Isca lea, Sartori & Derleth, 2010

Sartori, Michel & Derleth, Pascale, 2010, The dipterous Leptophlebiidae of Borneo (Insecta, Ephemeroptera), Zootaxa 2490, pp. 33-39 : 34-35

Isca lea sp. nov.

Material examined. Holotype: 1 female larva, Indonesia - East Kalimantan, Malinau Basin, Seturan (1998- bloc 28), Kipah , affl. Seturan Riv., 116°29'48''E / 3°01'48''N; 29.03.2001, (B0913), P. Derleth [ MZL]

Paratypes: 11 larvae, same data as holotype ; 3 larvae, Seturan (2000-bloc 45), Wok (Sungai Guang), affl. Seturan Riv., 116°33'30''E / 2°59'11''N, 29.06.2000, (B0631), P. Derleth ; 12 larvae (of which one mounted on microscopic slide), Seturan (1999-bloc 27), Seturan Riv., 116°30'31''E / 3°00'57''N, 10.07.2000, (B1111), P. Derleth ; 9 larvae, same locality, 26.03.2001, P. Derleth & B. Feldmeyer [of which 3 in FAMU] ; 14 larvae (of which one mounted on microscopic slide), Langap Sud (1995), Ngayo, affl. Rian Riv., 116°31'15''E / 3°04'41''N, Alt. 160 m . a.s.l., 12.07.2000, (B0421), P. Derleth [of which 3 in LIPI] ; 1 larva, Seturan (2000- bloc 43), Temalat (Sungai Guang), affl. Seturan Riv., 116°33'29''E / 2°59'29''N, 16.08.2000, (B0812), P. Derleth & R. Schlaepfer ; 1 larva, Seturan (2000-bloc 43), Temalat (Sungai Guang), affl. Seturan Riv., 116°33'29''E / 2°59'29''N, 04.04.2001, (B0823), P. Derleth ; 1 larva (gills mounted on slide in glycerine), Langap Sud (1997-bloc 6), Belakau, affl. Rian Riv., 116°30'26''E / 3°04'04''N, 100 m . a.s.l., 20.04.2001, (B0113), P. Derleth & M. Sartori.

Nymph. Body length up to 2.8 mm and 3.4 mm for male and female nymphs respectively. Cerci subequal to body length, terminal filament slightly longer.

General colouration medium brown to greyish brown, without specific patterns, except area between ocelli on the head washed with black; dorsal portion of male nymphs’ compound eyes reddish brown; legs uniformly yellowish.

Head prognathous, antennae more than 2.2 times length of the head. Labrum ( Fig. 1) ca 2 times wider than long, lateral margins clearly divergent and rounded at angles, distal margin slightly cordiform, anteromedian incision narrow; dorsal side with an even distal row of short setae and a sub distal row of long setae, scattered long setae on the ventral side. Left and right mandibles rather similar, outer margin regularly rounded, with a tuft of ca 10 long setae in the middle; outer incisors with 3 teeth, inner incisors with 3 teeth and 2 teeth on the left and right mandible respectively; a row of 6–8 long and thin setae under the mola of the right mandible. Maxilla with galea-lacinia broad and covered with dense crown of setae; maxillary palp ( Fig. 3) 3-segmented, segment 1 the longest, and segment 2 slightly shorter than segment 3, the latter with a bunch of thin setae and 3–4 long and stout setae on its outer margin. Hypopharynx with superlinguae well developed, rounded at apex, row of setae on the outer margin ending well before the apex. Labium as in other Isca species , glossae small and rounded, paraglossae large and slightly pointed on the antero internal margin; labial palp 3- segmented, a little bit shorter than the glossae.

Legs with femur ca 2 times longer than wide, with scattered long, stout and blunt setae on the outer margin, short, stout and slightly pointed setae on the inner margin; tibia slightly shorter than femur, outer margin without setae, inner margin with a dense row of feathered setae; tarsus 2 times shorter than tibia, with a row of simple pointed setae on inner margin; tarsal claw very distinctive, with a row of 9–11 teeth, the last one much larger than the others.

Abdominal terga characteristic of Isca , extending on the ventral side, especially on segments V –VII. Gills present on segments II–VII, clearly in ventral position on segments V –VII, each constituted of a dorsal and a ventral slender and unbranched lamella ( Fig. 5). No posterolateral projection on segments II–VII, small on segments VIII, and slightly larger on segment IX.

Male and female adults unknown.

Affinities. Isca lea presents all characteristics of Isca nymphs proposed by Peters & Edmunds (1970), with one major exception; gill VII is not constituted by a single lamella but by a dorsal and a ventral lamella as in other gills. Among the four known species of the genus, Isca lea is the only one to possess this character. Edmunds & Polhemus (1990) mentioned the presence of an undescribed species on Sulawesi, supposed to be more primitive than others, but did not mention on which characters this statement was made. Isca lea seems closer to Isca janiceae Peters & Edmunds , known from Thailand and Vietnam ( Nguyen & Bae 2003). But it differs from it, as well as from Isca fascia Nguyen & Bae, 2003 , from Vietnam by the shape and ornamentation of the labrum ( Figs 1–2), setation of the maxillary palp ( Figs 3–4), general coloration of the abdomen, and above all by the shape of gill VII ( Figs 5–6). Comparative material of I. janiceae used in this study comes from: Thailand, torrent on Ko Chang Island, 102°19’08’’E, 12°03’58’’N, 280 m. a.s.l., 03.02.2006, J.-M. Elouard leg., 8 larvae [ MZL].

Etymology. This species is dedicated to Miss Lea Lafuente (Penticton, BC, Canada) and is a noun in apposition.

Distribution and ecology. Isca lea is relatively abundant in the studied area, and has been found significantly more often in disturbed, recently logged habitats than in pristine ones ( Derleth 2003). This is the only mayfly species, together with an undescribed species of Caenidae , to exhibit such preference.