Abstract
Many taxa of mites inhabit long-lived freshwater environments, but the few known to live in small, ephemeral rock pools (lithotelmata) are brachypyline Oribatida. One of these is in the South African genus Aquanothrus (Ameronothridae). We describe adults and juveniles of two new rock-pool species from the USA and propose the sister-genus Paraquanothrus n. gen. to include them. The type-species, Paraquanothrus grahami n. sp., inhabits shallow weathering-depressions (‘pans’) on barren sandstone in the Colorado Plateau, especially southeastern Utah, where it seems to be an opportunistic grazer on microflora and rotifers. Paraquanothrus spooneri n. sp. inhabits rock pools on granite outcrops, is known only from the type-locality in eastern Georgia and appears to ingest mostly plant fragments. Like Aquanothrus, these mites are active only when free water exists. Paraquanothrus shares multiple apomorphic traits with Aquanothrus, for which a new diagnosis is based on corrected information on the type-species, A. montanus, and two undescribed species (one of which is represented in the paratype series). After reviewing historical concepts of Ameronothridae, we propose a new diagnosis (excluding Podacaridae) and propose a new rank and diagnosis for the subfamily Aquanothrinae, which includes Aquanothrus and Paraquanothrus. Molecular studies that have revealed links among Ameronothroidea, Cymbaeremaeoidea and Licneremaeoidea—in ways that question the monophyly of all three superfamilies—are reviewed, and a preliminary evaluation shows morphology to have a modest level of congruence with these results.
Highlights
Oribatid mites form a dominant component of the soil fauna, being abundant and diverse in complex organic horizons of moist forest floors, where they feed primarily on decaying plant remains and fungi
We propose Paraquanothrus n. gen. to include these new species and consider it the sister-genus of Aquanothrus, the type species of which—A. montanus Engelbrecht, 1975—inhabits rock pools in South Africa (Engelbrecht 1975; Jocqué et al 2006; Vanschoenwinkel et al 2009)
Respiratory organs of legs — Engelbrecht (1975) neither mentioned nor illustrated the respiratory organs of legs in A. montanus: in juveniles, the trochantero-femoral system is in the typical form of porose areas, but in adults of all three species of Aquanothrus that we studied, they are invaginated as tracheae
Summary
Oribatid mites form a dominant component of the soil fauna, being abundant and diverse in complex organic horizons of moist forest floors, where they feed primarily on decaying plant remains and fungi. Oribatid mites in exposed terrestrial microhabitats—e.g. Scutovertex and Scapheremaeus species living in arboreal or epilithic mosses and lichens—may be inactive during dry periods (Travé 1963a; Walter 1999; Smrž 2002; Colloff 2010) This differs little from ‘aquatic’ species in the ameronothroid genera Aquanothrus and Chudalupia, which become immobile when their temporary rock pool habitat no longer contains water (Engelbrecht 1975; Wallwork 1981). Our main purpose is to describe and discuss two new species inhabiting such rock pools (= lithotelmata, gnammas, pans) These are small, temporary lentic environments formed by the accumulation of rainwater in shallow depressions—typically solution or weathering pits—on rock surfaces. Secondary objectives are to: (1) improve knowledge of Aquanothrus montanus by adding ontogenetic data, correcting some errors in the original description, critiquing the supposed high variability of the species, and proposing a new generic diagnosis; (2) discuss the systematic position of Paraquanothrus and Aquanothrus by reviewing and critiquing past concepts of Ameronothridae and recasting Aquanothridae as a subfamily of Ameronothridae; and (3) evaluate morphological support for molecular studies that have brought the monophyly of Ameronothroidea, Cymbaeremaeoidea and Licneremaeoidea into question
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