A new genus and species of Amerobelbidae (Acari: Oribatida) from Vietnam

A new genus, Roynortonia n. gen., with its type species, Roynortonia vietnamica n. sp., belonging to the family Amerobelbidae, is proposed and described from dark loamy soil of Lagerstroemia forest of Cat Tien National Park (southern Vietnam). An identification key to the known genera of Amerobelbidae is presented.


INTRODUCTION
In the course of faunistic studies of oribatid mite fauna of Cat Tien National Park (southern Vietnam), I found a new species of the family Amerobelbidae (Ameroidea). This small family includes five genera with 11 species distributed in the Holarctic region (Subías 2004(Subías , online version 2010, but no species was known from Vietnam. On the basis of analysis of generic character states, I propose a new genus, Roynortonia n. gen., with Roynortonia vietnamica n. sp. as type species.

MATERIALS AND METHODS
Collection locality and habitat of the new species are characterized in the "Material examined" section.
Specimens were studied in lactic acid, mounted in temporary cavity slides, then stored in 70% alcohol in vials. All body measurements are presented in micrometers. Body length was mea-sured in lateral view, from the tip of the rostrum to the posterior edge of the ventral plate, to avoid discrepancies caused by different degrees of notogastral distension. Notogastral width refers to the maximum width in dorsal aspect. Length of body setae was measured in lateral aspect.
Etymology -The genus is named in honor of Prof. Dr. Roy A. Norton (State University of New York, College of Environmental Science and Forestry, Syracuse, USA), the distinguished acarologist, for his extensive contributions to our knowledge of the oribatid mites.
Remarks -The family Amerobelbidae comprises five genera: Amerobelba Berlese, 1908, Berndamerus Mahunka, 1977, Hellenamerus Mahunka, 1974, Mongaillardia Grandjean, 1961, Rastellobata Grandjean, 1961. Two other genera, Yambaramerus and Grypoceramerus, have been included in Amerobelbidae, but I question this placement. Aoki (1996) described Yambaramerus including it in Amerobelbidae. However both known representative of Yambaramerus, Y. arcuatus Aoki andYamamoto, 2000 andY. itoi Aoki, 1996, differ from other Amerobelbidae by body proportions (prodorsum and notogaster approximately equal in length in Yambaramerus; prodorsum obviously shorter than notogaster in other Amerobelbidae), lamellar setae inserted on well-developed apophyses, close to each other (not inserted on well-developed apophyses, and not close each other in other Amerobelbidae), lamellar lines well-developed (lamellar lines absent or slightly developed in other Amerobelbidae), presence of ring-like structures adjacent to interlamellar setae (absent in other Amerobelbidae), notogaster with two pairs of long and strongly developed thorn-like processes in humeral region (thorn-like structures absent or only one pair of small tubercles or spines present in other Amerobelbidae). Suzuki and Aoki (1970) described Grypoceramerus and included it in Amerobelbidae. However, the representative of Grypoceramerus, G. acutus Suzuki and Aoki, 1970, strongly differs from other Amerobelbidae by body proportions (prodorsum and notogaster approximately equal in length in Grypoceramerus; prodorsum obviously shorter than notogaster in other Amerobelbidae), notogastral setae c and la adjacent to each other and separated from other setae (not adjacent to each other or removed from other setae in other Amerobelbidae).
In my opinion, based on these character states Yambaramerus and Grypoceramerus are dissimilar to other genera of Amerobelbidae, and should not be considered members of this family. I do not discuss a place of Yambaramerus and Grypoceramerus in Ameroidea herein, their placement should be addressed in a separate publication.
Roynortonia n. gen. clearly differs from all other genera of Amerobelbidae by the following characters: 1) epimeral setae 3b modified, long, thorn-like, 2) epimeral setae 3b, 3c, 4b and 4c positioned adjacent to each other, 3) absence of aggenital neotrichy. Modified epimeral seta 3b is unique in Ameroidea and as far as I know it is unknown in Brachypylina. The presence of one pair of aggenital setae is unique in Amerobelbidae, all other genera express aggenital neotrichy; the type species of the new genus has an unusual structure -a long, rigid projection posterior to the bothridium. This is the first record of a bothridia bearing projection in Brachypylina. However, there are a small number of oribatid species with short bothridial projections in a same position in the Ameroidea, for example, Staurobates schusteri Grandjean, 1966 andStauroma cephalotum Grandjean, 1966 in Staurobatidae.
The new genus is most similar to Amerobelba in morphology of lamellar setae, absence of lamellar lines, absence of well-developed notogastral tubercles in humeral region (absent in Amerobelba, only very short spines developed in Roynortonia n. gen.), position of notogastral setae.
Integument -Body color light brown. Surface of body smooth. Granular and cloud-like cerotegument covers lateral parts of body and regions of dorsosejugal scissure and sejugal apodemes. Granules very small (diameter less than 1 µm).