Stempellinella saltuum (Goetghebuer)

Ekrem, Torbjørn, 2007, A taxonomic revision of the genus Stempellinella (Diptera: Chironomidae), Journal of Natural History 41 (21 - 24), pp. 1367-1465 : 1435-1441

Stempellinella saltuum (Goetghebuer)

Tanytarsus saltuum Goetghebuer 1921, p 115 . Lectotype „ (RBINS) Belgium, Flandern,

Meirelbeke, 6 May 1920, M. Goetghebuer. Paralectotypes: 3 „„ as lectotype [all examined]. Lectotype here designated. Stempellina saltuum ( Goetghebuer, 1921) . Goetghebuer (1937 –54) description, key.

Additional material examined

Belarus (VM): 2 „„, 1♀, 3 LP, 2 LP (♀), Rayon Petrikov, Snyadin, brooklet of River Pripyat in floodplain forest, 14 May 2002, H. Moller-Pillot .

Diagnostic characters

Stempellinella saltuum can be separated from other Stempellinella species by the following combination of characters: adult male with wing length ca 1.5 mm, 3.6 times longer than broad; AR about 1.3; frontal tubercles large, conical; anal point with several (7–14) small spinulae between v-shaped crests; numerous (11–16) median tergite setae of which a few small setae are usually placed close to anal point; superior volsella oval with posteromedially directed apex; median volsella without microtrichiae, with fan of simple lamellae. Adult female with AR 0.27; vaginal floor small, concave following lateral margins of vagina; spermathecal ducts almost as long as notum and rami combined; rami as long or longer than notum; diameter of seminal capsules lower than length of notum. Pupa with welldeveloped, broadly conical cephalic tubercles; thoracic horn long and thin with numerous small chaetae scattered on distal two-thirds; median precorneal shorter than anterior and posterior precorneals; thorax with scattered sculpturing anteriorly; anterior dorsocentrals usually longer than 50 Mm, longer than anterior dorsocentrals; anal lobe with 18–25 taeniae in anal fringe. Larva with moderate (ca 24 Mm long), digitiform spur on antennal pedestal; AR 1.19–1.48; S3 split in three or four branches; both Lauterborn organs on short pedicels.

Redescription

Adult male (n 5 5, unless otherwise stated). Total length 1.8–2.1, 1.9 mm; wing length 1.40– 1.63, 1.55 mm.

Colour: head pale brown with dark pedicels and eyes; thorax with olive green ground colour, dark brown scutal stripes, brown postnotum, preepisternum and median anepisternum, scutellum and halteres pale, abdomen pale brown.

Head ( Figure 25A, B ): eyes without dorsomedian elongation; frontal tubercle large, conical, 15–21, 18 Mm long; antenna ( Figure 25B ) with 13 flagellomeres of which only 10 are easily discernible; AR (on 10 flagellomeres) 1.28–1.40, 1.33; lengths of palpomeres (in Mm, n 54): 30–36, 32; 36–48, 43; 114–120, 116; 105–120, 113; 144–168, 154 (n 53). Clypeus about 60 Mm long with 11–15, 14 setae; tentorium ca 120 Mm long, 25 Mm wide; two to four inner verticals, three or four outer verticals, two or three postorbitals.

Thorax: scutal tubercle absent; acrostichals 10–11; dorsocentrals 7–8; humerals absent; prealars 1; scutellars 5–7; halterals 5.

Wing ( Figure 25C ): cuneiform, 3.6 times longer than broad; VR 1.42–1.52, 1.47; wing setation as in Figure 25C .

Legs ( Figure 25D ): fore tibia with 14–24, 19 Mm long spur; mid and hind tibiae with well separated, 14–18, 16 Mm long combs, one mid tibial comb with 34–43, 38 Mm long spur, one hind tibial comb with 38–48, 41 Mm long spur; mid tarsus 1 without sensilla chaetica; pulvilli absent. Lengths and ratios of leg segments in Table III.

