Unionicola (Unionicola) formosa (Dana and Whelpley 1836) Plates 184-187 in Vidrine (1996a) Synonomy-- Hydrachna formosa Dana and Whelpley 1836 Atax ypsilophorus in Leidy (1883), Girod (1893), Koenike (1895), and Wolcott (1899). Atax adensameri Thon 1901 Unionicola ypsilophora (Bonz 1783) in Wolcott (1905 and 1918), Welsh (1930, 1931, and 1932), Waterford (1937), Mitchell and Pitchford (1953), Mitchell (1955), Conroy (1968), and Goldenstein and Boles (1970). Unionicola ypsilophora haldemani (Piersig 1900), in Marshall (1926, 1927, and 1929), and Mitchell (1954). Unionicola (Unionicola) ypsilophora in Viets (1936), Harvey 1998, Edwards and Vidrine 2013. Unionicola ypsilophora formosa in Mitchell (1954) Unionicola (Parasitatax) ypsilophora in Viets and Plate (1954) Unionicola (Parasitatax) formosa (Dana and Whelpley, 1836) in Mitchell 1957b and 1965, Crowell 1961, Murray 1965, Dobson 1966, Habeeb 1967, Del Portillo and Dimock 1982, Dimock 1981, 1983, 1985, and 1988, LaRochelle and Dimock 1981, Dimock and Davids 1985, Edwards and Dimock 1988 and 1991, Edwards 1993, LaRochelle 1979, Roberts 1977, Roberts and Dimock 1977 and 1978, and Roberts et al. 1978, Vidrine 1973, 1974a, 1977b, 1980a, 1986c, 1986e, and 1992b, Calnan 1976, Vidrine and Bereza 1978b, Vidrine 1996a-e and Wen and Zhu 1999. Unionicola (Unionicola) formosa (Dana and Whelpley, 1836) in Harvey 1998, Edwards and Vidrine 2013 Type locality and host-- Anodonta fluviatilis Dillw. (= Pyganodon cataracta (Say)), Connecticut. Etymology-- Formos means "graceful and beautiful". Diagnosis-- Character states of the subgenus; male dorsum with an elongate plate; female dorsum with 2, small, widely separated, weakly sclerotized plates, sometimes divided into 3 or 4 smaller plates with varied degrees of fusion between them; female posterior coxal group usually not
elongated nor extending much posterior of the junction with the fourth walking leg; male posterior coxal group with poorly sclerotized and indistinct posterior borders and with extensive secondary sclerotization fusing coxal plates to one another along midline and to the genital field. Male -- Length including capitulum 1300 (all measurements in micrometers (µm)); dorsal lengths of pedipalp segments: Ge 110; Ti 210; Ta 70; dorsal lengths of leg segments: leg I: Ge 295; Ti 275; Ta 190; leg IV: Ge 460; Ti 590; Ta 500. Female -- Length including capitulum 1650; dorsal lengths of pedipalp segments: Ge 100; Ti 160; Ta 75; dorsal lengths of leg segments: leg I: Ge 250; Ti 230; Ta 165; leg IV: Ge 470; Ti 580; Ta 470. Notes-- Unionicola formosa is generally a parasite of members of the mussel genera Pyganodon in North America. Specimens measured are from Pyganodon cataracta from Fisher's Pond, the type locality of U. foili. Edwards and Dimock (1988) began a re-evaluation of the mite species and populations in this group and suggest a larger number of species are involved. Hoeh (1990) has re-evaluated the host genera. This mite has been reported from Sacramento, California (Marshall, 1943), western Canada (Conroy, 1968), and Wisconsin (Marshall, 1933b). This mite is part of an American-Eurasian complex (U. ypsilophora-formosa-foili complex), and the complex requires more detailed study. These mites are not only commonly encountered, but they are among the most intensely studied mites of the genus. Ron Dimock and colleagues have conducted numerous studies on varied members of this complex, and in the process, behavior and physiology of these mites is far better understood for the group. Since Vidrine s (1996) books, U. formosa has been reported from Finland (Jouni Taskinen) and China (Wen and Zhu 1999). Close relatives have also been described from Africa (Ramadan and Aboul-Dahab 2002) and Russia (Tuzovskij and Semenchenko 2015). Hosts: These mites are typically found in species in the genus Pyganodon.
Figure 1: Drawings of U. formosa (after Vidrine 1996).
Map 1. Distribution of U. formosa (after Vidrine 1996).
Plate 184: Unionicola formosa from Pyganodon cataracta in North Carolina: Top left: male venter. Top right: female venter. Middle left: male posterior venter. Middle right: female genital field. Bottom left: male pedipalp. Bottom right: genu of first walking leg.
Plate 185: Unionicola formosa from Pyganodon cataracta in North Carolina: Top left: male venter. Top right: male venter. Middle left: male venter. Middle right: male pedipalp. Bottom left: male posterior venter. Bottom right: male anterior venter.
Plate 186: Unionicola formosa from Pyganodon cataracta in North Carolina: Top: male leg I. Middle left: female posterior venter. Middle right: tarsi of legs III and IV. Bottom left: female genital field.
Plate 187: Unionicola formosa from Pyganodon grandis in Louisiana: Top left: male venter. Top right: female venter. Middle left: pedipalp. Middle right: female venter. Bottom: tarsal claw of leg IV.
New plates: Plate 1: Unionicola formosa male from Pseudanodonta complanata in Finland. Specimen provided by Jouni Taskinen. Plate 2: close-up view of Plate 1 of male posterior coxal group margin obviously fused with genital field and without distinct posterior border.
Plate 3: Unionicola formosa male from Pyganodon cataracta in North America.
Plate 4: Unionicola formosa female from Pyganodon cataracta in North America.