Collohmannia johnstoni n. sp. (Acari, Oribatida) from West Virginia (U.S.A.), including description of ontogeny, setal variation, notes on biology and systematics of Collohmanniidae
2014 - Volume: 54 Issue: 3 pages: 271-334DOI: 10.1051/acarologia/20142134
KeywordsAppalachian soil fauna oribatid mite vertitions sexual dimorphism nuptial feeding
Collohmannia (Collohmanniidae) is a genus of physically large oribatid mites with low extant diversity and high endemism. It includes the only species outside Brachypylina known to exhibit strong sexual dimorphism and courtship behavior, including nuptial feeding, and it has phylogenetic importance as a possible close outgroup of the diverse mixonomatan taxon Ptyctima. Herein, we describe all instars of the first member of the genus known outside of Eurasia: Collohmannia johnstoni n. sp. from forest litter in the mountains of northern West Virginia, USA. Males are distinguishable by the apparatus on genu IV used to hold the nuptial fluid: a hypertrophied seta with flattened, asymmetrical diamond shape and an absence of small cuticular tubercles. We also redescribe the genus Collohmannia using characters of both adults and juveniles, and give a new diagnosis of Collohmanniidae; noted for the first time is an extensive association of setae with dermal glands. Field samples suggest that C. johnstoni is highly aggregated, with a mean density of 100 per m2. Sample data are consistent with a 1:1 sex ratio and with the continual presence of all instars in the population, probably even during winter. Females are ovoviviparous, retaining eggs in their oviducts until the development of the larva, and larvae were found within females on all sampling dates. The prelarva (within eggs removed from females) is moderately regressed, retaining distinct leg remnants. Based on laboratory observations and gut contents of field-collected specimens, all active instars appear to feed directly on decomposing leaves of deciduous trees. Insemination was not directly observed, but courtship is generally similar to that previously described for C. gigantea. Morphological and molecular data concerning relationships between Collohmanniidae and Ptyctima are summarized but the issue remains unresolved. Ptyctima Oudemans, 1906 is considered equivalent to Euptyctima Grandjean, 1967.
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