Epeorus (Caucasiron) psi Eaton, 1885

Vasanth, M., Selvakumar, C., Subramanian, K. A., Sivaramakrishnan, K. G. & Sinha, Bikramjit, 2021, Contribution to the study of Epeorus Eaton, 1881 (Ephemeroptera: Heptageniidae) from India, Zootaxa 4991 (3), pp. 499-522 : 516-519

Epeorus (Caucasiron) psi Eaton, 1885

( Figs 102–116 )

Material examined: 12 larvae, INDIA, Arunachal Pradesh, West Kameng district, Dirang, Showda village , Dirang river , 27.32675 N, 92.23180 E, 1877 m, 13.iii.2018, coll. Bikramjit Sinha [ZSI/ SRC-I /E-295] ; 18 larvae, Arunachal Pradesh, Lower Dibang valley district, Roing, Iphipani river , 28.18728 N, 95.84094 E, 488 m, 04.iv.2016, coll. Santabala & Party [ZSI/ SRC / I/E-306-308] ; 4 larvae, Arunachal Pradesh, West Kameng district, Sangti valley, Khechalu , KhendoRong (stream), 27.420841 N, 92.269538 E, 1790 m, 12.iii.2018, coll. Bikramjit Sinha [ZSI/ SRC-I /E-322] ; 2 larvae, India, Arunachal Pradesh, West Kameng district, Dirang , Chakpa village , Chakpar Rong (stream), 27.420265 N, 92.21811 E, 1749 m, 11.iii.2018, coll. Bikramjit Sinha [ZSI/ SRC-I /E-328] .

Description: Mature larva: Body length 14 mm, cerci 16 mm. General colour brown ( Figs 101–102 ).

Head: Body slightly convex dorsally. Frontal and lateral margins of head expanded, ( Fig. 102 ). Labrum rather small with hair-like setae dorsally and laterally; 2 times as wide as long, antero-lateral margins rather angulate; shallow excavation medially, anterior margin almost straight ( Fig. 104 ). Hypopharynx pale brown, lingua with anterolateral lobes; superlinguae slightly expanded ( Fig. 105 ). Mandible with scattered setae along molar area; incisor well developed; outer incisor longer than inner incisor ( Figs 106–107 ). Maxilla as in Fig. 108 . Labium: glossae with U-shaped separation; paraglossae slightly expanded laterally; apical segment of palp acutely pointed, dorsal surface with dense row of comb setae ( Fig. 109 ).

Thorax: Pronotum brown; mesonotum dark brown anteriorly and a pair of lateroparapsidal sutures inside curved posteriorly ( Fig. 102 ). Legs: yellowish brown; femora with rounded medial hypodermal femur spot; joint of the femur and tibiae dark brown; outer margin of tibiae of all legs with dense row of long setae ( Figs 110–112 ). Claw with 2 denticles ( Fig. 113 ).

Abdomen: Abdominal terga pale brown, abdominal terga with overturned letter Ψ on terga V–VIII; sterna II–VII with a pair of black slanting streaks and a brown line medially ( Fig. 103 ); segments I–IX medially with small hair-like setae along the mid-dorsal line. Posterolateral margins of segments I–VII with short and blunt extension ( Figs 102–103 ). Sterna pale brown with a pair of black slanting streaks and median black line ( Fig. 103 ). Gills: gill I very large, greatly extended beneath abdomen ( Figs 103 , 114 ); costal rib of gills II–VII with short thumb-like projection ( Figs 115–116 ); gill VII meets beneath body with short fibrilliform gills ( Fig. 116 ). Cerci dark brown.

Adult: Description provided by Eaton (1885).

Diagnosis: Epeorus (Caucasiron) psi can be identified by the following combination of characters: (i) femora with rounded medial hypodermal spot ( Figs 110–112 ); (ii) claw with 2 denticles ( Fig. 113 ); (iii) abdominal terga with overturned letter Ψ on terga V–VIII; sterna II–VII with a pair of black slanting streaks and a brown line medi- ally ( Fig. 103 ).

Distribution: India (Himachal Pradesh and Arunachal Pradesh) Nepal and Taiwan.

Remarks: The larval description of Epeorus (C.) psi from Nepal was provided for the first time by Braasch (1980). Unfortunately, it is inaccurate and poorly illustrated with schematic drawings. An improved description is given herein which enables its inclusion is the subgenus Caucasiron as per the following diagnostic features provid- ed recently in Hrivniak et al. (2020a). 1. Coloration of abdominal terga, including overturned letter Ψ on abdominal terga V–VIII ( Fig. 103 ). 2. Coloration of abdominal sterna, including slanting streaks on sterna II–VIII ( Fig. 103 ). 3. Medial hypodermal femoral spots ( Fig. 110–112 ). 4. Claw with 2 denticles ( Fig. 113 ). 5. Shape of gills II–VII ( Fig. 114–116 ) with an outer thumb-like projection.

Figures

FIGURES 102–107. Larva of Epeorus (Caucasiron) psi 102. Dorsal view; 103. Ventral view; 104. Labrum; 105. Hypopharynx; 106. Right mandible; 107. Left mandible.

FIGURES 108–116. Larva of Epeorus (Caucasiron) psi 108. Maxilla; 109. Labium; 110. Foreleg; 111. Midleg; 112. Hindleg; 113. Claw; 114. Gill I; 115. Gill V; 116. Gill VII.

FIGURES 92–101. Larva of Epeorus (Epeorus) petersi 92. Maxilla; 93. Labium; 94.Foreleg; 95. Dorsal surface of femur; 96. Midleg; 97. Hindleg; 98. Claw; 99. Gill I; 100. Gill III; 101. Gill VII.