﻿New species of Nigrobaetis from Southeast Asia (Ephemeroptera, Baetidae)

﻿Abstract Based on larvae collected in the Philippines, Borneo (Kalimantan), Sumba, and Sumatra, the presence of the genus Nigrobaetis in the Philippines and Indonesia is reported for the first time. Six new species are described and illustrated, two from the Philippines and four from Indonesia. A larval key to all Nigrobaetis species of the Philippines, Indonesia and neighbouring continental Southeast Asia is provided, morphological differences to the species of Taiwan are discussed as well. The eggs of three new species are described, and the morphology of the eggs of Nigrobaetis is briefly discussed.

New species of Nigrobaetis from Southeast Asia (Ephemeroptera, Baetidae) Introduction Nigrobaetis Novikova & Kluge, 1987 is a genus of Baetidae, which is the most diverse family of mayflies in number of genera and species (Sartori and Brittain 2015;Jacobus et al. 2019). Nigrobaetis has a wide distribution across the Afrotropical (six species), Palearctic (15 species) and Oriental regions (12 species), being absent from the Nearctic, the Neotropics region and Australasia (Barber-James et al. 2013).
They are mostly small species with a body length of 3-5 mm for the mature larvae, and present the following characters: larval antennae standing closely together, with a longitudinal keel between them (Lugo-Ortiz and de Moor 2000: fig. 1); right mandible with row of long, setae-like processes between prostheca and mola (Fig. 10c); left mandible usually with row of minute denticles between prostheca and mola (Fig. 2d); rarely absent or with tuft of medium, setae-like processes (Figs 10d,16d); labial palp segment II without distomedial protuberance, segment III generally roughly quadrangular, apically truncated (Fig. 4a, c); subimaginal gonostyli developing under cuticle of male last instar larvae folded in the Nigrobaetis-type (Figs 6c, 26c;Kluge 2004: fig. 29G; Kluge 2022).
From the Oriental region, Nigrobaetis species were described from continental Southeast Asia (Müller-Liebenau 1984), from Taiwan (Müller- Liebenau 1985;Kang et al. 1994;Kang and Yang 1996), and from India (Kubendran et al. 2015;Sivaruban et al. 2022). The important diversity reported from Taiwan (six species), points into the direction that we may expect many more species in other parts of the generally species-rich Southeast Asia. In comparison, the Afrotropical diversity is much lower with a single species widely distributed in continental Africa, and three species endemic to a single island (Anjouan, Madagascar, or la Réunion; Lugo-Ortiz and de Moor 2000; Gattolliat 2004;Kaltenbach et al. 2021). Nigrobaetis presently encompasses 33 species, 27 of them being described in the last forty years. In this study, we report the genus Nigrobaetis for the first time from the Philippines and Indonesia. We describe and illustrate six new species based on larvae and partly also on eggs.
Indonesia is an immense archipelago of more than 18.000 islands extending over a huge area from 95°E to 141°E and from 6°N to 11°S. It is one of the most biologically rich countries in the world. The high levels of species richness and endemism are mainly explained by a geological history that brought together two different biological realms (Oriental realm and Australasian realm), separated by a transitional region (Wallacea) (Hall 2010;Kingston 2010). The archipelago includes the main part of the Sundaland Biodiversity Hotspot, influenced by a dynamic and highly complex geophysical history including changing climates, fluctuating sea levels, volcanism, and orogenic activity with subsequent erosion (Quek 2010).
Similarly, the Philippines are a complex archipelago with more than 7100 islands, spanning the Asian-Australian faunal zone interface directly at the Wallace Line. The Huxley Line is dividing the country into Palawan and associated islands, the presumed former land-bridge to northern Borneo, and the truly oceanic portions of the Philippines. It has an extraordinary biodiversity, presumably supported by ancient land mass movements, environmental gradients along steep volcanic slopes and alterations of connectivity between neighbouring islands induced by changing sea levels (Brown and Diesmos 2010).
