Flavalona costata ( Sars, 1862 ) 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 : 6-12

Flavalona costata ( Sars, 1862) comb. nov.

Figs 1–2

Alona costata Sars, 1862: 286 .

Alona lineata Schoedler, 1862 : taf. I, fig. 23.

Phryxira rectirostris Müller, 1867: 184–185 , tab. IV, fig. 15.

Lynceus costatus Norman & Brady, 1867: 28 , pl. XVIII, fig. 2, pl. XXI, fig. 7.

Lynceus costata Lilljeborg, 1901: 465–468 , tab. LXVIII, fig. 9–15.

Alona costata – Hellich 1877: 90, figs 47–48. — Behning 1941: 299–301, fig. 123. — Šrámek-Hušek et al. 1962: 336–338, fig. 124. — Herbst 1962: 86, fig. 61. — Frey 1965): 159–162, figs 1–6. — Flössner & Frey 1970: 327, figs 4, 6–7. — Smirnov 1971: 371–373, figs 345–340. — Flössner 1972: 299–301, figs 140–141. — Negrea 1983: 291–292, fig. 118. — Margaritora 1985: 313–315, fig. 124. — Sars 1993: 135, pl. 98. — Alonso 1996: 322–323, fig. 143. — Flössner 2000: 315–322, fig. 117. — Sinev 1999a: 132–138, figs 1–5. — Sinev 2002: 394, figs 3в,м, 4в, 5в, З. — Hudeč 2010: 319–322, fig. 77. — Sinev et al. 2015: fig. 1A–C.

Alona lineata – Müller 1867: 178, table IV, figs 2–3.

non Alona costata – Idris 1983: 106–108, fig. 50.

Differential diagnosis

Flavalona costata comb. nov. differs from F. setigera comb. nov. by having three main head pores, and from F. natalensis comb. nov. and F. cheni comb. nov. by the deep pockets of the lateral head pores; in these species the depth of the pockets is less than half the depth of the pore. It also differs from F. natalensis comb. nov. by the costata-like sculpture of its valves. Flavalona costata comb. nov. is similar in morphology to F. margipluma comb. nov. too but differs by the basal spine of its postabdomen exceeding the width of the claw base and by having a bilobed exopodite V.

As Flavalona costata comb. nov. is the type species of Flavalona gen. nov., a detailed description follows.

Type material

Material in Sars’ collection (Zoological Museum of Oslo University, F12410) labeled “ Norway ”; no exact locality or dates given.

Material studied earlier

See Sinev (1999a) for list of material from Norway, Poland, Germany, Russia and Mongolia.

Material studied here

NORWAY: 11 parthenogenetic ♀♀, over 30 ephippial ♀♀, 13 ♁♁ from littoral zone of Randsfjorden Lake, 60º14.37ʹ N, 10º23.94ʹ E, 9 Oct. 2015, coll. A.Y. Sinev & T. Jensen.

CHINA: over 30 parthenogenetic ♀♀ from littoral zone of Erhai lake, Yunnan Province, 25º49.887ʹ N, 100º13.166ʹ E, 19 Jan. 2015, coll. A.Y. Sinev & Y. Gu; 3 parthenogenetic ♀♀ and exuviae from artificial lake in Botanical Garden of Changsha City, Hunan Province, 28º06.253ʹ N, 113º01.783ʹ E, 10 Apr. 2014, coll. A.Y. Sinev & Y. Gu; 8 parthenogenetic ♀♀ from artificial lake in Botanical garden of Guangzhou City, Guangdong Province, 23º11.225ʹ N, 113º21.834ʹ E, 5 Apr. 2014, coll. A.Y. Sinev & Y. Gu; over 30 parthenogenetic ♀♀ from Shuisheng reservoir, Hainan island, 18°53.097ʹ N, 110°23.514ʹ E, 24 Apr. 2014, coll. A.Y. Sinev & Y. Gu.

Type locality

Lake Ostensjovand, Oslo, Norway.

Description

Parthenogenetic female

Length of adult up to 0.5 mm. In lateral view body oval or slightly ovoid ( Fig. 1A ), maximum height at middle or somewhat behind it, height-length ratio ca 0.58–0.65. Dorsal margin uniformly curved. Postero-dorsal and postero-ventral angles broadly rounded. Posterior margin uniformly curved. Ventral margin almost straight, with about 50–60 setae ( Fig. 1B ), about 10 first setae of moderate length, next 15 setae short, other setae of moderate length. Setae of the anterior group ( Fig. 1C ) not longer than those of the posterior group ( Fig. 1D ), longest setae of anterior group located at the middle of the group. Groups of small setules located between the bases of all ventral setae. Posteroventral angle ( Fig. 1E ) with only 10–15 short setules protruding beyond margin of valves. A row of about 150 setules along posterior margin on inner side of carapace. In ventral third of the row these setules uniform, in middle third, row formed by long setules and groups of shorter setules between them, in dorsal third by long setules only. Carapace covered by moderately thick, sparsely spaced longitudinal lines, without intervening striae.

