Cirrula austrina (Coquillett 1900)

Cirrula austrina (Coquillett)

Ephydra austrina Coquillett, 1900:36.—Aldrich, 1905:629 [catalog].

Caenia [sic] virida Hine, 1904:65 [description].—Cresson, 1916:152 [synonymy].

Ephydra viridis.—Aldrich, 1912:100 [review].

Dimecoenia austrina.—Cresson, 1916:152 [diagnosis].—Sturtevant and Wheeler, 1954:166 [review].—Wirth and Stone, 1956:472 [review].—Wirth, 1965:755 [catalog].—Steyskal, 1970:463 [review, figures of male and female terminalia].

DIAGNOSIS.—Specimens of C. austrina may be distinguished from those of C. gigantea by the following combination of character states.

Adults: Lateroclinate fronto-orbital bristles large; cruciate intrafrontal bristles large, over two-thirds length of arista, overlapping apically; parafrons brownish to brownish gray, pollinose but not velvety; aristal rays slightly longer than aristal width at base; face lacking dense patch of long bristles subdorsally; dorsocentral bristles 5 pairs, well developed, all subequal; presutural bristles well developed, equal to or longer than anterior notopleural bristle; tarsi of front leg normal, cylindrical, similar to those of middle leg; hypandrium evident as well-sclerotized process; setae of epandrium around cercal cavity similar to other epandrial setae.

Third-Instar Larva: Transverse sclerotized strap of third segment approximately 10 times as wide as long and lacking posterior projection; overall length up to 14 mm; cephalopharyngeal skeleton 0.7–0.8 mm in length.

DESCRIPTION OF ADULT.—Moderately large to large shore flies, length 4.83 to 6.81 mm; mostly dull, olivaceous to grayish brown with subshiny to shiny areas on dorsum.

Head (Figures 1, 2): Head width-to-height ratio averaging 1: 0.58; frons width-to-height ratio averaging 1: 0.51, mesofrons with median shallow depression between median ocellus and ptilinal suture, shiny, with metallic olivaceous to greenish blue luster; cruciate intrafrontal bristles 1 pair, large, overlapping apically; remainder of mesofrons with small, generally inconspicuous setulae; ocellar triangle and parafrons mostly concolorus, brownish to brownish gray, parafrons becoming slightly darker anteriorly; ocelli arranged to form equilateral or isosceles triangle, if latter posterior ocelli closer to each other than to median ocellus; lateroclinate fronto-orbital bristles large; postocellar setae only moderately well developed; postocular setae more or less uniform in size. Antenna mostly unicolorous, brownish gray to charcoal gray; arista longer than combined length of first 3 antennal segments, tapering gradually from thickened base to stylelike apex; subpectinate dorsally from base to just apicad of midpoint, rays less than one-half width of second antennal segment. Face width-to-height ratio averaging 1 : 0.73, interfoveal carina prominent, dorsum shiny, nearly concolorus with shiny mesofrons; antennal fovea deeply depressed, ventral margin sloping ventrally at conspicuous angle, more or less concolorous with remainder of face but less pollinose and tending to be somewhat subshiny with very light greenish blue reflections; face olivaceous to argenteous, darker dorsally; marginal facial setae larger, extending from interfoveal carina to posteroventral corner of face more or less uniformly, gently curved, posteroclinate; oral margin shallowly emarginate toward middle. Eye width-to-height ratio averaging 1 : 1.2, eye-to-cheek ratio averaging 1 : 0.29; gena moderately wide, mostly bare except for small setae paralleling parafacial suture, mostly concolorous with face, becoming darker and setulose posteriorly.

Thorax (Figure 3): Mesonotum generally subshiny, slightly darker and shinier posteriorly, with longitudinal pollinose vittae between shiny ones, particularly evident anteriorly, color varying from grayish blue to metallic olivaceous green; acrostichal setae unseriated; dorsocentral bristles 5 pairs, all subequal in size, well developed. Pleural areas lighter and more pollinose than mesonotum, becoming lighter and grayer toward venter. Legs generally dark colored, dull, pollinose, unicolorous for the most part, apices generally tawny; legs of male differing as follows: hind femur (Figure 4) enlarged, swollen, particularly basal half, with row of stout setae along anteroventral surface; hind tibia (Figure 4) with several long hairs on ventral surface near apex; hind tarsomeres generally shorter, slightly more swollen, bearing tufts of long hairs on ventral surfaces, more pronounced on basal tarsomeres. Wing (Figure 111) length averaging 4.76 mm; generally hyaline, or but slightly infumated, grayish brown; costal vein index averaging 1 : 0.19; vein M index averaging 1 : 1.1; wing length-to-width ratio averaging 1 : 0.40.

