Rheocricotopus emeiensis Wang & Zheng 1989

Rheocricotopus emeiensis Wang & Zheng, 1989 (Figs 1A; 2; 3) Examined material. 2 larvae (SHOU & BOLD sample ID: CHLA517, CHLA557): China, Sichuan, Liangshan Yi Autonomous Prefecture, Huidong, Canyuhezhen, 26.485°N, 102.584°E, 1406 m a.s.l., hand net, 24.X.2019, leg. Xin-Yu Ge; 1 Larva (SHOU & BOLD sample ID: CHLA549): China, Sichuan, Yibin, Pingshan, 26.932°N, 99.958°E, 1783 m a.s.l., hand net, 19.X.2019, leg. Xin-Yu Ge; 1 Larva (SHOU & BOLD sample ID: CHLA1007): China, Hainan, Sanya, 18.346°N, 109.524°E, 21 m a.s.l., hand net, 25.IV.2022, leg. Hong-Ying Sun; 1 Larva (SHOU & BOLD sample ID: CHLA1021): China, Hainan, Sanya, 18.388°N, 109.451°E, 169 m a.s.l., hand net, 16. VI.2022, leg. Hong-Ying Sun; 1 Larva (SHOU & BOLD sample ID: XL2803): China, Guizhou, Qiandongnan Miao and Dong Autonomous Prefecture, Leishan, Leigongshan Natural Reserve, Guluncun, Yegongzhai, 26.444°N, 108.060°E, 786 m a.s.l., hand net, 22.VIII.2019, leg. Hai-Jun Yu; 1 Larva (SHOU & BOLD sample ID: ZJ921): China, Zhejiang, Wenzhou, Yueqing, Furong, Benjue temple, 28.299883°N, 120.991455°E, 64 m a.s.l., hand net, 31.III.2019, leg. Xiao-Long Lin; 5 larvae (SHOU & BOLD sample ID: NLCH796, NLCH804, NLCH812, NLCH813, NLCH814): China, Jiangxi, Ganzhou, Longnan, Jiulianshan National Nature Reserve, Daqiutian, Qiu River, 24.583°N, 114.446°E, 400 m a.s.l., hand net, 21.VIII.2020, leg. Xiao-Long Lin. 2 larvae (SHOU & BOLD sample ID: HJR230, HJR246): China, Hubei, Shiyan, Zhushan, Loutai, Qinyu River, 32.335°N, 110.297°E, 400 m a.s.l., hand net, 19.VII.2020, leg. Zhen-Yuan Liu. 1 Larva (SHOU & BOLD sample ID: HJR298): China, Shaanxi, Shangluo, Shangzhou, Yancun, Jinqian River, 33.681°N, 109.844°E, 978 m a.s.l., hand net, 19.VII.15, leg. Zhen-Yuan Liu. Description. Fourth instar larva (n = 8). Total length 3.3−5.6, 4.3 mm. Body yellow with brown thoracic striations. Head Capsule (Fig. 2A). Length 353−435, 388 μm, width 250–311, 281 μm, length/width 1.24−1.46, 1.33; mental and mandibular teeth dark brown. Antenna (Figs 2B, 3A). Composed of one basal segment bearing five antennal segments. Segment 1 demonstrates significant elongation and an increased diameter compared to segment 2, with segment 2 exceeding the length of segments 3−5. Segment 5 marginally surpasses segment 4 in linear extension. Blade length 21−27, 24 μm. Lauterborn organ clearly visible on segment 3. Antennal segment length (in μm): 47−61, 54; 17−23, 19; 3−7, 5; 4−6, 5; 4−7, 6. AR: 1.30–1.83, 1.54. AAR: 0.34−0.58, 0.42. LOR: 0.22−0.33, 0.27. Mandible (Figs 2C, 3B). The mandible has one apical tooth and three inner teeth, and the length of the apical tooth is slightly less than the total width of the three inner teeth. Seta interna 5–6 branches, simple. Mandible 91−117, 102 μm long and 24−28, 26 μm wide. Seta subdentalis 8−10, 9 μm. Labrum. Pecten epipharyngis has three teeth; the middle tooth is straight, while the teeth on both sides are more curved. The three teeth are of comparable length, but the teeth on both sides are wider than the middle teeth. SI is bifurcated and other sensory bristles are simple. Premandible (Fig 3C) is single, and it only has one apical tooth without clear seta interna or inner teeth. Premandible length 49−60, 55 μm. premandibular apical tooth length 13−19, 15 μm. Mentum (Figs 2D, 3D). The mentum exhibits a bilaterally symmetrical structure comprising two median teeth, two accessory teeth, and five paired lateral teeth.The ventromental plate demonstrates prominent developmental characteristics, featuring a rounded basal configuration that collectively forms a distinct tear-shaped morphology. Mental setae present as robust chaetae, predominantly distributed along the mental extension. Submental setae are positioned in a ventral orientation relative to the mentum. Mentum median teeth 21−24, 22 μm long. VMp distance ventromental plate 32−45, 41 μm. VMp/MMT 1.51−2.86, 1.95. Mentum 77−92, 85 μm long. Postmentum 114−143, 125 μm long. Body. Procercus 18−22, 20 μm wide and 26−30, 28 μm long. Anal tubules are shorter than posterior parapods and the average length is around 127 μm. The average length of claws is 51 μm. Remarks. The larva of R. emeiensis can be distinguished from other related species by AR: 1.30−1.83, AAR: 0.34−0.58, LOR: 0.22−0.33, short antennal lobe, SI bifurcated, the mentum with two median teeth, large mental accessory teeth, and light postmentum color. Distribution. China (Guangdong, Guizhou, Hubei, Jiangxi, Shaanxi, Sichuan, Yunnan, Zhejiang), Thailand, Vietnam.