Megalabiops madagasikara gen. et, 2021

Kaltenbach, Thomas & Gattolliat, Jean-Luc, 2021, A new genus from Madagascar with strongly enlarged labium (Ephemeroptera, Baetidae), African Invertebrates 62 (2), pp. 465-484 : 465

Megalabiops madagasikara gen. et sp. nov.

Figures 1 , 2 , 3 , 4 , 5 , 6 , 7

Diagnosis.

Nymph. See genus diagnosis. Otherwise, if more species are discovered, specific differences in shape of labial and maxillary palps, and in setation of the legs are expected. Species with less derived characters (setation of pedicellus, shape of mentum) may also be expected.

Etymology.

Madagasikara is the Malagasy name of Madagascar.

Type-material.

Holotype. Madagascar • female nymph; Bas. Rianila, Riv. Affluent non nommé, Loc. Camp: route vers Lakato; 19°03'30"S, 48°21'50"E; 25.04.2003; leg. Mission MZL and M. Monaghan; on slides; GBIFCH00592692, GBIFCH00592693, GBIFCH00592728; GenBank OK510778; MZL. Paratype. Madagascar • nymph; Andasibe National Park, Antanambotsira; 18°56'09"S, 48°24'52"E; 30.11.2001; on slide; GBIFCH00592729; leg. R. Oliarinony; MZL.

Description.

Nymph. (Figs 1 - 6 ). Body length ca. 4.5 mm. Cerci broken, but longer than paracercus; paracercus ca. ½ body length.

Colouration (Fig. 1 a-d ). Head, thorax and abdomen dorsally light brown, without visible pattern, fore protoptera light brown. Head, thorax and abdomen ventrally light brown. Legs and caudalii light brown.

Head. Antenna (Fig. 3a ). Pedicellus covered with many long, stout, slightly lanceolate, pointed setae; scapus bare.

Labrum (Fig. 3b ). Lateral margins straight, distal margin largely V-shaped, length 0.8 × maximum width. Distal margin with small, square process. Dorsal surface scattered with long, fine, simple setae; on each side long, pointed, submedian seta and submarginal arc restricted to two long, pointed setae. Ventrally with distal, marginal row of long, simple setae. Ventral surface with ca. two short, spine-like setae near lateral margin.

Right mandible (Fig. 3c-e ). Incisor and kinetodontium cleft. Incisor with two denticles, outer denticle blade-like; kinetodontium with three denticles. Prostheca stick-like, apicolaterally denticulate. Margin between prostheca and mola straight; with brush of medium setae between prostheca and mola, length of setae ca. 1/4 of prostheca length. Tuft of setae present at apex of mola.

Left mandible (Fig. 3f-h ). Incisor and kinetodontium partially cleft. Incisor with two denticles, outer denticle blade-like; kinetodontium with three denticles. Prostheca robust, apically denticulate and with comb-shape structure. Margin between prostheca and mola straight; with brush of medium setae between prostheca and mola, length of setae ca. 1/4 of prostheca length; and with minute denticles toward subtriangular process. Subtriangular process long and slender, above level of area between prostheca and mola. Tuft of setae at apex of mola absent.

Both mandibles with lateral margins convex. Basal half laterally with short, fine, simple setae.

Hypopharynx and superlinguae (Fig. 4a ). Lingua longer than wide and longer than superlinguae, with prominent central protuberance; with large medial tuft of stout setae. Superlinguae distally rounded, lateral margins rounded; long, fine, simple setae along distal margin.

Maxilla (Fig. 4b, c ). Galea-lacinia ventrally with two simple, apical setae under canines. Medially with one bifurcate seta and four medium, simple setae. Maxillary palp ca. 1.4 × as long as length of galea-lacinia; palp segment II 1.4 × length of segment I; short, fine, simple setae scattered over surface of segment II; apex pointed and with short, stout seta at tip.

Labium (Figs 2b-d , 4d, e ). Inner margin of glossa with marginal row of long, simple setae, on ventral surface row of very long, simple setae close to margin; apex with four long, very robust setae, curved toward inner side, and two equally long, spine-like, pectinate setae; outer margin bare. Paraglossa with outer margin and apex convex and inner margin concave, curved inward; ventrally with three rows of long, robust, pectinate setae in apical area and two short, fine, simple setae in anteromedial area; dorsally with row of four long, spine-like setae near inner margin. Mentum strongly enlarged (extended and thickened), especially on ventral side; laterally with medium, fine, simple setae. Labial palp very long, with segment I 0.9 × length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II elongated, conical, without protuberance; ventral surface with short, fine, simple setae; dorsally with three spine-like setae near distal margin. Segment III slightly pentagonal; length subequal to width; ventrally covered with short, spine-like setae and short, fine, simple setae.

Thorax. Hind protoptera well developed.