Hypopygium ( Figure 25E, F ): anal tergite 120–153, 137 Mm long with transverse anal tergite band; 11–16 median tergite setae, of which none to four are smaller and placed close to anal point base, one lateral seta, 24–32, 30 apical setae; anal point 57–72, 66 Mm long, basally 21–30, 25 Mm broad with well-developed crests surrounding V-shaped anal point pit, anal point distally thin and pointed; 7–14, 11 small spinulae between crests on anal point; small microtrichia-free areas present at base of anal point. Gonocoxite 105–127, 115 Mm long; gonostylus 61–87, 79 Mm long; HR 1.41–1.52, 1.45. Superior volsella ( Figure 25F ) oval with apical point, posteromedially directed, with five or six dorsal and two median setae on setiger, superior volsella otherwise bare; digitus absent; median volsella 39–54, 44 Mm long, posteromedially directed, stem simple, bare, with fan of simple 35 Mm long lamellae; inferior volsella ca 90 Mm long, club-shaped, with several distal setae, dorsal surface without microtrichia, well-developed microtrichose wart at base.

Adult female (n 5 1, unless otherwise stated). Total length 1.8 mm; wing length 1.48 mm. Colour: as male.

Head: as male, except cephalic tubercles ca 18 Mm long; antenna with five flagellomeres, ultimate flagellomere ca 62 Mm long, AR 0.28–0.29 (n 52); lengths of palpomeres (in Mm): 24; 30; 96; 96; 138. Clypeus with 14 setae.

Thorax (n 52): acrostichals 11–13; dorsocentrals 8; humerals 2–3; prealars 1; scutellars 6; halterals 6.

Wing: as male, except 3.1 times longer than broad. VR 1.27.

Legs: as male.

Genitalia ( Figure 25G ): tergite IX semicircular, about 45 Mm long; sternite VIII with 35– 45 (n 52) setae, of which none or one are placed on vaginal floor; vaginal floor small, concave following lateral margins of vagina; gonapophysis VIII single lobe with long posteromedially directed microtrichia; gonocoxapodeme slightly curved; coxosternapodeme well developed with obvious anterior and posterior lobes. Notum including rami 135–180 Mm long, notum alone ca 75 Mm long. Seminal capsules ovoid, diameter 57–71 (n 52) Mm with 150–165 (n 52) Mm long spermathecal ducts. Postgenital plate triangular. Cercus 45 Mm long.

Pupa (n 5 5, unless otherwise stated). Total length 2.6–2.8 mm; abdomen 1.9–2.0 mm long. Colour of pupal exuviae pale brown with darker lateral margins on abdominal segments VII – VIII and anal lobe.

Cephalothorax ( Figure 26A, B ): cephalic tubercle well developed, broad conical, 33–43, 39 Mm long; frontal setae taeniate, ca 180 Mm long; pedicel sheath tubercle absent. Thoracic horn 312–465, 400 Mm long, 18–24, 22 Mm wide with 6–9 Mm long chaetae scattered on distal two-thirds; precorneals taeniate, arranged in a slight triangle on obvious mound, anterior and posterior setae ca 200 Mm long, median seta ca 150 Mm long, anterior two placed closer together; median antepronotal taeniate, two lateral antepronotals: one taeniate, one sensillum basiconicum; two pairs of fine dorsocentrals, anterior pair 48–90, 70 Mm long, posterior pair 30–60, 40 Mm long. Area of fine sculpturing anteriorly on thorax, a few stronger granules present along median suture line. Prealar tubercle well developed, wide; nose of wing sheath well developed.

Abdomen ( Figure 26C ): TII with large triangular posteriomedian point patches which start anteriorly to seta D1; hook row 95–120, 112 Mm wide with 41–60, 47 hooks. TIII – VI with large, p -shaped point patches; TVII with anterior patches of points and shagreen; TVII –IX with anterolateral patches of shagreen. Segment II with pedes spurii B; segment IV with pedes spurii A. Segment II with 2 D, 2 V, 3 L setae; segment III with 3 D, 2 V, 2–3 simple and 0–1 semi-taeniate L setae; segment IV with 3 D, 3 V, 2–3 simple and 0–1 semitaeniate L setae; segment V with 3 D, 3 V, 3 taeniate L setae; segment VI – VII with 3 D, 3 V, 4 taeniate L setae, segment VIII with 1 D, 1 semi-taeniate V, 3 taeniate L setae; segment IX with 1 D seta on anal lobe, occasionally 1 taeniate V seta on anal lobe, 18–25, 21 (n 54) taeniate setae in anal fringe. One pair of O-setae present anteriorly on tergites II – VII and anterolaterally on sternites II – VIII. Pleura IV with small field of weak shagreen. Posterolateral spur on segment VIII well developed.