Despite many collection efforts and progress done in the past decade in Southeast Asia, the Baetidae and Ephemeroptera in general still remain poorly known. During this study, we identified several additional new species of Nigrobaetis from both the Philippines and Indonesia, but refrained to describe them because of insufficient material (mostly one larva only). Therefore, we may expect a substantial amount of additional new species of Nigrobaetis with more collections in the future.

Materials and methods
Specimens used in the study were obtained by kick-sampling and preserved in 70%-96% ethanol.
Eggs of three species were extracted from the abdomen of mature female larvae, and preserved in 96% alcohol before preparation (desiccation; application of a 15 nm layer of palladium) for SEM photos.
Dissection of larvae was done in Cellosolve (2-Ethoxyethanol) with subsequent mounting on slides with Euparal liquid, using an Olympus SZX7 stereomicroscope.
Photographs of larvae were taken using a Canon EOS 6D camera and processed with the programs Adobe Photoshop Lightroom (http://www.adobe.com) and Helicon Focus version 5.3 (http://www.heliconsoft.com). Photographs of larval parts on slides were taken with an Olympus BX43 microscope equipped with an Olympus SC 50 camera and the program Olympus CellSense v. 3.2. SEM pictures were taken using a FEI Quanta FEC 250 electron microscope (Thermo Fisher). All photographs were subsequently enhanced with Adobe Photoshop Elements 13.
The DNA of part of the specimens was extracted using non-destructive methods allowing subsequent morphological analysis (see Vuataz et al. 2011 for details). We amplified a 658 bp fragment of the mitochondrial gene cytochrome oxidase subunit 1 (COI) using the primers LCO 1490 and HCO 2198 (Folmer et al. 1994; see Kaltenbach and Gattolliat 2020 for details). Sequencing was done with Sanger's method (Sanger et al. 1977). The genetic variability between specimens was estimated using Kimura-2-parameter distances (K2P, Kimura 1980), calculated with the program MEGA 7 (Kumar et al. 2016, http://www.megasoftware.net). Additionally, we downloaded a COI sequence of N. minutus (Müller-Liebenau, 1984) from GenBank. There were no other COI sequences of Nigrobaetis from Southeast Asia available on GenBank. GenBank accession numbers are given in Table 2.
The distribution maps were generated with the program SimpleMappr (https://simplemappr.net, Shorthouse 2010); the GPS coordinates of the sample locations are given in Table 1.
Labrum (Fig. 2a, b). Slightly conical, length 0.76× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submedian seta and two long, simple, submarginal setae. Ventrally with marginal row of setae composed of anterolateral long, feathered setae and medial long, bifid, pectinate setae.
Right mandible (Fig. 2c). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with four denticles, inner margin of innermost denticle with row of thin setae. Prostheca stick-like, apicolaterally denticulate. Margin between prostheca and mola straight, with row of setae-like processes. Tuft of setae at apex of mola present.
Left mandible (Fig. 2d). Incisor and kinetodontium fused. Incisor with four or five denticles; kinetodontium with three denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with row of minute denticles. Tuft of setae at apex of mola absent.
Maxilla . Galea-lacinia ventrally with two simple, apical setae under canines. Medially with one spine-like seta and ca. four long, simple setae. Maxillary palp 1.3× as long as length of galea-lacinia; 2-segmented; palp segment II approx. as long as segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment pointed.
Labium . Glossa basally broad, narrowing toward apex; nearly as long as paraglossa; inner margin with ca. ten spine-like setae; apex with two long and one medium, robust setae; outer margin with ca. six spine-like setae; ventral surface with fine, simple, scattered setae. Paraglossa curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and two medium, simple setae in inner anterolateral area; dorsally with row of three long, spine-like, simple setae near inner margin. Labial palp with segment I 1.2× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II without protuberance; ventral surface with short, fine, simple setae; dorsally with row of four long, spine-like setae. Segment III sub-quadrangular; inner apical margin slightly concave, with some setae-like processes; apex with rounded protrusion; length subequal to width; ventrally with short, spine-like, simple setae and short, fine, simple setae.
