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Arachnida is an exceptionally diverse class in the Arthropoda, consisting of 20 orders and playing crucial roles in the terrestrial ecosystems. However, their interordinal relationships have been debated for over a century. Rearranged or highly rearranged mitochondrial genomes (mitogenomes) were consistently found in this class, but their various extent in different lineages and efficiency for resolving arachnid phylogenies are unclear. Here, we reconstructed phylogenetic trees using mitogenome sequences of 290 arachnid species to decipher interordinal relationships as well as diversification through time. Our results recovered monophyly of ten orders (i.e. Amblypygi, Araneae, Ixodida, Mesostigmata, Opiliones, Pseudoscorpiones, Ricinulei, Sarcoptiformes, Scorpiones and Solifugae), while rejecting monophyly of the Trombidiformes due to the unstable position of the Eriophyoidea. The monophyly of Acari (subclass) was rejected, possibly due to the long-branch attraction of the Pseudoscorpiones. The monophyly of Arachnida was further rejected because the Xiphosura nested within arachnid orders with unstable positions. Mitogenomes that are highly rearranged in mites but less rearranged or conserved in the remaining lineages point to their exceptional diversification in mite orders; however, shared derived mitochondrial (mt) gene clusters were found within superfamilies rather than interorders, confusing phylogenetic signals in arachnid interordinal relationships. Molecular dating results show that arachnid orders have ancient origins, ranging from the Ordovician to the Carboniferous, yet have significantly diversified since the Cretaceous in orders Araneae, Mesostigmata, Sarcoptiformes, and Trombidiformes. By summarizing previously resolved key positions of some orders, we propose a plausible arachnid tree of life. Our results underline a more precise framework for interordinal phylogeny in the Arachnida and provide new insights into their ancient evolution.

The genus Calepitrimerus (Acari: Eriophyoidea) comprise more than 90 extant species. Most species infest angiosperms, while only five were reported from gymnosperms. Herein, we describe and illustrate three new species of the genus Calepitrimerus from China: two from angiosperms, C. huayanlingense sp. nov. on Ficus erecta (Moraceae), C. cryptocaryaer sp. nov. on Cryptocarya concinna (Lauraceae), and one from a gymnosperm, C. liuanense sp. nov. on Cryptomeria japonica (Cupressaceae). All new species were found vagrant on lower surfaces of their hosts’ leaves, albeit inducing no apparent symptom. A list of Calepitrimerus species in China is tabulated.

Eriophyoid mites (Acari: Eriophyoidea) are among the smallest of terrestrial arthropods and the most species-rich group of herbivorous mites with a high host specificity. However, knowledge of their species diversity has been impeded by the difficulty of their morphological differentiation. This study assembles a DNA barcode reference library that includes 1850 mitochondrial COI sequences which provides coverage for 45% of the 930 species of eriophyoid mites known from China, and for 37 North American species. Sequence analysis showed a clear barcode gap in nearly all species, reflecting the fact that intraspecific divergences averaged 0.97% versus a mean of 18.51% for interspecific divergences (minimum nearest-neighbour distances) in taxa belonging to three families. Based on these results, we used DNA barcoding to explore the species diversity of eriophyoid mites as well as their host interactions. The 1850 sequences were assigned to 531 barcode index numbers (BINs). Analyses examining the correspondence between these BINs and species identifications based on morphology revealed that members of 45 species were assigned to two or more BINs, resulting in 1.16 times more BINs than morphospecies. Richness projections suggest that over 2345 BINs occurred at the sampled locations. Host plant analysis showed that 89% of these mites (BINs) attack only one or two congeneric host species, but the others have several hosts. Furthermore, host-mite network analyses demonstrate that eriophyoid mites are high host-specific, and modularity is high in plant-mite networks. By creating a highly effective identification system for eriophyoid mites in the Barcode of Life Data Systems database (BOLD), DNA barcoding will advance our understanding of the diversity of eriophyoid mites and their host interactions.

