Rheocricotopus angustus Namayandeh & Hudson 2024, sp. nov.
Creators: name: Namayandeh, Armin
name: Guerra, Sergio
name: Islam, Natasha
name: James, Taylor
name: Hudson, Patrick L.
name: Ghaderi, Edris
name: Yusuf, Thameena
name: Vasquez, Adrian A.
name: Ram, Jeffrey L.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Chironomidae
Rheocricotopus
Rheocricotopus angustus

description: Rheocricotopus (s. s.) angustus Namayandeh & Hudson sp. nov.
Figs 10, 11, 12
Type material.
Holotype 1 male; Canada, Newfoundland, Terra Nova National Park; Blue Hill Road, 48.598 ° N, - 53.9702 ° W; leg. E. Perry; 21. v. 2013, dep. CBG. Paratypes 2 females, CANADA, Yukon Territory, Ivvavik National Park, 69.169 ° N, - 140.167 ° W; leg. N. Perry; 29. vi. 2014, dep. CBG. Paratype 1 larva; USA, Michigan, Detroit, Palmer Park, Pond A; 42.42766 ° N, 83.11741 ° W; leg. P. L. Hudson; 30. vi. 2022, dep. ARC.
Additional material examined.
Rheocricotopus (s. s.) effusus (Walker, 1856), 1 male, associated pupa and larval exuviae; USA, South Dakota, Yankton, Ed’s Creek, Gavins Point National Fish Hatchery, leg. P. L. Hudson, det. O. A. Sæther, dep. PLH. Rheocricotopus (s. s.) effusus (Walker, 1856), 1 male, associated pupa and larva exuviae; USA, South Dakota, Yankton, Ed’s Creek, Gavins Point National Fish Hatchery, 11. x. 1971, leg. P. L. Hudson, dep. PLH. Rheocricotopus (s. s.) effusoides Sæther, 1985, 1 male, associated pupa and larva exuviae; USA, South Dakota, Yankton, Marne Creek, 12. iii. 1972, leg. P. L. Hudson, dep. PLH. Rheocricotopus (s. s.) unidentatus Sæther & Schnell, 1988, 1 larva. GERMANY, Federal State Hessen, Freiensteinau, Nature Park Vogelsberg, (north-east f. Frankfurt), forest spring, 02. iv. 2017, leg. T. Bendt, dep. TB. Rheocricotopus (s. s.) pauciseta Sæther, 1969, holotype, 1 male, associated pupa and larval exuviae; CANADA, British Columbia, Marion Lake, University of British Columbia Forestry Farm, Haney, small mountain stream, 15. vii. 1967, leg., A. L. Hamilton and O. A. Sæther, dep. CNC, No. 9990.
Diagnostic characters.
R. angustus sp. nov. can be separated from other Rheocricotopus by the combination of the following characteristics: Adults with elongate ellipsoid humeral pits, without smaller basal pit, narrowing at the base for the male. Adult male with AR 1.4, anal point very short with 6 lateral setae, superior volsella with caudomedian projection strongly bent, thick, short and triangular. Adult female with AR 0.29, costa extension 115–119 µm long, notum 207–228 µm long. Fourth instar larva with AR 2.2, SI bifid with equal branches, SII long and thin, 37 μm long, mentum’s cardinal beard with 27 setae, seta submenti very long.
Description.
Male (n = 1). Total length 3.3 mm. Wing 1.8 mm long and 0.55 mm wide.
Coloration. Head, thorax, halters, legs, tergites, sternites, and hypopygium blackish brown. Wings pale brown.
Head (Fig. 10 A, B). Antenna with 13 flagellomeres, last flagellomere with 14 sensilla chaetica, groove starts at 4 th flagellomere (Fig. 10 A), AR 1.4 (n = 1). Eyes hairy, without dorsomedial extension. Temporal setae 5, including 2 frontals, 2 postoculars and 1 outer vertical. Tentorium 178 μm long (Fig. 10 B). Clypeus rectangular, 89 μm long and 136 μm wide, bearing 18 setae, setae 56–65, 60 μm long. Palpal segment lengths (in μm): 97, 69, 122, 135, 190. Third palpomere with single thin sensilla clavata.