Abdominal terga (Fig. 6a). Surface with irregular rows of U-shaped scale bases. Posterior margin of terga: I-III smooth, without spines; IV and V with rudimentary spines or smooth; VI-IX with triangular, sharply pointed spines.
Abdominal sterna. Posterior margins smooth, without spines. Tergalii (Fig. 5d). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Tergalius I ca. ½ length of segment II; Tergalius IV as long as length of segments V and ½ VI combined; Tergalius VII as long as length of segments VIII and ½ IX combined. Paraproct (Fig. 6b). With 6-9 stout, marginal spines. Surface scattered with U-shaped scale bases. Cercotractor with numerous small, marginal spines.
Adult stages. Unknown. Eggs (Fig. 7a, b). Ovoid; surface cone-like with numerous papillae-like structural elements (polygonal to rounded structure, centrally with a smaller, rounded, slightly elevated area surrounded by a round trench).
Labrum (Fig. 10a, b). Length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submedian seta and two long, simple, submarginal setae. Ventrally with marginal row of setae composed of anterolateral long, feathered setae and medial long, bifid, pectinate setae.
Right mandible (Fig. 10c). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with four denticles, inner margin of innermost denticle with row of thin setae. Prostheca stick-like, apicolaterally denticulate. Margin between prostheca and mola straight, with row of setae-like processes. Tuft of setae at apex of mola present.
Left mandible (Fig. 10d). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with three denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, smooth without denticles. Tuft of setae at apex of mola absent.
Maxilla (Fig. 11b, c). Galea-lacinia ventrally with two simple, apical setae under canines. Medially with one spine-like seta and ca. four long, simple setae. Maxillary palp approx. as long as length of galea-lacinia; 2-segmented; palp segment II approx. 1.1× as long as segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment pointed. Labium . Glossa basally broad, narrowing toward apex; as long as paraglossa; inner margin with ca. ten spine-like setae; apex with two long and one medium, robust setae; outer margin with ca. four spine-like setae; ventral surface with fine, simple, scattered setae. Paraglossa curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and two medium, simple setae in anteromedial area; dorsally with row of three long, spine-like, simple setae near inner margin. Labial palp with segment I 0.9× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II without protuberance; ventral surface with short, fine, simple setae; dorsally with row of three or four long, spine-like setae. Segment III pentagonal; inner apical margin with some setae-like processes; length 1.1× width; ventrally with short, spine-like, simple setae and short, fine, simple setae.
Middle and hind legs. As foreleg, but tibia at dorsal margin with 1-4 spinelike setae.
Abdominal sterna. Posterior margins smooth, without spines. Tergalii (Fig. 13e). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Tergalius II as long as length of segments III and ½ IV combined; Tergalius VII as long as length of segments VIII and ½ IX combined.
Adult stages. Unknown. Etymology. Referring to the island of Palawan, where the species was collected. Distribution (Fig. 8). Philippines: Palawan. Biological aspects. The specimens were collected below 100 m in primary and secondary forest, on bottom gravel and on root packs in the run. Differential diagnosis. Larva. Following combination of characters: A) dorsal surface of labrum with submedian seta and two long, simple setae in submarginal position (Fig. 16b); B) right mandible: incisor with four denticles, kinetodontium with three denticles (Fig. 16c); C) left mandible: incisor with four denticles, kinetodontium with three denticles; margin between prostheca and mola straight, with four or five long, setae-like processes (Fig. 16d); D) fore femur very slender, length ca. 4.8× maximum width, dorsal margin with eight or nine curved, spine-like setae (Fig. 19a); E) tibia dorsally with row of spine-like setae; F) claw with 14-17 relatively long denticles (Fig. 19c); G) hind protoptera absent; H) tergalii on abdominal segments I-VII; I) paraproct with 10-14 marginal spines (Fig. 20b); J) posterior margins of abdominal terga: I smooth, without spines; II-IX with triangular, pointed spines (Fig. 20a).