Eriophyoid mites (superfamily Eriophyoidea) comprise >4400 species worldwide. Despite over a century of study, the phylogenetic position of these mites within Acariformes is still poorly resolved. Currently, Eriophyoidea is placed in the order Trombidiformes. We inferred the high-level phylogeny of Acari with the mitochondrial (mt) genome sequences of 110 species including four eriophyoid species, and the nuclear small subunit (18S) rRNA gene sequences of 226 species including 25 eriophyoid species. Maximum likelihood (ML), Bayesian inference (BI) and Maximum parsimony (MP) methods were used to analyze the sequence data. Divergence times were estimated for major lineages of Acari using Bayesian approaches. Our analyses consistently recovered the monophyly of Eriophyoidea but rejected the monophyly of Trombidiformes. The eriophyoid mites were grouped with the sarcoptiform mites, or were the sister group of sarcoptiform mites+non-eriophyoid trombidiform mites, depending on data partition strategies. Eriophyoid mites diverged from other mites in the Devonian (384Mya, 95% HPD, 352-410Mya). The origin of eriophyoid mites was dated to the Permian (262Mya, 95% HPD 230-307Mya), mostly prior to the radiation of gymnosperms (Triassic-Jurassic) and angiosperms (early Cretaceous). We propose that the placement of Eriophyoidea in the order Trombidiformes under the current classification system should be reviewed.

The Eriophyoidea, notable for specific morphological characters (four-legged mites) and gall-formation in host plants (gall mites), is one of the most species-rich superfamilies of Acari. Monophyly of the superfamily Eriophyoidea is accepted by all acarologists; however, monophyly of most genera has not been evaluated in a molecular phylogenetic network. Furthermore, most eriophyoid mites, especially species in the genus Diptilomiopus, are morphologically similar, challenging their identification. Here we test the phylogeny and cryptic diversity of Diptilomiopus species using fragments of two mitochondrial (COI and 12S) and two nuclear (18S and 28S) genes. Our results revealed the monophyly of Diptilomiopus. Sequence distance, barcode gap, and species delimitation analyses of the COI gene allowed us to resolve cryptic diversity of Diptilomiopus species. Additionally, we supposed that characteristics of genu fused with femur on both legs and seta ft′ absent on leg II evolved only once within Diptilomiopus, which are potential morphological synapomorphies. In contrast, characteristics of both setae ft′ and ft″ divided into a short branch and a long branch were supposed evolving multiple times independently. Our findings contribute to the understanding of phylogeny and morphological evolution of Diptilomiopus species and provide a DNA-based approach for species delimitation of Diptilomiopus mites.

Two new species of the family Eriophyidae (Acari: Eriophyoidea) from Mount Trusmadi, Malaysia, are described and illustrated. They are Neodicrothrix grandcaputus sp. nov. on Stachyurus himalaicus (Stachyuraceae) and Latitudo asiaticis sp. nov. on Psychotria asiatica (Rubiaceae). Both of the two new species are vagrant on the lower leaf surface. No damage to the host was observed. In addition to the description, a key to species of Neodicrothrix is provided.

A few eriophyoid mites have two forms of adult female, called protogyne and deutogyne. The latter form is thought to increase survival under unfavorable conditions. The two forms have distinct morphological characters, which often cause them to be recognized as different species. Molecular species delimitation provides a useful tool to solve these misunderstandings. Here we describe a new species of eriophyoid mite, Tegolophus celtis sp. nov., that has protogyne and deutogyne forms infesting Chinese hackberry, Celtis sinensis Pers. (Cannabaceae), an ornamental tree in China. The two forms can be easily differentiated by body shape (fusiform and triangular, respectively) and body color (light yellow and red, respectively). The putative protogyne and deutogyne forms of T. celtis were identified by using fragments of three genes, a mitochondrial gene (COI) and two nuclear genes (18S rRNA and 28S rRNA). Kimura-2-parameter distances of these three fragmental sequences were between 0.0 % and 0.9 %. Phylogenetic topologies strongly support the occurrence of the protogyne and deutogyne forms with high bootstrap and Bayesian values. The population structure of T. celtis changed with the seasons, with deutogynes being most abundant in summer and protogynes being most abundant in spring. The new species described herein are vagrants on their host plants.

