Arcobaetis sripadai, Kaltenbach & Kluge & Gattolliat, 2023

Kaltenbach, Thomas, Kluge, Nikita J. & Gattolliat, Jean-Luc, 2023, A new, widespread genus of Baetidae from South Asia (Insecta, Ephemeroptera), ZooKeys 1168, pp. 231-266 : 231

Arcobaetis sripadai sp. nov.

Figs 13 , 14 , 15 , 16 , 17 , 18 , 19

Type material.

Holotype. ♂ imago reared from larva, with its larval and subimaginal exuviae {specimen [XVIII] (5)2020}, Sri Lanka, foot of Sri Pada ( Adam’s Peak), Delhausie, river Seetha gangula; 6°50′3.48″N, 80°34′3.36″E; 7.II.2020; leg. N. Kluge & L. Sheyko; SPbU.

Diagnosis.

Larva (Table 1 ). The following combination of characters distinguish A. sripadai sp. nov. from other species of Arcobaetis gen. nov.: A) distal margins of segments in middle part of flagellum without enlarged spines (Fig. 14a ); B) labial palp segment III sub-quadrangular, at base approx. as wide as distal margin of segment II (Fig. 14i ); C) hind protoptera absent; D) claw with single row of denticles, most distalmost denticles larger, basal denticles small to minute (Fig. 15c ); E) tergalii present on abdominal segments II-VII; F) posterior margin of tergum IV with triangular spines, slightly wider than long (Fig. 15f ).

Descriptions.

Larva (Figs 13 - 18 ).

Cuticular colouration (Fig. 13a-g ). Head, thoracic terga and pleura with diffusive brown, ochre, and colourless areas (Fig. 13d ); thoracic sterna colourless. Legs pale ochre with brown apex of femur, base of tibia and band in distal part of tibia (Fig. 13a-c ). Abdominal terga I-VII with nearly uniform colour pattern consisting of diffusive ochre and pale brown areas (Fig. 13e-f ); tergum VIII nearly uniformly darker brown, with paler ochre anterior margin and anterolateral angles (Fig. 13f ); terga IX-X uniformly pale ochre (Fig. 13g ); all sterna I-IX and paraprocts pale ochre. Caudalii ochre.

Hypodermal colouration. Unknown.

Antenna (Fig. 14a ). Spines at distal margins of flagellum segments not enlarged.

Labrum (Fig. 14b ). Length 0.7 × maximum width. Dorsally with submedian setae and few long setae, not forming distinct submarginal arcs.

Right mandible (Fig. 14c ). Number of denticles of incisor unclear (worn); kinetodontium with three denticles.

Left mandible (Fig. 14d ). Number of denticles of incisor unclear (worn); kinetodontium with three denticles.

Hypopharynx and superlinguae (Fig. 14e ). Lingua shorter than superlinguae, longer than broad. Superlinguae distally almost straight; lateral margins rounded; fine, long, simple setae along distal margin.

Maxilla (Fig. 14f ). Galea-lacinia ventrally with two simple setae just proximad of canines. Medially with one spine-like seta and four simple setae. Maxillary palp approx. 1.1 × as long as galea-lacinia; palp segment II slightly shorter than segment I.

Labium (Fig. 14g, h ). Inner margin of glossa with 14 or 15 spine-like setae, increasing in length distally; apex with three long and robust setae; outer margin with ca. ten spine-like setae; paraglossa ventrally with ca. four medium, simple setae in anteromedial area; dorsally with arc of ca. ten long, spine-like setae in distal area. Labial palp with segment I 0.8 × length of segments II and III combined. Labial palp segment II dorsally with row of three or four spine-like setae. Segment III sub-quadrangular; at base approx. as wide as distal margin of segment II; ventral surface with short, spine-like, simple setae and short, fine, simple setae.

Hind protoptera absent.

Legs (Figs 15a-c ). Long and slender; middle and hind legs slenderer than fore legs; hind leg slightly longer than others; on fore leg, tibia and tarsus of subequal length, with patella-tibial suture on proximal ¹/2 of tibia; on middle and hind legs, tibia much longer than tarsus, with patella-tibial suture on proximal ¹/3 of tibia. Segments ratio of fore leg 1.4:1.0:1.0:0.2, middle leg 1.3:1.0:0.7:0.2, hind leg 1.2:1.0:0.7:0.2. Femur. Length 4.6 × maximum width. Outer margin with row of 5-7 short, spine-like setae, larger on fore leg and smaller on middle and hind legs; two apical setae larger, equal on all legs (Fig. 15a ). Ventral side of femur with smaller pointed spine-like setae, larger and denser on fore legs, smaller and fewer on middle and hind legs. Tibia. Pointed, feathered, spine-like setae irregularly located on inner side of fore tibia (Fig. 15a ) and on all sides of middle and hind tibiae (Fig. 15b ); one preapical seta on outer side of each tibia. Tarsus. Ventral margin with row of short, curved, feathered, spine-like setae. Claw with one row of ca. ten denticles increasing from basal to distal ones and directed distally (Fig. 15c ).

Abdominal terga (Fig. 15d-k ). Posterior margin of terga: I smooth, without spines; II-X with triangular spines, increasing in length toward X; slightly longer than wide on tergum IV; row of spines on tergum IX interrupted behind bases of submedian setae (Fig. 15j ). Posterior margin of tergum X with median concavity with smaller spines in it (Fig. 15k ).

