Baetis aureus Yanai & Gattolliat

Yanai, Zohar, Gattolliat, Jean-Luc & Dorchin, Netta, 2018, Taxonomy of Baetis Leach in Israel (Ephemeroptera, Baetidae), ZooKeys 794, pp. 45-84 : 45

Baetis aureus Yanai & Gattolliat sp. n. Figures 4A, 5, 6

Differential diagnosis.

Baetis aureus is unique within its potential species groups in having a relatively short median caudal filament (half-length of cerci) and scale bases on the surface of the abdominal terga only slightly wider than seta bases. In Israel it is distinguishable by the long gills, elongate body, and wide, triangular spines along the distal margin of terga.

Description.

Length (mature nymphs). Female (n = 17): 4.2-4.5 mm (summer generation) to 5.3-7.2 mm (winter generation); cerci 2.6-5.4 mm; median caudal filament 1.7-2.7 mm. Male (n = 8): 4.5-4.7 mm (summer) to 6.0-7.1 mm (winter); cerci 2.9-4.1 mm; median caudal filament 1.6-2.6 mm.

Colouration. General colour light brown to yellow (Figure 4A). Head light brown, antennae, clypeus and labrum ecru. Turbinate eyes in male nymph amber-orange. Thorax brown with a few pale marks but without clear pattern. All legs whitish, brownish hue sometimes on middle of trochanter and femur, brown shade on claw and distal 1/3 of tarsus. Abdominal terga yellowish brown, with pale narrow posteriomedial triangular spot forming dashed dorsal line along abdomen. Abdominal sterna ecru to pale yellow. Gills milky, semi-transparent, costal margins darker, tracheation brownish purple. Cerci and median caudal filament uniformly ecru without bands or pattern.

Head. No carina between antennae; pedicel almost bare (Figure 5A). Labrum (Figure 5B): dorsal surface with scattered, fine, short setae and seta bases, with one median pair of long setae; lateral margins each with distal arc of 5-6 long, simple, stout setae and 4-5 lateral setae; ventral surface with 5-6 small, stout setae laterodistally; distal margin with row of 30-40 fine, long, feathered setae. Hypopharynx (Figure 5D): lingua tri-lobed; surface covered with minute hair-like setae, denser and stouter apically; lingua and superlingua covered with minute, stout setae; base of superlingua laterally serrated. Right mandible (Figure 5C) with incisors composed of two sets of four and three denticles, outer denticles more prominent than others; prostheca with 6-7 denticles; mola apex with tuft of setae. Left mandible (Figure 5E) with incisors composed of six denticles, outer one broadest and most prominent; prostheca with six denticles and few long, soft setae; space between prostheca and mola slightly crenulate; mola apex without tuft of setae; base of mola with few spines. Maxillae (Figure 5F) with four broad teeth; lacinia with one row of small setae and long, serrated setae; row of 4-6 setae at base of lacinia; one seta perpendicular to lacinia margin; palpus 2-segmented, segments of similar length; segment II with small nipple, covered with sparse minute setae, apical scale absent. Labium (Figure 5G): glossa slightly shorter than paraglossa; glossa inner margin and apex with long, simple setae; paraglossa not curved; apex with apical stout, blunt seta and distal quarter with three rows of long setae; labial palpus 3-segmented; segment I as long as segments II and III combined; segment II with noticeable distolateral protuberance ( “thumb”) and dorsal row of 5-7 long, pointed setae.

Thorax. Forelegs (Figure 6A): coxa almost bare. Trochanter with few short, stout setae. Femora with dorsal row of ca. 50 short, stout setae, and ventral row of ca. 30 minute setae, both evenly distributed along margin; dorsoapical setal patch composed of 5-7 stout setae and 2-3 thin setae. Tibiae with dorsal and ventral rows of stout, pointed setae; tibiopatellar suture present. Surface of trochanters, femora and tibiae with scattered feathered scales. Tarsi with 10-20 minute dorsal setae; 13-20 ventral pointed setae and submarginal row of shorter setae; one pointed seta, shorter than most ventral setae, at ventral tarsus-claw meeting point. Tarsal claws (Figure 6B) hooked, with row of 15-17 acute teeth. Mid- and hindlegs similar to forelegs.

Abdomen. Terga shagreened with few thin setae, seta bases and very small scale bases (only slightly wider than seta bases); distal margin of all terga with row of triangular spines as broad as long (spines longer and more pointed on terga VII to IX), with spaces between them no broader than spine length (Figure 6C). Gill I oval, reduced, without marginal spines and visible tracheation (Figure 6D); gills II to VII elongate, 1.7 times longer than following tergum; margins thicker with very fine serration in proximal half; branched tracheae clearly visible (Figure 6E). Paraproct (Figure 6F) with elongate scales, hair-like setae and seta bases; margin with 20-30 regular triangular spines; postero-lateral extension with few scales, margin with 14-20 triangular spines of similar size.

Affinities.

Baetis aureus exhibits the main characters of the B. vernus and B. buceratus species groups sensu Müller-Liebenau (1969) and cannot be assigned to any of them with certainty. Therefore, it is compared here to species of both species groups. Characters typical to both groups include mandibles with bigger outer tooth, labrum with submarginal arc of less than eight setae, tarsal claws without subapical setae, distal margin of abdominal terga with triangular spines, relatively long gills, and generally inconspicuous pattern of the terga ( Bauernfeind and Soldán 2012). Baetis aureus differs from all known species of these two species groups by the median caudal filament that is slightly longer than half the length of its cerci (whereas in other species the median caudal filament is almost as long as the cerci, except in B. zdenkae Soldán & Godunko, 2009), and by the small size of the scale bases on the surface of the abdominal terga.

