Flavalona rustica rustica ( Scott, 1895 ) Sinev & Dumont, 2016

Sinev, Artem Y. & Dumont, Henri J., 2016, Revision of the costata-group of Alona s. lato (Cladocera: Anomopoda: Chydoridae) confirms its generic status, European Journal of Taxonomy 223, pp. 1-38 : 19-25

Flavalona rustica rustica ( Scott, 1895) comb. nov.

Figs 4–5

Alona rustica Scott, 1895: 189–190 , pl. 5, figs 5, 17.

Alona estonica Maëmets, 1958: 260–264 , figs 1–3, photos 1–2.

Alona rustica – Frey 1965: 162–169, figs 1–7. — Flössner 1967: 443–444, fig. 2. — Smirnov 1971: 360–363, figs 416–418. — Flössner 1972: 301–304, fig. 142. — Van de Velde & Dumont 1978: 306, fig. 1A–C. — Dumont 1983: 102–105, pl. 4. — Negrea 1983: 228–190, fig. 117. — Margaritora 1985: 316–318, fig. 125. — Alonso 1996: 323–325, fig. 144. — Flössner 2000: 318, fig. 118. — Margaritora & Vagaggini 2002: 61–59, figs 1–10. — Sinev 1999a: 146, fig. 10. — Sinev 2001: 118, figs 26–34. — Sinev 2002: 396, figs 3д,о, 4д, 5и. — Hudeč 2010: 322–324, fig. 78.

Alona estonica – Maëmets 1960: 35–40, fig. 1, photos 1–2.

Differential diagnosis

Flavalona rustica rustica comb. nov. differs from F. iheringula comb. nov. by its middle major head pore located halfway between the posterior and anterior pores and by the oval, an unbilobed exopodite of limb V, from F. sphagnophila comb. nov. by its transverse, not dot-like lateral head pores and by an oval, not bilobed exopodite of limb V, from F. bicolor comb. nov. by a smaller size, short rostrum and labral keel without denticles, from F. hudeci comb. nov. by a smaller size, presence of numerous setules on posteroventral corner of valves, and by seta 6 of exopodite III almost as long as seta 3. Male of F. rustica comb. nov. differs from F. iheringula comb. nov. and F. bicolor comb. nov. by marginal setules of postabdomen in distal groups of moderate length, little more than width of postabdominal claw base (in F. iheringula comb. nov. they are short, less than width of postabdominal claw base, and in F. bicolor comb. nov. they are long, about two postabdominal claw bases).

We provide a full description of F. rustica comb. nov. as typical of the rustica- clade.

Type material

Non-existent.

Material studied here

Four parthenogenetic ♀♀ from Lake Motjønn, west coast of Nisser Lake, Norway, 59º08.62′ N, 8º27.32′ E, 4 Oct. 2015, coll.A.Y. Sinev & B. Walseng; 47 parthenogenetic ♀♀ from Bol’shoe Torfyanoe lake, Bolshoi Solovetskiy Island (White Sea), Russia, 24 Jul. 1997, coll. A. Evseev; 12 parthenogenetic ♀♀ from Karelia Republic, Russia, exact location unknown, from collection of N.N. Smirnov.

Type locality

Scotland.

Description

Parthenogenetic female

Length of adult 0.35–0.52 mm. In lateral view body ( Fig. 4 A–D) regular oval or slightly ovoid, maximum height at mid-body or somewhat behind it, height-length ratio ca 0.6–0.65. Dorsal margin uniformly curved. Postero-dorsal and postero-ventral angles broadly rounded. Posterior margin uniformly curved. Ventral margin ( Fig. 4E ) almost straight, with about 50–60 setae, about 12 first setae long, next 15 setae short, other setae of moderate length. Setae of anterior group ( Fig. 4F ) longer than of posterior group ( Fig. 4G ), posteriormost seta of group the longest. Groups of small setules located between bases of all ventral setae. Posteroventral angle ( Fig. 4H ) with ca 50 long setules protruding beyond margin of valves. A row of about 150 setules along posterior margin on inner side of carapace. Sculpture of carapace either thin, weakly developed longitudinal lines without striae, or rows of tubercles ( Fig. 4D ).

Head relatively small, triangular-round in lateral view, rostrum short, pointing downward. Eye larger than ocellus. Distance from tip of rostrum to ocellus greater than between ocellus and eye.

Head shield ( Fig. 4I ) with maximum width behind mandibular articulation, without any sculpture in specimens with linear sculpture of valves, or covered by tubercles. Rostrum more elongated than in costata -clade, broadly rounded. Posterior margin of head shield broadly rounded, wavy in tuberculated specimens. Three major head pores ( Fig. 4 J–K) with thin connection between them, middle pore slightly smaller than others, located at the middle PP about 1–1.5 IP. Transverse lateral head pores of about 0.3–0.4 IP length, located about 0.5 IP distance from midline, at a level between anterior and middle main head pores. Lateral pore pockets semicircular, with depth ca 0.5–0.9 pore lengths.