Labrum (Fig. 16a, b). Length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submedian seta and two long, simple, submarginal setae. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid, pectinate setae.
Right mandible (Fig. 16c). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with three denticles, inner margin of innermost denticle without row of thin setae. Prostheca stick-like, apicolaterally denticulate. Margin between prostheca and mola straight, with row of setae-like processes. Tuft of setae at apex of mola present.
Left mandible (Fig. 16d). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with three denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with four or five long, setae-like processes. Tuft of setae at apex of mola absent.
Maxilla (Fig. 17b-d). Galea-lacinia ventrally with two simple, apical setae under canines. Medially with one spine-like seta and ca. four long, simple setae.    Maxillary palp ca. 1.3× as long as length of galea-lacinia; 2-segmented; palp segment II ca. 1.3× as long as segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment pointed. Labium (Fig. 12a-e). Glossa basally broad, narrowing toward apex; slightly shorter than paraglossa; inner margin with nine or ten spine-like setae; apex with two long and one medium, robust setae; outer margin with ca. eight spine-like setae; ventral surface with fine, simple, scattered setae. Paraglossa curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and ca. four medium, simple setae in anteromedial area; dorsally with row of four long, spine-like, simple setae near inner margin. Labial palp with segment I 0.7× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II without protuberance; ventral surface with short, fine, simple setae; dorsally with row of ca. five long, spine-like setae. Segment III slightly pentagonal, inner distal margin slightly concave, with few setae-like processes; length ca. 1.2× maximum width; ventrally with short, spine-like, simple setae and short, fine, simple setae.
Hind protoptera: Absent. Foreleg (Fig. 19a-c). Ratio of foreleg segments 1.3:1.0:0.6:0.2. Femur. Very slender, length ca. 4.8× maximum width. Dorsal margin slightly concave, with eight or nine curved, spine-like setae; length of setae 0.29× maximum width of femur. Apex rounded, with pair of spine-like setae and medium, fine, simple setae. Row of stout, lanceolate setae on ventral margin; femoral patch absent. Tibia. Dorsal margin with row of medium, spine-like setae, on apex one seta somewhat longer and with rounded apex. Ventral margin with row of short to medium curved, spine-like setae, on apex two longer, spine-like, pectinate setae. Anterior surface with stout, lanceolate setae along ventral margin. Patellatibial suture present on basal half. Tarsus. Dorsal margin bare. Ventral margin with row of curved, spine-like setae. Claw with one row of 14-17 relatively long denticles; distally pointed; subapical setae absent.
Middle and hind legs. As foreleg. Abdominal terga (Fig. 20a). Surface with irregular rows of U-shaped scale bases. Posterior margin of terga: I smooth, without spines; II-IX with triangular, pointed spines.
Abdominal sterna. Posterior margin of sterna: I-V smooth, without spines; VI with rudimentary spines; VII-IX with triangular spines.
Tergalii (Fig. 19d, e). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae extending from main trunk to inner and outer margins. Tergalius I as long as length of segments II and ⅓ III combined; Tergalius IV as long as length of segments V and VI combined; Tergalius VII reaching beginning of segment X. Paraproct (Fig. 20b). With 10-14 stout, marginal spines. Surface scattered with U-shaped scale bases. Cercotractor with numerous small, marginal spines.
Right mandible (Fig. 22c). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with four denticles, inner margin of innermost denticle without row of thin setae. Prostheca stick-like, apicolaterally denticulate. Margin between prostheca and mola straight, with row of setae-like processes. Tuft of setae at apex of mola present.
Left mandible (Fig. 22d). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with three denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with row of short, setae-like processes. Tuft of setae at apex of mola absent.
