Stempellinella boltoni, Ekrem, 2007

Ekrem, Torbjørn, 2007, A taxonomic revision of the genus Stempellinella (Diptera: Chironomidae), Journal of Natural History 41 (21 - 24), pp. 1367-1465 : 1378-1382

Stempellinella boltoni sp. n.

Stempellinella sp. 2 . Bolton (2006) identification key to larva.

Type material

Holotype: P „ ( USNM) USA, OH: Wayne Co. Izaak Walton tributary, Cedar Valley Rd , 1 June 2005, E. Moore.

Paratypes: two P „„, one P ♀, one prepupa, one P, six L as holotype; two L as holotype except collected 4 April 1998, M. J. Bolton .

Etymology

The species is named after my good colleague Mike Bolton who made the type material available for this study .

Diagnostic characters

Stempellinella boltoni can be separated from other Stempellinella species by the following combination of characters: adult male with AR 0.8–0.95; anal point long, triangular, with 11–16 strong double spinulae between well-developed anal crests; strong median setae on anal tergite; lateral anal tergite setae absent; setiger of superior volsella strongly angled, narrow basally, width shorter than horizontal distance between superior and median volsellae; median volsella 45 Mm long with microtrichose, palmate stem. Pupa with conical cephalic tubercles and moderately wrinkled frontal apotome; thorax completely brown pigmented, slightly granulated and wrinkled anterodorsally; thoracic horn comparatively short and broad (ca 280 Mm long) with strong chaetae along dorsal margin; median antepronotal not on tubercle; one lateral seta on abdominal segment III and IV taeniate, anterolateral patches of shagreen on tergites VIII –IX only; pleura apparently without shagreen. Larva with 35 Mm long, slightly curved spur apically placed on antennal pedestal; AR ca 0.9; premandible with three teeth; S3 split in two long and several small branches.

Description

Adult male (n 5 3, unless otherwise stated). Total length 1.7–2.0, 1.85 mm; wing length not measurable.

Colour: head and thorax brown with somewhat darker scutal stripes, eyes dark brown, abdomen and legs pale yellow-brown.

Head ( Figure 2A, B ): eyes without dorsomedian elongation; frontal tubercle large, conical, 12–19, 15 Mm long; antenna with 13 flagellomeres of which only 10 are easily discernible ( Figure 2B ); AR (on 10 flagellomeres) 0.84–0.92, 0.88; lengths of palpomeres (in Mm, n 52): 20; 25; 55–70; 75–85; 110–130. Clypeus about 30 Mm long with 8–10, 9 setae; tentorium ca 90–100 Mm long, 15 Mm wide; two or three inner verticals, two to four outer verticals, three postorbitals.

Thorax (n 52): scutal tubercle absent; acrostichals 8–10; dorsocentrals 5; humerals 0; prealars 1; scutellars 4–6; halterals 5 (n 51).

Wing: not measurable since all males were pharate.

Legs ( Figure 2C ): fore tibia with 15 Mm long spur; mid and hind tibiae with wellseparated, 10–12 Mm long tibial combs, one comb on each tibia with 25–30, 27 Mm long spur; tarsi without sensilla chaetica; pulvilli absent. Lengths and ratios of leg segments in Table III.

Hypopygium ( Figure 2D–F ): anal tergite 88–93, 91 Mm long with transverse anal tergite band, three to five, four strong median setae far from anal point base, one small setae near base; lateral anal tergite seta absent; anal point 40–50, 45 Mm long, basally 18–20 (n 52) Mm broad with well-developed crests, distally thin and pointed downwards; 11–16, 14 strong spinulae between anal crests; microtrichia present around base of anal point. Gonocoxite 83–85, 84 Mm long; gonostylus 52–55, 54 Mm long; HR 1.55–1.60, 1.56. Superior volsella ( Figure 2F ) comparatively large, setiger medially bent, base narrower than horizontal distance between superior and median volsellae, four or five dorsal setae, two or three median setae, basomedian on setiger margin, superior volsella otherwise bare; digitus absent; median volsella 45 Mm long, posteromedially directed, palmate stem with long microtrichia, with simple 15 Mm long lamellae; inferior volsella 65 Mm long, slightly clubshaped, with five distal setae, dorsal surface without microtrichia.

Adult female. The condition of the pharate adult female in the type material is not good enough for description.

Pupa (n 5 5, unless otherwise stated). Total length 2 mm; abdomen 1.5–1.6, 1.5 mm long. Colour of pupal exuviae: thorax completely brown, abdomen clear with darker lateral margins on segments VII –IX, tergites VII and VIII with dark pigmentation posteriorly.

