Scatella marinensis (Cresson 1935)

Scatella marinensis (Cresson)

Parascatella marinensis Cresson, 1935:358.—Wirth, 1965:757 [catalog].

Scatella (Parascatella) marinensis.—Sturtevant and Wheeler, 1954:178.

DIAGNOSIS.—Members of this species and S. triseta very closely resemble each other and care must be exercised in distinguishing between them. Scatella marinensis specimens are recognized by the following combination of characters: 2 pair of larger, lateroclinate fronto-orbital setae, between larger pairs there is a smaller pair, always less than one-half the length of larger setae; mesonotum and scutellum darker brown and becoming shinier posteriorly; disc of scutellum slightly convex, not distinctly flattened.

DESCRIPTION.—Moderately small to medium-sized shore flies, length 2.72 to 3.56 mm; generally subshiny dorsally, brown to dark brown, becoming duller and more pollinose ventrally.

HEAD (Figure 55): Mesofrons mostly shiny, appearing brassy in luster, background color black but overlaid with sparse brown pollinose vestiture, giving brassy appearance, anterior portion bordering frontal suture generally dull, pollinose, at most weakly subshiny; parafrons densely pollinose, brown; dorsalmost postocular setae weakly developed, less than one-third length of ocellar bristles; 2 pair of strong, lateroclinate fronto-orbital bristles, between larger pairs is a smaller pair of setae much less than one-half length of either larger pair. Antenna mostly unicolorous; third segment more pubescent; arista slightly longer than combined length of antenal segments, micropectinate above over most of length. Color of dorsal portion of interfoveal carina brown, concolorous with parafrons, contrasting distinctly with silvery white color over lower three-fourths of face; space between antennal bases charcoal black in color; dorsum of interfoveal carina with distinct crease; facial setae extending from interfoveal carina toward posteroventral corner of face and those along oral margin much larger than remaining facial setae, the latter setae uniformly smaller. Gena concolorous with face or slightly less silvery.

Thorax (Figure 56): Brown to gray, darker dorsally. Mesonotum dull and pollinose anteriorly, becoming darker and shinier posteriorly and with very faint indication of a vitta along acrostichal setal tract; acrostichal setae weakly developed, often with a slightly larger pair of setae where transverse suture would cross mesonotum; scutellum concolorous with posterior portion of mesonotum, slightly convex. Notopleuron and posterodorsal portion of mesonotum concolorous, brown; remaining areas of mesopleuron lighter, becoming grayer, especially ventrally, and concolorous with sternopleuron and front coxa; pteropleuron grayish brown, intermediate between brown and gray color of mesopleuron. Legs concolorous, femora densely pollinose, mostly gray but with some faint greenish tinges; tibiae less pollinose than femora, becoming black ventrally; tarsi mostly black but paler ventrally, tawny in some specimens. Wing (Figure 53) mostly hyaline or very lightly infuscated, light brown; pattern of white spots similar to P. triseta, often not very evident.

Abdomen: Generally brown or blackish brown dorsally, becoming grayer on venter; posterior margins of posterior segments often banded with grayer border; segments 2 to 4 of male specimens more or less subequal in length, fifth segment about twice the length of fourth.

TYPE-MATERIAL.—Holotype male, labeled: “Redwood Canon [sic] Marin Co., V, 17, '08 Cal./ / TYPE Parascatella MARINENSIS E. T. Cresson, Jr. 6525 (red).” The holotype is in good condition and is double mounted. Cresson's original description also lists 4 male and 4 female paratopotypes. The type series is in the Academy of Natural Sciences of Philadelphia, type number 6525.

