Onchodellus masani Ahadiyat, Ghasemi Moghadam & Abutaleb Kermani, 2020

Ahadiyat, Ali, Moghadam, Sahebeh Ghasemi, Kermani, Reyhaneh Abutaleb & Harchi, Omid Jo-, 2020, Review of the Iranian species of Pachylaelapidae, with description of a new species of Onchodellus (Acari: Mesostigmata), Zootaxa 4778 (1) : -

Onchodellus masani Ahadiyat, Ghasemi Moghadam & Abutaleb Kermani , sp. nov.

Figs 1–11 .

Diagnosis. Dorsal shield medium-sized (length/width ratio: 1.53–1.76), setae smooth and uniform in shape and length. Median section of idiosoma between setae j -J slightly reticulated. Seta J4 slightly longer than J5 (J4 / J5 ratio: 1.20–1.57). Two slit-like pores (gd8, gd9) present on each posterolateral dorsal margin. Sternal shield with delicate polygonal reticulation on the surface. Genitiventral shield approximately as long as wide (length/width ratio: 0.95–1.04), weakly lineate-reticulate. Setae st5 and JV1 equal in size. Anal shield subtriangular and almost smooth, length/width ratio: 0.59–0.63. Peritremes moderately shortened with the anterior ends extending well beyond the anterior margins of coxae II. Soft lateral and opisthogastric integument with 13 pairs of setae, containing five pairs of marginal and eight pairs of opisthogastric setae. Spermathecal tubes long, tenuous, weakly sclerotised. Cheliceral fixed digit with a simple apical hook and two well-developed teeth followed by two minute teeth, and movable digit with two conspicuous teeth and a simple apical hook.

Description. Female (n = 3).

Dorsal idiosoma. Dorsal shield ( Fig. 1 ) medium-sized, 442–490 long, 260–320 wide, oval (length/width ratio: 1.53–1.76), with 30 pairs of setae and 22 pairs of pore-like structures (one pair, gd?, invisible in one specimen). Shield slightly reticulate medially between setae j–J, reticulation between setae j6–J3 a little more distinct. Area anterior to setae j4 smooth, with no reticulation. Lateral dorsal shield with slight and delicate reticulation. Posterior opisthonotal region slightly reticulated. Dorsal setae uniform, smooth, acicular, short, most setae relatively equal in size. Two slit-like gland pores (gd8, gd9) ( Figs 1 , 8 ) on each posterolateral dorsal margin present: the first one with antiaxial position to alignment Z1–Z2, located near Z2, between the setae S3 and S4, and the second one located between the setae S4 and S5. Openings of gd8 slightly closer to the insertions of setae S3 than S4, and gd9 closer to the insertions of setae S4 than S5.

Ventral idiosoma ( Figs 2–3 ). Tritosternum ( Fig. 3 ) with a base, 13–15 long, 12–13 wide proximally, 5–6 wide apically, and a pair of laciniae, 64–66 long. Sternal shield 156–161 long, 77–83 wide (between the mid-level of coxae II), 97–100 wide (at the level of setae st2), with distinct but relatively delicate polygonal reticulation on surface. Two oblique lines arising from the bases of setae st2 to the anterior portion of sternal shield, making an arcshaped structure at the anteromedian section of the shield. A delicately arcuate line approximately connects two setae st2–st2. Sternal shield with four pairs of setae, setae st3 shortest, and three pairs of poroids. Genitiventral shield approximately as long as wide, 162–170 long, 162–178 wide, length/width ratio: 0.95–1.04, only slightly longer than sternal shield (length of sternal shield/length of genitiventral shield: 0.93–0.96), with weak lineate reticulation on surface, very indistinct from the middle to the posterior section of the shield. Setae st5 and JV1 equal in size. A pair of poroids iv5 inserted on the lateral sides of genitiventral shield, 21–29 from setae st5. Anal shield 52–58 long, 87–94 wide, length/width ratio: 0.59–0.63, subtriangular, almost smooth, but with zig-zag sculptural lines on the anterior section. Anal opening subtriangular, 10–13 long, 9–11 wide. Peritremes ( Figs 2 , 10 ) moderately shortened with the anterior ends extending well beyond the anterior margins of coxae II, but not reaching the anterolateral margins of sternal shield. Posterior sections of peritrematal shields with three or four pairs of small pore-like structures, the first two located close to posterior margins of stigmata, the others located on the posterolateral surfaces of peritrematal shields. Soft lateral and opisthogastric integument bearing 13 pairs of smooth setae, comprising five pairs of marginal setae (r-R series), and eight pairs of opisthogastric setae (JV -ZV series) (15–25). Metapodal platelets narrow, 19–22 long, 3–5 wide. Lengths of idiosomal setae and distances between some of them as presented in Tables 1 and 2.

