Classification of the sand-mite family Walchiidae (Acariformes: Trombiculoidea)

The priority of Walchiinae Ewing, 1946 based on Walchia Ewing, 1931 or Gahrliepiinae Womersley, 1952 based on Gahrliepia Oudemans, 1912 as Walchia regarded as subgeneric taxon had been a controversy for almost half a century since 1952. Both genera are valid now. Wen (1999) redefined both subfamilial characters and in turn promoted Walchiinae to a full familial status. Walchiidae (Ewing, 1946) Wen, 1999 is characterized by SIF=4B/4Bs/5B/6B-N/B-3/2-2(1)1(0)1(0)0.0000, small to large sized sand-mites, IP=320 - 1220. Scutum is small to large size, extending backward over part of dorsum, and pentagonal with acuminate posterior angle or tongue-shaped. The scutum is never provided with anteromedian setae (AM or vi) and anteromedian projection (A or N=0). Scutal setae have AL and PL pairs basically, frequently in addition with 2 -40 accessories (PPLs), and rarely 1 - 2 pairs of intermedial setae (IM). Sensillae (Sn or sci) are short and expanded. Leg segments are 7.6.6 always without variations. Casting off the anteromedian setae on scutum, increasing the leg segments and reducing the tactile body setae are the plesiomorphic characters of sand-mites, that means Walchiidae in higher advance of evolution than both Trombiculidae (Ewing, 1929) and Leeuwenhoekiidae (Womersley, 1944). It is rationally to unify three families of vertebrate parasitic larvae into a single superfamily, Trombiculoidea nec Welbourn (1991), that separable from superfamily Trombidioidea of arthropod parasitic larvae and standing at most advanced evolution of Parasitengona. Family Walchiidae has 2 subfamilies, Walchiinae Ewing, 1946 sensu Wen 1999 and Gahrliepiinae Womersley, 1952, sensu Wen 1999. Each subfamily contains two tribes, Walchiini (Ewing, 1946) Wen 1984 and Schoengastiellini Wen 1984 for Walchiinae, and Gahrliepiini sensu Wen 1984 and Intermedialiini Wen, 1984 for Gahrliepiinae. Currently this family has 18 genera and 28 subgenera, 248 nominated species and subspecies. Walchiid sand-mites are essentially an Old World family and best developed in the Oriental Region with the center of development in Southeast Asia.