Abdominal sterna (Fig. 15l-m ). Posterior margins of sterna: I-V smooth, without spines; VI-VIII with triangular spines (Fig. 15l ). On sternum IX of male row of narrow pointed spines between protogonostyli, smaller and narrower spines laterad of protogonostyli and larger pointed spines laterad of them (Fig. 15m ).

Paraproct (Fig. 15n ). Posterior margin with ca. 16 stout spines. Surface scattered with scales.

Caudalii (Fig. 15o-p ). Cerci and paracercus with small, elongate spines on posterior margin of each segment; on outer side of cercus several spines on each 2nd segment greatly enlarged and pointed; no such enlarged spines on paracercus.

Tergalii (Fig. 13f ). Present on abdominal segments II-VII, subequal.

Subimago (Figs 16a-e , 17d, e, I, j ).

Cuticular colouration. Head and prothorax mostly brown. Mesonotum brown, medioparapsidal suture contrastingly colourless (Figs 16d , 17e ). Meso- and metathoracic pleura and sterna brown with colourless areas (Fig. 17d ). Wing membrane colourless with microtrichial circles ring-like, brown (Fig. 16c ). Legs mostly colourless with microtricha and microlepides dark brown, with brown markings on femur, at base and apex of tibia and margins of tarsomeres (Figs 16a, b , 17i, j ). Abdominal terga I-X and sterna I-VI uniformly brown, with all sigilla of the same colour as background; sterna VII-VIII with submedian sigilla paler than background, sternum IX of male with distal part and gonostyli colourless (Fig. Fig. 16e ). Cerci colourless with setae dark brown.

Texture. Mesonotum with cross-striated polygonal areas bordered with microtrichia (Fig. 16d ). Abdominal terga and sterna with outlined polygonal areas bearing two or more microtrichia each; sigilla diminished (Fig. 16e ). On fore leg of male, 1st-4th tarsomeres covered with blunt microlepides, 5th tarsomere covered with pointed microlepides; on middle and hind legs, all tarsomeres co-vered with pointed microlepides (Fig. 16a, b ).

Male imago (Fig. 17a-c, f-h, k ). Head ochre with reddish. Antennae with scape and pedicel ochre with reddish-brown apices. Turbinate eyes narrow, cylindrical, red. Thorax ochre-brownish. Fore wings with membrane colourless, proximal portions of C and Sc+RA reddish-brown, other veins ochre-brownish. Pterostigma with ca. three crossveins. Hind wings absent. Legs of all pairs ochre with inner side reddish (Fig. 17f-h ). Middle and hind tarsi with two apical spines (on 1st +2nd, and 3rd segments). Abdominal segments I-VI white with yellow stripe on posterior margin of each tergum and blackish spot on each stigma; terga VII-X yellow-ochre. Cerci whitish, with brown marking at each joining (Fig. 17k ). Gonostyli whitish.

Genitalia (Fig. 18a-c ). Unistyligers widely separated, with shallow, not sclerotised, conic projection between them. Each unistyliger cylindrical, distally widened and projected medially. First segment of gonostylus narrowing toward apex, poorly separated from 2nd segment. 3rd (apical) segment extraordinary small, much narrower than apex of 2nd segment. Gonovectes sharply bent. Sterno-styligeral muscle distinctly developed, but attached far from anterior margin of sternum; in single examined specimen sharply asymmetric.

Dimension. Fore wing length (and body length) 3.5 mm.

Etymology.

Specific epithet refers to the type locality at the foot of the Sri Pada ( Adam’s Peak).

Distribution.

Sri Lanka (Fig. 19 )

Figures

Figure 13. Arcobaetis sripadai sp. nov., larval exuviae (with same magnification): a-c fore, middle and hind legs (triangles show points where patella-tibial suture crosses inner margin) d half of pronotum and mesonotum e sternum and tergum V f sterna and terga VII-VIII g sterna and terga IX-X.

Figure 14. Arcobaetis sripadai sp. nov., larval exuviae (with same magnification) a antenna b labrum (dorsal side) c right mandible d left mandible e hypopharynx and superlinguae f maxilla g labium (dorsal focus) h labium (ventral focus) i labial palp.

Figure 15. Arcobaetis sripadai sp. nov., larval exuviae a, b fore and middle legs (triangles show points where patella-tibial suture crosses inner margin c claw d-k posterior margins of abdominal terga II-VI and VIII-X l-m posterior margin of abdominal sterna VIII and IX of male larva n paraproct. o-p fragments of cerci (lateral view).

Figure 16. Arcobaetis sripadai sp. nov., subimaginal exuviae a hind tarsus b apex of fore tarsus c wing membrane d fragment of mesonotum e fragment of abdominal tergum VII with two right submedian sigilla.

Figure 17. Arcobaetis sripadai sp. nov. a male imago b head and thorax c apex of abdomen d subimaginal exuviae of meso- and metapleura e subimaginal exuviae of half of mesonotum f, g fore and middle legs h tarsus of middle leg I, j subimaginal exuviae of fore and middle legs k cercus.

Figure 18. Arcobaetis sripadai sp. nov. a genitalia of male imago b, c imaginal genitalia and their subimaginal exuviae with the same magnification. Abbreviation: m. s asymmetric sterno-styligeral muscle (arrows show its base and apex)

Figure 19. Arcobaetis gen. nov., distribution.