Gnathosoma. Epistome ( Fig. 4 ) with a relatively short and widened neck-like median projection, concave laterally, distinctly serrated apically, anterolateral margins denticulate. Corniculi short, 33–35 long, horn-like, widened basally. Palp 158–165 long, lengths of palp segments: trochanter 47–48, femur 44, genu 34, tibia 36. Chelicera ( Figs 5 , 9 ) with fixed digit with a simple apical hook and two well-developed teeth followed by two minute teeth, and movable digit with a simple apical hook and two conspicuous teeth. Pilus dentilis visible.

Insemination apparatus ( Figs 6 , 10–11 ). Spermathecal tubes 50–60 long, tenuous, weakly sclerotised, opened at the distal end. Basal section associated with posterior section of coxa III, bearing irregular wavy lines almost as long as the spermathecal tube.

Legs. Tarsus II ( Fig. 7 ) with one spur-like distal seta pl1, 17–18 long, extending beyond the tarsal apex.

Male and immature stages. Not found.

Specimens examined. Holotype (AA-20180714-1a): Female, Iran, Yazd Province, Taft County, Shirkuh Rural District , Deh-e Bala Village (31° 36’ 08” N, 54° 07’ 34” E, altitude: 2,482 m a.s.l.), soil of walnut tree, 1 April 2013, leg. Zahra Dehghan. Paratypes: 1 female (AA-20180714-1b), same data as holotype ; 1 female (AA-20180714-1c), Iran, Yazd Province, Meybod, Baharan Park (32° 12’ 52” N, 54° 01’ 28” E, altitude: unmeasured), soil, 10 March 2012, leg. Omid Joharchi.

Etymology. The species is named in honor of Peter Mašán (Institute of Zoology, Slovak Academy of Sciences, Bratislava, Slovakia) for his valuable contributions to the classification of mesostigmatic mites, especially the family Pachylaelapidae .

Differential diagnosis: The short peritreme is a distinct morphological feature for some species of the genus Onchodellus . Eleven other species of Onchodellus bear shortened peritremes, including O. brevicrinitus ( Hirschmann & Krauss, 1965) , O. brevis ( Berlese, 1920b) , O. intermedius ( Moraza & Peña, 2005) , O. islandicus ( Sellnick, 1969) , O. jurassicus ( Schweizer, 1961) , O. michaelcostai Mašán & Halliday, 2014 , O. minutus ( Moraza & Peña, 2005) , O. mixtus Mašán, 2007 , O. parvulus ( Koroleva, 1977a) , O. procerus Mašán, 2007 , and O. volkovae ( Goncharova & Koroleva, 1974) . Since the description of the species presented by Berlese (1920b) was incomplete with no figures, we could not compare the characteristics of O. masani sp. nov. with O. brevis . Also, for O. mixtus , since the female stage was not recognised by Mašán (2007), we were unable to determine the deferences between this species and the new one. Differential diagnosis between female specimens of O. masani sp. nov. with other species are presented herein.

The ratio of J4 / J5 is an important character for separating O. masani sp. nov. (1.20–1.57) from O. brevicrinitus (more than 2.0) based on the illustrations in Hirschmann & Krauss (1965). Also, the anterior end of the peritreme in the female of O. brevicrinitus extends not only beyond the anterior margin of coxa II, but also the level of anterolateral margin of the sternal shield. It does not reach the anterolateral margin of the sternal shield in O. masani sp. nov.. Numbers of teeth in cheliceral fixed and movable digits in O. masani sp. nov. are four and two, while are two and one in O. brevicrinitus , respectively.