Labrum of moderate size ( Fig. 5 A–B). Distal labral plate without setulation. Labral keel of moderate width, with a blunt or rounded apex. Anterior margin of keel convex, posterior margin with two clusters of setules. Clusters of lateral setules observed in anterior half of the keel in some specimens.

Thorax and abdomen subequal in length, dorsal surface of abdominal segments not saddle-shaped. Second abdominal segment with two transverse rows of short setules.

Postabdomen ( Fig. 4 L–M) wide, narrowing distally, with a prominent broadly rounded distal angle, length ca 2.0–2.3 height. Ventral margin straight. Inflated basis of claws bordered from distal margin by clear incision. Distal margin strongly convex. Dorsal margin with distal part about 2.5 times longer than preanal part, with postanal portion about 1.3–1.5 times longer than anal one. Postanal and anal portions of distal margin weakly concave. Preanal angle well-defined, postanal angle weakly defined. Preanal margin almost straight. Postanal portion of postabdomen with 7–8 well developed composite marginal denticles, each with several spinules on anterior margin, anal portion with 2–3 marginal denticles, similar to postanal ones, and with 2–3 groups of thick setules. Length of denticles decrease basally, length of longest denticles about 1.5 widths of postabdominal claw base. Ten–twelve lateral fascicles of thin setules; in postanal fascicles middle seta being longest, 1.5 times shorter than marginal denticles. Postabdominal claw of moderate length, somewhat longer than preanal portion of postabdomen. Basal spines short, their length less than width of postabdominal claw base.

Antennule ( Fig. 5C ) of moderate length, not reaching the tip of rostrum, with four transverse rows of short thick setules at anterior face. Antennular sensory seta slender, 2 times shorter than antennule, arising at ⅔ distance from the base. Nine aesthetascs, two of which longer than others, of about 3/4 length of antennule, others of similar length.

Antenna ( Fig. 4N ) of moderate length. Antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Basal segment robust, branches elongated, slender, all segments cylindrical, with short setules around distal margin and groups of thick lateral setules. Seta arising from basal segment of endopodite short and thin, not reaching tip of distal segment. Seta arising from middle segment of endopodite of similar size with apical setae. Spine on basal segment of exopodite shorter then middle segment. Apical spines slightly longer than respective apical segments.

Thoracic limbs six pairs.

LiMB i ( Fig. 5 D–E). Epipodite oval, with finger-like process as long as epipodite itself. Accessory seta about half the length of ODL. IDL with three setae and clusters of setules on ventral surface, IDL seta 1 small, thin, setae 2 and 3 subequal in length to ODL seta, both with thin setules in distal part. Endite 3 with inner seta (1) shorter than outer (a–c). Endite 2 with three outer setae (d–f) and short inner seta (2) and sensillum near its base, setae e–f short, about half length of limb, seta f slightly longer than seta e. Endite 1 with inner seta (3) longer than inner seta of endite 2 and sensillum near its base, two 2-segmented setae (g–h), both setulated in distal part, and a flat seta (i) of characteristic shape, with shortened distal portion, armed with long setules. Seven rows of thin long setules on ventral face of limb. Two ejector hooks, one of them 1.5 times longer than the other. Maxillar process elongated, with single seta.

LiMB ii ( Fig. 4 F–G). Exopodite oval, with seta almost as as long as exopodite. Eight scraping spines, scrapers 1–5 long, scrapers 6–8 much shorter, armed with small setules. Scrapers 3 and 6 of similar length as its neighbours, but thicker and armed with thicker setules. Distal armature of gnathobase with four elements. Filter plate with seven setae, posteriormost seta considerably shorter and thicker than other, armed with long setules, next seta of same morphology with others, but two times shorter.

LiMB iii ( Fig. 4 H–I). Epipodite oval, without process. Exopodite ( Fig. 3I ) trapezium-shaped, with seven setae. Seta 3 being longest, setae 6 almost as long as seta 3, seta 7 ca 3/4 the length of seta 3, other setae short. Setae 6 and 7 unilaterally armed with short setules in distal portion, all other setae flat, plumose, setules on seta 3 considerably longer than on short setae. Distal endite with three setae, two distalmost members (1–2) slender, sharp, of similar length, with distal parts unilaterally armed thick sharp denticles; basalmost seta (3) thicker, bilaterally armed with long setules. Basal endite and gnathobase as with four plumose outer setae (a–d), increasing in size in basal direction. Four inner setae (4–7) increasing in size basally, a small sensillum near the base of distalmost seta (4). Distal armature of gnathobase with four elements. The first one elongated, cylindrical sensillum, second thin, bent seta, others two - blunt spines with fused bases. Filter plate III with seven setae.

LiMB iV ( Fig. 5 J–K). Pre-epipodite setulated; epipodite without process. Exopodite quadrangular, with six setae. Seta 3 being longest, seta 1–2 slightly about 3/4 length of seta 3, setae 4 ca ⅓ the length of seta 3, setae 5–6 cahalf length of seta 3. Setae 1–4 flat, plumose, setae 5–6 slender, unilaterally armed with short setules in distal portion. Inner-distal portion of limb IV with four setae and small rounded sensillum. Seta 1 slender, sharp, armed with long spinules. Distal flaming-torch seta (2) of typical for Aloninae shape, broad, with curved distal portion, armed with about 6 long thick setules. Two other flaming-torch setae (3–4) thin and straight, with straight distal portion, armed with very thin, hairlike setules, a small sensillum located near their bases. Three inner setae (a–c) long, increasing in size basally. Gnathobase with a short 2-segmented seta, only little longer than seta 1, and hillock with sensilla distally. Filter plate with five setae.