Abdomen: Generally pollinose, grayish blue to grayish brown, each tergum darker anteriorly and along median, becoming more grayish blue toward posterior and lateral margins. Fifth tergum of male slightly longer than fourth, as wide as long.

Male Terminalia (Figures 6, 7): Epandrium more or less parallel sided in caudal view, somewhat flattened in profile, with anterovental margin distinctly angulate; surstylus a simple, long, slender process with apex slightly recurved; gonite almost as wide as long, narrowing apically to curved point; aedeagal apodeme long, pointed ventrally, dorsal portion broad, curved posteriorly; aedeagus bifurcate (Figure 6), posterior lobe somewhat rectangular, anterior margin rounded, posteroventral corner drawn out to form acuminate narrow process, anterior lobe with ventrolateral process, process enlarged apically, rounded, otherwise lobe tapering ventrally, forming pointed process; hypandrium with long anterior process, anterior portion broadly bifurcating and folded back on itself.

Female Terminalia: Female ventral receptacle (Figure 5) with operculum as high as wide, lateral margins arched, dorsum flat, extending process narrowed apically, slightly curved apically. Segments 6–7 complete; sixth spiracle situated near anteroventral corner of tergum; sixth sternum rectangular, about 3 times longer than wide, slightly wider anteriorly; seventh sternum rectangular, about one and one-half times longer than anterior width, anterior margin distinctly wider. Eighth segment as follows: tergum divided into 2 lateral tergites, each becoming gradually wider ventrally; sternum divided longitudinally, each sternite 3 to 4 times longer than wide, becoming more setose posteriorly, with 3 to 4 apical long setae. Ninth sternum also divided longitudinally, short, each sternite bearing 1 large bristle posteriorly; ninth tergites fused with cerci, each bearing 1 large bristle posteroventally.

DESCRIPTION OF IMMATURE STAGES.—Egg (Figure 8): Length 0.70–0.80 mm (x = 0.76); maximum width in dorsal view 0.28–0.32 mm (x = 0.30). Pale to light pink just after oviposition; becoming cloudy with pink center after 12 hours; larval structures becoming visible through chorion after 36 hours. Ellipsoidal, somewhat flattened ventrally. Chorion surface reticulate with hexagonal pattern, becoming irregular and interspersed with light spines at micropylar end. Micropylar end bluntly rounded; micropyle on pedicel in center of apical circular depression and surrounded by thin, spinelike processes. (Based on 26 specimens, 23 reared and 3 field collected.)

First-Instar Larva: Main body length 1.40–2.28 mm, respiratory tube length 0.24–0.40 mm; maximum width in dorsal view 0.24–0.37 mm. Integument transparent with numerous hairlike spinules and fleshy, unbranched sensilla. Similar to third-instar larva except in the following characters. Segment 1 (Figure 10) with oral spinules smaller and much less pigmented distally; lobes posterolateral to atrium well armed with long, thin spines; antennae entirely pale. Segment 2 with much weaker postoral spine band; small, light hairs on posterior one-third of segment; anterior spiracles absent. Segment 3 with scattered light hairs; sensilla unbranched. Segments 4–11 with sparse hairs; dorsal patterns absent; sensilla reduced and unbranched; tubercles not evident. Crochets on prolegs lighter; crochets of anterior row one-third larger then those of second row; those of posterior row very small; 3 obvious rows of crochets on terminal proleg. Posterior spiracular caps (Figures 14, 17) lightly pigmented; each hydrofuge lamella with fewer apical branches in each group; 2 moderately distinct spiracular openings; spiracular scar absent (Figure 14). Cephalopharyngeal skeleton (Figures 20, 21) length 0.27–0.32 mm; generally less pigmented. Mouthhooks lightly pigmented except along distal edges; medial and lateral edges each tapering to a fine point posteriorly. Ligulate sclerite absent; dentate sclerite present and well developed. Inner and outer longitudinal rods (subhypostomal sclerites) of hypostomal sclerite fused together. Epistomal sclerite lightly pigmented, gradually expanded posteriorly; parastomal bars and hypostomal sclerite fused to pharyngeal sclerite. Pharyngeal sclerite without anterolateral processes; dorsal bridge lightly pigmented and not reticulate; ventral cornua without windows. (Based on 9 reared specimens.)

