Alona begoniae, Sinev & López-Blanco, 2018

Sinev, Artem Y. & López-Blanco, Charo, 2018, А new species of Alona Baird, 1843 (Cladocera: Chydoridae) from the ancient Lake Ohrid, Zootaxa 4526 (4), pp. 434-446 : 435-442

Alona begoniae sp. nov.

( Figs. 1–3 )

Etymology. The species was named after Begoña López Blanco, the sister of the second author.

Type locality. Submerged sands and stones in the littoral zone of the St. Naum Bay, in southern shore of Lake Ohrid, Republic of North Macedonia.

Type material. Holotype. Parthenogenetic female from the type locality, which was deposited at Zoological Museum of M.V. Lomonosov Moscow State University, ML-169. Coll. Z. Levkov and C. López-Blanco, August 2017.

Allotype. Adult male from the type locality, deposited at Zoological Museum of M. V. Lomonosov Moscow State University, ML-170. Coll. Z. Levkov and C. López-Blanco, August 2017.

Paratypes. Over 50 parthenogenetic females, 20 ephippial females and 20 males from type locality deposited at the Zoological Museum of M. V. Lomonosov Moscow State University, ML-171. Coll. Z. Levkov and C. López- Blanco, August 2017 .

Description. Parthenogenetic female. General: In lateral view, body low oval, moderately compressed laterally ( Fig 1 A–B, 2A–B). Maximum height at middle of body. Height-length ratio 0.65–0.7 in adults. Dorsal margin convex, postero-dorsal and postero-ventral angles broadly rounded. Posterior margin convex, ventral margin almost straight, antero-ventral angle rounded. Ventral margin ( Fig. 1C ) with 40–50 setae. About 8–10 anterior setae longer than others. Postero-ventral angle ( Fig 1D ) with about 80 setulae not organized into groups. Carapace covered by longitudinal lines, in most specimens clearly visible only during SEM examination ( Fig. 2 A– B).

Head relatively small, triangle-round in lateral view, rostrum short, pointing downward. Eye and ocellus of similar size. Distance from the tip of rostrum to the ocellus equal or slightly greater than that between the ocellus and the eye. Head shield with maximum width behind mandibular articulation, without any prominent sculpture ( Fig. 1E , 2C ). Rostrum short, broadly rounded. Posterior margin of head shield broadly rounded. Three narrowly connected major head pores ( Fig. 1F , 2D ), middle pore slightly smaller than others, located at the middle between others. PP about 0.3–0.5 IP. Lateral head pores located about 0.8 IP distance from midline, at the level between anterior and middle major head pore.

Labrum relatively large ( Fig. 3 A–B). Labral keel of moderate width (height/width ratio about 1.5), with a rounded or blunt apex. Anterior margin of keel convex, posterior margin without clusters of setulae.

Thorax two times longer than abdomen. Dorsal surface of abdominal segments not saddle-shaped. No abdominal projections.

Postabdomen ( Fig.1 G–H, 2E) short, of moderate width, with almost parallel margins and broadly rounded dorsodistal angle. Length about 2.2–2.4 height. Ventral margin almost straight. Basis of claws bordered from distal margin by clear incision. Distal margin weakly convex. Dorsal margin with distal part about two times longer than preanal one, with postanal portion slightly longer than anal portion. Postanal portion weakly convex to straight, anal portion weakly concave to straight. Preanal angle moderately defined, postanal angle not defined. Preanal margin weakly convex. Two-three large composite marginal denticles in distal portion, followed by 5–7 clusters of smaller elemental marginal denticles, decreasing in size basally, along preanal and anal margin. About 10 lateral fascicles of setulae; 6–7 distalmost fascicles wide, closely spaced, with setulae longer than marginal denticles, with distalmost setula only slightly thicker than others. Additional groups of smaller fascicles in anal portion above the main row. Postabdominal claw ( Fig 2F ) weakly curved, of moderate length, slightly shorter than preanal portion of postabdomen. Basal spine long and thin, about 1/3 of length of claw, a cluster of 2–4 long setulae located near its base.

Antennule ( Fig. 3C ) comparatively large, almost reaching tip of rostrum, with four clusters of long setulae at anterior face. Length/width ratio about 2.5. Antennular sensory seta slender, two times shorter than antennule, arising at 2/3 distance from the base. Nine aesthetascs, two longest about 2/3 length of antennule.

