Contribution to the knowledge of the oribatid mite genus Microzetes (Acari, Oribatida, Microzetidae)

The oribatid mite genus Microzetes (Oribatida, Microzetidae) is recorded for the first time in the Philippines; one new species is described herein from secondary forest litter in Samar Island. Microzetes (Microzetes) samarensis n. sp. differs from other species of the subgenus by the insertions of notogastral setae c and la (close to each other vs. distanced in the other species). Updated generic and subgeneric diagnoses for Microzetes are given. The taxonomic status of Teraja Mahunka, 1995 and the systematic placement of representatives of this genus are discussed, resulting in the following taxonomic proposals: Microzetes Berlese, 1913 (=Teraja Mahunka, 1995) n. syn.; M. (Microzetes) asymmetricus (Mahunka, 2001) n. comb.; M. (Microzetes) sungai (Mahunka, 1997) n. comb.; M. (Megazetes) wongi (Mahunka, 1995) n. comb. The initial systematic placement of Microzetes flagellifer and M. tuberculatus (in the subgenus Microzetes) is supported, and the inclusion of M. fimbriatus in Microzetes (Megazetes) and Megazetes rugosus (Mahunka, 1986) in M. (Microzetes) is proposed. An identification key to the known taxa of Microzetes is provided.


INTRODUCTION
Microzetes is an oribatid mite genus of the family Microzetidae (Acari, Oribatida) that was proposed by Berlese (1913) with Sphaerozetes (Tectoribates) mirandus Berlese, 1908 as type species. At present, it comprises three subgenera (Microzetes Berlese, 1913, Megazetes Balogh, 1959and Stylozetes Balogh and Mahunka, 1969 and 35 species (see Discussion section below), which are distributed in the southern Palaearctic, Ethiopian and Neotropical regions (see summarized data in Subías 2004Subías , updated 2016. Among the oribatid mite material collected from the Philippines, we found one new species of Mi-crozetes. The main goal of this paper is to describe and illustrate the adults of M. (Microzetes) samarensis n. sp. Earlier, only one identified species of Microzetidae, Berlesezetes ornatissimus (Berlese, 1913), was registered in the Philippines (Corpuz-Raros 1979).
In addition, updated generic and subgeneric diagnoses and an identification key for Microzetes taxa are given. The systematic placement of some microzetid species and genus Teraja Mahunka, 1995 is also discussed.
Methods -Specimens were mounted in lactic acid on temporary cavity slides for measurement and illustration. The body length was measured in lateral view, from the tip of the rostrum to the posterior edge of the ventral plate. Notogastral width refers to the maximum width in dorsal aspect. Lengths of body setae were measured in lateral aspect. All body measurements are presented in micrometers. Formulas for leg setation are given in parentheses according to the sequence: trochanter -femur -genu -tibia -tarsus (famulus included). Formulas for leg solenidia are given in square brackets according to the sequence: genutibia -tarsus. Morphological terminology used in this paper follows that of F. Grandjean: see Travé & Vachon (1975) for general references, Norton (1977) for leg setal nomenclature, and Norton & Behan -Pelletier (2009), for overview. Drawings were made with a camera lucida using a Carl Zeiss transmission light microscope "Axioskop-2 Plus".

Genus Microzetes Berlese, 1913
Type species: Sphaerozetes (Tectoribates) mirandus Berlese, 1908, p. 5 Generic diagnosis Adult -Rostrum narrowly rounded or truncated, usually with short, median, longitudinal ridge. One pair of lobed structures present (triangular or dentate) or absent. Rostral setae long, thin, setiform or flagellate. Lamellar setae thornlike, sometimes setiform, exceptionally globulelike, inserted in distal part of lamellae, rarely in antero-medial part or on ventral side of lamellae. Interlamellar setae setiform, long, medium sized or minute, inserted on the basal parts of lamellae. Bothridial setae setiform or thickened, di-rected backward, with curved or straight tip, ciliate or barbed. Lamellae wide, long, usually with small or strong outer teeth and rounded medial parts, indentation between them present or absent, rarely medial teeth present or distal parts of lamellae broadly rounded, sometimes triangular. Inner margins of lamellae slightly separated, parallel, often with pentagonal, trapezoid or triangular gaps above interlamellar region, basally free or connected by translamella. Interlamellar region trapezoid or triangular. Lamellar and interlamellar apophyses absent. Anterior margin of notogaster slightly convex. Notogaster smooth or with longitudinal and transverse granular bands. Pteromorphs small, rounded or with teeth laterally. Notogastral setae short, thin. Epimeral setal formula 3 -1 -3 -3, setae setiform, sometimes some median setae thickened. Borders of sejugal apodemes usually fused medially. Six pairs of genital, one pair of aggenital, two pairs of anal and two to three pairs of adanal setae short (except g 1 which is often longer). One pair of adanal lyrifissures located near and parallel to anal plates.

