Chironomus (Camptochironomus) biwaprimus Sasa

Adult (from Sasa & Kawai 1987)

Length 6.96-8.11; wing length 3.58-4.05; VR 1.02-1.06.  AR 3.17-3.89
LR: Ant. 1.34-1.58; mid 0.50-0.56; hind 0.58-0.64.  BR 1.6.
Coloration unusual - antennal shaft brown, hairs brownish yellow;
ground color of scutum greenish yellow or pale yellow, vittae dark brown;
legs with femur and tibia largely yellow with a narrow apical dark ring;
tarsi darkening from brown to dark brown.
Head with relatively small frontal tubercles 22 micron long, 14 micron wide.
Thorax: Antepronotum united and expanded in the middle, without lateral setae.
Setae: Acrostichal 6-14; dorsolateral 19-36; prealar 6-10; scutellar 24-36 in a double row.
Legs: Front tibia with 4 subterminal setae arising on a rounded terminal scale.

Hypopygium (above) typical for the members of the camptochironomus-group, apparently closest to C. tentans.  No setae shown in center of TIX.  Anal point parallel sided, reaching just past the base of the gonostyle; Superior volsella essentially straight, not reaching the end of the anal point; Inferior volella long and gently curved with setae along the distal third; reaching two thirds along the dististyle, which is broad and narrows from about a third of its length.

Fourth instar larva:  A moderate sized, up to 20mm, plumosus-type larva.  Lateral tubules well developed, about 300 µm long.  AT nearly as long as the posterior prolegs and are constricted in the middle, about 2.5-2.7 times longer than wide.  Gula dark on posterior half, frontoclypeus dark, particularly towards the rear.
Mentum with broad c1 tooth, closest to type IIB but c2 teeth more separated; 4th laterals hardly reduced (type I).
Ventromental plates separated by about a third of the mentum width, about 3-3.3 times longer than depth to base of striae; about 48-49 striae; VMR 0.40-0.41.  PE with about 14 teeth of type B.
Distance between the antennal bases greater than that between the S4 setae, which are separated by about 72% of the frontoclypeus width.
Antenna with A1 about 3.2 times longer than wide and 0.4 of the VHL; RO about 0.4 up from base of segment, AR about 2.14; segment proportions (micron): 135 : 32 : 10 : 13 : 8.
Premandible with teeth about equal in length, inner tooth about twice as wide as the outer tooth.
Mandible about 250 µm in length, third inner tooth pale and incompletely separated (type 1A); about 21 furrows on the outer surface at the base and probably normally about 14 setae in Pecten mandibularis although one mandible of the available specimen had about 18 generally narrower setae.

Cytology:  Four polytene chromosomes with the Camptochironomus cytocomplex combination AB, CF, DE, G.  Specimens available did not have particularly good chromosomes, but some banding patterns could be determined.    Arm G may have a nucleolus but main nucleolus is in a long chromosome, probably near the centromere of the AB chromosome.  One heterozygote, probably in arm B.

biwE1:    1 - 2b, 7h - 10b, 3e - 2c, 7g - 3f, 10c - 13                        i.e. as dilutus E1
biwF1:    possibly 1a-d, 12-9b, 2f-3b, 13-14c, 5d-6, 9a-7a, 14d-16, 5c-3c, 1e-2e,.17-23

Found: Type locality - Lake Biwa (35.33°N, 136.17°E), Honshu, JAPAN; Lake Kasumigaura (36.42°N, 140.39°E); NEIS, Tsukuba (36.08°N, 140.08°E), Yatabe, Ibaraki.

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Modifieded: 2 January 2023
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