Mosillus bidentatus (Cresson 1926)

Mosillus bidentatus (Cresson)

Gymnopa bidentatus Cresson. 1926:249; 1942:106 [review, Nearctic].—Wirth and Stone, 1956:466 [key, California].

Mosillus bidentatus.—Wirth, 1965:734 [generic combination; Nearctic catalog]; 1969:151–152 [review].—Cole, 1969:396 [list, California].

DESCRIPTION.—.Moderately small to medium-sized shore flies, length 2.10 to 3.25 mm.

Head (Figures 1–6): Frons wider than long, frons width-to-length ratio averaging 0.74; mesofrons U-shaped, bare of microtomentum, more coarsely microsculptured than parafrons, appearing somewhat granulose; parafrons with very fine microsculpturing, mostly smooth. Antenna, including arista, black; flagellomere 1 with moderately dense vestiture of grayish black pubescence. Face, except for silvery gray microtomentose in antennal grooves, bare of microtomentum; lateral surfaces of face coarsely grooved and pitted; clypeus finely microsculptured; anteriormost facial projection tear-drop shaped, mostly smooth; ventral margin of antennal grooves evenly rounded, lacking prominence. Parafacial wide, width subequal to twice width of anterior ocellus; parafacial at level of antenna with 2 silvery gray microtomentose patches, dorsal patch slightly larger. Gena with a few shallow wrinkles toward anterior margin, otherwise bare, shiny, very smooth; gena high, eye-to-cheek ratio averaging 0.52.

Thorax (Figures 7–12): Mesonotum extensively and moderately densely microtomentose, microtomentum mostly whitish gray or a shade thereof but with 3 stripes (median and where dorsocentral setae would be) of bronzish microtomentum with faint metallic luster, also bare linear area as short medial extension from dorsal angle of notopleuron; scutellum broadly trapezoidal, posterior margin very shallowly convex; lateral scutellar setae 2, each arising from a tubercle; anepisternum coarsely microsculptured, a few to several mostly vertical striae on a granular background, with faint metallic, mostly bronzish luster. Spine-like setae of fore femur small; fore tibia mostly black, apex with silvery gray vestiture of microtomentum; middle tibia yellowish orange; basal 3 tarsomeres of fore tarsi yellow; hind basitarsomere yellow. Wing costal vein ratio averaging 0.42; vein M ratio averaging 0.65.

Abdomen (Figures 13–18): Generally shiny, with moderately sparse setulae; 2nd abdominal tergum with median depression narrow, linear posteriorly; 5th tergum with dorsomedial area slightly microsculptured, bearing dense setulae and microtomentum. Male terminalia (Figures 13–18) as follows: epandrium comparatively short, anterior extension in lateral view extended to about ventral margin of cerci; surstylus tapered to moderately rounded ventral margin, both margin in lateral view more or less straight; postgonite in lateral view with large, dorsal, secondary lobe, setal bearing lobe short, attached toward base; aedeagus distinctly angulate, with distinct posterior projection medially, apical portion tapered to acute pointed apex; aedeagal apodeme more or less evenly triangular in lateral view; hypandrium bare, moderately elongate, anterior margin truncate, not invaginated anteriorly to form a pocket.

TYPE MATERIAL.—The holotype male is labeled “[USA. Salt Lake County] Saltair VII [Jul] 08 [1908] Utah JM Aldrich//TYPE Gymnopa BIDENTATA E.T. Cresson, Jr. 6318 [species name and holotype number handwritten, maroon]/ANSP [yellow].” The holotype is double mounted (minuten in a rectangular piece of cardboard), is in good condition (left wing slightly torn), and is deposited in the ANSP (6318).

OTHER SPECIMENS EXAMINED.—MEXICO. Baja California Sur: Isla San Jose (S end, landlocked lagoon), 2 Apr 1974, J.T. Doyen, L. Cheng (2, 1 CAS). Angel de la Guardia Island, Pond Island Bay, Gulf California, 20 Jun 1921, E.P. Van Duzee (4, 1 CAS).

CANADA. British Columbia. Kamloops (alkali lake), 2 Jul 1968, W.W. Wirth (5, 2; USNM); Vernon, 22 Jul 1947, H.B. Leech (1; USNM).

