Gratia baibungensis, Shi, Weifang & Tong, Xiaoli, 2015

Shi, Weifang & Tong, Xiaoli, 2015, First record of the genus Gratia Thomas (Ephemeroptera, Baetidae) from China with the description of a new species, ZooKeys 478, pp. 129-137 : 131-134

Taxon classification Animalia Ephemeroptera Baetidae

Gratia baibungensis sp. n.

Material examined.

Holotype. 1 mature nymph in ethanol, China, Tibet, Medog County, Baibung Town (29°14.65'N, 95°10.59'E, alt. 860m), 29.ix.2010, coll. Xianfu Li.

Paratypes.

2 nymphs on slides and 2 nymphs in ethanol, same data as holotype.

Other material examined.

Gratia sororculaenadinae Thomas: 3 mature nymphs, Thailand, Chiang Mai, Mae Hlang Stream, 16.i.2007; Gratia narumonae Boonsoong & Thomas: 3 mature nymphs, Thailand, Loei Province, Tarn Sawan waterfall, 12.ii.1999.

Description.

Mature nymph (Fig. 2a). Body length 4-4.5 mm, cerci slightly longer than body length, terminal filament only one segment.

Head. Capsule yellowish-brown with transverse irregular markings on vertex and frons. Antennae approximately 1.5 times the width of head; dorsal surface of scape and pedicel scatter with fine setae, and with 3-4 and 2-3 scale-like setae respectively (Fig. 1a). Labrum (Fig. 1b) rectangular, approximately 2.0 times wider than long; anteromedial notch deep with a small rounded lobe at the base, and each side with one medial long seta and a row of 7-8 robust, simple and glabrate submarginal setae sublaterally, fine and simple setae scattered posteriorly; ventrally bordered with feathered setae along the anterior margin and a distomedial arc of very fine setae. Left mandible (Fig. 1d): incisors fused with 7 denticles, prostheca robust with 5 blunt and 3-4 acute denticles apically. Right mandible (Fig. 1e): incisors fused with 6 or 7 denticles, inner incisor margin smooth without fine setae, prostheca with denticles apically and distinctly slender than the one on the left mandible, edge between prostheca and molar smooth with no serration, molar plated-like. Hypopharynx with lingua rounded and superlinguae broadly truncate, covered with abundant fine setae (Fig. 1c). Maxillae (Fig. 1f) with one canina and three dentisetae on crown of galealacinia, a row of 4 long basal setae and one short bristle-like hump seta on basis of galealacinia; maxillary palpus 2-segmented and subequal in length, terminal segment with a small tip at apex and slender than basal segment. Labium (Fig. 1g): glossae slightly shorter than paraglossae, with a row of 9 stout setae along the inner margin dorsally and 2 long robust blunt setae at the apex; paraglossae approximately 2.0 times wider than glossae, with two rows of setae ventrally and 2 stout acute setae along the inner margin dorsally; labial palpus 3-segmented, terminal segment conical with a distinctive tip at apex (Fig. 1h); the 2nd segment with an inner-apical lobe and an oblique row of 2-3 setae dorsally, the articulation between the 2nd and terminal segments obscure; dorsal surface with numerous pores on the 1st segment.

Thorax. Coloration pale brown with indistinct darker patterns. Surface of pronotum with four blunt tubercles. Metanotum with a finger-like protuberance medially (Fig. 1j). Hind wing pads reduced, approximately 2 times longer than wide (Fig. 1j). Legs (Fig. 1i) yellow brown with darker markings. Femora of all legs with a regular row of multilaterally ciliate bristles along dorsal margin, approximately 1/2 as long as femur width (Fig. 1l); stout short submarginal scale-like setae present; villopore present. Tibiae subequal to femur in length; irregular rows of simple fine setae present on the dorsal margin, with length subequal to the width of tibia, submarginal stout setae present. Tarsi half the length of tibia, with irregular row of sparse fine simple setae on dorsal margin and 5-6 robust point setae on ventral margin increasing in length towards the apex, tarsus of all leg without long ventral subapical bristle. Claw with one row of 8-9 denticles and a pair of bowed subapical bristles (Fig. 1k). All legs lack coxal gills.

Abdomen. Generally yellowish-brown. Mediodorsal posterior margin of terga I–IX each with a finger-like protuberance, successively decreasing in length backwardly (Figs 2a, d): length of protuberance subequal to the tergum length on segments I–IV, and approximately one third of tergum length on segment IX; surface of protuberance scattered with scale-like setae (Fig. 2b). Terga surface with scattered scale-like and fine setae, posterior margin with blunt denticles. Surface of sterna scattered with round scale-like setae and each sternum with a pair of friction pads on anterolateral area; posterior margin on sterna VI–IX each with a row of continuous long spatulate setae which length approximately 3-4 times the width in female nymphs (Fig. 2h) and 2-3 times the width in male nymphs. Paraproct (Fig. 2c) with numerous pores and fine bristles on the surface and 9-14 scale-like setae along the inner margin. Gills on segments I–VII, oval and untracheated, surface scattered with numerous pores, margin smooth with blunt and fine simple setae. Median caudal filament reduced to one segment (Fig. 2g), each segment of cerci on inner margin with 1-4 (increasing in number towards terminal) swimming bristles (Fig. 2e).

Adult.

Unknown.

Etymology.

This new species is named after Baibung, the small town near the type locality.

Distribution.

China (southeastern Tibet).

Remarks.

Comparison with Thai specimens of two Gratia species (Table 1) shows that this new species can be readily distinguished from other members of the genus by the absence of a protuberance on tergum X. In appearance, the new species is most similar to Gratia narumonae Boonsoong & Thomas, but it can be readily distinguished from the latter by the following characters:

all dorsal submarginal setae on labrum are glabrate and simple (vs. all but two innermost setae are branched and fimbriate in Gratia narumonae );

posterior margin on sterna VI–IX each with a row of continuous long spatulate setae approximately 2-4 times longer than wide (Fig. 2h), but only 1.5-2 times in Gratia narumonae (cf. Fig. 2i);

gill margin with blunt setae, absent in Gratia narumonae .

Habitat.

Nymphs of Gratia baibungensis sp. n. inhabit the riffles area with cobble and gravel substrates in a 2nd-order shallow subtropical stream (approximately 1 m wide). However, both Thai species are found clinging to rock surfaces of tropical cascades: Gratia sororculaenadinae lives in limimadicolous zones and Gratia narumonae is more abundant in petrimadicolous zones.