Baetis pacis Yanai & Gattolliat

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

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Baetis pacis Yanai & Gattolliat

sp. n.

Baetis pacis Yanai & Gattolliat  sp. n. Figures 4E, 14, 15

" Baetis  L12": Samocha 1972: 45, pl XIX, fig. 10.

" Baetis  sp.": Alhejoj et al. 2014: 352, fig. 2B.

Differential diagnosis.

Within the Baetis lutheri  species group, B. pacis  is distinguishable by the following combination of characters: greatly reduced median caudal filament, non-sclerotized protuberances next to coxae, and body not covered with spatulae. In Israel it is easily recognized by its very short median caudal filament.


Length (mature nymphs). Female (n = 13): 5.0-7.6 mm; cerci 2.7-4.5 mm; median caudal filament minute (< 0.2 mm). Male (n = 10): 4.0-6.0 mm; cerci 2.2-4.1 mm; median caudal filament minute (< 0.2 mm). Usually, specimens from the Perat Stream population are smaller than those in northern Israel.

Colouration. General colour brown (Figure 4E). Head brown with light vermiform mark, antennae ecru. Turbinate eyes in male nymph amber. Thorax brown. Legs ivory to whitish, claws, apex of femora and tibiae dark brown, dorsal face of femora with medium brown central mark. Abdominal terga light brown with two central dark brown spots more or less expanded, generally also darker laterally and distally, terga V, VI, IX and X brighter. Abdominal sterna ecru to pale brown. Gills milky, semi-transparent, almost no visible tracheation. Cerci ecru to light brown, without bands or pattern.

Head. No carina between antennae; pedicel almost bare, without distal lobe (Figure 14A). Labrum (Figure 14B): dorsal surface with scattered fine, short setae and seta bases, with one median pair of long setae; lateral margin with distal arc of five long, simple, stout setae and 6-8 lateral setae; ventral surface with 5-6 small, stout setae laterodistally; distal margin with a row of 30-50 fine, long, feathered setae. Hypopharynx (Figure 14D): lingua tri-lobed; surface of lingua and superlingua densely covered with medium thin setae; lateral margin of superlingua serrated proximally. Right mandible (Figure 14C) with incisors composed of two sets of four and three denticles, outer denticles of each set more prominent; prostheca with small, pointed denticles; space between prostheca and mola without setae or crenulation; mola apex with tuft of setae; base of mandible with many short, thin setae and seta bases. Left mandible (Figure 14E) with incisors composed of 6 denticles, inner denticle with additional minute teeth; prostheca with 4-5 broad denticles and comb-shaped structure; space between prostheca and mola without setae or crenulation; base of mola with no spines; base of mandible with many setae and seta bases. Maxillae (Figure 14F) with four broad teeth; lacinia with one row of small setae and long, serrated setae; base of lacinia with row of four long, stout setae; one seta perpendicular to lacinia margin; palpus 2-segmented, segments I and II subequal; segment II with few minute, thin setae apically, and apical nipple with single scale. Labium (Figure 14G): glossa shorter than paraglossa; inner margin and apex of glossa with medium, stout setae; paraglossa not curved, dorsal side with inner 4-6 setae; apical stout, blunt seta; paraglossa apex and distal third with four rows of long, simple setae; labial palpus 3-segmented; segment I similar in length to segments II and III combined; segment II with distolateral protuberance slightly developed, and dorsal row of 4-5 long pointed setae; conic segment III symmetrical, with apical distinct nipple, covered with needle-shaped blunt setae.

Thorax. Forelegs (Figure 15A): coxae almost bare. Trochanters with few ventral minute, stout setae. Femora with one or two dorsal rows with total of ca. 40 stout setae, no longer than 1/4 of femur width, denser proximally; ventral row of ca. 20 minute, stout setae; dorsoapical setal patch made of maximum five minute setae and few thin setae; surface almost bare. Tibiae with dorsal row of thin, short setae and few scales; ventral margin with minute, stout setae and apical brush of thin setae; tibiopatellar suture present. Tarsi with 6-13 ventral pointed setae; dorsal margin with row of short, thin setae; one pointed seta, shorter than most ventral setae, at ventral tarsus-claw meeting point. Tarsal claws (Figure 15B) hooked, with one row of 7-11 acute teeth and two subapical thin setae. Dorsal margin of femora, tibiae and tarsi with scattered feathery scales. Mid- and hindlegs similar to forelegs. Round, unsclerotized protuberances, sometimes hardly seen, adjacent to coxa bases (Figure 9).

Abdomen. Terga shagreened with few thin setae and many seta bases, without scales; distal margin with row of blunt quadrangular spines (Figure 15C). Gills I to VII oval, without marginal spines, main tracheation not pigmented and poorly branched (on gills II to VI main trachea sometimes slightly visible; Figures 15D, E); gills I and VII slightly reduced. Paraproct (Figure 15F) surface with few hair-like setae and seta bases; margin with 10-15 short triangular spines and short thin setae; postero-lateral extension with seta bases, margin with 15-20 small triangular spines. Median caudal filament extremely short, approximately ten segments long.


The species belongs to the Baetis lutheri  species group sensu Müller-Liebenau (1969) based on its morphological characteristics (see details under B. golanensis  above).

