According to OConnor(1984), the Trombidiformes are characterized by several charcters thatunite the Prostigmata (which makes up the majority of the group) with theSphaerolychidae and Lordalychidae. These characters are: anamorphicsegments AN and PA not added in ontogeny; hysterosomal segment C with fewerthan four pairs of setae; and hysterosomal segments D and E with fewer thantwo pairs of setae. OConnor's cladogram also indicates that the character'hysterosoma without primary segmentation' is a feature of theTrombidiformes; however, as it also occurs in a number of sarcoptiformtaxa, it is not a unique character. Lindquist (1996) notes that most (butnot all) members of the Trombidiformes can be differentiated from theSarcoptiformes by having chelicerae with a hooklike or styletlike movabledigit rather than the ancestral chelate form. Likewise, many trombidiformmites have a padlike or rayed median empodium in contrast to the clawlikeor disk-shaped empodium of sarcoptiforms. Within the Trombidiformes, theProstigmata are united by having the stigmatal openings tothe tracheal systemlocated anteriorly (e.g. on the prodorsum or near the baseof the mouthparts).
OConnor (1984) performed a cladistic analysis of the major taxawithin the Acariformes and determined that the Sphaerolichida andProstigmata shared two developmental and two setal characters, while theProstigmata were united by the presence of anterior openings to thetracheal system. Lindquist (1996) and Norton et al. (1993) provide recentcladograms of taxa within the Prostigmata. As these relationships arebased on unpublished analyses, it is difficult to discuss the rationale forlinking different taxa; however, Lindquist (1996) does provide a list ofcharacters uniting the superfamily Eriophyoidea.
There are severaldifferences between Lindquist's tree, presented above, and that of Nortonet al. (see below). While both divide the Prostigmata into three majorgroups, the Anystina, Eleutherengona and Eupodina, Lindquist nests theEleutherengona within the Anystina while Norton et al. present them ascompletely separate clades:
Other differences are that Norton et al. shift Bdelloidea and Halacaroideato the base of the Eupodina, and depict the Parasitengona as relativelyderived within the Anystina. Finally, Norton et al. have moved a number ofgroups typically considered to belong to the Anystina (Pterygosomatoidea,Pomerantzioidea, Pseudocheylidae, Paratydeidae and Stigmocheylidae) to theEleutherengona; however, they do not provide the rationale for thisrestructuring.
"Features of Balaustium sp. include resistance to intense heat and desiccation, affinity for hot surfaces in bright light, abundance in semi-arid/arid biotopes, and a large pair of secretory glands called urnulae with no known function (defense secretion excepted). Here we show that the urnulae secrete a waterproofing barrier that reduces the mite's cuticular permeability to water. Exposure to white light was used to stimulate release of the secretion; the urnulae protruded and exuded streams of red fluid at the tip of this structure that covered the entire body. Results showed that mites coated with urnulae secretion lost water at approximately half the rate of mites that did not secrete. Similarly, urnulae secretion coated mites demonstrated an increase in water-tightness of the cuticle reflected by a 9 OC elevation in temperature threshold for water loss on an evaporation curve, increasing their optimal temperature tolerance for survival (lethal permeability temperature, LPT). Results also show a 10 kJ/mol drop in activation energy (Ea) for water loss, representative of a substantial cuticular modification, and a decrease in Arrhenius frequency steric factor A, indicating an overall decrease in body water losses. The absence of a critical transition temperature (CTT), however, reveals that urnulae secretion coating functions to resist a phase change as the temperature rises, permitting the mites to cope with high temperature without succumbing to water and heat stress, by inhibiting cuticular breakdown." (Yoder et al. 2008:419) Learn more about this functional adaptation.
Yoder JA; Rigsby CM; Tank JL. 2008. Function of the urnulae in protecting the red velvet mite, Balaustium Sp., against water loss and in enhancing its activity at high temperatures. International Journal of Acarology. 34(4): 419-425.
"The red lumps on the feet and legs of this southern lubber grasshopper are not part of its colouring, but are the nymphal stages of the velvet mite. The nymphs hatch from eggs buried in the ground, then attach themselves to a grasshopper, driving their knife-like mouthparts through its cuticle to suck blood." (Foy and Oxford Scientific Films 1982:49) Learn more about this functional adaptation.
Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
Barcode of Life Data Systems (BOLD) Stats Specimen Records:23231 Specimens with Sequences:20910 Specimens with Barcodes:19418 Species:935 Species With Barcodes:871 Public Records:18747 Public Species:182 Public BINs:2334
The Trombidiformes is ahuge and diverse assemblage of mites, characterized more by the lack ofcharacters found in the other major group of acariform mites(Sarcoptiformes) than by many synapomorphies of their own (Lindquist 1996). Itincludes some medically important mites (chiggers, scrub itch mites) andmany agriculturally important ones. Among the latter are spider mites(Tetranychidae) and gall mites (Eriophyidae). With the exclusion of theSphaerolichida, the Trombidiformes is also known as the Prostigmata becausethe openings to the tracheal system are towards the dorsal prosoma of themite.