the remaining species are new to science.Nevertheless, a few conclusions can be drawn.In the northern part of Oman (locations north of 23°N), some typical Oriental genera were found.The genera Bharatvolzia and Tiramideopsis are only known from the Oriental region (including the south of Iran).
Bharatohydracarus was thus far only known from the Oriental region.Gerecke (2004) found one species of this genus in the north and one in the south, but they represent two distinct evolutionary lines.In the south of Oman (locations south of 16°N) one widespread Afrotropical species, Hygrobates soari, is found.However, this species occurs in northern Oman as well.There are no records of this species from the Oriental region.No typical Ethiopian genera or species were found in southern Oman.Limnesia pinguipalpis is an Oriental species, but it occurs in southern Oman as well.The record of the Protolimnesia species from southern Oman is very unusual, as all members known of the genus thus far were recorded from the southern United States to South America.