The new species can be easily distinguished from O. intermedius by the length of the peritreme, the idiosomal ornamentation and the numbers of marginal and opisthogastric setae. In O. intermedius , the pertireme is shorter than that of O. masani sp. nov., with the anterior end not reaching the anterior margin of coxa II. The idiosomal shields are densely granulated in O. intermedius , but delicately reticulated in O. masani sp. nov.. The numbers of marginal and opisthogastric setae are totally 12 and 13 pairs in O. intermedius and O. masani sp. nov., respectively.

Onchodellus masani sp. nov. differs from two species, O. islandicus and O. jurassicus , by lengths and widths of dorsal and ventral idiosomal shields, which are smaller in the new species. For instances, the lengths and widths of dorsal shields in O. islandicus and O. jurassicus are 585–625 and 345–380, and 620–630 and 388, respectively, compared with 442–490 and 260–320 in O. masani sp. nov.. The marginal and opisthogastric setae are fewer in these two species ( O. islandicus with 10–11 pairs, O. jurassicus with 11 pairs). Lengths of each J4 and J5 setae are almost twice as long in these two species than those setae in O. masani sp. nov. ( O. jurassicus : J4 40–44, J5 29–33; O. islandicus : J4 35–40, J5 25–31; O. masani sp. nov.: J4 18–23, J5 14–16). The chelicerae differ in the numbers of teeth in O. islandicus and O. masani sp. nov. (fixed digit with three teeth in O. islandicus and four teeth in O. masani sp. nov.).

Onchodellus masani sp. nov. can be distinguished from O. michaelcostai by the length and width of the genitiventral shield, the lengths of setae J4 and J5, and the number of opisthogastric setae. The length and width of genitiventral shield in O. michaelcostai are greater (195 and 200, respectively) than those in O. masani sp. nov. (162–170 and 162–178, respectively). The dorsal setae J4 and J5 are slightly longer in O. michaelcostai (≈ 29–31 and 20, respectively) than O. masani sp. nov. (18–23 and 14–16, respectively). Based on Costa’s (1971) illustrations, the marginal+opisthogastric setae in O. michaelcostai are 0+7 pairs, compared with 5+8 pairs in O. masani sp. nov..

The main morphological differences between O. masani sp. nov. and O. minutus the are lengths of the peritremes, lengths of the dorsal setae, the number of gland pores on the posterolateral dorsal margin, and the marginal and opisthogastric setae. In O. minutus , the pertireme is slightly longer, with the anterior end extending beyond the anterior margin of coxa II, overlapping the level of anterolateral margin of sternal shield (not reaching the anterolateral margin of sternal shield in O. masani sp. nov.). The dorsal setae are heterogeneous in length in O. minutus , with setae j2, j3, j4, z2, z4, s2, r2, and r3 nearly twice as long as the other dorsal setae, while they are almost homogeneous in O. masani sp. nov.. Lengths of J4 and J5 are 35–40 and 20–25 in O. minutus , while they are 18–23 and 14–16 in O. masani sp. nov., respectively. Onchodellus minutus bears 12 pairs of marginal and opisthogastric setae (13 pairs in O. masani sp. nov.).

The differences between O. masani sp. nov. and O. parvulus are as follows: width of the dorsal shield, 260–320 in the new species, and 200–220 in O. parvulus ; peritreme extends well past the anterior margin of coxa II in O. masani sp. nov., while it is clearly shorter in O. parvulus , with the anterior end extending to the posterior level of coxa II; the genitiventral shield is almost as long as wide in O. masani sp. nov. (162–170 long, 162–178 wide), but longer than wide in O. parvulus (140–160 long, 110–120 wide); the number of marginal and opisthogastric setae is 13 pairs in O. masani sp. nov., and about ten pairs in O. parvulus ; the ratio of J4 / J5 is 1.20–1.57 in O. masani sp. nov., and about 2.0 in O. parvulus . The number of teeth on the cheliceral fixed digit is four in O. masani sp. nov. and three in O. parvulus .