Second-Instar Larva: Main body length 2.33–4.92 mm, respiratory tube length 0.58–0.91 mm; maximum width in dorsal view 0.42–0.83 mm. Similar to third-instar larva except in the following characters. White to grayish white; integument transparent with numerous small spines, most obvious dorsally. Spines smaller and lighter than those of third-instar larva, no dorsal patterns; sensilla somewhat more obvious, often with dark tips. Anterior spiracles (Figure 9) with 5–6 less distinct marginal papillae, moderately pigmented. Posterior spiracular caps (Figures 15, 18) moderately pigmented, dark basally, subtriangular and constricted near the middle; each hydrofuge lamella composed of fewer, shorter hairs. Cephalopharyngeal skeleton (Figure 22) length 0.44–0.46 mm; generally less pigmented. Hook part of mouthhook basally with strong anteroventral tooth. Parastomal bars nearly free from hypostomal sclerite. Pharyngeal sclerite more closely appressed to hypostomal sclerite; dorsal cornua with 1 or more faintly pigmented windows. (Based on 13 specimens, 10 reared and 3 field collected.)

Third-Instar Larva (Figures 26,27): Main body length 6.25–10.25 mm, posterior respiratory tube length 1.41–2.58 mm; maximum width in dorsal view 1.17–1.58 mm. Internal structures mostly white, integument transparent with numerous spinules, spines, and scales. Shape cylindrical, tapering somewhat anteriorly; first 2 segments retractile, evaginated or invaginated in preserved specimens; caudal segment elongated to form posterior respiratory tube, telescoping and branching distally. Segment 1 (pseudocephalic) bilobed anteriorly; each lobe with small, 3-segmented antenna directed anterodorsally, segments 1 and 3 pale, segment 2 light brown; circular sensory plate on each lobe ventral to antenna (Figures 13, 31, 32); facial mask with row of 4 subequal comblike oral spinules between sensory plates, light to dark brown apically; second row of 8 slightly larger spinules posterior to first, just anterior to atrium (mouth opening); additional oral spinules in 2–3 indefinite lateral rows on each side of atrium and extending into buccal cavity (Figure 13). Evaginated specimens (Figure 30) with spinose lobe on each side posterolateral to atrium; 2 patches of minute spinules arranged in rows posteromedially. Invaginated specimens (Figure 31) with posterolateral spinose lobes not evident, contained within buccal cavity; patches of minute spinules bordering atrium posteriorly. Segment 2 (prothoracic) with postoral spine band weak anteroventrally, widening laterally into well developed spine patches consisting of dark spines arranged in definite rows, and absent dorsally; remainder of segment with uneven rows of peglike structures, subrectangular spine patch dorsally; banded on anterior one-third by 10 trilobed sensilla; anterior spiracles laterally near posterior border, palmate, usually with 6 marginal papillae (may also be 4, 5, or 7), dark at tips (Figures 11, 33). Segments 3–5 heavily spinose dorsally and laterally; spines interrupted on these 3 segments by small, oval, glabrous patches, arranged in 2 arcs on each side dorsolaterally (Figure 12). Segment 3 (mesothoracic) heavily spinose; 10 trilobed sensilla (Figure 34) near anterior one-third; dark transverse strap at anteroventral border (Figure 13); remainder of segment with scattered lighter spines. Segment 4 (metathoracic) heavily spinose; dorsally with 2 indistinct dark patches formed by flattened, scalelike spines; lateral and ventral areas less spinose; banded midway by 10 small tubercles, each bearing trilobed sensillum centrally. Segments 5–11 (1–7 abdominal) spinose, more or less with 3 annuli, variously wrinkled and tuberculate; each bearing ventral proleg; dorsal patterns present, consisting of flattened, scalelike spines, reduced or absent on segments 10 and 11. Dorsal tubercles