Description of a new ant-associated species (Acari: Mesostigmata: Laelapidae) from Iran

A new species of laelapid mite of the genus Myrmozercon, Myrmozercon iranicus Babaeian and Nemati n. sp., is described and illustrated based on adult female specimens collected in the nest of Messor sp., in Yazd and Shahrekord regions (Yazd and Chaharmahal and Bakhtiari provinces, respectively) of Iran.


INTRODUCTION
Mites of the family Laelapidae Berlese are cosmopolitan; they have a wide ecological diversity including insect paraphages, parasites of vertebrates, and free-living predators inhabiting soil, litter habitats and nests of vertebrates and arthropods (Evans and Till, 1966;Strong and Halliday, 1994;Lindquist et al., 2009). Nests of social insects provide habitats for diverse genera within the family Laelapidae such as Holostaspis Kolenati, Laelaspis Berlese, Gymnolaelaps Berlese and occasionally Gaeolaelaps Evans and Till and Cosmolaelaps Berlese (Lindquist et al., 2009). Others such as the genus Myrmozercon have a more ambiguous association with their hosts.
A new species of Myrmozercon, associated with Messor sp. (Hymenoptera: Formicidae) is described and illustrated in this paper.

MATERIALS AND METHODS
Mite specimens were extracted from soil samples collected from the nest of an unidentified species of the genus Messor using Berlese-Tullgren funnels. Specimens collected were then cleared in Nesbitt's solution and mounted in Hoyer's medium. Measurements are presented in micrometers (µm) as: minimum-maximum or in a single value. Dorsal shield length and width were taken from anterior to posterior margins along the midline, and at broadest level, respectively. Length of the epigynal shield was measured along the midline from the posterior margin of the sternal shield to the posterior margin of epigynal shield, and the width at widest point. Length and width of the sternal shield were measured along the midline from its anterior to posterior margins and at the level of setae st2, respectively. Length of the anal shield was measured along the midline from its anterior to posterior margin including the cribrum (which is often folded under), and the width at the widest points. Length of legs was taken from the base of the coxa to the apex of tarsus, excluding the pretarsus. The second segment of the chelicera was measured from the base to the apex of the fixed digit. The length of the movable cheliceral digit was taken from the base to its apex. Setae were measured from the bases of their insertions to their tips. Idiosomal setal notation follows that of Lindquist and Evans (1965), the leg chaetotaxy that of Evans (1963a) and the palp chaetotaxy that of Evans (1963b). Idiosomal notation for glands and lyrifissures follows Johnston and Moraza (1991).
The holotype and two paratype specimens are preserved as permanent slides and deposited in the Jalal Afshar Zoological Museum, College of Agriculture, University of Tehran, Iran (JAZM) and one paratype specimen in the Acarological Collection, Acarological Society of Iran, Faculty of Agriculture, University of Tehran, Karaj, Iran.
Diagnosis -The concept of Myrmozercon used here is based on that of Shaw and Seeman (2009) and Joharchi and Moradi (2013).
Legs -Genu I and tibia I has three ventral setae, femur IV and genu IV with six and nine setae, respectively.
Etymology -The name "iranicus" is referred to the country of origin (Iran) where the type specimens were collected.
Notes -According to the key to species of Myrmozercon occurring in the Palaearctic Region presented by Joharchi and Moradi (2013), M. iranicus Babaeian and Nemati n. sp., keys out to Myrmozercon michaeli Joharchi, 2013 (dorsal shield hypotrichous and truncated, peritreme long, metasternal setae st4 present and almost all dorsal setae barbed in apical end).
It is interesting to note that these two species of Myrmozercon were collected in the nest of an unidentified species of Messor, and in nearly similar geographical locations.

DISCUSSION
Defining the genus Myrmozercon as well as other melittiphine or hypoaspidine groups is difficult because of lack of apomorphies or autopomorphies.
Species of this genus share some characters: corniculi and cheliceral digits are short, fixed digit reduced, leg chaetotaxy highly variable and deutosternal groove has at least six rows of denticles. These features create a very heterogeneous genus with instability in several morphological characters: dorsal shield hypertrichous or hypotrichous; with free or fused sternal shield with endopodal plates between coxae III and IV; presence or absence of palp seta v2 on palp-trochanter and short or elongate peritreme.

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The leg chaetotaxy of Myrmozercon species shows some variation, with a reduction or increase in number of setae on some leg segments (usually femur, genu and tibia I or femur and genu IV). Although not enough is known about leg chaetotaxy in other species to be sure.
Species of Myrmozercon have host-specificity and their distribution may be influenced by their host specificity. At least ten genera of ants have been reported so far as hosts in the world and among them Crematogaster, Camponotus and Messor are the most common (Babaeian et al., 2013). The biology of species of Myrmozeron has not been studied. Some species are often found clining to the thorax, abdomen and head of the ants, but the ecological role of these species and nature of their relationship is not known. Joharchi et al., (2011) and Joharchi and Moradi (2013) speculated that reduced peritreme, fixed cheliceral digit and weakly sclerotised corniculi in Myrmozercon indicate that they may be parasitic on its ant hosts.