Thorax (Fig. 10 C). Acrostichals 12, start close to antepronotum; dorsocentrals 19–20; prealars 5; scutellars 12 in single row; antepronotals 7. Humeral pit elongate ellipsoid narrowing at the base, about half the size of antepronotum, and no smaller basal pit.
Wing (Fig. 10 D). Brachiolum with 1 seta. Squama with 13 setae. R with 10 setae; all other veins bare. Costa extension is 44 μm long. Anal lobe developed.
Legs. Fore tibia spur and tarsal segments missing, mid tibia spurs 26 and 22 μm long, hind tibia spurs 55 and 17 μm long, hind tibia comb with 13 spines. Lengths and proportions of legs as in Table 5.
Hypopygium (Fig. 10 E). Laterosternite IX 62 μm long, with 12 setae. Anal point very short, 19 μm long and 14 μm wide at the base, triangular with apex pointed and with 6 lateral setae. Transverse sternapodeme with well-developed oral projections; sternapodeme 135 μm long. Phallapodeme 48 μm long. Superior volsella with caudomedian projection tick, short and triangular, parallel but not touching in middle, strongly bent, 35 μm long. Inferior volsella triangular lobe covered in numerous simple setae, apex slightly bent. Gonocoxite 208 μm long. Gonostylus 98 μm long; crista dorsalis very large covering more than half of gonostylus, mega setae 12 μm long. HR 2.1, HV 3.4.
Female (n = 2). Total length 1.8–2.5, 2.2 mm. Wing 1.5–1.9, 1.7 mm long and 0.56–0.61, 0.58 mm wide.
Coloration. Same as the male.
Head (Fig. 11 A). Antenna with 5 flagellomeres, last flagellomere with 6 sensilla chaetica, Antennal segments 1–5 (in μm): 71–101, 86; 42–55, 48; 39–48, 44; 62; 78; AR 0.29. Eyes hairy, reniform. Temporal setae 5 including 1 frontal, 2 outer verticals, and 2 postoculars. Tentorium 144–174, 159 μm long. Clypeus rectangular, 65–82, 74 μm long and 96–110, 104 μm wide, bearing 12 setae, setae 53–63, 59 μm long. Palpal segment lengths (in μm): 27–31, 29; 31–34, 32; 57–71, 64; 61; 72–90, 81.
Thorax (Fig. 11 B). Acrostichals 21; dorsocentrals 12–18, 15, in a single row; prealars 3; scutellars 6 in single row; antepronotals 5. The humeral pit is similar to that of the male but not narrow at the base.
Wing (Fig. 11 C). Brachiolum with 1 seta. Squama with 10 setae. R with 10 setae; R 1 with 5–8, 7 setae; R 4 + 5 9–14, 12 setae; other veins without setae. Costa extension 115–119, 117 μm.
Legs. Fore tibia spur missing, mid tibia spurs 17 and 21 μm long, hind tibia spurs 17 and 36 μm long; hind tibia comb with around 13 spines. The lengths and proportions of the legs are shown in Table 6.
Genitalia (Fig. 11 D, E). Seminal capsules ovoid, 82–119, 102 μm long, and 56–80, 66 μm wide; spermathecal ducts without loop, with well-developed bulb. Notum 207–228, 218 µm long, notum and ramus 256–285, 270 µm long. Gonapophysis VIII divided into large ventrolateral covering smaller dorsomesal lobe. Apodeme lobe distinct. Gonocoxite developed, with around 8 setae (Fig. 11 E). Tergite IX divided in two pale ovoid sections each bearing around 8–9 setae. Cercus large, base semi-circular, apex pediform, 66–89, 78 µm long, and 71–96, 83 µm wide.
Immatures. The pupa is unknown. The larva is associated by molecular DNA-barcoding.
4 th instar larva (n = 1). Total length 7.1 mm. Head 354 μm long and 381 μm wide.
Coloration of the mounted specimen. Head capsule yellowish brown with occipital region darker than rest of the head capsule, body greyish brown.