In the B. vernus species group, seven species were reported from the West Palearctic region, and differ from B. aureus as follows: Baetis vernus Curtis, 1834 has a mola with two small auxiliary spines at the outer side of the subtriangular process (figure 91 in Eiseler 2005). In B. liebenauae Keffermüller, 1974 the outer sets of incisors in the mandibles are fused, and the spines on the distal margin of terga are blunt and rounded ( Keffermüller 1974). In B. macrospinosus Koch, 1985 the setae on the dorsal margin of femora are longer and apically rounded, terga are covered with abundant scale bases, spines on distal margin of terga are blunt and rounded, and dorsal pattern of abdomen is well-marked ( Koch 1985). In B. macani Kimmins, 1957 the distolateral protuberance on segment II of the labial palpus ( “thumb”) is considerably developed ( Müller-Liebenau 1969). The gill tracheation of B. tracheatus Keffemüller & Machel, 1967 is conspicuous. The submarginal arc of setae on the labrum of B. tracheatus and B. subalpinus Bengtsson, 1917 is reduced to 2-3 setae ( Müller-Liebenau 1969). Finally, B. samochai Koch, 1981 is characterized by long and sharp spines along the distal margin of terga, its maxillary palpus is longer than the galealacinia, and the dorsal pattern on its abdomen is different ( Koch 1981).

Baetis aureus differs from all other known species of the B. buceratus species group (see Soldán and Godunko 2009) as follows: in B. buceratus Eaton, 1870, the submarginal distal arc on the labrum consists of only 3 setae, and spines on the distal margin of terga are narrow and blunt ( Müller-Liebenau 1969). In B. spei Thomas & Dia, 1985, a geographically close relative from Lebanon, the shape of the labial palpus is different, teeth on the outer set of the left mandible incisor are wider, spines on the distal margin of terga are rounded and blunt, marginal spines on paraproct are irregular and of variable shapes ( Thomas and Dia 1985). In B. pentaphlebodes Ujhelyi, 1966 segment III of the labial palpus is shorter (compared to segment II). In B. zdenkae from Rhodes, Greece, the incisors of the right mandible are not arranged in a decreasing size order, more setae are present on the paraglossa base, and less marginal spines are found on the paraproct ( Soldán and Godunko 2009). Finally, in B. monnerati the setae on the dorsal margin of femora are long, and the gills are oval ( Gattolliat et al. 2012).

Etymology.

Aureus (Latin for golden) refers to the general colour of the nymph body.

Distribution and ecology.

This species is common in the northern regions of Israel: Lower and Upper Galilee, Hula Valley and Golan Heights, and rare in the Yarqon stream. It is found in habitats of running, pristine water, particularly in small creeks but also in larger streams such as the Keziv and Zippori (Figure 2C, E, F). The substrate is usually composed of stones of different sizes, and localities with dense submerged vegetation are preferred. Mature nymphs were collected mostly in spring ( March–May) and fall ( October–November).

Material examined.

Holotype. ISRAEL: 1 Nymph, Gamla Stream (Peham Springs), 32.9672°N, 35.8201°E, ca 690 m a.s.l., 04.iv.2016, Z. Yanai, SMNHTAU291999. Paratypes. ISRAEL: 88N, Barqan Stream, 25.v.2011, Y. Hershkovitz; 1N, Gilbon Stream (upstream Devora Waterfall), 09.iv.2014, Z. Yanai; 1N, Yarqon Stream (national park), 10.iv.2014, Z. Yanai; 4N (1N on slide), Ammud Stream (Yaqim Spring), 20.v.2014, Z. Yanai; 1N, Fit Spring, 10.vi.2014, Z. Yanai; 9N (2N on slides), Gaaton Junction, 17.vi.2014, Z. Yanai & D. Mayer; 3N, Zippori Stream (Ras Ali), 02.iii.2015, Z. Yanai; 1N, Gilbon Stream (upstream Devora Waterfall), 29.x.2015, Z. Yanai & Y. Brenner; 107N (1N on slide), Keziv Stream (Hardalit Spring), 07.xi.2015, Z. Yanai & S. Cohen; 17N, Keziv Stream (Tamir Spring), 07.xi.2015, Z. Yanai & S. Cohen; 1N, Zippori Stream (Zippori Springs), 07.xi.2015, Z. Yanai & S. Cohen; 40N, Zippori Stream (Ras Ali), 07.xi.2015, Z. Yanai & S. Cohen; 19N, Gamla Stream (Peham Springs), 04.iv.2016, Z. Yanai; 154N (1N on slide), Zippori Stream (Zippori Springs), 19.iv.2016, Z. Yanai; 24N (1N on slide), Rosh Pinna Stream (Rosh Pinna ), 15.x.2016, Z. Yanai; 6N, Yarqon Stream, 14.v.2017, Y. Hershkovitz. Other material. ISRAEL: 4N, Zippori Stream (Yivqa Spring), 21.ii.2014, Z. Yanai; 5N (1N on slide), Keziv Stream (Hardalit Spring), 17.vi.2014, Z. Yanai & D. Mayer; 4N, Ammud Stream (Poem Spring), 18.v.2015, Y. Hershkovitz & T. Eshcoly.