Baetis lutheri  differs from B. pacis  by having longer setae on the dorsal margin of femora, densely shagreened terga surface and less reduced median caudal filament ( Müller-Liebenau 1969). Baetis mirkae  from Cyprus differs from B. pacis  by having wider labrum with fewer dorsal long setae, only three rows of setae on the paraglossae, broader labial palpus, more setae on the femora and tibiae, terga not shagreened, rounded teeth on distal margin of terga, and generally more spatulas and setae on the body surface than in B. pacis  ( Soldán and Godunko 2008). The European species B. vardarensis  is characterized by having unique sclerotized, pointed protuberances next to the coxae ( Müller-Liebenau 1974: fig. 4i; Eiseler 2005: figs 76-77), which, in the case of B. pacis  , are rounded and not sclerotized, exhibiting the more common situation in the group. Moreover, B. vardarensis  has a hypopharynx with a uni-lobed lingua, and dorsal line of long setae on the femur margin ( Ikonomov 1962). Within the lutheri  species group, B. pacis  , B. estrelensis  , B. mirkae  and B. nigrescens  can be distinguished by their greatly reduced median caudal filament, only a few segments long, while other species have a medial caudal filament which is at least as long as 1/4 ( B. vardarensis  ) or 1/2 ( B. golanensis  , B. lutheri  , B. meridionalis  ) of the cerci. The number of rows of long setae on the proximal part of the dorsal margin of femora varies among species: one row in B. lutheri  and B. golanensis  , 2-3 rows in B. mirkae  , and 4-5 rows in B. vardarensis  ( Müller-Liebenau 1974: fig. 5a, b; Soldán and Godunko 2008). Baetis pacis  generally has one or two rows of setae, with occasional additional setae that may appear as a third row. Variations can be observed between specimens and even between legs of the same individual. Baetis pacis  clearly differs from B. estrelensis  and B. nigrescens  by the shape of the labial palp (much slenderer in B. estrelensis  and B. nigrescens  ), and the much less shagreened surface of the abdominal terga ( Müller-Liebenau 1971, 1974).

This species corresponds to the undescribed " Baetis  L12" of Samocha (1972: 45 and pl XIX) and probably also to " Baetis  sp." mentioned by Alhejoj et al. (2014) from Jordan.


This species occurs in Israel, the Palestinian Authority, and apparently also in Jordan. Its name reflects our yearning for regional peace.

Distribution and ecology.

Baetis pacis  is distributed mainly in the tributaries of the Jordan River (i.e., Senir, Dan and Iyyon; Figure 2A) but is occasionally encountered in small numbers in smaller Golan streams (Figure 2E) and in the vicinity of the Sea of Galilee (e.g., Arbel Stream). Based on details in Samocha (1972), it may also occur in the Hermon (Panyas) and Ammud streams. An isolated population is found in Perat Stream (Wadi Qelt; Figure 2G). Alhejoj et al. (2014) referred to " Baetis  sp." from Wadi Hisban in Jordan, about 50km east of Perat Stream. Additional study may confirm that this population indeed belongs to B. pacis  . The Israeli populations probably represent the southeastern limit of distribution for the B. lutheri  species group. The distribution of B. pacis  is limited to small- and medium-sized streams with moderate water flow and stony substrate. While water temperature in its habitats may vary, low salinity (< 300 ppm) and high oxygen concentration (>85%) are more important for the species. Mature nymphs were found mostly in spring ( April–May) and fall ( October–November).

Material examined.

Holotype: ISRAEL: 1N, Senir Stream (nature reserve), 33.2331°N, 35.6223°E, ca 130 m a.s.l., 09.iii.2017, Z. Yanai & J.-L. Gattolliat. SMNHTAU292001.-Paratypes. ISRAEL: 80N (1N on slide), Senir Stream (nature reserve), 09.iii.2017, Z. Yanai & J.-L. Gattolliat; 6N, Iyyon Stream (nature reserve), 05.iv.2016, Z. Yanai; 30N (1N on slide), Senir Stream (nature reserve), 17.v.2016, Z. Yanai & A. Charvet; 13N (1N on slide), Dan Stream (Dan), 31.v.2016, Y. Hershkovitz; 2N, Dan Stream (Dafna), 31.v.2016, Y. Hershkovitz; 16N, Senir Stream (Bet Hillel), 09.iii.2017, Z. Yanai & J.-L. Gattolliat; 1N, Dan Stream (Tel Dan), 10.iii.2017, Z. Yanai & J.-L. Gattolliat. Other material. ISRAEL: 1N, Divsha Spring, 06.xi.2015, Z. Yanai & S. Cohen; 1N, Divsha Spring, 11.v.2016, Z. Yanai & N. Dorchin; 1N, Iyyon Stream (nature reserve),, Y. Hershkovitz; 1N, Divsha Spring, 02.x.2016, Z. Yanai & J.-L. Gattolliat. -PALESTINIAN AUTHORITY: 1N, Perat Stream (nature reserve),, Z. Yanai; 37N, Perat Stream (nature reserve), 11.xi.2015, Z. Yanai & S. Cohen; 22N, Perat Stream (nature reserve), 23.v.2016, Z. Yanai & L. Friedman; 6N (2N on slides), Perat Stream (nature reserve), 24.i.2017, Z. Yanai & K. Tamar; 2N, Perat Stream (nature reserve), 30.i.2017, Z. Yanai & N. Truskanov; 12N, Perat Stream (nature reserve), 08.iii.2017, Z. Yanai & J.-L. Gattolliat.