small, 3 per side, 1 bordering pattern medially and 2 laterally; each bearing trilobed sensillum centrally. Remainder of each segment moderately and evenly spinose. Two lateral tubercles arranged vertically above each proleg, each with trilobed sensillum centrally. Prolegs well developed, slightly bilobed; all subequal except slightly smaller on segment 5. Lobes of prolegs each with 3 distinct rows of long, stout, curved spines, (hereafter referred to as crochets). Crochets directed posteriorly; anterior row largest, 4 crochets per side; crochets of second row ½–⅔ as large, 4 per side; 1 smaller crochet laterally between rows 1 and 2; crochets of third (posterior) row much smaller, 4–6 per side. Segment 12 with dorsal pattern reduced or absent; bearing posterior respiratory tube distally and large, subcylindrical proleg ventrally (the anal or terminal proleg). Four rows of crochets anterodistally on proleg, slightly tapering laterally and divided medially by small cleft; directed anteriorly; crochets of posterior row largest, 5 per side; crochets of third row somewhat smaller, 5 per side; crochets of most anterior row much smaller, 5 or more per side. Perianal pad apical on proleg; subcircular, somewhat bilobed posteriorly and glabrous; small patch of small, dark spinules at medioposterior border; anus longitudinal in middle of pad. Respiratory tube spinose at base, tapering and slightly less spinose distally; branches bearing spiracles without spines; paired ventrolateral tubercles bearing trilobed sensilla on basal one-fifth; 2 similar sensilla near middle. Posterior spiracular caps (Figures 16, 19, 35) light to dark brown, bluntly pointed apically; 4 elongate ellipsoidal spiracular openings apically, each bordered basally by a broad, hydrofuge lamella; each lamella split into 10 or more pale branching areas apically; spiracular scars located medially, facing one another, each scar rounded and lightly pigmented. Cephalopharyngeal skeleton (Figure 25) length 0.68–0.80 mm, mostly darkly pigmented. Mouthhooks paired, not interconnected, length 0.12–0.14 mm; hook part of each mouthhook slightly decurved, rounded and spatulate, toothed laterally and apically, median edge with teeth slightly larger; without windows; basal part with weak lateral flange apically and bluntly rounded dorsal projection. Dentate sclerite located ventrolateral to mouthhook on each side. Ligulate sclerite paired, each piece long and thin, with 2 or more small, angular bends; posterior part lying beneath anterior edge of hypostomal sclerite, directed anteriorly toward midline. Hypostomal sclerite paired, length 0.24–0.29 mm, composed of 2 pairs of longitudinal sclerites (rods) and 2 transverse bridges; each outer longitudinal rod stoutest at junction with parastomal bar, anteroventral portion expanded laterally to articulate with mouthhook; anterior hypostomal bridge intersecting anterior one-fourth of outer longitudinal rods, thin, slightly curved and bowed ventrally; posterior hypostomal bridge intersecting posterior one-third of outer longitudinal rods, much like anterior bridge but more strongly bowed; inner longitudinal rods articulating with anterior and posterior bridges, angled near midlength, slightly diverging posteriorly. Epistomal sclerite strongly convex, mostly darkly pigmented, bracing outer longitudinal rods of hypostomal sclerite dorsomedially; shaped as figured (Figure 24). Pharyngeal sclerite length 0.36–0.40 mm; indentation index 67–73; anteroventral edge ventral to and free from hypostomal sclerite; paired lateral pharyngeal processes rounded, flat, disclike and free from main pharyngeal sclerite; dorsal bridge highly reticulate (Figure 23); dorsal cornua with small posterior window; ventral cornua with subovate to subtriangular window posterodorsally. (Based on 23 specimens, 4 reared and 19 field collected.)

