Stilocladius keithsomersi, Namayandeh & Hudson & Bogan & Hudson, 2024

Namayandeh, Armin, Hudson, Patrick L., Bogan, Daniel L. & Hudson, John P., 2024, Chironomidae (Diptera: Insecta) of Alaska, USA, with descriptions of new species and a checklist, Zootaxa 5511 (1), pp. 1-95 : 34-36

Stilocladius keithsomersi sp. nov.

urn:lsid:zoobank.org:act:8DC6249E-3292-44BE-88F2-3045630C7F75

Fig. 7A–D

Type materials. Holotype male; USA, Alaska, Juneau, Montana Creek , 19.viii.2019; leg. J. Hudson. Paratype 1 male same as holotype; dep. UAM .

Etymology. The new species is named in honor of Dr. Keith Somers of the University of Toronto, and Trent University, Canada, who has made tremendous contributions to the knowledge and application of macroinvertebrates in the biomonitoring of freshwaters.

Diagnosis. The adult male of S. keithsomersi sp. nov. can be separated from other adult males of Stilocladius by the combination of the following characteristics: Antenna with 13 flagellomeres; AR 0.51–0.52; wing with a short costal extension; a V-shaped tergite band present and reaches the base of anal point; virga with 2 outer and 3 inner spines; anal point very short, triangular, rounded at apex without dense basal microtrichia.

Male (n = 2)

Total length 2.2–2.3 mm; wing 1.4 mm long and 0.52 mm wide.

Coloration of mounted specimen. Head, thorax, and legs brown. Abdomen yellowish brown. Halteres and wings greyish brown.

Head ( Fig. 7A–B ).Antenna with 13 flagellomeres, plume moderate, last segment with around 8 sensilla chaetica, each of segments 2 and 3 with 2 sensilla chaetica, groove starts at 4 th flagellomere, AR 0.51–0.52 ( Fig. 7A ). Eyes hairy, microtrichia extending beyond ommatidia, short wedge-shaped dorsomedial extension is present. Tentorium 90–102, 96 μm long, narrow and pointed apically, tentorial pit close to center ( Fig. 7B ). Temporal setae 4 uniserial. Clypeus triangular, bearing 4 setae, clypeus 63–71, 67 μm long and 85–91, 88 μm wide (maximum), clypeus setae 46–64, 57 μm long. Palpal segments lengths (in μm): 31–32; 33–35, 34; 66–73, 71; 60–61; third palpomere with 1 sensilla clavata.

Thorax ( Fig. 7C ). Acrostichals 2 in mid-scutum, dorsocentrals 4 in single row and well separated, prealars 2, antepronotal lobes with 4 setae basolaterally ( Fig. 7B ).

Wing ( Fig. 7D ). Brachiolum with 1 seta, R with 4 setae, R 1 bare, R 4+5 with 4 setae close to apex, other veins bare. Costa extension 61 μm long.

Legs. Fore tibial spur 29–32, 31 μm long, mid tibial spurs 13 μm long, hind tibial spurs 39–41, 40 and 16–17 μm long, hind leg comb with around 13 spines. Lengths and proportions of legs as in Table 8.

Hypopygium ( Fig. 7E ). Tergite IX with around 4 simple setae close to the anal point. Anal point short, triangular, apex rounded. A V-shaped tergite band is present and reaches the base of anal point. Virga inconspicuous, consists of two long outer and around 3 shorter inner spines, outer spines 18 μm long, inner spines 13 μm long. Sternapodeme straight without oral projections, 43–46, 45 μm long. Phallapodeme 31–33, 32 μm long. Inferior volsella prominent squared basally. Gonocoxite 144–167, 155 μm long. Gonostylus bent medially, crista dorsalis absent, gonostylus 60–63, 62 μm long, megaseta 8–12 μm long. HR 2.4–2.7, 2.5; HV 3.6–3.7.

Remarks

The adult male of S. keithsomersi sp. nov. is very similar and probably forms a sister group to Stilocladius orientalis Makarchenko & Makarchenko, 2003 . S. keithsomersi is smaller species in comparison to S. orientalis , and its antennal ratio is much lower (0.51–0.52) than S. orientalis (1.1–1.3). S. keithsomersi sp. nov. anal point is very short like S. orientalis ; however, it lacks the dense basal microtrichia, its inferior volsella lacks finger-like emargination unlike S. orientalis , its virga is shorter (13–18 μm long) with 5 spines and costal extension of the wing is 61 μm long. S. orientalis virga is 26–28 μm long, and consists of 8 spines, the costal extension of the wing is 66–98 μm long (E. Makarchenko, personal communication, Nov 12, 2023). The adult male of S. keithsomersi sp. nov. can be separated from other Stilocladius males based on the diagnosis and the key provided below. We produced the following key based on those provided by Makarchenko & Makarchenko (2003) and Wang (1998) with modifications and additions.

A key to adult males of Stilocladius Rossaro, 1979

1. Antenna with 13 flagellomeres. Wing costal extension ≤ 108 μm long............................................ 2

- Antenna with less than 13 flagellomeres. Wing costal extension> 108 μm long.................................... 4

2. Anal point long, ≥ 80 μm long ( Rossaro 1979: Fig. I; Rossaro 1984: Fig. 1e ). Crista dorsalis present and conspicuous.......................................................................................... S. montanus Rossaro

- Anal point short, << 80 μm long. Crista dorsalis absent or inconspicuous......................................... 3

3. AR 0.51–0.52. Virga with 5 blades. Anal point 17 μm long; base of the anal point without dense basal michrotrichia ( Fig. 7D ). Inferior volsella without finger-like emargination ( Fig. 7D ).................................. S. keithsomersi sp. nov.

- AR 1.1–1.3. Virga with 8 blades. Anal point 8–14 μm long; base of the anal point with michrotrichia ( Makarchenko & Makarchenko 2003: Figs. 1–5 ). Inferior volsella with finger-like emargination ( Makarchenko & Makarchenko 2003: Figs. 2 & 6 )................................................................ S. orientalis Makarchenko & Makarchenko

4. Antenna 10 segmented; AR 0.74............................................ S. kurobekayakius (Sasa & Okazawa)

- Antenna 12 segmented; AR <0.74........................................................................ 5

5. Costa extension 133 μm long. Anal point 18–24 µm. Crista dorsalis present ( Wang 1998: Fig. 1 )....... S. intermedius Wang

- Costa extension 158–221 μm long. Anal point 23–40 µm. Crista dorsalis absent.................... S. clinopecten Saether

Figures

FIGURE 1. A map of Alaska, USA, indicating the bioregions. The black circles represent the present study and historical collection sites of Chironomidae.

FIGURE 2. Krenopelopia cf. narda Roback, 1971 pupa (A), larva (B–G). A. thoracic horn, B. ventral cephalic setae of head capsule, C. dorsal cephalic setae of head capsule, D. antenna, E. mandible, F. ligula, and paraligula, G. claws of posterior parapods. Scale bars are 20 µm.

FIGURE 6. Heleniella parva Saether, 1984 adult female (A–C), pupa (D–H). A. antenna, B. genitalia ventral, C. genitalia dorsal, D. thoracic horn and precornial setae, E. tergites I–IX, anal lobes, genitalia sacs, and macrosetae, F. posterior simple spines of tergites, G. sternites I–III, H. anteromedial patch of long spines. Scale bars are 50 µm.

FIGURE 7. Stilocladius kiethsomersi sp. nov. adult male (A–E).A. antenna. B. head. C. thorax. D. wing. E. hypopygium. Scale bars are 100 μm.