The new species can be distinguished from O. procerus mainly by the following characteristics: length of the dorsal shield, lengths of J4, J5 and ratio of J4 / J5, number of slit-like gland pores on the posterolateral dorsal margin, and the marginal and opisthogastric setae. Length of dorsal shield is slightly smaller in O. masani sp. nov. (442–490) than O. procerus (490–555). The setae J4 and J 5 in O. masani are shorter than those in O. procerus ( O. masani sp. nov.: J4 = 18–23, J5 = 14–16, J4 / J5 ratio = 1.20–1.57; O. procerus : J4 = 25–33, J5 = 20–31, J4 / J5 ratio = 1–1.30). The number of slit-like gland pores on the posterolateral dorsal margin of the idiosoma, and marginal and opisthogastric setae are respectively one pair (gd9) and 10–11 pairs in O. procerus , and two pairs (gd8, gd9) and 13 pairs in O. masani sp. nov..

The differences between O. masani sp. nov. and O. volkovae are related to the specific metric data and measurements given, including the length and width of the dorsal shield (LDS & WDS), length of the genitiventral shield, length of seta J4, and the ratio of J4 / J5. The LDS and WDS in O. masani sp. nov. are smaller (442–490 and 260–320, respectively) than those in O. volkovae (510–560 and 350–380, respectively). The length of the genitiven- tral shield in O. masani sp. nov. is shorter than that of O. volkovae (162–170 in O. masani sp. nov., and 180–190 in O. volkovae ). The length of seta J4 and the ratio of J4 / J 5 in O. masani sp. nov. are less than those in O. volkovae ( O. masani sp. nov.: J4 = 18–23, J4 / J5 ratio = 1.20–1.57; O. volkovae : J4 = 26–28, J4 / J5 ratio ≈ 2). The number of teeth on the cheliceral fixed digits is four in O. masani sp. nov. and two in O. volkovae .

Taxonomic remarks: Mašán (2007) established five species groups of Onchodellus based on the European species, but O. masani sp. nov. does not clearly fit into that classification. One of the main morphological characters of the O. strigifer group, namely the existence of two pairs of slit-like gland pores (gd8, gd9) on the posterolateral dorsal margins, suggest that we can place the new species in this group. However, the lack of male specimens of O. masani sp. nov. prevented us from examining the cheliceral spermatodactyl, so we cannot place it definitely in that group. This new species differs from the O. alpinus , O. falcifer , O. islandicus , and O. karawaiewi groups, which have just one pair of slit-like gland pores (gd9) on the posterolateral dorsal margins ( Mašán, 2007).

The new species also resembles the O. strigifer group in the short length of seta J5: it is 14–16 in O. masani sp. nov., which is as short as the length of J 5 in the O. strigifer group (less than 20). The length of the peritreme in O. masani sp. nov. does not agree with the O. strigifer group, because in the species of this group lengths of peritremes are not reduced and their anterior ends reach the marginal dorsal surface between setae z1 and z2, unlike O. masani sp. nov.. The shortened peritreme in O. masani sp. nov. resembles the species of the O. islandicus group, in which the anterior ends of peritremes are usually situated close to the anterolateral corners of sternal shield and do not reach the marginal dorsal surface. Considering the given differences, we are currently unable to place O. masani sp. nov. in any of the above-mentioned groups of Onchodellus .

Figures

FIGURES 1–7. Onchodellus masani sp. nov., female. 1. Dorsal idiosoma; 2. Ventral idiosoma; 3. Tritosternum; 4. Epistome; 5. Chelicera; 6. Sperm induction structures associated with coxae III; 7. Tarsus II.

FIGURES 8–11. Onchodellus masani sp. nov., female. 8. Opisthonotal region with selected setae, gland pores, and poroids; 9. Gnathosoma; 10. Anterior idiosoma, peritremes, and sperm induction structures associated with coxae III directed forward; anterior ends of peritremes showed by black arrows. 11. Sperm induction structures associated with coxae III directed backward. Not scaled.