Maxilla (Fig. 23b-d). Galea-lacinia ventrally with two simple, apical setae under canines. Medially with one spine-like seta and ca. five long, simple setae. ment II bent inwards, distal half sclerotised; palp segment II ca. 1.2× as long as segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment slightly pointed. Labium (Fig. 24a-f). Glossa basally broad, narrowing toward apex; slightly shorter than paraglossa; inner margin with ca. eight spine-like setae; apex with two long and one medium, robust setae; outer margin with ca. six spine-like setae; ventral surface with fine, simple, scattered setae. Paraglossa curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and ca. three medium, simple setae in medial and anteromedial area; dorsally with two long, spine-like, simple setae near inner margin. Labial palp with segment I 0.7× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II without protuberance; ventral surface with short, fine, simple setae; dorsally with row of ca. three long, spinelike setae. Segment III subquadrangular; length ca. 0.9× maximum width; inner apical margin with some setae-like processes (Fig. 24f); ventrally with short, spine-like, simple setae and short, fine, simple setae.
Labrum (Fig. 29a-c). Length 0.8× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submedian seta and two long, simple, submarginal setae. Ventrally with marginal row of setae composed of anterolateral long, feathered setae and medial long, bifid, pectinate setae.
Right mandible (Fig. 29d). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with five denticles, inner margin of innermost denticle without row of thin setae. Prostheca stick-like, apicolaterally denticulate. Margin between prostheca and mola straight, with row of setae-like processes. Tuft of setae at apex of mola present. Left mandible (Fig. 29e). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with four denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with row of few short, setae-like processes. Tuft of setae at apex of mola absent.
Hypopharynx and superlinguae (Fig. 30a). Lingua shorter than superlinguae. Lingua longer than broad; medial tuft of stout setae poorly developed; distal half laterally not expanded. Superlinguae distally rounded; lateral margins rounded; fine, long, simple setae along distal margin.   (Fig. 30b-d). Galea-lacinia ventrally with two simple, apical setae under canines. Medially with one spine-like seta and ca. four long, simple setae. Maxillary palp ca. 1.2× as long as length of galea-lacinia; 2-segmented; palp segment II ca. 1.3× as long as segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment slightly pointed.

Maxilla
Labium (Fig. 31a-f). Glossa basally broad, narrowing toward apex; approx. as long as paraglossa; inner margin with ca. eight spine-like setae; apex with two long and one medium, robust setae; outer margin with ca. six spine-like setae; ventral surface with fine, simple, scattered setae. Paraglossa curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and ca. two medium, simple setae in anteromedial area; dorsally with three long, spine-like, simple setae near inner margin. Labial palp with segment I 0.9× length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II without protuberance; ventral surface with short, fine, simple setae; dorsally with row of ca. three long, spine-like setae. Segment III slightly pentagonal; length subequal to maximum width; inner apical margin with some setae-like processes (Fig.31f); ventrally with short, spinelike, simple setae and short, fine, simple setae.
Middle and hind legs. As foreleg. Abdominal terga (Fig. 33). Surface with irregular rows of U-shaped scale bases. Posterior margin of terga: I smooth, without spines; II-IX with triangular, pointed spines.
Abdominal sterna. Posterior margin of sterna smooth, without spines. Tergalii (Fig. 32e). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae restricted to main trunk and few branches, not reaching margins. Tergalius I as long as length of segment II; Tergalius IV as long as length of segments V and 1/2 VI combined; Tergalius VII as long as segments VIII and 1/2 IX combined.
Paraproct. With six or seven stout, marginal spines. Surface scattered with U-shaped scale bases, fine, simple setae, and micropores. Cercotractor with numerous small, marginal spines.
Adult stages. Unknown. Etymology. Referring to the island of Borneo, where the species was collected. Distribution (Fig. 40c). Indonesia, Borneo (East Kalimantan). Biological aspects. The specimens were collected at an altitude of 160 m in a large (width ca. 36 m), shallow (depth ca. 0.1 m), fast flowing (ca. 0.9 m/s)   stream. The stream was characterised by equally run/riffles and pools. Water temperature was 25 °C, substrate was dominated by boulder and cobble.