Larva (n 5 4, unless otherwise stated). Total length not measurable, larval case ca 3 mm long. Head capsule brown, somewhat darker postoccipital rim, teeth on mandible and mentum. Live specimens not examined.

Head ( Figure 26D–J ): AR 1.19–1.48, 1.33; antennal pedestal 66–81, 76 Mm long with well-developed, 21–27, 24 Mm digitiform spur; antenna ( Figure 26D ) with all segments well sclerotized, segment lengths (in Mm): 90–96, 93; 35–51, 43; 12–13, 12; 9–12, 10; 5–7, 6; segment 3 inserted subapically on segment 2; AAR 0.73–0.89, 0.81. Antennal seta placed at base just above ring organ; antennal blade ca 87–93, 89 Mm long, pale, reaching well beyond tip of distal Lauterborn organ; peg of antennal segment 2 placed subapically on segment. Lauterborn organs large, bulbous, 15 Mm long; proximal organ placed close to base of segment 2 on 6 Mm long pedicel, apical organ on 9–10 Mm long pedicel; SII ( Figure 26E ) slightly plumose, chaetae pectinate, chaetulae simple; S3 ( Figure 26F ) split in three or four branches; pecten epipharyngis consist of three well-developed chaetae and a broad anterior scale; labral lamella with 20–24 (n 52) teeth. Mentum ( Figure 26G ) with 13 teeth, median tooth with weak lateral notches, somewhat paler, all lateral teeth set in equal distance to each other; ventromental plates medially reaching third lateral tooth of mentum, MVR 1.20–1.26, 1.23; premandible ( Figure 26H ) with two teeth, well-developed brush; mandible ( Figure 26I ) with pecten mandibularis slightly convex, seta subdentalis 45–48, 47 Mm long; postoccipital plate ( Figure 26J ) narrow, split in middle.

Body: anterior parapods with long, simple spines; hind parapods with 16 simple hooks; L2 apparently simple; anal tubules not visible in larval exuviae; supraanal seta strong, 315 Mm long; procercus ca 30 Mm long with two short (ca 200 Mm long) and four long (ca 600Mm long) anal setae, the short setae situated individually, and not on the common base of the long setae.

Remarks

A lectotype is here designated for future stabilization of taxonomy. Although the measurements and ratios of the male in the original description are written in singular, I regard it as very likely that Goetghebuer examined all the specimens with the identical locality labels ‘‘Meirelbeke, 6.5.20’’ when describing the species. Which exact specimen was used for the original description is not certain, thus all the four male adults in RBINS are considered part of the type material .

Stempellinella saltuum has been recorded from Austria, Belarus, Belgium, Germany, Poland, Romania, and Sweden ( Saether and Spies 2004), but I have only seen material from Belarus and Belgium, and cannot confirm the other records in Fauna Europaea. The species is very similar to S. brevis in the adult male, but can be separated by the v-shaped anal point crests and the numerous median tergite setae. The larva and pupa are apparently most similar to those of S. ciliaris , but S. saltuum can be separated from this species by the longer thoracic horn, longer anterior dorsocentrals and more taeniate setae in the anal fringe in the pupa, and by a higher AR and longer distal Lauterborn organ pedicel in the larva.

The larvae of S. saltuum build small, straight transportable cases of detritus, and are found in floodplain streams and brooklets.

Figures

Figure 25. Stempellinella saltuum (Goetghebuer), imagines. (A–F) Male: (A) head; (B) antennal flagellum; (C) wing; (D) fore, mid, and hind tibiae; (E) hypopygium; (F) superior, median and inferior volsellae. (G) Female: genitalia.

Figure 26. Stempellinella saltuum (Goetghebuer), immatures. (A–C) Pupa: (A) frontal apotome; (B) thorax; (C) abdomen, dorsal view. (D–J) Larva: (D) antenna; (E) labral seta SII; (F) clypal seta S3; (G) mentum and ventromental plates; (H) premandible; (I) mandible; (J) postoccipital plate.