Head (Fig. 12 A – D). Antenna 5 segmented; segments length in μm: 86, 14, 10, 7, 7; AR 2.2; basal antennal segment 20 μm wide, distance from the ring organ to base of basal segment 8 μm. Lauterborn organ robust covering the 3 rd segment, blade damaged. Labral SI bifid with equal branch, SII – SIII simple, SII long and thin (Fig. 12 B). Premandible simple, 78 μm long (Fig. 12 B). Mandible much paler in basal half, apical tooth shorter than combined width of three inner teeth; seta subdentalis reaches the base of first inner tooth; setae interna with several long branches (Fig. 12 C), mandible 137 μm long. Mentum dark, with large median tooth and 5 pairs of lateral teeth, median tooth slightly notched (possibly worn off), median tooth 35 μm wide, 3.6 × the 1 st lateral teeth; seta submenti very long, upright reaching the base of median tooth, base aligned with the 4 th inner teeth (Fig. 12 D); mentum 92 μm long and 134 μm wide; ventromental plate large, extended beyond the mentum, 116 μm long, and 29 μm wide, cardinal beard with 27 lateral setae. Postmentum 242 μm long.
Abdomen (Fig. 12 E, F). Posterior parapods 301 μm long and 208 μm long, bearing around 15 simple claws. Procercus 34 μm long and 18 μm wide, bearing two small basal spurs and 4 apical setae (Fig. 12 F), apical setae 447 μm long, supraanal setae 49 μm long. 4 anal tubules present, 78–92 μm long.
Etymology.
The new species is named after the city of Detroit. The name of the city comes from the French word détroit meaning strait or river, which translates to angustus in Latin.
Distribution.
Canada (Manitoba, New Brunswick, Newfoundland, Nunavut, Ontario, Yukon Territory); USA (Michigan).
Remarks.
Based on the shape of superior volsella, R. angustus sp. nov. belongs to the effusus group. A detailed examination and comparison of the species in this group is provided by Namayandeh and Beresford (2018). Here, we mentioned that the elongate ellipsoidal shape of the humeral pit of R. angustus sp. nov. adults are quite distinguishable from other known species in this group, except Rheocricotopus (s. s.) unidentatus Sæther & Schnell, 1988. However, in R. angustus sp. nov., no additional smaller basal pit is present. Another distinguishing characteristic of R. angustus sp. nov. male is the very short anal point of the male with few lateral setae. The female of R. angustus sp. nov. can be separated from the known females of this group by a lower antennal ratio and longer notum and costa extension.
The key to adult males of the effusus group we provided in this study is based on a previous key by Namayandeh and Beresford (2018), which was based on a key by Sæther (1985). The provided key can only partially separate the species in this group. Rheocricotopus (s. s.) effusoides Sæther, 1985 and Rheocricotopus (s. s.) effusus (Walker, 1856) can be separated based on the size and ratio in all life stages (Sæther 1985). R. unidentatus is quite distinguishable from other species based on the larval mentum characteristic.
The larva of R. angustus sp. nov. can be separated from other known larvae in this group by a higher antennal ratio, a bifid SI with equal branches, and SII 37 μm long. Except for R. unidentatus, which has a distinguishing single median mental tooth, there are overlapping characteristics of larvae in this group, which makes their separation difficult. These include but are not limited to the length of the head, postmentum, and basal antennal segment, and number cardinal beard setae (Table 7). However, R. effusus and Rheocricotopus pauciseta Sæther, 1969 are in the lower range of the basal antennal length in comparison to other known larvae of this group. R. unidentatus and R. effusoides are in the higher range of cardinal beard setae than other species in this group, and R. angustus sp. nov. and R. pauciseta are in the lower range. We found that the length and shape of labral SII could also distinguish the larvae in this group (see Table 7). We examined the larval procercus of all species in this group, except for the voucher specimen of R. effusoides, in which the abdomen was missing, and consulted Mr. Thomas Bendt on the larva of R. unidentatus from Germany, which confirms that all larvae possess a pair of small procercal spurs. However, the shape and size of these spurs are very similar (Table 7).
* The labral SI of the examined larvae appears bifid. However, the length of the branches is hard to detect due to the condition of the mount.
description: Published as part of Namayandeh, Armin, Guerra, Sergio, Islam, Natasha, James, Taylor, Hudson, Patrick L., Ghaderi, Edris, Yusuf, Thameena, Vasquez, Adrian A. & Ram, Jeffrey L., 2024, New species and a fascinating diversity of Chironomidae (Diptera, Insecta) in and around an overlooked urban vernal pool, pp. 133-163 in ZooKeys 1208 on pages 133-163, DOI: 10.3897/zookeys.1208.124495