A review of the Japanese Cryptochironomus Kieffer, 1918 (Diptera, Chironomidae)

Abstract The genus Cryptochironomus Kieffer, 1918 from Japan is reviewed based on material composed of male adults. New combinations of three species are established and they are re-described based on male adult of: C. misumaiprimus (Sasa & Suzuki, 1998), comb. n., C. tokaraefeus (Sasa & Suzuki, 1995), comb. n. and C. tonewabeus (Sasa & Tanaka, 2002), comb. n. Additional taxonomic notes are also provided: C. albofasciatus (Staeger, 1839), which is a senior synonym of Parachironomus inafegeus Sasa, Kitami & Suzuki, 2001 and C. rostratus (Kieffer, 1921) as the senior synonym of Paracladopelma inaheia Sasa, Kitami & Suzuki, 2001. A key to the known adult males of the genus from Japan is given.


Introduction
Cryptochironomus is a diverse genus and widely distributed worldwide. Kieffer (1918) erected this genus based on Chironomus (Cryptochironomus) chlorolobus Kieffer, 1918 as type species. Subsequently, the genus in all its life stages was studied by a number of authors (Townes 1945;Roback 1957;Curry 1958;Shilova 1966;Beck and Beck 1969; A large amount of material composed of adult males belonging to the genus Cryptochironomus was examined based on slide-mounted following the procedures outlined by Saether (1969). Morphology and terminology follow Saether (1980). All of the examined specimens are deposited in the Department of Zoology, National Science Museum, Tokyo, Japan.
Coloration. Thorax yellow-white, with yellow-brown spots. Femora of front legs yellow-brown, tibia and tarsi dark brown; femora, tibiae and tarsi I of mid and hind legs yellow-brown, tarsi II-V dark brown. Abdomen yellow-brown, hypopygium dark brown.
Head Legs. Front tibia with three subapical setae, 185 μm and 188 μm, the other lost. Mid legs with two spurs, 30 mm and 33 mm; tibial comb with 52 teeth, 14 mm long. Spurs of hind tibia 30 mm and 33 mm long, tibial comb with 62 teeth, 15 mm long.
The sensilla chaetica of tarsus I of mid leg and metapedes were not distinguishable. Lengths (in μm) and proportions of thoracic legs as in Table 1.
Hypopygium (Fig. 1). Tergite IX with 11-13 setae placed dorsally and ventrally on each side of the base of anal point. Laterosternite IX with three lateral setae. Anal point parallel-sided, slender, lateral setae and microtrichia absent. Anal tergite bands "Y"shaped. Phallapodeme 125 mm long. Transverse sternapodeme 80 mm long. Superior volsella semicircular, bearing five strong setae at apex, covered with microtrichia. Inferior volsella finger-shaped, swelling at apex, bearing two setae at apex, free microtrichia. Gonocoxite 140 mm long, bearing six strong setae along inner margin. Gonostylus 175 mm long, widest at base, curved slightly at 1/3 distance from base, tapered to the apex, bearing seven short setae along inner margin and one seta at apex. HR: 0.89; HV: 3.11.
Remarks. The characters of frontal tubercles, superior and inferior volsella, and gonostylus of this species followed the generic character of the genus Cryptochironomus emended by . The small frontal tubercles and "Y"-shaped anal tergite bands separate this species from other members of the genus. Figure 2 Chironomus rostratus Kieffer, 1921 (Sasa & Suzuki, 1998), comb. n. Length (μm) and proportions of legs. Diagnostic characters. Thorax with dark brown spots; the posterior margin of tergite IX shoulder-like or slightly cone-like; anal point slender, tapering distally or parallel-sided. Superior volsella crescent-like; inferior volsella tuberculate, bearing 1-3 stout setae, free microtrichia. Anal tergite bands "V" shaped, the junction of gonostylus and gonocoxite distinctly concaved, curved at 1/3 distance from base, apex with a small protrusion, bent inwards and bearing one seta.
Coloration. Thorax yellow-white, with yellow-brown spots. Femora of front legs yellow-brown, tibiae and tarsomeres dark brown; femora and tibiae of mid and hind legs yellow-brown, tarsi I yellow-brown except for dark yellow-brown at ends, tarsi II-V dark yellow brown. Abdomen yellow-brown, hypopygium dark brown. Legs. Front tibia with three subapical setae, 165μm and 168μm, the other lost. Mid legs with two spurs, 30 mm and 35 mm, tibial comb with 44 teeth, 15 mm long. Spurs of hind tibia 35 mm and 37 mm long, tibial comb with 60 teeth, 15 mm long. Tarsus I of mid leg with nine sensilla chaetica, Tarsus I of metapedes leg with six sensilla chaetica. Lengths (in μm) and proportions of thoracic legs as in Table 2.
