Flavalona, 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 : 3-4

Flavalona gen. nov.

urn:lsid:zoobank.org:act:8CC51B78-C807-4A31-8808-F167B8E5095A

Type species

Alona costata Sars, 1862 .

Diagnosis

Female

Aloninae of moderate size, maximum length of adult female 0.5–0.7 mm. Body oval, of moderate height, compressed laterally. Maximum height usually at mid-body. Valves and head shield without keel, valves from previous molts sometimes retained. Dorsal, posterior and ventral margins of valves evenly curved, postero-dorsal, postero-ventral angles and anterior-ventral angles of valves broadly rounded. Posteroventral angle of valves without denticles. Valves with moderately to well-developed linear sculpture or tubercles.

Head small, triangular to round in lateral view, rostrum short, pointing downward. Eye larger than ocellus. Head shield broad, with broadly rounded rostrum. Posterior margin of head shield usually broadly rounded. Three, in one species two, main head pores, narrowly connected. Lateral head pores transverse slits (rounded in F. sphagnophila ( Van Damme & Eggermont, 2011)) , with flattened pocketlike cavities below. Labrum with moderately broad keel, keel apex rounded, posterior margin of keel with two small clusters of setae.

Thorax 1.5 times longer than abdomen.

Abdomen without abdominal joint, middle abdominal segment not saddle-shaped.

Postabdomen moderately long, narrowing distally in postanal part. Ventral margin straight. Basis of claws bordered from distal margin by clear incision. Distal margin straight or convex, distal angle usually acute, with rounded tip. Dorsal margin concave in anal portion, straight in postanal portion. Preanal angle well-defined, postanal angle weakly-defined. Postanal margin with well-developed composite marginal denticles with spines at anterior margin. Lateral fascicles of setules narrow, weakly developed, distalmost setules in fascicles not thicker than others, shorter than marginal denticles. Postabdominal claw of moderate length, weakly curved. Basal spine short.

Antennule not protruding beyond the tip of rostrum, with 3–4 transverse rows of short setules on anterior surface. 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 not reaching end of endopodite. Seta of middle segment of endopodite and apical setae of same morphology, similar length and thickness. Antennal spines well developed.

Six pairs of thoracic limbs. LiMB i. With accessory seta. IDL with 3 setae, seta 1 short, setae 2 and 3 of similar size, armed with thin setules in distal portion. Endite 3 with four setae. Endite 2 with three outer setae and short inner seta. Endite 1 with two 2-segmented setae, shortened, stub-like flat seta, and inner seta longer than inner seta of endite 2. Ventral surface of limb with rows of long setules. Two ejector hooks, of unequal size. Maxillar process with single seta.

LiMB ii. Exopodite narrow, elongated, with seta. Inner portion of limb with eight scraping spines, spines either of similar morphology, evenly decreasing in size basally, or spines 3 and 6 more robust, armed with thicker denticles. Distal armature of gnathobase with four elements. Filter plate II with seven setae, posteriormost considerably shorter than others.

LiMB iii. Exopodite rounded, with seven setae, seta 3 being longest, setae 6–7 of moderate length, setae 1–2 and 4–5 very short. Setae 1–5 plumose, setae 6–7 armed with short setules or naked. Distal endite with three setae, two distalmost ones slender, sharp, with denticles; basalmost seta shorter, geniculated, with thin setules. 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 short setules or naked. Inner portion of limb IV with four setae and small sensillum. Distalmost seta robust, sharp, first flamingtorch seta (2) wide, armed with thick setules, two other 2–3 times thinner, armed with thin setiules. 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 separated into two lobes, with 4 plumose setae, seta 1 longest, evenly decreasing in width basally. Inner limb portion as elongated lobe. At inner face, two setae with wide bases, one 1.5–2 times longer than other. Filter comb V with three setae.

LiMB Vi. Large, of same size or larger than exopodite V, an oval lobe with setulated margin.

Male

Body lower than in female, similar to that of juveniles, with weakly convex dorsal margin. Postabdomen moderately long, narrowing distally, with obtuse preanal angle, gonopores located at of the end of the genital process protruding above the postabdominal claws. Clusters of setules in place of female marginal denticles, lateral fascicles of setules as in female. Postabdominal claw much shorter than in female, weakly curved, with short basal spine or without spine. Antennule shorter and wider than in female, with twelve terminal aesthetascs, male seta long. Limb I with U-shaped copulatory hook. IDL seta 1 absent, male seta large, of similar size with setae 2 and 3.

Etymology

The name is formed by adding the prefix flavo-, from the Latin adjective flavus, “yellow”, to the preexisting name Alona , to express the fact that many of its species often are yellow-golden in color.

Differential diagnosis

Stands out from other Aloninae by the morphology of the lateral head pores. Also differs from all other Alona s.l. by a male postabdomen with gonopores at the end of a penis-like process (similar structures only in Leydigia Kurz, 1875 and Armatalona Sinev, 2004 ). Flavalona gen. nov. belongs to the Hexalonabranch of Alona s.l. and differs from Alona s. str. (see Van Damme & Dumont 2008 b), Ovalona (see Sinev 2015 b) and genera of the Coronatella -branch (see Van Damme & Dumont 2008 a) by the presence of six trunk limbs and a filter plate V of three setae. Within Hexalona, Flavalona gen. nov. also differs from the affinis -group (see Alonso 1996; Sinev 2009) by its smaller size, shape of postabdomen, weakly developed lateral setules on the postabdomen, and weakly developed IDL seta 1; from the intermedia - group (see Alonso 1996) by the shape of the postabdomen, strong marginal denticles of the postabdomen, and by weakly developed lateral setules of the postabdomen; from the guttata -group (see Alonso 1996; Sinev & Silva-Briano 2012) by a more elongated postabdomen with weakly developed preanal angle. Flavalona gen. nov. clearly differs from Matralona Van Damme & