Supplementary description of Digamasellus punctum ( Berlese ) ( Mesostigmata , Digamasellidae ) , and a key to the world species of Digamasellus Berlese

Herein, the genus Digamasellus Berlese, 1905 is reported for the first time from Iran on the basis of a newly collected specimen ofD. punctum (Berlese, 1904) from cow manure in Kermanshah Province, Western Iran. A complementary description of adult female of the species is presented based on a single collected specimen to present additional information about the species. Also, a key to the world species of the genus is presented.


Introduction
proposed Digamasellus as a subgenus of Gamasellus Berlese, and designated a new species, G. (D.) perpusillus, as its type species. Lindquist (1975) reviewed conceptual and nomenclatural problems of Digamasellus and Dendrolaelaps Halbert, presented a complete diagnosis for these genera and also for the family Digamasellidae and showed that Digamasellus perpusillus is junior synonym of D. punctum (Berlese, 1904). Although before it, several species belonging to other genera had been described under Digamasellus by some authors (e.g. Womersley 1942;Leitner 1949;Ryke 1962;Hurlbutt, 1967), a few subsequent authors used the previous taxonomic rank and described/referred to some species belonging to other genera as members of Digamasellus (e.g. Bhattacharyya 1978;Pugh 1993;Castilho et al. 2016). Afterward, the only described species under Digamasellus that well match with all diagnostic characters of the genus is D. variabilis Wiśniewski & Hirschmann, 1989. Therfore, following Lindquist's (1975) diagnosis for Digamasellus, this genus currently comprises only three described species: D. punctum, D. australis Lindquist, 1975 and D. variabilis. Mites of the genus Digamasellus usually occur in high organic substrates such as manure and rotting organic material and also under the bark of trees (Hirschmann 1960;Lindquist 1975, Wiśniewski & Hirschmann 1989. Hirschmann (1960) redescribed D. punctum and illustrated the dorsal idiosoma, epistome, part of leg II of female, and the ventral idiosoma and gnathosoma (partially) of deutonymph, male and female of the species. However, details of some structures such as the palp and the legs and also the peritrematal shield of the species have not been presented yet.
The Iranian mites of the family Digamasellidae are poorly known. Until now, only 12 species belonging to two genera of digamasellid mites have been recorded from Iran, including 11 Dendrolaelaps Halbert and one Dendroseius Karg species (Faraji et al. 2006;Kazemi & Rajaei 2013;Abolghasemi & Kazemi 2016;Nemati et al. 2018;Moradi Faradonbe et al. 2018). Haddad Irani-Nejad et al. (2001) reported the genus Digamasellus from Iran on the basis of a male specimen of an unknown species. Apparently, this specimen got lost (Haddad Irani-Nejad pers. comm. with SK), so we could not examine it. However, in spite of the poor-quality illustrations of the species (of the male specimen), the small anal opening of the species clearly indicates that it does not belong to the genus Digamasellus. Additionally, the presence of setae st5 on the posterior edges of the sternitigenital shield demonstrates that the species does not belong to the family Digamasellidae. So, the report of Digamasellus punctum from Iran in this paper effectively represents the first record of the genus from the country. Despite the relatively good redescription of D. punctum by Hirschmann (1960), he did not present a complete description/illustration of the legs, palp, peritreme and peritrematal shield and also idiosomal adenotaxy, poroidotaxy and sigillotaxy of the species. Therefore, here we present a complete description of the female of the species based on a single collected specimen in western Iran. Additionally, a key to the world species of Digamasellus is presented.

Material and methods
The mite specimen was removed from a sample of cow manure collected in Javanrood Region, Kermanshah Province by a Berlese-Tullgren funnel, cleared in Nesbitt's fluid and then mounted on a microscope slide using Hoyer's medium.
Morphological observations, measurements and illustrations were made using a compound microscope equipped with differential interference contrast and phase contrast optical systems, and a drawing tube (Olympus BX51). Measurements were made in micrometers (μm). The length of podonotal and opisthonotal shields was taken from the anterior to posterior shield margins along the midline; the length of the idiosoma was measured at the same level and the width at level of setae j6. The width of the sternal shield was taken from lateral margins of the shield at the level of setae st2, and its length from the level of poroids iv1 to posterior margin of shield along the midline. The length of epigynal shield was measured from the anterior margin of the hyaline extension to the posterior margin of the shield along the midline; shield width was taken at level of the genital setae. The ventrianal shield length and width were measured along the midline from the anterior to posterior margins, including the cribrum, and at the broadest level, respectively. The legs' lengths were measured from the base of the coxae to the apex of tarsi, excluding pretarsus. The length of the second cheliceral segment was taken from its base to the apex of the fixed digit. The length of the fixed cheliceral digit was measured from the dorsal lyrifissure to the apex and that of the movable digit from the base to apex.