Labrum (Fig. 35a, b). Length 0.7× maximum width. Distal margin with medial emargination and a small process. Dorsally with medium, fine, simple setae scattered over surface; submedian seta and several long, simple, submarginal setae. Ventrally with marginal row of setae composed of anterolateral long, feathered setae and medial long, bifid, pectinate setae.
Right mandible (Fig. 35c). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with four denticles, inner margin of innermost denticle without row of thin setae. Prostheca stick-like, apicolaterally denticulate. Margin between prostheca and mola straight, with row of setae-like processes. Tuft of setae at apex of mola present.
Left mandible (Fig. 35d). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with three denticles. Prostheca robust, apically with small denticles and comb-shaped structure. Margin between prostheca and mola straight, with row of short, setae-like processes. Tuft of setae at apex of mola absent.
Maxilla (Fig. 36b-d). Galea-lacinia ventrally with two simple, apical setae under canines. Medially with one spine-like, pectinate seta and ca. five long, simple setae. Maxillary palp ca. 1.3× as long as length of galea-lacinia; 2-segmented; palp segment II approx. as long as segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment slightly pointed. Labium (Fig. 37a-f). Glossa basally broad, narrowing toward apex; approx. as long as paraglossa; inner margin with ca. seven spine-like setae; apex with two long and one medium, robust setae; outer margin with ca. six spine-like setae; ventral surface with row of fine, simple, setae along inner margin. Paraglossa curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and ca. three medium, simple setae in distal area; dorsally with three long, spine-like, simple setae near inner margin. Labial palp with segment I slightly longer than segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II without protuberance; ventral surface with short, fine, simple setae; dorsally with row of ca. four long, spinelike setae. Segment III slightly pentagonal; length ca. 1.2× maximum width; inner apical margin with some setae-like processes (Fig. 37f); ventrally with short, spine-like, simple setae and short, fine, simple setae.
Middle and hind legs. As foreleg.
Abdominal sterna. Posterior margin of sterna smooth, without spines. Tergalii (Fig. 38f). Present on segments I-VII. Margin with small denticles intercalating fine simple setae. Tracheae restricted to main trunk and few branches, not reaching margins. Tergalius I as long as length of segment II; Tergalius IV as long as length of segments V and 1/3 VI combined; Tergalius VII as long as segments VIII and IX combined.
Paraproct. With six or seven stout, marginal spines. Surface scattered with U-shaped scale bases and micropores. Cercotractor with numerous small, marginal spines.
Adult stages. Unknown. Eggs (Fig. 40a, b). Egg of Fig. 40a still in early stage of development, probably not showing the final shape (see Fig. 40b, pack of developing eggs extracted from same larva). Surface with numerous papillae-like structural elements (polygonal to rounded structure, centrally with a smaller, rounded, slightly elevated area surrounded by a round trench).

Assignment to Nigrobaetis
For the assignment of the new species to Nigrobaetis we refer to Kluge (2022).
Larval antennae of all new species are standing closely together, with a longitudinal keel between them (not figured); right mandibles always have a row of long, setae-like processes between prostheca and mola (Figs 2c,10c, 16c, 22c, 29d, 35c); left mandibles usually have a row of minute denticles between prostheca and mola (Figs 2d, 22d, 29e, f, 35d), in one case the margin between prostheca and mola is bare (Fig. 10d), and in another case there is a tuft of medium, setae-like processes (Fig. 16d); labial palps segments II are without distomedial protuberance in all new species (Figs 4a, 12a, 18a, 24a, 31a, 37a); for N. plures sp. nov. and N. suma sp. nov., we observed the subimaginal gonostyli developing under cuticle of male last instar larvae and they are folded in the "Nigrobaetis-type" (Figs 6c, 26c). Further, as usually in Nigrobaetis, there is no real submarginal arc of setae dorsally on the labrum (Figs 2b, 10b, 16b, 22b, 29b, c), except for N. kaliman sp. nov., which has a short arc (Fig. 35b). The femoral patch is always absent.