Traditional morphology-based taxonomy of eriophyoid mites (Acari: Eriophyoidea) has been challenged by molecular-based technologies in the detection of cryptic species. However, the implications of such cryptic diversity appear to differ when methods based on different types of data are used. Here, samples of a host-associated eriophyoid mite species,Tetra pinnatifidae, collected from different host plants and localities are evaluated. The congruence of results based on morphometric (32 characters), mitochondrial (16S), and nuclear (28S) data were evaluated and showed a host-associated cryptic diversity dividing this morphospecies into several groups/clades that were morphometrically indistinguishable. In comparison, the 16S data confirmed cryptic speciation and intra-clade host-associated diversity, while 28S did not. In contrast, 28S data revealed potential gene flow between host-associated populations. High mitochondrial divergence, as well as low nuclear and morphological divergence indicated very recent stage of cryptic diversity of this eriophyoid mite.

Three mite species of the family Eriophyidae from Iran are described and illustrated. They are: Tegolophus marrubiumer sp. nov. on Marrubium vulgare L. (Lamiaceae); Phyllocoptes sp. cf. balasi Farkas, 1962 on Sanguisorba minor Scop. subsp. minor (Rosaceae) and Aceria fasciculifolis sp. nov. on Astragalus fasciculifolius Boiss. (Fabaceae). Both new species described herein are vagrants on their respective host plants.

Herbivorous arthropods can diversify as a consequence of evolutionary changes in response to their plant hosts. Current patterns of host association of herbivores are likely to reflect a long evolutionary history of herbivore-plant co-evolution. Here, we used molecular phylogenetics to track the evolutionary history of host shifts and diversification of 66 eriophyoid mites (Acari, Eriophyoidea), and linked past patterns of evolutionary diversification to more recent patterns of divergence by tracking population genetic variation in 13 of the eriophyoid mite species feeding on different gymnosperm hosts. This allowed us to explore the relationship between a past history of diversification and the current potential of mites to undergo host range shifts. We found that population-level diversity across gymnosperm hosts as measured by 28S rRNA markers was greater in species from the mite clade that had radiated across evolutionary time to utilize a variety of hosts including angiosperms, compared to species from the clade that has remained restricted to ancestral gymnosperm hosts. Species from the radiated clade exhibited higher variation in host use. Lineages of mites that have in the past been able to radiate and adapt to diverse plants may therefore be predisposed to continue their expansion on new hosts, although additional clades need to be tested.

The subclass Acari (mites and ticks) comprises two super-orders: Acariformes and Parasitiformes. Most species of the Parasitiformes known retained the ancestral pattern of mitochondrial (mt) gene arrangement of arthropods and their mt tRNAs have the typical cloverleaf structure. All of the species of the Acariformes known, however, have rearranged mt genomes and truncated mt tRNAs. We sequenced the mt genomes of two species of Eriophyoidea: Phyllocoptes taishanensis and Epitrimerus sabinae. The mt genomes of P. taishanensis and E. sabinae are 13,475 bp and 13,531 bp, respectively, are circular and contain the 37 genes typical of animals; most mt tRNAs are highly truncated in both mites. On the other hand, these two eriophyoid mites have the least rearranged mt genomes seen in the Acariformes. Comparison between eriophyoid mites and other Aacariformes mites showed that: 1) the most recent common ancestor of Acariformes mites retained the ancestral pattern of mt gene arrangement of arthropods with slight modifications; 2) truncation of tRNAs for cysteine, phenylalanine and histidine occurred once in the most recent common ancestor of Acariformes mites whereas truncation of other tRNAs occurred multiple times; and 3) the placement of eriophyoid mites in the order Trombidiformes needs to be reviewed.