Subgeneric diagnosis
Bothridial setae setiform, with attenuate, curved tips. Interlamellar setae minute. Notogastral setae c and la usually distanced from each other.

Subgeneric diagnosis
Bothridial setae setiform, with attenuate, curved tips. Interlamellar setae of medium size or long. Notogastral setae c and la usually inserted close to each other.

Subgeneric diagnosis
Bothridial setae bacilliform, with thickened, straight tips. Interlamellar setae minute. Notogastral setae c and la usually distanced from each other.

Leg
Tr Note: Roman letters refer to normal setae, Greek letters to solenidia (except ɛ = famulus). Single prime (' ) marks setae on the anterior and double prime (" ) setae on the posterior side of a given leg segment. Parentheses refer to a pair of setae. Tr -trochanter, Fe -femur, Ge -genu, Ti -Tibia, Ta -tarsus.
Type deposition -The holotype is deposited in the collection of the Senckenberg Institution, Görlitz, Germany; two paratypes are deposited in the collection of the Tyumen State University Museum of Zoology, Tyumen, Russia.
Etymology -The specific name samarensis refers to the Philippine Island, Samar, where the new species was collected.
Remarks -Microzetes (Microzetes) samarensis n. sp. differs from other species of the subgenus by the insertions of notogastral setae c and la (close to each other vs. distanced in the other species). Additional distinctive characters of the new species from other Microzetes-species can be found in the identification key given below.

DISCUSSION
System of the genus Microzetes and some morphologically similar taxa is not clearly defined (e.g. see Grandjean 1936;Mahunka 1995;Subías 2004Subías , updated 2016Ermilov and Anichkin 2011), therefore we offer some explanations.
1. Grandjean (1936) described the genus Nellacarus with Nellacarus petrocoriensis Grandjean, 1936 as type species; however, after studying the type materials Mahunka (1980) showed the morphological similarity of this genus to Microzetes, and he concluded Nellacarus as a junior synonym of Microzetes.  (Mahunka, 1998) as type species. Subías (2004) considered Megazetes and Stylozetes as subgenera of Microzetes, and Nellacaroides as a junior synonym of the latter genus. Generally, Microzetes, Megazetes and Stylozetes are morphologically similar, but differ from one another (see subgeneric diagnoses above) only by the morphology of bothridial setae and length of interlamellar setae. These differences are insignificant for the genus level status, and therefore, we support the Subías's decision on giving them subgeneric statuses..

Several genera with similar characters to
The genus Nellacaroides differs from Microzetes mainly by the absence of complete border between sejugal apodemes, but this character is variable among different genera of Microzetidae, so we agree with Subías's synonymy.
Our analysis of morphological traits of Teraja show that indeed this is similar to Microzetes. Mahunka (1995) listed three main differences: a) lobed structures (Mahunka incorrectly considered it as tutoria) dentate distally; b) two pairs of adanal setae present; and c) borders of sejugal apodemes and apodemes IV fused medially among themselves, forming X-structure. However, later, combining M. fimbriatus and M. tuberculatus (Mahunka 1987(Mahunka , 1988b and describing new species of Teraja, Mahunka (1997Mahunka ( , 2001 recognized that the first two characters are species level ones, because lobed structures showe morphological variability, and the number of adanal setae may be either two or three pairs. Also, similar localization of borders of sejugal apodemes and apodemes IV (as X-structure) is known in some Microzetes, for example, M. (Microzetes) lunaris (Aoki, 1984) and M. (Microzetes) samarensis n. sp.
Hence, there are no clear morphological differences between the genera Microzetes and Teraja. Therefore Teraja must be considered as a junior synonym of Microzetes (not Caucasiozetes as proposed by Subías (2004)