Puparium (Figures 28, 29): Main body length 5.56–7.89 mm (x = 6.83), breathing tube length 2.41–3.32 mm (x = 2.85), maximum width in dorsal view 1.74–2.41 mm (x = 2.14). Yellowish brown to brown; translucent to moderately transparent; entirely rigid. Venter generally arcuate in lateral view, dorsum flattened; anterior end flattened dorsally and tapering; posterior end elongate. Segment 1 and most of segment 2 invaginated. Anterior spiracles arising just behind anterolateral corner of puparium, slightly diverging; usually with 6 marginal papillae. Dorsal cephalic cap delineated by line of weakness extending laterally along segments 2–5, strongly indented near posterior margin of segment 4, transversing segment 5 dorsally near its posterior margin. Ventral cephalic cap delineated by line of weakness transversing segment 5 near it midlength, proleg of segment (P1) borne on cap. Markings similar to those described for third-instar larva; sensilla not evident. Segments 6–11 with intersegmental indentations strongest dorsally, becoming faint creases ventrally. Prolegs on segments 5–11 flat to weakly protruding. Segment 12 with slightly darker, subovate to ellipsoidal perianal pad ventrally and greatly elongated, distally branching breathing tube posteriorly. Respiratory tube evenly upcurved with ventrolateral tubercles on basal one-fifth; branches diverging between 0° and 90°; posterior spiracular caps more darkly pigmented than those on mature larvae, structures less discernible. (Based on 11 specimens, 3 reared and 8 field collected.)

TYPE MATERIAL.—Lectotype male [here designated] of the senior synonym is labeled: “Fl[orid]a. [Georgiana]/Collection, C. V. Riley [Mr. William Wittfeld, collector]/Type No. 4299 U.S.N.M. [number handwritten, red]/Ephydra austrina Coq. [handwritten, black bordered]/Dimecoenia austrina A. Coq. [handwritten, black bordered]/Cirrula austrina (Coquillett) Det. W. N. Mathis 1979 [handwritten, black bordered].” Six paralectotypes [here designated] have the same locality data as the lectotype. Coquillett's original description of S. austrina listed nine syntypes; apparently two are lost. The lectotype is pinned directly, is in fairly good condition (slightly dirty, dorsum of thorax partially split), and is deposited in the National Museum of Natural History, Smithsonian Institution, USNM type number 4299. The lectotype female [here designated] of the junior synonym is labeled: “Brownsville, Texas [Charles Dury, collector] apr 12 may 20 [1903]/TYPE [red].” The latter lectotype is in the Ohio State University insect collection, Columbus; apparently it is the only extant specimen of the orginal syntype series.

OTHER SPECIMENS EXAMINED.—MEXICO. NAYARIT: Isabel Island, 24 May 1925, H. H. Keifer (5; USNM). SONORA: San Jose Beach, 40 mi SE Obregon, 18 May 1961, Howden and Martin (3; CNC). UNITED STATES. ALABAMA: Mobile Co., Coden, 2 Oct 1916 (2, 4; USNM). CALIFORNIA: Alameda Co., 26 Oct 1968, R. S. Lane (1, 1; CAS); Albany, hatched in Laboratory, 12 Mar 1921, C. T. Dobbs, B. Brookman (2, 3; CAS). Marin Co., Mazaneto, 27 Oct 1907, Bradley (1, 1; CU). Orange Co., Corona del Mar, 16 May–11 June 1944–1949, A. L. Melander (2, 1; USNM); Laguna, 1 Aug 1932, J. M. Aldrich (1; USNM); Newport Beach, 27 Oct 1928 (2; USNM); Santa Ana, 31 Mar 1961, J. Bath (1; CU). San Diego Co., San Diego, 5 Apr 1915, M. C. Van Duzee (5, 3; CAS). San Luis Obispo Co., Morro Bay, 30 Aug 1945, A. L. Melander (1; CAS). Santa Clara Co., Palo Alto, 20–26 Apr 1906, J. M. Aldrich (10, 1; USNM); San Jose Beach, 40 mi SW Obregon (1; USNM). FLORIDA: Broward Co., Hollywood, 12 May 1967, B. V. Peterson (2, 1; CNC). Charlotte Co., Punta Gorda, 12 Apr 1952, J. R. McGillis (1; CNC). Collier Co., Everglade, 15 Apr 1912 (2, 2; AMNH). Dade Co., Biscayne Bay (1; AMNH); Homestead, Subtropical Experiment Station, 2 May 1967, B. V. Peterson (1; CNC); Miami, 3 Mar 1938, C. T. Green (1, 1; USNM). Highland Co., Archbold Biological Station, 20 Apr–23 Apr 1947–1967, J. G. Needham, B. V. Peterson (5; CNC, CU). Indian River Co., Sebastian, 9 Feb 1919, A. Wetmore (4, 1; USNM). Lee Co., Sanibel Island, 11 May 1973, W. W. Wirth (2; USNM). Monroe Co., Cape Sable, 24 Mar–25 Apr. 1953–1955, K. V. Krombein, H. E. Evans (3, 6; CU, USNM); Flamingo, 25 Jan–7 May 1939–1967, A. L. Melander, B. V. Peterson (9, 19; CNC, USNM); Key Largo, 25 Jan–4 Apr 1932–1966, A. L. Melander, H. V. Weems (3, 2; CU, USNM). Palm Beach Co., Lake Worth, Slosson (1, 1; AMNH, USNM). LOUISIANA: Calcasieu Par., Sabine River Ferry, 20 Jun 1917 (2, 1; CU). MISSISSIPPI: Jackson Co., Ocean Springs, Gulf Coast Research Labortory, 14 Jun 1962, D. L. Deonier (2, 1; DLD, USNM). TEXAS: Padre Island near Pt. Aransas, 23 Mar 1965, J. G. Chillcott (1; CNC). Cameron Co., Brownsville, 12 Apr–20 May (2; AMNH, USNM). Galveston Co., Galveston, 11 Feb-Jun 1900–1932, L. D. Tuthill (1, 1; USNM). VIRGINIA: Accomack Co., Assateague Island, Tom's Cove, 25 June–12 Aug 1970–1971, K. W. Simpson (13, 9; CU); Chincoteague Island, salt marsh, 25 Jun 1970, K. W. Simpson (8, 3; CU); Cockle Creek, 0.2 mi W, salt marsh, 1–13 Aug 1970–1971, K. W. Simpson (2, 5; CU); Eel Creek Marsh, E of Chincoteague, 13 Aug 1971, K. W. Simpson (4, 12; CU). Virginia Beach, 14 Aug 1913, Knab (1; USNM).

