Clypeocaenis laosensis Vannachak, Malzacher & Sangpradub sp. nov. (Figs. 1–5)

Materials examined. Holotype (in ethanol): Male larva (THNHM-I-00029764), Lao PDR, Khammouane Province, Xebangfai District, Xe Nou River, 17°4’5.56”N, 105°4’13.68’’E, 154 m a.s.l., 6.I.2022, V. Vannachak leg, deposited in the Natural History Museum, Thailand.

Paratypes (in ethanol): 3 male and 2 female larvae (THNHM-I-00029765–00029769) same data as holotype, deposited in the Natural History Museum, Thailand. 10 male and 3 female larvae (Cl / Laos.002) same data as holotype, deposited in NUoL-AIC.

Other materials: 1 male and 2 female larvae (Cl / Laos.003), Lao PDR, Savannakhet Province, Xaybury District, Tha Hao Stream, 16°51’54.47”N, 104°54’3.77”E, 140 m a.s.l., 23.XI.2019, deposited in KKU-AIC. 4 female and 2 male larvae (Cl / Laos.004), Savannakhet Province, Songkhone District, Xe Bang Hieng River, 16°05’51.42”N, 105°22’33.13”E, 126 m a.s.l., 24.XI.2019, deposited in NUoL-AIC, all V. Vannachak leg.

Mature Nymph. Body length (excl. cerci): 2.5–3.5 mm (males) and 3.3–3.7 mm (females); cerci 1.2–1.5 mm; antennae 0.9–1.1 mm. General coloration light yellow to pale yellow. Epidermal pigmentation: vertex in females with a transverse dark brown band between the lateral ocelli. Pronotum with a distinctive pattern as in Fig. 1. Females with a dark brown, butterfly-like pattern between the wing pads. Abdominal terga I, II, and VII –IX in both sexes with broad transverse dark brown bands, contrasting to the light foundational coloration (Fig. 1A, B). Head: Head length 0.5 mm, width 1.8 mm, light yellow color. Compound eyes black; ocelli with the apical half black, basal half whitish. Antennae transparent; pedicel with 2–3 short setae distally on inner margin, 3 shorter setae on ventral surface. Pedicel’s length three times of scape, one and a half times of antennal segment III. Clypeus protruded, with 2 moderately long setae, longer than pedicel (Fig. 2A). Labrum three times wider than long, with anterior margin and semicircular curved lateral margin’s apical half bearing bipinnate setae. The dorsum presents long, fine frayed setae and long, thin setae, with a few long, thin setae scattered near basal half (Fig. 2B). Outer incisor of mandibles with five denticles, situated below molar with 4–5 long, thin setae. The dorso-lateral surface with two curved transverse rows of long setae; 8–12 setae on basal row and 5 setae on topical row (Fig. 2C). Maxillae and labium with setation patterns (Fig. 2D, F). Maxillary palp segment I narrow, about half as wide as galea-lacinia. Base of labial palp segment III not significantly broad. Hypopharynx’s superlingua with stout setae and lingua’s apical margin with thin setae at the apical margin (Fig. 2E). Three segmented labial palps; segment III more or less sickle-shaped, with bluntly pointed tip, as long as segments I and II together, segment III 4.2–4.5 times of segment II. (Fig. 2F). Thorax: Pronotum slightly convex sides with anterior protrusion (Fig.1A, B). Mesonotum light yellow coloration. Legs: light yellow to whitish, cover with knobs, interspersed with very delicate microtrichia, each with a few needle-shaped branches (pine-needle like, Fig. 4E). Foreleg: length of femur/ tibia/ tarsus/ claw viz., 0.52/ 0.42/ 0.41/ 0.16 mm. Coxal processes sickle-shaped with a denticulated surface featuring thin setae and a serrated margin. Trochanter with one regular and another irregular row of short setae (Fig. 3C). Femur with three long filtering setae at the middle of the inner margin, short setae on the outer margin’s proximal half, and approximately ten large, broadly spatulate bristles arranged in a transverse row on the distal half’s dorsal surface. Area apical to transverse row with denticulated and scattered with long, pine-needle-like setae (Figs. 3A, B). Dorsal side of tibia with two transverse rows of very long filtering setae, extending longitudinally on the ventral side. Tarsus with a row of long filtering setae, inner margin with eight stout setae, outer margin with scattered, thin, hair-like setae. Claw long, slender, apically bent, with 3–5 denticles, smallest basal (Fig. 3D). Midleg: length of femur/ tibia/ tarsus/ claw viz., 0.47/ 0.29/ 0.33/ 0.16 mm. Coxa and trochanter similar to foreleg. Femur with rows of spatulate setae, strongly narrowed at base on outer margins, microscopic setae on inner margin, proximal half of dorsal surface with scattered, short spatulate setae. Inner margin of tibia with a row of 8–12 stout setae and submarginal row of spatulate setae, outer margins with a few hair-like setae. Inner margin of tarsus with of seven stout setae, outer margin with scattered hair-like setae (Fig. 3E). Claw long, slightly bent apically, with 4 denticles increasing in size distally (Fig. 3F). Hindleg: lengths of femur/ tibia/ tarsus/ claw viz., 0.50/ 0.30/ 0.28/ 0.11 mm. Coxa similar to foreleg. Femur outer margin with a row of spatulate setae, inner margin’s proximal half with short spatulate setae. Tibia with a row of 13–15 stout setae on inner margin, outer and submarginal inner margins with spatulate setae. Tarsus with a row of 8–10 stout setae on inner margin, outer margins with a few hair-like setae (Fig. 3G). Claw, similar to midleg, with 4–5 denticles, basal denticle minuscule (Fig. 3H). Abdomen: Terga I, II, and VII –IX with marked broad transverse dark brown bands. Posterolateral processes short, slight elongated segment II (Fig. 4A). Tergum II with a triangular posteromedian process, pronounced denticulation at posterior margin, surface with scales (Fig. 4B). Terga VII –IX with strongly denticulate posterior margin, very small spatulate setae on tergum VII (Fig. 4A). Sternum IX slightly concave hind margin (Fig. 4C), shagreen field on dorsal surface with 4 irregular rows of small denticles parallel to the hind margin. Gill I short, two segments, length one-third of gill cover. Operculate gill quadrate, with the dorsal side covered with knobs and scattered long, leaf-like, pine-needle-shaped microtrichia as described in the section on the thorax (Fig. 4E). A strongly developed medial ridge forms an elevated keel, basally with 8–10 stout spatulate setae (Fig. 4F). The outer ridge narrow and inconspicuous, featuring a row of very small denticles. The lateral margin adorned with short setae, the inner margin with moderate-length thin bipinnate setae, and the posterior margin with very short, broadly spatulate setae (Fig. 4D, G). The microtrichia band on the ventral side of the gill cover absent (Figs. 4G, 12F). Gill III possesses a single filament with three branches and 30–35 filaments, each with simple or bifurcated branches (Fig. 5A). The cerci translucent with whorls of setae on each segment.