Hypopygium (Fig. 2). Tergite IX broad with cone-like posterior margin, bearing approximately 30 setae located dorsally and ventrally near the base of anal point. Laterosternite IX with six lateral setae. Anal point 88 mm long, slightly wider at base, almost parallel-sided, apically rounded, lateral setae and microtrichia absent. Anal tergite bands "V"-shaped. Phallapodeme 135 mm long. Transverse sternapodeme 75 mm long. Superior volsella spherical to bulb-like, covered with microtrichia, bearing six strong setae at apex. Inferior volsella tuberculate, bearing three setae at apex, free microtrichia. Gonocoxite 138 mm long, with six stout setae placed along inner margin. Gonostylus 170 mm long, base widest, slightly curved in the middle, tapered to the apex, bearing seven short setae along inner margin and one stronger seta at apex. HR: 0.81; HV: 3.21.
Remarks. The holotype of Paracladopelma inaheia belongs to the well-known European Cryptochironomus rostratus based on morphological characters of the hypopygium and metric measurements (Kieffer 1921;Pinder 1978: fig. 147B). Populations of C. rostratus from both Japan and other European areas key close together despite some minor morphological differences mainly related to geographical variation, especially the general shape of tergite IX, anal point, superior volsella, inferior volsella, and gonostylus. Thus, Paracladopelma inaheia can be considered as a junior synonym of Cryptochironomus rostratus (Kieffer, 1921).  (Kieffer, 1921). Lengths (μm) and proportions of legs. Diagnostic characters. Frontal tubercles and the posterior margin of tergite IX are highly variable in this species. The main distinguishing features are as follows: superior volsella bulbous to globular, both sides of the inferior volsella stretching upward at base, formed into flank-shaped, free microtrichia, bearing two long apical setae at apex. The junction of gonostylus and gonocoxite concaved obviously, gonostylus abruptly narrowed near apex and apically pointed, bearing one seta at apex. Distribution. China (Hebei, Zhejiang, Fujian, Hubei, Guangdong, Hainan, Sichuan); Japan; Russian Far East.
Diagnostic characters. AR 2.56. Frontal tubercles present; tergite IX bearing three setae, posterior margin tapering. Anal point parallel-sided. Anal tergite bands "V"-shaped. Superior volsella about twice as long as wide, with four long setae; inferior volsella extending well beyond posterior margin of superior volsella. Gonostylus wider at base and tapering towards apex, with one single apical seta.
Coloration. Thorax yellow-white, with yellow-brown spots; femora, tibiae and tarsi I of mid and hind legs yellow-brown; tarsi II-V dark yellow-brown. Abdomen yellow brown; hypopygium dark brown.

Cryptochironomus tonewabeus (Sasa & Tanaka
Diagnostic characters. AR 2.53, frontal tubercles cylindrical. Tergite IX broadly semi-circular, with 16 setae (eight on each side of base of anal point). Anal point wide at base, parallel-sided medially and distally, rounded apically. Anal tergite bands "wide V"-shaped, not fused in the middle, and abruptly interrupted at the end. Superior vol- Table 3. Male adult of Cryptochironomus tokaraefeus (Sasa & Suzuki, 1995), comb. n. Length (μm) and proportions of legs. Coloration. Thorax light yellow-brown, with yellow-brown spots, Femora of front legs yellow-brown, tibia and tarsomeres dark brown; femora, tibiae and tarsi I of mid and hind legs brown; tarsi II-V dark yellow-brown, hypopygium dark brown.
Distribution. Japan. Remarks. Frontal tubercles cylindrical, superior volsella peanut-like, and concave medially combined with a thumb-like inferior volsella, bearing four long setae at apex, and free microtrichia followed the generic characters of . The "V" shaped anal tergite bands, not fused medially, are similar to Cryptochironomus albofasciatus (Staeger, 1839), but C. tonewabeus can be differentiated by the frontal tubercles, superior volsella and inferior volsella.