GEOGRAPHIC DISTRIBUTION (Figure 36).—Cirrula austrina occurs on both the Atlantic and Pacific coasts of North America below 40° north latitude. Steyskal (1970) recorded this species as far south as Isabel Island (Mexico, off the coast of the State of Nayarit). Wirth (1965) also listed a record from Bermuda.

NATURAL HISTORY.—Along the coast of southeastern United States, this species occurs commonly in or on mats of filamentous algae in salt marshes. Adults are strong fliers and commonly fly several yards when disturbed, although they could be collected in abundance by sweeping just above the mats. Populations seemed to reach their highest densities where the habitat had partially dried, rendering firmer mats and leaving them on solid ground (Figures 115, 116).

Courtship behavior was observed on two days in the field, the 12th and 13th of August, 1971. As a female was approached by a male, she flicked both wings quickly every few seconds. After approaching slowly, the male extended one wing perpendicularly for one or two seconds, then returned it to its normal position. After repeating this process a few times, he maintained the wing in its extended position and circled behind the female in such a way that the tip of the extended wing was always quite close to her. The male then mounted the female from behind and was either allowed to copulate or was rejected. Both copulation and rejection were followed by a posterior dismounting and short wing spreading display.

Specimens to be reared were collected in Virginia, Accomack County, at the following localities and dates: Chincoteague National Wildlife Refuge, Tom's Cove and vicinity, 25 June 1970 and 9 August 1970; Eel Creek Marsh, 12 August 1971 and 30 May 1972; Route 175, 0.5 mi W Cockle Creek, 9 August 1970, 12 August 1971, and 30 May 1972.

Adults maintained in the laboratory fed readily on field-collected salt marsh algae, occasionally supplemented with a honey and brewers' yeast paste. Field-collected males lived 11–18 days in laboratory colonies; females, 11–25 days. Laboratory-reared adults usually died within seven days of emergence.

In the laboratory, eggs were laid in various moist substrates but were concentrated in salt marsh algae when the latter was provided. Oviposition was not observed directly in nature, but a cluster of six eggs was recovered from a field-collected algal mat. Eggs were usually found in crevices or folds in the algae, located either on top of or just beneath the surface. Maximum recorded egg production for this species was 125 eggs over a six day period; the maximum daily output, 32 eggs. The incubation period at room temperature was two to three days, with 12 of the 20 observed eggs hatching on the third day. Newly hatched larvae began feeding as soon as they found a suitable food source. The first stadium lasted three days (18 observations); the second, three to seven days (15 observations); and the third, 14–20 days (8 observations).