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 that between ocellus and eye.

Head shield with maximum width behind mandibular articulation, without any sculpture ( Fig. 1F ). Rostrum short, broadly rounded. Posterior margin of head shield broadly rounded. Three major head pores ( Fig. 1 G–H), middle pore slightly smaller than others, located closer to posterior pore. Connection between anterior and middle pores narrow, connection between middle and anterior pores varies from narrow to rather wide in some populations (see Alonso 1996; Sinev et al. 2015). PP a. 0.5–0.8 IP. Transverse lateral head pores ca 0.5–0.8 IP lengths, located about 0.5 IP distance from midline, at a level between anterior and middle main head pores. Lateral pore pockets large, rounded, with depth ca 1.5–2 pore lengths.

Labrum moderate size ( Fig. 2A ). 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.

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

Postabdomen ( Fig. 1I ) wide, narrowing distally, with well defined, acute angle between distal and dorsal margins, length about 2.2–2.5 times height. Ventral margin straight. Inflated basis of claws bordered from distal margin by clear incision. Distal margin weakly convex to straight. Dorsal margin with distal part about 3 times longer than preanal one, with postanal portion about 1.5 times longer than anal one. Postanal portion of distal margin straight, anal portion weakly concave. Preanal and postanal angles weakly defined. Preanal margin almost straight. Postabdomen with 8–9–10 well-developed composite marginal denticles, each with several spinules on anterior margin, and with two groups of marginal spinules and 2–3 groups of short setules on anal margin. Length of denticles decrease basally, length of longest denticles exceed the width of postabdominal claw base. Ten–twelve lateral fascicles of thin setules; in postanal fascicles distalmost seta being longest, 1.5 times shorter than marginal denticles. Postabdominal claw of moderate length, somewhat longer than preanal portion of postabdomen. Basal spine ca 0.2 of length of claw.

Antennule ( Fig. 1J ) moderate length, almost reaching the tip of rostrum, with four transverse rows ofshort setules at anterior face. Antennular sensory seta slender, 1.5 times shorter than antennule, arising at ⅔ distance from base. Nine aesthetascs, two of them longer than others, of about 2/3 length of antennule, others of similar length..

Antenna ( Fig. 1K ) 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. 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. 2 B–D). Epipodite oval, with finger–like process 2 times longer than epipodite itself. Accessory seta about 1/3 length of ODL seta. IDL with three setae and several clusters of small setules on ventral face, 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 setae (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 itself, 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 reduced distal portion, armed with long setules. Seven rows of thin long setules on ventral surface of limb. Two ejector hooks, one of them 1.5 times longer than the other. Maxillar process elongated, with single seta.

LiMB ii ( Fig. 2E ). 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 with neighbors, but slightly thicker and armed with slightly more thick setules. Distal armature of gnathobase with four elements. Filter plate with seven setae, the posteriormost seta considerably shorter and thicker than other, armed with very long setules, next seta of same morphology with others, but two times shorter.

LiMB iii ( Fig. 2 F–H). Еpipodite oval, without finger-like process. Exopodite trapezium-shaped, with seven setae. Seta 3 being longest, setae 6 and 7 of ⅔ and ½ length of seta 3, respectively, other setae short. Setae 6 and 7 naked, all other plumose, setules on seta 3 considerably longer than on short setae. Distal endite with three setae, two distalmost members slender, sharp, of similar length, with distal parts unilaterally armed small sharp denticles; basalmost seta thicker, bilaterally armed with long setules. Basal endite 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. 2 I–J). Pre-epipodite setulated; epipodite with a finger-like process longer than epipodite itself. Exopodite subquadrangular, with six setae. Seta 3 the longest, seta 1–2 slightly shorter, setae 4–6 ca 2/3 length of seta 3, setae 5–6 slightly longer than seta 4. Setae 1–4 flat, plumose, setae 5–6 slender, seta 5 with short setules at the middle, seta 6 naked. Inner-distal portion of limb IV with four setae and small rounded sensillum. Seta 1 slender, sharp, armed with short spinules. Distal flaming-torch seta (2) of typical for Aloninae shape, broad, with curved distal portion, armed with about 10 long thick setules. Two other flaming-torch setae (3–4) thin and straight, with straight distal portion, armed with thin, hair-like 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 a hillock with sensilla distally. Filter plate with five setae.