Egg: Oval shape (Fig. 5B), length 121–133 μm, 92–100 μm width. Chorion smooth with a single epithema that forms a cap consisting of fine threads, terminating in numerous very small knobs (Fig.5C). Positioned subequatorially, micropyle moderate length, mouth not broadened and encircled by a circular sperm-guide (Fig. 5B, D).

Imago: Unknown.

Diagnosis. Clypeocaenis laosensis sp. nov. exhibits distinctive morphological characteristics, and is closely related to Cl. kaveri Balasubramanian & Muthukatturaja, 2021, and Cl. gayathri Balasubramanian & Muthukatturaja, 2020 (Table 1). The following combination of features distinguishes this new species from its congeners: i) the pedicel is one and a half times the length of the third antennal segment (Fig. 2A); ii) below the molar, there are 4–5 thin setae; iii) the forefemur, at the middle of the inner margin, is equipped with three long filtering setae; the outer margin features short, simple setae, and the dorsal surface presents a transverse row of large, broadly spatulate setae (Fig. 3A, B); iv) the mid and hind femora are adorned with short, marginal bristles that are basally strongly narrowed (Fig. 3E, G); v) tarsal claws are long, slender, and slightly bent apically, with 3–5 denticles (Fig. 3D, F, H); vi) the posterior margin of abdominal tergum VII is strongly denticulate and bears small spatulate setae, whereas terga VIII–IX are only denticulated (Fig. 4A); vii) the operculate gill features short setae along the lateral margin, thin bipinnate setae along the inner margin, and very short spatulate setae along the posterior margin (Fig. 4D, G); the middle ridge is notably developed with 8–10 stout spatulate setae (Fig. 4F); viii) the operculate gill on the ventral side lacks a microtrichia band (Figs. 4G, 12F); ix) the egg’s epithema is cap-shaped, constituted by fine threads terminating in numerous small knobs; the micropyle is of moderate length, the mouth is not broadened, and it is encircled by a circular sperm-guide (Fig. 5B–D).

Etymology. The specific epithet laosensis is derived from the country of collection, Lao People’s Democratic Republic (Lao PDR), indicating the geographical origin of the new species.

Distribution and Habitat. Clypeocaenis laosensis sp. nov. has been collected in the Khammouane and Savannakhet Provinces of the Lao PDR (Fig. 14). Specimens were collected from stream and rivers situated in the central and southern regions of Lao PDR, within an elevation range of 126–154 m above sea level. The Xe Nou River (Fig. 13A) meanders through a village setting, bordered on one side by agricultural lands and forested areas. The riverbed primarily consists of bedrock and boulders, complemented by patches of gravel and sand. The water current exhibits a moderate to fast flow, particularly intensifying in the river’s central channel. The Tha Hao Stream (Fig. 13B) flows adjacent to a small village, encircled by agricultural fields and a stretch of forest. Its current is characterized as moderately fast. The streambed’s composition largely includes bedrock, boulders, and sand, interspersed with snags and leaf litter, providing a diverse substrate. Bordering the Xe Bang Hieng River (Fig. 13C), residential dwellings and vegetable gardens are prevalent. The riverbed here is distinguished by a foundation of bedrock, boulders, and remnants of concrete from old bridges, with minor sections of gravel, sand, mud, large wood debris (snags), and plant litter. This river features a moderate to fast current, especially intensifying in the river’s central channel. Larvae of this newly described species were predominantly found in the littoral zones, which are defined by their boulder, gravel, and sand substrates, accompanied by slower current velocities, providing a specific ecological niche for Clypeocaenis laosensis sp. nov.