Five new eriophyoid mite species from Zhejiang Province, China are described and illustrated: Diptacus coreanus sp. nov. from Litsea coreana H. Lév. (Lauraceae), Neorhynacus camphoratus sp. nov. from Cinnamomum camphora (L.) J. Presl (Lauraceae), Rhinotergum boehmerius sp. nov. from Boehmeria gracilis C.H. Wright (Urticaceae), Rhyncaphytoptus cathayensis sp. nov from Carya cathayensis Sarg. (Juglandaceae) and Rhyncaphytoptus lanceolatus sp. nov. from Cunnighamia lanceolata (Lamb.) Hook (Cupressaceae). All species were vagrant on their host plants with no visible damage observed.

In this paper, three new Phyllocoptini eriophyoid mite species from Yunnan Province, China are described and illustrated: Proiectus rodgeseta sp. nov. on Pinus armandii Franch. (Pinaceae), Proiectus granularpro sp. nov. on Pinus tabuliformis Carr. (Pinaceae) and Phyllocoptrutajuniperiana sp. nov. on Juniperus chinensis Linn. (Cupressaceae). All are vagrants causing no apparent damage to their host plants. A key to the species of Proiectus is provided.

We describe and illustrate herein one new genus and eighteen new eriophyoid mite species (Acari: Eriophyoidea) collected in northeast China. They are: Shevtchenkella huzhongiensis sp. nov. on Ulmus davidiana Planch. var. japonica (Sarg. ex Rehder) Nakai (Ulmaceae), Shevtchenkella jingboicus sp. nov. on Acer sp. (Aceraceae), Calepitrimerus flexuosus sp. nov. on Spiraea flexuosa Fisch. ex Cambess. (Rosaceae), Calepitrimerus maximowiczii sp. nov. on Crataegus maximowiczii Schneid. (Rosaceae), Calepitrimerus pilosus sp. nov. on Agrimonia pilosa Ledeb. (Rosaceae), Calepitrimerus yichunensis sp. nov. on Sorbaria sorbifolia (L.) A.Br. (Rosaceae), Cupacarus oxyphyllus sp. nov. on Euonymus oxyphyllus Miq. (Cel-astraceae), Epitrimerus sambucus sp. nov. on Sambucus williamsii Hance (Caprifoliaceae), Epitrimerus wuyingensis sp. nov. on Acer sp. (Aceraceae), Longisolenidionus amurensis gen. novsp. nov. on Tilia amurensis Rupr. (Tiliaceae), Phyllocoptes jiagedaqiensis sp. nov. on Cunninghamia sp. (Taxodiaceae), Aculops huzhongensis sp. nov. on Salix sp. (Sali-caceae), Aculus huzhongsalixus sp. nov. on Salix sp. (Salicaceae), Tetra angelica sp. nov. on Angelica sp. (Apiaceae), Tetra jiagedaqia sp. nov. on Lespedeza sp. (Fabaceae), Vittacus mandshurica sp. nov. on Corylus sieboldiana Blume var. mandshurica (Maxim.) C. K. Schneid. (Betulaceae), Vittacus cannabus sp. nov. on Cannabis sativa L. (Moraceae), and Peralox dentatis sp. nov. on Ulmus sp. (Ulmaceae). Two species formerly assigned to Rhyncaphytoptus, R. abiesis (Xue, SongHong, 2006) and R. fabris (Xue, SongHong, 2006) were reassigned to Nalepella, based on the presence of seta vi on the apical shield, and other characteristics of Nalepella. One species formerly assigned to Rhyncaphytoptus, R. fargesis (Xue, SongHong, 2006) was reassigned to Pentaporca, based on the presence of seta vi on the apical shield, opisthosoma with five ridges and other characteristics of Pentaporca. At the same time, four new eriophyoid mite records from China are provided, Acaphyllisa distasa (Keifer, 1961) rec. nov. on Betula costata Trautv. (Betulaceae), Shevtchenkella ulmi (Farkas, 1960) rec. nov. on Ulmus sp. (Ulmaceae), Calepitrimerus cariniferus Keifer, 1938, rec. nov. on Artemisia argyi H. Lev.Vaniot (Asteraceae), Aculodes dubius (Nalepa, 1891) species complex, rec. nov. on Roegneria sp. (Poaceae). With this publication, the number of eriophyoid mite species in the region reaches 101. A list of these eriophyoid mites is provided.