Flavalona weltneri Sinev & Dumont 2016, comb. nov.

Flavalona weltneri (Keilhack, 1905) comb. nov.

Fig. 3 E–F

Alona weltneri Keilhack, 1905: 158–159, figs 13–14.

Alona weltneri – Keilhack 1908: 464, fig. 20. — Flössner 1972: 306–308, fig. 144. — Smirnov 1971: 365–366, figs 425–426. — Flössner 2000: 322–323, fig. 119. — Van Damme, Elais-Gutierrez & Dumont 2011: 51–53, figs 3–4.

Diagnosis ( according to Flössner 2000 and Van Damme et al. 2011).

Female

Length of adult up to 0.45–0.53 mm. Body regular oval, maximum height after the middle of body, height/length ratio about 0.57 (the holotype, studied by Van Damme et al. (2011) was deformed, and its reconstruction (Van Damme et al. 2011: fig. 3A) is uncertain). Valves from previous molts not retained. Posteroventral angle without setules protruding beyond valve margins. Ventral margin with ca 45 setae. Valves covered by thin, sparsely spaced longitudinal lines.

Eye larger than ocellus. Rostrum short, broadly rounded. Posterior margin of head shield broadly rounded. Three major head pores (Fig. 3E), middle pore slightly smaller than others, located near posterior pore. Connections between pores narrow. PP ca 0.4 IP. Lateral head pores of ca 0.5 IP length, lateral pore pockets not studied in details, but probably shallow. Labral keel without denticles.

Postabdomen (Fig. 4F) truncated, length 2.3 heights. Unlike all other species, no incursion between postabdominal claw base and distal margin. Distal margin straight, distal angle obtuse, not prominent, with rounded tip. Dorsal margin straight in preanal part, concave in anal part, straight in postanal part. Distal part of dorsal margin 3 times longer than preanal one, with preanal portion only slightly times longer than anal one. Preanal and postanal angles weakly defined. Postanal margin of postabdomen provided with 6–8 marginal denticles.Anal margin with 2 clusters spinules in distal portion. 10–12 lateral fascicles of setules, distal setules in fascicle being longest. Postabdominal claw of moderate length, 1.5 times longer than preanal portion of postabdomen. Basal spine ca 0.25 of length of claw.

Antennule with longest aesthetasc of ca ½ length of antennule. Exopodite III with seta 6 of about ⅔ length of seta 3. Exopodite IV with seta 3 being longest, setae 1–2 slightly shorter, setae 4–6 ca 2/3 length of seta 3.

Male

Unknown.

Differential diagnosis

Flavalona weltneri comb. nov. differs from all members of the costata -clade by its postabdomen with obtuse distal angle and no incursion between base of claws and distal margin, and by a longer basal spine of postabdominal claw, about 0.25 of claw length, 1.5 times the width of the claw base.

Type material

Holotype

Adult parthenogenetic ♀, in Museum für Naturkunde, Berlin, no. 18948.

Type locality

POLAND: Madü-See (=Jezioro Miedwie), Pyrzyce (Pyritz), West Pomerania.

Distribution

Switzerland, Germany, Poland, Norway, Sweden and Finland (Van Damme et al. 2011).

Rustica -clade

Characteristic features of the rustica -clade clade include: (1) valves with weakly developed linear or tubercular sculpture; (2) anterior group of setae on valves with longest setules in posterior part of the group; (3) short lateral head pores with small pockets, length of pore less than 0.5 IP. (4) postabdomen with prominent rounded distal angle; (5) lateral fascicles of setules on postabdomen with middle setae being longest; (6) male postabdomen with long genital process, its length over 1/2 length of claw. Species of rustica -group have a thicker cuticle than the costata -clade, and more thick, spine-like short setules on antenna and limb I. Species of the rustica -clade frequently retain valves from the 1–2 previous molts, a situation never recorded in the costata -clade.

The rustica -clade is less uniform than the costata -clade. Species of the group differ in size, morphology of posteroventral angle of valves, length of rostrum, morphology and position of major head pores, labrum, armament of postabdomen, morphology of scrapers on limb II, proportions of setae of exopodite III and shape of exopodite V. Male morphology is known for four taxa, viz. F. rustica rustica comb. nov., F. rustica americana comb. nov., F. iheringula comb. nov. and F. bicolor comb. nov., differing in shape of postabdomen, morphology of postabdominal claw and length of its distal setules.