UNITED STATES. California: Alameda Co., Berkeley, 31 Aug 1949, L.W. Quate (2; USNM); Oakland, 20 Jun–4 Aug 1949, L.W. Quate (2; USNM). Imperial Co., Salton Sea, 9 Mar 1950, A.H. Sturtevant (1; USNM); Salton Sink, 29 Mar 1929, A.H. Sturtevant (1 ; USNM); San Felipe, 20 Jun–8 Jul 1932 (1, 1; ANSP, USNM). Inyo Co., Lone Pine, 28 Jul 1940, R.H. Beamer (2, 1; USNM). Lake Co., Borax Lake, 14 May–8 Aug 1911, 1922, 1948, J.M. Aldrich, E.P. Van Duzee, W.W. Wirth (4, 10, ANSP, USNM). Los Angeles Co., Claremont (near mountains), C.F. Baker (1; USNM); Redondo, 23 May 1898 (1; ANSP). Mono Co., Black Lake (shore), 13 Aug 1988, D.B. Herbst (10, 4; DBH); Mono Lake (S and W shore), 22 Jun-12 Aug 1974, 1980, W.N. Mathis, R.S. Zack (5, 1; USNM, WSU). Orange Co., Laguna Beach, C.F. Baker (1; USNM). Riverside Co., Andreas Canyon, 23 Mar–27 Oct 1934, 1951, A.L. Melander (2; USNM); Elsinore, 19 Feb 1950 (4, 5; UTA); Elsinore Lake, 19 Feb-2 Aug, 1911, 1950, J.M. Aldrich, A.L. Melander, A.H. Sturtevant (10, 20; USNM); Indio (near), 23 Feb 1949, A.L. Melander (1; USNM); Joshua Tree National Monument, Hidden Valley, 18 May 1946, A.L. Melander (1; USNM); Palm Springs, 17 Mar 1949, A.L. Melander (1; USNM). San Bernardino Co., Joshua Tree National Monument, Quail Spring, 5 Oct 1934, A.L. Melander (4, 3; ANSP, USNM); Trona, 31 Mar 1953, A.H. Sturtevant (1; USNM). San Diego Co., Borrego, 16 Mar 1950, G.H. and J.D. Sperry (1, 1; USNM); Carlsbad, 1 Jun 1954, J.C. Hall (1, 1; USNM); El Cajon, 28 Jun 1945, A.L. Melander (1; USNM); Palm Canyon, 7 Nov 1934, A.L. Melander (1; USNM); San Diego, 11 Mar 1897, W.M. Wheeler (1; AMNH); Yaqui Wells, 20 Mar 1951, A.H. Sturtevant (1; USNM). Santa Clara Co., Palo Alto, 29 Apr 1906, J.M. Aldrich (5, 3; ANSP, USNM); C.F. Baker (1; USNM). Siskiyou Co., Lower Klamath Lake, 16 Aug 1963, J. Schuh (1, 2; WSU).

Colorado: Denver Co., Denver, 9 Aug 1939 (1; ANSP). Garfield Co., Rifle (5400 ft, = 1646 m), 19–21 Jul 1919 (1; AMNH). Idaho: Butte Co., Craters of the Moon National Monument, 2 Aug 1964, D.S. Horning (1; USNM). Carnas Co., Magic Reservoir, 2 Jul 1973, G.E. Bohart (1 USU). Latah Co., Moscow, 10 Sep 1922, A.L. Melander (l USNM). Oneida Co., Rock Creek, 13 Jul 1972, G.F. Knowlton (1 USU); Twin Springs, 10 Aug 1972, G.F. Knowlton (1 USU). Michigan: Keweenaw Co., Isle Royale, 3–7 Aug 1936, C.W. Sabrosky (1 USNM). Wayne Co., Detroit, 16 Aug 1930,. G.C. Steyskal (1, 3 ANSP, USNM). Montana: Chouteau Co., Geraldine, F.T. Cowan (1 USNM). Sheridan Co., Medicine Lake, 9 Jun 1969, W.W. Wirth (1 USNM). Yellowstone Co., Billings, 17 Aug 1914 (4, 3 AMNH). Nebraska: Cherry Co., Twin Lake (alkali lake), 2 Jun 1969, W.W. Wirth (2 2 USNM). Grant Co., Hyannis, 3 Sep 1969, C.D. Michener (3, 3 USNM). Hooker Co., Mullen, 31 Jul 1953, R.R. Dreisbach (2 USNM). Kimball Co., Kimball (5000 ft), 6 Aug 1934, H.A. Scullen (1 USNM). Lancaster Co., Lincoln, 9 Aug 1914, E.M. Partridge (1 USNM). Sioux Co., Glen Canyon, 28 Aug 1959, O.W. Isakson, W.E. LaBerge (1 USNM). C.V. Riley (1 USNM). Nevada: Churchill Co., Soda Lake (6 mi [9.6 km] NW Fallon, Alkaline), 28 Aug 1983, R.S. Zack (5 WSU). Washoe Co., Pyramid Lake, 25 Jun 1970, R.F. Lagier (1 WSU).

