Rhithrogena sartorii Zrelli & Boumaiza

Zrelli, Sonia, Sartori, Michel, Bejaoui, Mustapha & Boumaiza, Moncef, 2011, Rhithrogena sartorii, a new mayfly species (Ephemeroptera: Heptageniidae) from North Africa, Zootaxa 3139, pp. 63-68 : 64-67

Rhithrogena sartorii Zrelli & Boumaiza , sp. nov.

( Figs. 2 19)

Material examined. Holotype: 1 nymph (preserved in ethanol), Ennour, 36.80072N 8.65871E 418 m., 28 IV 2010, S. Zrelli ( MZL). Paratypes: same data as the holotype: 30 nymphs, 1 male subimago, 2 females subimagos ( MZL, LBE).

Other material examined. Same locality 24 V 2005, 1 nymph, 30 IV 2006, 1 nymph; Berbeg, 36.74968N 8.69693E, 558 m., 21 V 2005, 1 nymph; Rennagha, 36.85997N 8.72096E, 58 m. 29 VII 2005, 1 nymph; Ghezala, 36.64313N 8.69852E, 229m, 24 V 2005, 1 nymph.

Description. Nymph. Body length of final instar, excluding caudal filaments, up to 4.5 mm and 7.5 mm for male and female nymphs respectively. Cerci, 5.0 7.3 mm. Color: body brownish with visible tracheation on the whole body.

Head dark brown, subtrapezoidal with convex sides and rounded hind corners ( Fig. 2 ). Labrum narrow, with distinct anterior teeth ( Fig. 3 s), 9 11 comb-shaped bristles on fore margin of maxilla with 6 7 teeth ( Fig. 4 ). Glossae subovoidal with rounded apex ( Fig. 5 s).

Dorsal surface of femora of all legs with few spines and an ovoid dark spot well visible on the center of the median pale area ( Fig. 6 ). Bristles on hind femora very short with diverging margins ( Fig. 7 s). Tarsal claws with two or three denticles. Lateral sclerites of the first abdominal sternite rectangular with their anterior margin perpendicular to the body axis ( Fig. 8 ). Posterior margin of abdominal tergites regularly dentate in central part, with few supplementary microdenticles ( Fig. 9 ). All gill lamellae crenulated (10a, 10b and 10c). Plica on the first gill triangular with slightly concave apex ( Fig. 10 a).

Male subimago. Body length 9.0 mm, forewing 8.0 mm. Cerci 9.0 mm. General color brown except the thorax, lighter. Eyes darkish brown. Sterna lighter than terga. Fore legs brown, femora with an elongated dark spot. Mid- and hind legs lighter, yellowish brown, and femora with a dark spot more elongated. Styliger plate and forceps brown, posterior margin deeply incised in the middle ( Fig. 11 ). Forceps uniformly brown, 3 segmented with a well defined basal segment, the 1st segment the longest, the 2nd and the 3rd equal in length. Genitalia as in Fig. 12 . Titillators with apical margin bearing 3 4 teeth with 3 subapical teeth visible on their surface ( Fig. 13 ).

Female subimago. Body length 7.3 8.0 mm, forewings 5.7 7.0 mm. General color yellowish brown. Thorax brown, abdomen with color pattern similar to male. All legs with elongated spots on the dorsal side of femora.

Eggs. Length: 180 200 µm, width: 150 170 µm. General shape ovoid ( Fig. 14 ). Polar cap at one pole with numerous adhesive elements (KCTs). Micropyle with well developed margin ( Fig. 15 ). Chorionic surface with several KCTs and with microgranules irregularly arranged ( Fig. 16 ).

Male and female imagos unknown

Etymology. The species is named to honour Dr. Michel Sartori (Museum of zoology, Lausanne, Switzerland), who is a long-time investigator of the genus Rhithrogena .

Affinities. Rhithrogena sartorii sp. nov. seems to belong to the insularis -group which included up to now only R. insularis Esben-Petersen 1913 and R. nuragica Belfiore 1987 . According to Belfiore (1987) and Belfiore et al. (1992) the nymphs of both species shows a unique combination of characters: 1) lateral sclerites of the first abdominal sternite with anterior margin perpendicular to the body axis; 2) all gills crenulated; 3) a dark spot on the dorsal side of femora; 4) plica on the first gill triangular; and 5) the presence of well-developed tubercules on egg chorion. First 3 characters are also shared by species of the hybrida/hercynia species group, but the last two clearly differ from it. In the present state of our knowledge, R. sartorii is morphologically close to the species of the R. insularis group, but genetic data based on both mitochondrial and nuclear markers are congruent and place R. sartorii in a cluster quite distant from them (L. Vuataz, comm. pers.).

When compared to the species found in Morroco, R. sartorii clearly differs from R. mariae and R. ryszardi which belong to the semicolorata and the germanica species group respectively, which gills II VII are not crenulated. It also differs from R. ourika , R. ayadi and R. giudicelliorum , mainly by the shape of the male titillators.

The main diagnostic nymphal characters are described and compared with the two insularis -group species in Table 1 . The nymph of the new species can be distinguished especially by the number of comb-shaped bristles and the number of teeth on the comb-shaped bristles at the tip of lacinia. The shape of the chorionic tubercles is somewhat intermediate between those of R. insularis and R. nuragica . KCTs lack the finger-like processes found in R. insularis , and the arrangement of the KCTs is less regular than in R. nuragica ( Belfiore, 1987) .

insularis .

Character Rhithrogena sartorii Rhithrogena nuragica Rhithrogena insularis sp. nov. Belfiore 1987 Esben-Peterson 1913

Mean body length (mm) 6 7,5 6,8 Ecology. Nymphs of the new species were collected in four different sites in strong current of streams and riffles of rivers with cobble substrates. Streams ranged in width from 4 m (Berbeg) to 10 m (Ennour), and water depth not exceeding 65 cm at all collecting sites. The very low mineralization of water (<0.15 PSU) can explain the absence of the new species in the other streams of Northern Tunisia which are more mineralized.

Figures

FIGURES 2 – 10. Rhithrogena sartorii sp. nov., larva: 2. Head, dorsal. 3 s. Labrum, dorsal face 4. Comb-shaped setae from maxillary lacinia. 5 s. Labium (dorsal view). 6. Hind femur. 7 s. Bristles from the margin and the central part of hind femur. 8. First abdominal sternite. 9. Posterior margin of tergum V. 10 a. Gill I. 10 b. Gill II. 10 c. Gill VII. R. insularis, 3 i. 5 i. 7 i. R. nuragica, 3 n. 5 n. 7 n.

FIGURES 11 – 13. Rhithrogena sartorii sp. nov., male subimago: 11. Styliger plate and gonopods in ventral view. 12. Penis. 13. Titillator, lateral view.

FIGURES 14 – 16. Rhithrogena sartorii sp. nov., egg: 14. General view. 15. Detail of the micropyle. 16. Polar cap.