The larvae are basically infraneustonic, living within the top centimeter or so of the substrate and keeping their posterior spiracles in more or less constant contact with the air-water interface. The ventral prolegs are well adapted for helping the larva to move through tangled masses of filamentous algae. The dorsal spine patterns may also aid in locomotion by snagging strands of algae beneath the flattened scalelike spines (Simpson, 1979).

The posterior spiracles are periodically pulled beneath the surface, usually to enable the larva to move about freely within the substrate, but they remain beneath the surface for only a few seconds at a time. As the spiracles are submerged, the hydrofuge lamellae converge around the peritreme and envelop it in an air bubble. In this manner the tracheal system is protected from contamination by water and dirt. Some larvae of Ephydra remain submerged for long periods of time, utilizing the air bubble as a plastron to supplement cuticular respiration (Aldrich, 1912; Ping, 1921). There is no indication that larvae of Cirrula austrina have this capability.

All known larvae of Ephydrini share the same feeding habits, being microphagous (Simpson, 1979). The larval mouthhooks, including those of C. austrina, are scoop shaped and are well adapted for directing liquid or semi-liquid materials into the mouth. Several rows of comblike spinules surround the mouth and act in conjunction with the mouthhooks to filter particulate material from the water. As the mouthhooks are extended, these structures flare outwards (Figure 30). As the mouthhooks are withdrawn, these structures collapse around the mouth, straining particulate matter from the aqueous medium in the process (Figure 31). The larva further concentrates the particulate matter through the use of pharyngeal ridges, located on the floor of the pharynx. The roof of the pharynx is forced downward against the ridges, forcing excess water between the ridges. The larva then expels the water through its mouth and swallows the particulate matter which was retained above the ridges. This mechanism is common among microphagous maggots and was described in detail by Dowding (1967).

While the larvae are feeding, the mouthhooks can be seen moving in and out of the mouth at a rate of several (2–3) times per second. The larvae feed almost continuously, ceasing for extended periods only when they are about to molt or pupariate.

Pupariation occurs just beneath the surface of the substrate, with the posterior respiratory tube projecting above the surface and the cephalic cap located just beneath the surface. The main portion of the puparium usually is concealed beneath a thin layer of the substrate. Because the puparium is located close to the surface, the adult merely crawls out of the puparium and onto the substrate when it emerges. In laboratory rearings, adults emerged seven to nine days after the puparium had formed (7 observations).

Cirrula austrina (Coquillett)

Ephydra austrina Coquillett, 1900b:36.

Dimecoenia austrina.—Cresson, 1916:152 [generic combination].

Cirrula austrina.—Mathis and Simpson, 1981:9–21 [generic combination, revision].

SPECIMENS EXAMINED.—BELIZE. Stann Creek District: Carrie Bow Cay, Mar 1988, W.N. Mathis (1, 2); Stewart Cay, Mar 1988, W.N. Mathis (1); Twin Cays (Aanderaa Flats, West Pond), Mar 1988, W.N. Mathis (2, 19).

DISTRIBUTION.—Nearctic: Bermuda, USA (CA, FL, MD, TX, VA). Neotropical: Belize, Mexico (NAY, SON).

NATURAL HISTORY.—As elsewhere (Mathis and Simpson, 1981:19–21), this species occurs in Belizean cays on mats of filamentous algae in salt marshes. The species seems to be more abundant when the habitat is partially dried, leaving the mats firmer and the substrate more solid.

DIAGNOSIS.—Although somewhat similar to C. gigantea Cresson, the only other congener, this species can be distinguished by the following combination of characters: five pairs of dorsocentral setae, presutural seta, and crucinate intrafrontal setae well developed, conspicuously larger than surrounding setulae; face lacking dense patch of long setae subdorsally; parafrons brownish, microtomentose; foretarsi of male cylindrical, similar to those of middle leg.

Dimecoenia Cresson, 1916:152 [type species: Coenia spinosa Loew, 1864, by original designation].

Cirrula austrina is a species of shore flies in the family Ephydridae.