New Mexico: Catron Co., Zuni Salt Lake (20 mi [32 km] W Quemado), 2 Jul 1953, W.W. Wirth (1 USNM). Otero Co., Tularosa (25 mi [40 km] W), 1 Jul 1940, L.J. Lipovsky (4, 3 USNM). Socorro Co., Magdalena Mountains (19 Aug 1951, E.L. Kessel (1 USNM). North Dakota: Benson Co., Leeds (alkali lake), 5 Jul 1969, W.W. Wirth (10, 5 USNM). Oregon: Harney Co., Borax Lake (4.5 mi [7.2 km] NE Fields), 29 Jul 1975, W.N. Mathis (1 USNM); Harney Hot Spring, 23 May 1975, W.N. Mathis (12, 5 USNM); Mann Lake (19 mi [30.4 km] SW Oregon Route 78), 12 Sep 1981, R.S. Zack (1 WSU). Lake Co., Abert Lake, 16 Aug-9 Sep 1931, 1954, 1982, K. Gray, D.B. Herbst, J. Schuh, A.H. Sturtevant (5 6 USNM, WSU); Alkali Lake (NW shore), 12 Jul 1974, W.N. Mathis (3 USNM).

Utah: Box Elder Co., Antelope Island, 8 Jul 1970, G.F. Knowlton, D. Davis (1 USU); Clear Creek Canyon, Raft River Mountains, 5 Jul 1974, G.E. Bohart (1 USU); Corinne, 12 Jun 1929, G.F. Knowlton (1, 1 ANSP, WSU); Promotory Point, 11 Jul 1911, J.M. Aldrich (2 USNM); Snowville, 12 Aug 1972, G.E. Bohart (2 USU). Millard Co., Delta, 27 Jul 1927, G.F. Knowlton (1 AMNH). Salt Lake Co., Garfield, 9 Jul 1911, J.M. Aldrich (1, 1 USNM); Great Salt Lake, Saltair, 5–31 Jul-13 Aug 1908, 1950, J.M. Aldrich (12 13 ANSP, USNM, UTA); Great Salt Lake (beach), 31 Jul 1908, J.M. Aldrich (1 ANSP); Midvale, 2 Sep 1953, W.J. Hanson, G.W. Knowlton, J.B. Plant (1 USNM); Salt Lake causeway to Antelope Island, 21 Aug 1982, R.S. and V.L. Zack (1, 4 WSU); Salt Lake City, 26 Jun-18–20 Jul 1917, J.M. Aldrich, H.S. Barber (2, 2 USNM). Sanpete Co., Moroni, 27 Jun 1940, A.L. Melander (1, 1 USNM). Utah Co., Provo, 29 Jul-1 Aug 1920 (1 AMNH). Weber Co., Ogden, 25 Jul 1920 (1 AMNH); Utah Hot Spring, J Jun 1967, G.F. Knowlton (1 USU).

Washington: Adams Co., Columbia National Wildlife Refuge, Lower Crab Creek near Black Lake, 28 Aug 1980, R.S. Zack (1 WSU); Columbia National Wildlife Refuge, Black Lake (1.5 mi [2.4 km] S, alkalie pond), 30 Jul 1978, R.S. Zack (3 WSU); Washtucna (12 mi [19.2 km] W), Sand Hills County Park, 28 Mar 1978, R.S. Zack (2 WSU). Asotin Co., Asotin, 4 Jun 1930, J.M. Aldrich (1 USNM). Benton Co., West Richland, 8 Jun 1974, N.E. Woodley (1 WSU). Grant Co., Columbia National Wildlife Refuge, Juvenile Pond, 17–28 Aug 1977, 1980, R.S. and V.L. Zack (3, 4 WSU); Moses Lake, 7 Aug 1956, C. Johansen (1 WSU); Royal City (5.1 mi [8.2 km] W, irrigation pond), 13 Jul 1978, R.S. Zack (1 WSU); Soap Lake, 17–22 Jul-20 Aug 1919, 1922, 1949, 1968, M.T. James, W.N. Mathis, A.L. Melander (30, 36 AMNH, ANSP, USNM). Okanogan Co., Penley Lake (5 mi [8 km] SE Okanogan), 22 Jul 1983, R.D. Akre, R.S. Zack (1 WSU). Wyoming: Yellowstone National Park., Madison Junction, 27 Jul 1923, A.L. Melander (1 ANSP).

DISTRIBUTION (Figure 19).—NEW WORLD. Nearctic: Canada (BC, MB (unverified)), Mexico (BCS), USA (CA, CO, ID, MI, MT, NB, ND, NM, NV, OR, UT, WA, WY).

DIAGNOSIS.—This species is distinguished from congeners, especially those from North America, by the following combination of characters: face bare except for microtomentose antennal grooves; parafacial with 2 small microtomentose spots at level of antenna; mesonotum extensively microtomentose, microtomentum mostly white or a shade thereof; middle tibiae mostly yellowish orange; 2nd abdominal tergum with median depression narrow, linear posteriorly; and 5th tergum with dorsomedial area microsculptured, bearing setulae.

Mosillus bidentatus is a species of shore flies in the family Ephydridae.