Cephalothorax ( Figure 3A, B ): cephalic tubercle well developed, conical, 30 Mm long; frontal setae taeniate, 90–150, 116 Mm long; pedicel sheath tubercle absent. Thoracic horn 200–335, 278 Mm long with some 5–15 Mm long chaetae distributed dorsally on distal half; precorneals taeniate, arranged in slight triangular pattern, the two anteriormost setae situated closer to each other than to the third, anterior precorneal 125–190 (n 52) Mm long; median precorneal 125–150, 133 (n 53) Mm long; posterior precorneal 120–175, 140 (n 53) Mm long; one taeniate median antepronotal ca 100 Mm long, two lateral antepronotals (one sensillum basiconicum); two pairs of fine dorsocentrals, setae of each pair equally strong, 25–35 Mm long. Restricted field of granulation and fine sculpturing anterodorsally on thorax, a few stronger granules present along median suture line. Prealar tubercle well developed, wide; nose of wing sheath strong.

Abdomen ( Figure 3C ): TII with developed subtriangular point patches; hook row 50–70, 59 Mm wide with 23–35, 29 hooks. TIII – V with more or less p -shaped point patches, patches on TIII somewhat smaller; TVI with two long subrectangular point patches; TVII without shagreen or points; TVIII –IX with small anterolateral patches of shagreen. Segment II with well-developed pedes spurii B; segment IV with pedes spurii A. Segment II with 2–3 D, 2 V, 3 L setae; segment III with 3 D, 2 V, 2 L, 1 taeniate or semi-taeniate L setae; segment IV with 3 D, 2 V, 2 L, 1 taeniate L setae; segment V with 3 D, 2–3 V, 3 taeniate L setae; segment VI – VII with 2 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, 14–19, 17 taeniate setae in anal fringe. One pair of O-setae present anteriorly on tergites II – VIII. Pleurae apparently without shagreen. Posterolateral spur on segment VIII well developed.

Larva (n 5 5, unless otherwise stated). Total length ca 2–2.5 mm, house ca 3 mm. Head capsule yellow, brown postoccipital rim and teeth on mandible and mentum. Live individuals not examined.

Head ( Figure 3D–I ): AR 0.88–0.97, 0.95; antennal pedestal 65–70, 66 Mm long with strong, apical, 33–37, 35 Mm long, slightly curved, blunt spur; antenna ( Figure 3D ) with all segments well sclerotized, segment lengths (in Mm): 63–75, 69; 38–45, 42; 13–15, 15; 10– 12, 11; 5–6; segment 3 inserted subapically on segment 2; AAR 0.87–1.03, 0.96. Antennal seta ca 30 Mm long, placed at base just above ring organ; antennal blade 95–100 (n 52) Mm long, pale, reaching well beyond tip of antenna; peg of antennal segment 2 placed at twothirds length of segment. Lauterborn organs large, bulbous, 20–25, 23 Mm long; proximal organ placed at one-third length of segment 2 on 5–10 Mm long pedicel, apical organ on 15–20 Mm long pedicel; SII and chaetae plumose; chaetulae simple; S3 long and split in two long and several short branches ( Figure 3E ); pecten epipharyngis consist of three welldeveloped chaetae; labral lamella with ca 22 teeth. Mentum ( Figure 3F ) with 13 teeth, median tooth with low lateral notches, all teeth equally dark; ventromental plates medially reaching third lateral tooth of mentum, MVR ca 1.1–1.4; premandible ( Figure 3G ) with three teeth, with well-developed brush; mandible ( Figure 3H ) with pecten mandibularis slightly convex, seta subdentalis 35–40, 38 Mm long, reaching well beyond apex of mandible, mola bare or with two closely set spines; postoccipital plate ( Figure 3I ) well developed, split.

Body: anterior parapods with long, simple spines; hind parapods with 15 simple hooks; L2 apparently simple; anal segment with four 60 Mm long anal tubules; supraanal seta strong, 225– 275, 245 Mm long; procercus with two short (ca 140 Mm long) and four long (ca 550 Mm long) anal setae, the short setae situated individually, and not on the common base of the long setae.

Remarks

Stempellinella boltoni is very similar to S. fimbriata and S. tamaseptima in the adult male, but can be separated from the former by the more broadly triangular anal point and the broader, blunt apex of the superior volsella, and from the latter by the longer distance between superior and median volsellae (longer than width of setiger base in S. boltoni ). The three species can also be separated by their COI gene sequences (Table IV).

The species has been recorded from two localities in Ohio, USA. The larvae build transportable cases of comparatively coarse sand and detritus.

Figures

Figure 2. Stempellinella boltoni sp. n., male imago. (A) Head; (B) antennal flagellum; (C) fore, mid, and hind tibiae; (D) hypopygium; (E) anal point lateral view; (F) superior and median volsellae.

Figure 3. Stempellinella boltoni sp. n., immatures. (A–C) Pupa: (A) frontal apotome; (B) thorax; (C) abdomen, dorsal view. (D–I) Larva: (D) antenna; (E) clypal seta S3; (F) mentum and ventromental plates; (G) premandible; (H) mandible; (I) postoccipital plate.