Antenna short ( Fig. 1I , 2G ). Antennal formula: setae 0-0-3/1-1-3; spines 1-0-1/0-0-1. Basipodite robust, branches short and stout. Basal segments of both branches almost two times longer than middle and apical segments. Seta arising from basal segment of endopodite thin, almost as long as endopodite itself. Seta arising from middle segment of endopodite shorter than apical setae. Both apical segments with one shorter and two longer setae of similar thickness. Spine on basal segment of exopodite much longer than middle segment. Spines from apical segments much longer than apical segments.

Thoracic limbs: five pairs.

Limb I ( Fig. 3 D–E) of moderate size. Epipodite oval, with short curved process. Accessory seta short, about 1/3 length of ODL seta. ODL seta with minute setulation. IDL with 3 setae, seta 1 very small. Seta 3 as long as ODL seta; seta 2 about 2/3 length of seta 2. Setae 2 and 3 armed with robust spinules; basalmost spinule on seta 3 much thicker and longer than others. Endite 3 with four setae of same length. Endite 2 with seta (d) as long as setae of endite 3; seta (e) very long, as long as limb itself; seta (f) about 2/3 length of seta (e). Naked Endite 1 with 2 distally setulated 2-segmented setae (g–h) and a long flat seta (i) as long as setae a–d. No naked setae (2–3) and sensillae on endites 1 and 2. Six rows of thin long setulae on ventral face of limb. Two ejector hooks of similar size. Maxillar process with single seta.

Limb II ( Fig 3 F–G). Exopodite elongated, with seta almost as long as exopodite. Eight scraping spines armed with thin setulae: scrapers 1–5 long, increasing in length distally; scraper 3 thicker than neighbours; scrapers 6–8 short, of similar size. Distal armature of gnathobase with 3 elements. Filter plate with 7 setae, 2 posteriormost setae considerably shorter than others.

Limb III ( Fig 3 H–J). Epipodite oval, without process. Exopodite subrectangular, with 6 setae. Seta 3 being longest; seta 5 about 1/3 length of seta 3; setae 1 and 6 about 1/5 length of seta 3; setae 2 and 4 very short. Distal endite with three setae; two sensillae located between their bases. Two distalmost setae (1–2) slender, sharp, of similar length, with long denticles in distal part; basalmost setae shorter, flattened and setulated. Basal endite with 4 outer setae (a–d) slightly increasing in length basally. Gnathobase not clearly separated from basal endite. Four inner setae (4–7) slightly increasing in size basally; a sensillum near the base of distalmost seta. Distal armature of gnathobase with three elements: the first one an elongated, cylindrical sensillum; the second a geniculated seta; the third a short spine. Filter plate with seven setae.

Limb IV ( Fig 3 K–M). Preepipodite setulated; epipodite oval, with process almost as long as epipodite itself. Exopodite irregularly rounded, with 6 setae. Seta 3 longest; setae 1 and 2 about 4/5 length of seta 3; seta 5 about 2/ 3 length of seta 3; setae 4 and 6 shorter than seta 5. Setae 5 and 6 slender, plumose like other setae. Inner lobe of limb IV with 4 setae ( Fig. 3N ). Distalmost seta 1 slender, sharp; flaming-torch setae 2 with thick basal portion, armed with about 10 thick setules; flaming-torch setae 3–4 much smaller, with narrow bases, armed with shorter and thinner setules. Sensillum elongated. Three soft setae (a–c) increasing in size basally. Gnathobase with 2- segmented seta, and a small hillock distally. Filter plate with 5 setae.

Limb V ( Fig 3 N–O). Preepipodite setulated, epipodite oval with process as long as epipodite itself. Exopodite oval, not divided into two lobes, with four plumose setae, decreasing in size basally. Inner limb portion as elongated lobe, with setulated inner margin. At inner face, two setae, one 1.5 times longer than another. Filter plate not found.

Ephippial female ( Fig. 1J , 2H ) with body slightly higher than parthenogenetic female; dorsal margin with depression between valves and head shield. Ephippium dark brown in preserved specimens, with moderately developed egg locules, with longitudinal lines thicker than in the rest of the carapace.

Male. Body ( Fig 1K ) oval, lower than in female, height/length ratio about 0.55. Ocellus and eye of same size as female.

Postabdomen ( Fig. 1L ) short, slightly narrowing distally, with broadly rounded distal angle. Dorsodistal angle well-defined. Sperm duct openings located ventrally almost at the end of postabdomen. Preanal angle not defined, postanal angle well-defined. Distal part of postabdomen 1.5 times longer than preanal, anal portion 1.5 times longer than postanal one. Clusters of short setulae in place of marginal denticles; lateral fascicles of setulae same as in female. Postabdominal claw ( Fig 1M ) 1.5 times shorter than that of female; basal spine long, about 0.3–0.4 length of claw.