LiMB V ( Fig. 5 L–M). Pre-epipodite setulated, epipodite without process. Exopodite oval, with 4 plumose setae. Seta 1 being longest, setae 2–3 slightly shorter than seta 1, seta 4 two times shorter than seta 1. Inner limb portion an elongated oval lobe, with setulated inner margin. At inner face, two setae, one three times longer than other, and a triangular sensillum. Filter plate with three setae.

LiMB Vi ( Fig. 5N ) an oval lobe, its length about 1.3 times its maximum width, densely setulated along all of its margin.

Description of ephippial females and males taken from the literature ( Alonso 1996; Hudeč 2010).

Ephippial female

Outline similar to that of parthenogenetic female, dorsal margin more highly arched in most specimens. Ephippium in preserved specimens yellow-brown. Ephippium without sculpture.

Adult male

Length up to 0.39 mm. Body low oval ( Fig. 5O ), dorsal margin weakly convex. Maximum height at midbody, height/length ratio about 0.55. Ocellus larger than in female. Rostrum short, slightly truncated.

Postabdomen ( Fig. 5P ) moderately long, narrowing distally in postanal part. Ventral margin straight or wavy. Basis of claws bordered from distal margin by clear incision. Genital process long, about ⅔–¾ length of postabdominal claw. Distal margin concave, distal angle brioadly rounded, weakly prominent. Dorsal margin weakly concave in anal and in postanal portions. Preanal angle not defined, postanal angle weakly defined. Clusters of setules in place of marginal denticles, distalmost clusters consisting of numerous long setules, their length exceed width of postabdominal claw. Lateral fascicles of setules as in female. Postabdominal claw 2 times shorter than preanal portion of postabdomen, weakly curved. Basal spine short and thick.

Antennule shorter and broader than in female, with 12 terminal aesthetascs, longest almost as long as antennule, shortest about ½ length of antennule. Male seta arising at ¼ length from tip, about ⅓ length of antennule.

Thoracic limb I ( Fig. 3 ) with U-shaped copulatory hook, half as long as limb itself. IDL with three setae, IDL seta 1 absent. IDL setae 2 and 3 much thinner and two times shorter than in female, of similar length. Male seta curved, slightly shorter than seta 2. Copulatory brush seta about half length of IDL seta 2. Ventral surface of limb under copulatory brush with row of 20 stiff setules.

Distribution

Azores ( Van de Velde & Dumont 1978), Europe and Siberia ( Smirnov 1971). Bryophilic, typical of acid bogs with Sphagnum L., 1853, not found in neutral and alkaline waters. In Central and Southern Europe confined to mountainous regions. The only Flavalona gen. nov. species found in subterraneous waters ( Dumont 1983; Sabater 1987).

Figures

Fig. 4. Flavalona rustica (Scott, 1895) comb. nov. from Bol’shoe Torfyanoe lake, Bolshoi Solovetskiy Island (White Sea), Russia. A–B. Juvenile ♀♀ of instars I and II. C–N. Parthenogenetic ♀. C. Specimen with oblique valves. D. Specimen with tuberculated valves. E. Ventral margin of valves. F. Anterior setae of valves. G. Posterior setae of valves. H. Posteroventral corner and posterior margin of valves. I. Head shield. J–K. Head pores. L–M. Postabdomen. N. Antenna.

Fig. 5. Flavalona rustica (Scott, 1895) comb. nov. A–N. Labrum, antennule and thoraciс limbs of parthenogenetic ♀ from Bol’shoe Torfyanoe lake, Bolshoi Solovetskiy Island (White Sea), Russia. A–B. Labrum. C.Antennule. D. Limb I. E. IDL and ODL of limb I. F. Scrapers of limb II. G. Gnathobase of limb II. H. Exopodite of limb III. I. Inner portion of limb III. J. Exopodite of limb IV. K. Inner portion of limb IV. L. Limb V. M. Gnathobase of limb V. N. Limb VI. O–P. Adult ♁. O. Lateral view. P. Postabdomen. Figure O redrawn from Alonso (1996) and P from Sinev (1999a).

Fig.3. A. Flavalona cheni (Sinev, 1999) comb. nov., head pores of parthenogenetic ♀. B–C. Flavalona natalensis (Sinev, 2008) comb. nov., parthenogenetic ♀. B. Lateral view. C. Head pores. D. Flavalona setigera (Brehm, 1931) comb. nov., head pores of parthenogenetic ♀. E–F. Flavalona weltneri (Keilhack, 1905) comb. nov., parthenogenetic ♀. E. Head pores. F. Postabdomen. Figures A and D from Sinev (1999a), B–C from Sinev (2008), E redrawn from Flössner (2000) and F redrawn from Van Damme et al. (2010).