SPECIMENS EXAMINED.—286 specimens (87 , 199 ). CANADA. BRITISH COLUMBIA: Fairmont Hot Springs (CA). MEXICO. CHIAPAS: San Cristobal (CNC). UNITED STATES. ALASKA: Anchorage-Eagle River Flats (USNM). ARIZONA: Cochise Co., Chiricahua Mtns, 8500' (USNM), Huachuca Mtns-Miller Canyon (USNM), Huachuca Mtns-Ramsey Canyon, 15 mi S Sierra Vista, 6000' (CNC), Portal-SW Research Sta (USNM); Pima Co., Organ Pipe Cactus Nat. Mon.-Dripping Spring (WNM), Santa Rita Range Res.–Florida Canyon (WNM); Santa Cruz Co., Tumacacori Mtns.–Sycamore Canyon-Yanks Spring (CA, USNM). CALIFORNIA: Live Oak Park (USNM); Mountain Home (USNM); Ortega Hwy-El Cariso Camp (USNM); Alameda Co., Berkeley (CA, USNM), Berkeley Hill (ANSP); Contra Costa Co., Danville (CA), Mt. Diablo (USNM), San Ramon Creek-Danville (USNM); Imperial Co., Salton Beach (USNM); Los Angeles Co., Los Angeles (ANSP), Saugus, 10 mi NE (USNM); Marin Co., Lagunitas Canyon (ANSP), Mill Valley (CA), Muir Woods (USNM), Redwood Canyon (ANSP); Mariposa Co., Big Creek-Summerdale Forest Camp (CA); Monterey Co., Big Sur (USNM), Big Sur State Park-Pfeiffer (CA), Carmel (USNM), San Simeon (AMNH); Placer Co., Bear Valley, E end (CA); Riverside Co., Agua Caliente Indian Res.-Palm Canyon (CA), Cathedral Canyon (USNM), Cathedral City (USNM), Mag. Spring Canyon, near Indio (USNM), Palm Canyon (USNM), Palm Canyon-Palm Springs (USNM); San Benito Co., Pinnacles (USNM); San Bernardino Co., Big Pines (USNM), E Fork Devils Canyon, San Bernardino, 8 mi N (USNM); San Diego Co., Cuyamaca Park (USNM); San Francisco Co., San Francisco (CA); San Luis Obispo Co., Morro Bay (USNM), Pozo (USNM); San Mateo Co., Corte de Madera Creek (CA), Palo Alto (CA, USNM), Redwood City (USNM); Santa Clara Co., San Jose (CA), Stanford University (CA); Shasta Co., Bondary Campground (CA); Stanislaus Co., Del Puerto Canyon-Frank Raines Park-Del Puerto Creek, 335 m (CA); Tuolumne Co., Pinecrest (CA), Yosemite (USNM); Ventura Co., Santa Paula (USNM). IDAHO: Nez Perce Co., Culdesac (USNM). MONTANA: Thompson (USNM); Gallatin Co., Firehole River (USNM). NEW MEXICO: Catron Co., Whitewater Canyon (USNM). OREGON: Benton Co., Cary's Grove (WNM), Clackamas Co., Eagle Creek (USNM); Crook Co., Marks Creek-Cougar Campground (CA); Curry Co., Humbug Mtn State Park (USNM); Harney Co., Crane Hot Spring (WNM), Umatilla (USNM). TEXAS: Brewster Co., Big Bend Nat'l. Park-Pulliman Canyon (CNC). UTAH: Utah Co., Goshen Pond (WNM). WASHINGTON: Husam (WNM); Adams Co., Lind (WNM); Asotin Co., Asotin (WNM); Chelan Co., Entiat (WNM); Clallam Co., Sol Duc Hot Spring (WNM); Garfield Co., Central Ferry (WNM); Mason Co., Lilliwaup (WNM); Pierce Co., Ft. Lewis (WNM), Mt Rainier-Ohanapechosh (WNM); Walla Walla Co., Walla Walla (WNM).

GEOGRAPHIC DISTRIBUTION (Figure 57).—Scatella marinensis occurs primarily in the Rocky Mountains and westward, although we have examined specimens from Big Bend National Park (Brewster County), Texas. We have also seen specimens from as far north as Anchorage, Alaska, and as far south as 3 miles northeast of San Cristobal, Chiapas, Mexico. This species is sympatric over much of its range with S. triseta and it is not uncommon to collect specimens of both species at the same locality.

NATURAL HISTORY.—No detailed study on the natural history of this species is available and we can only offer the following descriptive data summarized from collecting notes. Mathis has collected specimens of this species from protected areas along the banks of small streams in Utah and Oregon. Specimens were taken while sweeping through emergent vegetation that consisted mainly of grasses and sedges. Backwater areas or pools left in alternative, high-water channels were especially fruitful collecting areas, although specimens were not encountered commonly anywhere.

PHYLOGENETIC RELATIONSHIPS.—Our remarks under S. triseta regarding the relationship of this species with the former also apply here.