Demicryptochironomus

Yan, Chuncai, Tang, Hongqu & Wang, Xinhua, 2005, Demicryptochironomus Lenz from China (Diptera: Chironomidae), Zootaxa 910, pp. 1-31 : 24-25

Demicryptochironomus sp. 1 ( Figs. 10 A–E)

Material examined: 1 larva, China, Hebei Province, Zunhua County Sahe River, 5. X. 1999, leg. X. Wang.

Fourth­instar larva

Small species, total length 2.89 mm, with pale brown color in alcohol. Head capsule and posterior occipital region pale. Head capsule 150 µm wide, 192.5 µm long, cephalic index (W/L) 0.78.

Antenna ( Fig. 10 A): Total length 118 µm long, about 0.61 times as long as head; with 6 segments, each segment length (in µm): 37.5, 15, 20, 25, 5, 2. AR 0.57–0.60. Basal segment 12.5 µm wide, ratio (L/W): 3.0. Ring organ located in apical third of basal segment, 4 µm in diameter, distance from base 27.5 µm. Second antennal segment relatively long, 7.5 µm wide, twice as long as wide. Blade situated at 1/2 of third segment, 37.5 m long, extending to apex of fifth segment. Accessory blade short. Style located at apex of fifth segment, about as long as fifth segment.

Labrum: SI hair­like, small. SII simple and strong, blade­like, 40 µm long, extending to posterior part of ungula. SIV divided into 3, each division length (in µm) 12.5, 10, and 5. Premandible ( Fig. 10 B) 45 µm long, with 3–4 teeth.

Mandible ( Fig. 10 C): Total length 60 µm long. With apical tooth and 2 sharp inner teeth. Apical tooth 15 µm long, combined width of inner teeth 7.5 µm. Seta interna with 2 long blade­like branches. Pecten mandibularis with 2 or 3 short branches, not extending beyond the inner margin of mandible.

Mentum ( Fig. 10 E): 62.5 µm wide, with 7 pairs of dark brown lateral teeth, and 1 semicircular pale median tooth. Each half of sclerotized lateral teeth 17.5 µm wide and median pale tooth 25 µm wide. Ventromental plate slender longer, 80 µm wide, with numerous striae; distance between ventromental plates 35 µm

Maxillary ( Fig. 10 D): Maxillary palp with 2 parts, basal portion about 3 times as long as wide (length 30 µm; width 10 µm), distal 1/3 not well sclerotized. Second part 20 µm long, with 4–6 short blades, b sensillum 3­segmented, with ratio between segments 2: 3: 1.

Abdomen: Posterior parapods 120 µm long, 60 µm wide. Procercus 22.5 µm high and 25 µm wide, with 8 anal seta, 450–500 µm long, two small subapical anal setae each 50 µm long. Supraanal seta 250 µm long, longer than posterior parapods. Anal tubules 2 pairs, upper pairs sausage­like, 62.5 µm long and 25 µm wide; lower pairs broadly triangular, 87.5 µm long, 37.5 µm wide.

Ecology: The larva was collected from sandy substrata in the Sahe River, a branch of the Luanhe River, in shallow water less than 0.5m deep.

Remarks: The larva is distinguished by having a 6­segmented antenna and a maxillary palpiger with well developed 3­segmented A seta, which differs from the diagnosis of the genus (antenna with 7 segments). Other characters agree with the generic diagnosis given by Pinder and Reiss (1983). Measurements (except for the number of antennal segments) resemble those of Demicryptochironomus fastigatus (Townes) and Demicryptochironomus sp. A sensu Epler (2001). The elongated fourth segment of D. sp.1 is subequal to the combined lengths of the fourth and fifth segments of other larvae in this genus. As only one larval specimen was examined, we temporarily treat it as D. sp. 1 in the preliminary key to known larvae of the genus (given below).

Figures

FIGURE 10. Demicryptochironomus sp. 1. Fourth­instar larva. A. Antenna B. Premandible. C. Mandible D. Maxilla. E. Mentum