Epeorus (Epeorus) unispinosus Braasch 1980

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 : 508

Epeorus (Epeorus) unispinosus Braasch 1980

( Figs 50–67 )

Epeorus sp. : Ueno 1955 (young larva)

Material examined: 1 larva, INDIA, Arunachal Pradesh, Tawang district, Jang, Tawang Chu River , Nuranang Falls , 27.59133 N, 91.9839 E, 2087 m, 07.iii.2018, coll. Bikramjit Sinha. [ZSI/ SRC-I / E 480 ] .

Description: Mature Larva: Body length 12.5 mm; length of cerci 9.5 mm. Body brown with pale yellowish maculae ( Fig. 50 ).

Head: Length 1.5 mm, width 2.7 mm; pale brown ( Fig. 50 ); without conspicuous markings, antennae short 2.6 mm; subquadrangular; anterior and lateral margins convex, with rows of dense hair-like simple setae directed anteriorly and medially; posterior margin slightly concave. Compound eyes black. Antennal scapes and pedicels pale brown, flagella pale. Labrum 7.8 mm in width; dark brown with a rectangular mesal emargination; long hair-like setae on lateral margin ( Fig. 54 ). Hypopharynx as in Fig. 55 . Mandible without scattered setae along molar area; incisors serrated; outer incisor longer than inner incisor ( Fig. 56 ). Maxilla as in Fig. 57 . Labium broad, glossae with narrow basal separation, subtriangular; paraglossae slightly expanded laterally; apical segment of palp pointed, dorsal surface with dense row of comb setae ( Fig. 58 ).

Thorax: Pronotum pale brown without dark marks ( Fig. 50 ). Legs ( Figs 59–62 ): dark brown with pale yellowish; dorsal surface of femur with hypodermal spots on middle and apex with small stout and ovate scattered setae on dorsal surface; femora of all legs with row of long hair-like setae on outer margin, apex of femora with blunt apical projection; ( Fig. 60 ); tibiae long, brownish yellow, tarsi yellowish with basal dark brown. Claw with 5–6 denticles ( Fig. 63 ).

Abdomen: Abdominal terga pale brown, abdominal terga II–IX each with single, prominent, acute median spine ( Fig. 52 ); posterior margin of abdominal terga I–X each with row of small spines ( Fig. 53 ); segments II–VII with small posterolateral extensions ( Fig. 51 ); terga I–V medially dark brown, terga VI–VII with submedian pale spot and segment VIII and IX brown; tergum X anteriorly pale and posteriorly brown ( Fig. 50 ); sterna pale yellow without markings ( Fig. 51 ). Lamellae of gill I somewhat extended beneath of abdomen ( Fig. 64 ). Gills II–VII with anal ribs on margin ( Figs 65–67 ). Cerci with row of hair-like setae dorsally.

Diagnosis: The larva of Epeorus (E.) unispinosus can be differentiated from other species by the following combination of characters: (i) abdominal terga II–IX each with single, prominent, acute median spine and without lateral spines fringing the posterior margin ( Figs 50–53 ); (ii) anterior margin of labrum with a rectangular mesal emargination ( Fig. 54 ); and (iii) gill I slightly expanded anteriorly ( Fig. 64 ).

Distribution: Nepal and India (Tawang district, Arunachal Pradesh).

Remarks: Way back in 1955, Ueno briefly described an imperfectly preserved larva collected during Japanese- Nepal Himalaya Expedition but did not provide formal species name. Braasch (1980) slightly improved the description and named it as Epeorus unispinosus . Present larval description is in conformity with that if E. unispinosus originally described from Nepal and its distribution is extended herein to Arunachal Pradesh state of India. It has the salient features of the subgenus Epeorus s.s. as pointed out by Kluge (personal communication).

Figures

FIGURES 50–57. Larva of Epeorus (Epeorus) unispinosus 50. Dorsal view; 51. Abdomen ventral view; 52. Closer view of abdomen; 53. Closer view of abdominal terga V; 54. Labrum; 55. Hypopharynx; 56. Mandible; 57. Maxilla.

FIGURES 58–67. Larva of Epeorus (Epeorus) unispinosus 58. Labium; 59. Foreleg; 60. Dorsal surface of forefemur; 61. Midleg; 62. Hindleg; 63. Claw; 64. Gill I; 65. Gill III; 66. Gill V; 67. Gill VII.