Antennule ( Fig. 3P ) thicker than in female, with 10 terminal and 2 lateral aesthetascs. Male seta arising at 1/5 length from tip, about 1/5 of antennule length.

Thoracic limb I ( Fig. 3 Q–S) stouter than that of female, with U-shaped copulatory hook, half as long as limb itself. IDL seta 1 absent, setae 2 and 3 setae much thinner and shorter than in female, armed with thick setulae, male seta thick, curved, almost as long as seta 3. Copulatory brush seta 2 times shorter than male seta. A row of about 15 short setulae on ventral face of limb under copulatory brush. Inner seta (1) of endite 3 more slender than in female, with long setulae distally.

Size. In instar I juvenile female length was 0.25–0.27 mm, height 0.15–0.16 mm; in instar II juvenile female length 0.30–0.34 mm, height 0.18–0.21 mm; in adult parthenogenetic female length 0.34–0.42 mm, height 0.22– 0.27 mm. In adult male, length 0.30–0.33 mm, height 0.17–0.18 mm.

Differential diagnosis. Alona begoniae sp. nov. shares all the diagnostic features of the elegans -group, which is a genus-level group within the Alona s. lato not formally recognized as a separate genus yet ( Sinev et al. 2009; Sinev 2015). These specific features are: 1) a long, well-developed seta of the basal segment of the antennal endopodite; 2) a rudimentary IDL seta 1; 3) absence of inner setae 2 and 3 on endites of limb I; 4) a small inner seta near the base of scraper 1 of limb II; 5) exopodite III with six seta, and, most importantly, 6) male antenna with a pair of lateral aesthetascs, which clearly separates Alona begoniae sp. nov. from the taxa of the genus Coronatella.

Alona begoniae sp. nov. differs from all species of the elegans -group by: 1) its smaller size and 2) by the IDL seta 3 of limb I with basalmost spinule much thicker and longer than the others. More specifically, it can be clearly distinguished from A. orellanai Alonso, 1996 by the presence of a single row of lateral fascicles of setulae on valves and, from A. elegans Kurz, 1875 and A. montana Hudec, 2010 by its weakly developed sculpture on valves and by the seta 4 of exopodite 3, which is much shorter than seta 5. It differs from A. salina Alonso, 1996 , A. irinae Sinev, Alonso & Sheveleva, 2009 and A. floessneri Sinev, Alonso & Sheveleva, 2009 by the spine on basal segment of exopodite of antenna being much longer than middle segment in Alona begoniae sp. nov. than in the species mentioned before. Other differences between Eurasian species of the elegans -group are summarized in Table 1.

Distribution: Alona begoniae sp. nov. might be an endemic species of the Lake Ohrid. However, more extensive sampling of the cladocerans in lakes throughout the whole Balkan Peninsula, especially in Lake Prespa, is needed to better determine its geographical distribution.

Ecology: A. begoniae sp. nov. seems to be associated with sandy and stony substrates, since it was found on bare bottoms at depths ca. 2 and 12 m, but it was absent in our samples from the Chara sp. belt at intermediate depths (ca. 10 m).

Figures

FIGURE 1. Alona begoniae sp. nov. from St Naum Bay, Lake Ohrid, Republic of North Macedonia (type locality). A, juvenile female of instar II. B–I, adult parthenogenetic female. B, lateral view. C, ventral margin of valves. D, posteroventral angle of valves. E, head shield. F, head pores. G–H, postabdomen. I, antenna. J, ephippial female. K–M, adult male. K, lateral view. L, postabdomen. M, postabdominal claw.

FIGURE 2. Alona begoniae sp. nov. from St Naum Bay, Lake Ohrid, Republic of North Macedonia (type locality). A–G, adult parthenogenetic female. A, lateral view. B, dorso-lateral view. C, head shield. D, head pores. E, distal portion of postabdomen. F, postabdominal claw. G, antenna. H, ephippial female.

FIGURE 3. Alona begoniae sp. nov. from St Naum Bay, Lake Ohrid, Republic of North Macedonia (type locality). A–O, parthenogenetic female. A–B, labrum. C, antennule. D, limb I. E, IDL and ODL of limb I. F, limb II. G, exopodite of limb II. H, exopodite of limb III. I–J, distal endite of limb III. K, exopodite of limb IV. L–M, inner portion of limb IV. N, exopodite of limb V. O, inner lobe of limb V. P–S, adult male. P, antennule. Q, limb I. R, copulatory hook and ODL of limb I. S, IDL of limb I.