Ovalona

Sinev, Artem Y., 2015, Revision of the pulchella - group of Alona s. lato leads to its translocation to Ovalona Van Damme et Dumont, 2008 (Branchiopoda: Anomopoda: Chydoridae), Zootaxa 4044 (4), pp. 451-492 : 454-455

Genus Ovalona Van Damme & Dumont, 2008 emend. Sinev, 2015.

Type species: Alona weinecki Studer, 1878 .

Diagnosis. Female. Aloninae of moderate to small size, length of adult female from 0.3 to 0.7 mm. Body oval, of moderate height, compressed laterally. Maximum height usually at middle of body. Valves and head shield without keel, valves from previous molts not retained. Dorsal, posterior and ventral margins of valves evenly curved, posterodorsal, posteroventral angles and anterior-ventral angles of valves broadly rounded. Posteroventral angle of valves with numerous uniform setae, in one species with 1–2 denticles. Valves oblique or with weakly developed linear sculpture.

Head small, triangle-round in lateral view, in lateral view rostrum short, pointing downward. Eye larger than ocellus, in some species eye strongly reduced. Headshield broad, with short, broadly rounded rostrum. Posterior margin of headshield usually broadly rounded, sometimes with notches, or, in some species, forms blunt or acute angle. Three main head pores, connection between pores narrow, continuous or interrupted, or absent. Lateral head pores minute, located at 1 or more IP distance from midline, in one species, lateral pores as small rounded cavities. Labrum with moderately broad keel, keel apex rounded, posterior margin of keel with two small clusters of setae or without them.

Thorax 1.5 times longer than abdomen. Abdomen without abdominal joint; middle abdominal segment not saddle-shaped.

Postabdomen from short and broad to moderately long and narrow, with parallel margins or weakly narrowing distally. Ventral margin weakly convex or straight. Basis of claws bordered from distal margin by clear incision. Distal margin straight or convex, distal angle from broadly rounded to acute and protruding. Dorsal margin concave in anal portion, straight, weakly convex or weakly concave in postanal portion. Preanal angle welldefined, postanal angle not defined or weakly-defined. Postanal margin with well-developed marginal denticles with spines at anterior margin. Lateral fascicles of setulae broad and long; distalmost setulae in fascicles thicker than others. Postabdominal claw of moderate length, weakly curved, with pecten of thin setulae. Basal spine from well-developed to very short.

Antennule not protruding beyond the tip of rostrum, with 2–3 transverse rows of short setulae at anterior face. Antennular seta thin. Nine terminal aesthetascs of variable length.

Antenna with antennal formula setae 0-0-3/1-1-3; spines 1-0-1/0-0-1. Basal segment robust, branches elongated, all segments narrow, cylindrical; basal segment of each branch 1.5 times longer than two others. Seta of basal segment of endopodite long, reaching after the end of endopodite. Seta of middle segment of endopodite and apical setae of same morphology, similar length and thickness. Antennal spines well-developed.

Five pairs of thoracic limbs.

Limb I with accessory seta. IDL with 3 setae, seta 1 well-developed, sharp, setae 2 and 3 of similar size, armed with thin setulae in distal portion. Endite 3 with four setae. Inner setae (1–2) and sensillae of endites 1 and 2 absent. Endite 2 with three setae. Endite 1 with two 2-segmented setae, flat seta (i) absent. Ventral face of limb with rows of long setulae. Two ejector hooks, one little larger than other. Maxillar process with single seta.

Limb II. Exopodite narrow, elongated, with seta. Inner portion of limb with eight scraping spines of similar morphology, evenly decreasing in size basally. Distal armature of gnathobase with four elements. Filter plate II with seven setae, the posteriormost one considerably shorter than others.

Limb III. Exopodite rounded with seven setae, seta 3 being longest, setae 1–5 plumose, setulation of seta 6–7 varies. Distal endite with three setae, two distalmost ones slender, sharp, with denticles; basalmost seta shorter, geniculated, with thin setulae. Basal endite with four stiff setae. Four soft setae increasing in size basally. Distal armature of gnathobase with four elements: elongated, cylindrical sensillum; thin, geniculated seta; and two short pointed spines. Filter plate III with seven setae.

Limb IV. Exopodite rounded with six setae, setae 1–4 plumose, setae 5–6 with long setulae. Inner portion of limb IV with four setae and small sensillum. Distalmost seta robust, sharp; flaming-torch setae of similar morphology, decreasing in size basally. Three short soft setae increasing in size basally. Gnathobase with one long 2-segmented seta and a blunt process near it. Filter plate IV with five setae.

Limb V. Exopodite V oval, not separated into two lobes, with 4 plumose setae, seta 1 especially long. Inner limb portion as a rounded lobe. At inner face, two setae with wide bases, one 1.5–2 times longer than other. Filter plate V absent.

Male: body lower than in female, similar to that of juveniles, with weakly convex dorsal margin. Postabdomen short, narrowing distally or with parallel margins, gonopores located at the end of postabdomen above the base of postabdominal claws. Clusters of setulae in place of female marginal denticles; lateral fascicles of setulae same as in female. Postabdominal claw much shorter than in female, curved, with or without basal spine. Antennule shorter and wider than in female, with ten lateral and two terminal aesthetascs; male seta short and broad. Limb I with Ushaped copulatory hook. IDL seta 1 absent or strongly reduced, male seta large, of similar size to setae 2 and 3.

Differential diagnosis. Ovalona differs from all groups of Hexalona -branch of Alona s. lato ( affinis , costata , guttata, intermedi a) and from Alona s. str. ( quadrangularis -group) by the presence of lateral aesthetascs on male antennule. It differs from affinis , intermedia, costata and guttata groups by absence of thoracic limb VI, setae 2–3 and “i” of endites of limb I and filter plate V; from affinis -group by number of head pores and morphology of IDL of limb I; from intermedia -group by the number of head pores; from costata -group by morphology of lateral head pores and morphology of male postabdomen; from guttata -group by well-developed lateral fascicles of setulae on postabdomen. Ovalona differs from quadrangularis -group by shape and armament of postabdomen; normal morphology of ventral face of limb I (in quadrangularis -group it is armed with large single setulae); by the absence of seta “i” of limb I, and by morphology of exopodite V. Ovalona differs from elegans -group of Alona s. lato by having 7 setae on exopodite III and by absence of seta “i” on endite 1 of limb I.