Foreleg (Fig. 5a, b ). Ratio of foreleg segments 1.8: 1.0: 1.1: 0.6. Femur. Rather broad, length 2.7 × maximum width; dorsal margin with ca. nine long, spine-like setae plus ca. five long, spine-like setae close to margin in basal part, length of setae ca. 0.3 × maximum width of femur; on apex three long, spine-like setae and some short, fine, simple setae; many short to medium, stout setae along ventral margin; femoral patch absent. Tibia. Stocky, slightly shorter than tarsus; dorsal margin with row of short, fine, simple setae; ventral margin with row of medium, curved, spine-like setae; patellotibial suture absent; connection to tarsus tight. Tarsus. Dorsal margin with row of scarce, short, fine, simple setae; ventral margin with row of short to medium, curved, spine-like setae. Claw strongly elongated, distally pointed, with two rows of numerous minute denticles; denticles decreasing in size distally; subapical setae absent.

Middle leg. Ratio of middle leg segments 1.7: 1.0: 1.0: 0.5. Femur. Length 3.4 × maximum width. With similar setation as foreleg; femoral patch absent. Tibia as hind leg; dorsal margin almost bare; ventral margin with row of short, spine-like setae. Patellotibial suture present on basal 1/3 area. Tarsus as hind leg; dorsal margin bare; ventral margin with row of short, spine-like setae. Claw as foreleg.

Hind leg (Fig. 5c ). Ratio of hind leg segments 1.8: 1.0: 1.0: 0.6. Femur. Length 4 × maximum width. Dorsal margin with ca. six long, spine-like setae plus ca. three long, spine-like setae close to margin; many short to medium, stout setae along ventral margin; femoral patch absent. Tibia. Dorsal margin almost bare; ventral margin with a row of short, spine-like setae. Patellotibial suture present on basal 1/3 area. Tarsus. Dorsal margin bare; ventral margin with a row of short, spine-like setae. Claw as foreleg.

Abdomen. Tergites (Fig. 6a ). Posterior margin of tergites with triangular spines, longer than wide.

Gills (Fig. 6c ). Gills on segments I-VII. Costal and anal margins with small denticles intercalating short, fine, simple setae. Tracheae extending from main trunk to inner and outer margins. Gill I as long as 1/3 length of segment II; gill IV as long as length of segments V, VI and 1/3 VII combined; gill VII reaching end of segment X.

Paraproct (Fig. 6b ). Posterior margin slightly expanded; with ca. 36 stout, marginal spines. Surface scattered with U-shaped scale bases, some fine, simple setae and micropores. Cercotractor with small, marginal spines.

Distribution.

(Fig. 7 ). Madagascar: Eastern coast.

Biology.

Larvae were collected in two pristine streams running in relatively preserved natural tropical rain forests. Environmental parameters of the type-locality: width 2-3m, depth 0.1-0.2m, velocity 0.6-0.8 m/s, temperature 16-18 °C. The riverbed was a mix of sand, gravel and rocks with a few small waterfalls and very limited riparian vegetation. Mayfly fauna is very diversified with around twenty species of Baetidae , including four carnivorous species ( Nesoptiloides electroptera (Demoulin, 1966), Herbrossus christinae Gattolliat & Sartori, 1998, Herbrossus edmundsorum McCafferty & Lugo-Ortiz, 1998, and Guloptiloides gargantua Gattolliat & Sartori, 2000), scrapers ( Dicentroptilum merina Lugo-Ortiz & McCafferty, 1998, Xyrodromeus spp.), and species adapted to fast flow ( Afroptiloides delphinae Gattolliat, 2000). Besides Baetidae , Caenidae and Tricorythidae were the most abundant families; larvae of the huge borrowing mayfly, Proboscidoplocia sp. ( Euthyplociidae ), were also collected in abundance. Both larvae were still in middle instar in April (end of rainy season) and November (beginning of rainy season); we hypothesize that Megalabiops madagasikara sp. nov has a long flight period as most of the Malagasy species of Baetidae .

Figures

Figure 1. Megalabiops madagasikara gen. et sp. nov., habitus, nymph a dorsal view b ventral view c, d lateral view. Scale bars: 1 mm.

Figure 2. Megalabiops madagasikara gen. et sp. nov., nymph morphology a frontal section of head b head, ventral view c labium, lateral view d head, ventrolateral view. Scale bars: 0.1 mm.

Figure 3. Megalabiops madagasikara gen. et sp. nov., nymph morphology a base of antenna b labrum (left: ventral view, right: dorsal view) c right mandible d right prostheca e right incisor and kinetodontium f left mandible g left prostheca h left incisor and kinetodontium. Scale bars: 0.1 mm.

Figure 4. Megalabiops madagasikara gen. et sp. nov., nymph morphology a hypopharynx and superlinguae b maxilla (ds: denti-seta) c seta at tip of maxilla d labium (left: ventral view, right: dorsal view) e apex of paraglossa (ventral view). Scale bar: 0.1 mm.

Figure 5. Megalabiops madagasikara gen. et sp. nov., nymph morphology a foreleg b fore claw c hind leg d head. Scale bars: 0.2 mm.

Figure 6. Megalabiops madagasikara gen. et sp. nov., nymph morphology a tergite IV (posterior margin) b paraproct c gill IV (with enlarged margins). Scale bar: 0.1 mm.

Figure 7. Megalabiops madagasikara gen. et sp. nov., distribution in Madagascar.