Diagnosis
The genus diagnosis of Lindquist (1975) was followed.
Note - Lindquist (1975) indicated the absence of seta z3 in Digamasellus species. Setae z3 and s2 both appeared in the deutonymphal instar in Gamasina, but s2 is inserted more laterally in comparison with z3. Therefore, the seta located posterolaterad to z2 in Digamasellus species is named z3 (instead of s2) in this paper. Lindquist (1975) referred to only two described species belonging to the genus Digamasellus (he had examined most related species in the Berlese collection in 1961 and1971;pers. comm. with SK). However, recently Castilho et al. (2016) transferred some species described by Berlese (1920) under Gamasellodes (Digamasellus) to the genus Digamasellus, including G. Berlese's (1920) descriptions of these species are inadequate. Therefore, we tried to obtain additional information about these species based on photographs taken of the type material in the Berlese collection in Florence by the Curator (Roberto Nanneli). Based on the photographs of the type material of G. ( D.) gracilis and G. ( D.) rhodacaroides, although quality of the slides was not good, both of these species can be easily excluded from the genus Digamasellus by their small anal opening. Although Berlese (1920) described G. ( D.) simplex with a small anal shield bearing only circumanal setae that clearly indicates the species does not belong to Digamasellus (also mentioned by Ryke (1962)), no specimens of G. ( D.) simplex were available in the Berlese collection. Castagnoli and Pegazzano (1985) also pointed out that this species is indicated with an "m" in the "Catalogue of the Berlese Acaroteca" (page 467) referring to its absence ("missing"). Therefore, we considered it as nomen dubium. Berlese (1920) also described G. ( D.) reticulatus that based on the photographs of its type material (deutonymph), and although this species does not have incisions on anterior margin of the opisthonotal shield (as in Dendrolaelaps), it has a small anal opening which excluds it from Digamasellus. Leitner (1949) described Digamasellus fallax very briefly, but Shcherbak (1980) redescribed it as a member of the genus Dendrolaelaps and the exclusion of the species is confirmed here based on the following characters: (1) presence of four scleronoduli behind setae j5; (2) anal opening very small; and (3) presence of two incisions in anterior margin of the opisthonotal shield. Bhattacharyya (1978) described Digamasellus sitalaensis lacking information about leg chaetotaxy. However, it can be easily excluded from this genus by the following characters: (1) podonotal shield bears 22 pairs of setae, s2 and z3 both present; (2) the sternal shield has three pairs of setae (st1-st3), and setae st4 inserted off the shield; and (3) four scleronoduli present behind setae j5. To establish its correct taxonomic placement, the type specimens should be carefully examined, but it was not possible in this study.

Discussion
In Hirschmann's (1960) redescription of D. punctum, a seta inserted well behind the insertion of S2 was designated as R1. However, the normal position of R1 in Gamasina is more anterior, slightly behind S1 (Lindquist & Evans 1965). Lindquist (1975)   (1989). On the other hand, normal insertion of poroids idR3 is between setae R3 and R4, so it can be useful to identify these two setae too. Seta R2 is inserted in soft cuticle of D. punctum and D. variabilis, but it is on the opisthonotal shield in D. australis (Lindquist 1975;Wiśniewski & Hirschmann 1989).
One pair of "double gland pores" are distinctly present in D. punctum between setae S4-S5 (denoted as PS4 and PZ4 by Hirschmann (1960)) and also illustrated by Lindquist (1975) for D. australis in the same region. Wiśniewski & Hirschmann (1989) illustrated a pair of pore-like structures each including only one of these structures between the mentioned setae for D. variabilis, and no other pore-like structures on the dorsal shields of the latter in contrast to many pairs of pore-like structures shown by Hirschmann (1960) for D. punctum, 21 pairs by Lindquist (1975) including eight pairs on the podonotal shield (gv4 present near the base of seta s4) and 13 pairs on the opisthonotal shield for D. australis and also 22 pairs including seven pairs on the podonotal shield (gv4 absent) and 15 pairs on the opisthonotal shield in the current paper for D. punctum. On the other hand, in the original description of D. australis and D. variabilis only poroids iv1-iv2 were illustrated on the sternal shield of these species, but Hirschmann (1960) illustrated iv3 for D. punctum, although they were not present on the shield in the specimen examined by us and also in three females of this species deposited in the Canadian National Collection of Insects and Arachnids (CNCI), Science & Technology Branch, Agriculture & Agri-Food Canada, Ottawa (personal communication of one of the authors (SK) with E.E. Lindquist).
We also observed fungal spores inside the ventriculus of the collected mite that confirms fungivorous behavior of D. punctum as reported by Lindquist (1975).
Key to world species of Digamasellus (female) 1. Short post-stigmatic extension of peritreme present; coxa II with seta pv slightly shorter or longer than av (pv/av ≈ 1.