LiMB V ( Fig. 2K ). Pre-epipodite setulated, epipodite with finger-like process longer than epipodite itself. Exopodite bilobed, 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. 2L ).An elongated lobe, its length about twice maximum width, its margin densely setulated in distal part.

Ephippial female

Outline similar to that of parthenogenetic female ( Fig. 1L ), dorsal margin more highly arched in most specimens. Ephippium of living specimens blackish, in preserved specimens yellow-brown. Ephippium ( Fig. 1M ) sculptured by anastomosing longitudinal lines, thicker than in ventral portion of valves.

Adult male

Length 0.36–0.42 mm. Body ( Fig. 1N ) low oval, dorsal margin weakly convex. Maximum height at the middle of the body, height/length ratio ca 0.55. Ocellus larger that in female. Rostrum short, slightly truncated ( Fig. 1P ).

Postabdomen ( Fig. 1O ) moderately long, narrowing distally in postanal part. Ventral margin straight or wavy. Basis of claws bordered from distal margin by clear incision. Genital process short, about ¼ – ⅓ length of postabdominal claw. Distal margin very short, distal angle obtuse. Dorsal margin concave in anal portion, straight in postanal portion. Preanal and postanal angles not defined. Clusters of short setules in place of marginal denticles, distalmost cluster consisting of 3–5 thick short setules. Lateral fascicles as in female. A cluster of short setules above the base of postabdominal claw. Postabdominal claw as long as preanal portion of postabdomen, weakly curved. Basal spine short and thin, visible only under oil immersion.

Antennule ( Fig. 1P ) shorter and broader than in female, with 12 terminal aesthetascs, longest about ¾ length of antennule, shortest ca ½ length of antennule. Male seta arising at ¼ length from tip, ca ⅓ length of antennule.

Thoracic limb I ( Fig. 2 M–N) 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 ca 2/3 length of IDL seta 2. Ventral face of the limb under the copulatory brush with row of 20 long stiff stiff setules. Inner seta (1) of endite 3 longer and thinner than in female, with long setules distally.

For description of juvenile males and females, see Sinev (1999a).

Our data agree with those of previous descriptions of the species, but add several features. Thin setules between ventral setae of the valves were overlooked by Sinev (1999), so Sousa et al. (2015) used this feature as diagnostic for F. margipluma comb. nov. Most authors also overlooked the basal spine of the male postabdomen.

Distribution

Presumed Holarctic ( Flössner & Frey 1970; Smirnov 1971). Flavalona costata comb. nov. is found in the whole of Europe, European and Asian Russia, Kazakhstan, Mongolia, China, Korea and Japan but its southern limit is unclear ( Smirnov 1971; Sinev 1999a). The southernmost certified record is from Hainan Island ( Sinev et al. 2015). It has been cited from mainland South-East Asia (see Korovchinsky 2013) and India (see Chatterjee et al. 2013), but these records were not accompanied by descriptions, and the related F. cheni comb. nov. is present in these regions. Flössner & Frey (1970) found no significant differences between North American and European F. costata comb. nov., but the appendages were not studied, so possibly Nearctic populations constitute a separate species.

Figures

Fig. 1. Flavalona costata (Sars, 1862) comb. nov., Randsfjorden Lake, Norway. A–K. Parthenogenetic ♀. A. Lateral view. B. Ventral margin of valves. C. Anterior setae of valves. D. Posterior setae of valves. E. Posteroventral corner and posterior margin of valves. F. Head shield. G–H. Head pores. I. Postabdomen. J. Antennule. K. Antenna. L. Ephippial ♀. M. Ephippium. N–P. ♁. N. Lateral view. O. Postabdomen. P. Antennule and outline of rostrum.

Fig. 2. Flavalona costata (Sars, 1862) comb. nov., Randsfjorden Lake, Norway. A–L. Labrum and thoraciс limbs of parthenogenetic ♀. A. Labrum. B. Limb I. C. ODL of limb I. D. Ejector hooks of limb I. E. Limb II. F. Exopodite of limb III. G–H. Inner portion of limb III. I. Exopodite of limb IV. J. Inner portion of limb IV. K. Limb V. L. Limb VI. M–N. Thoracic limb I of adult ♁.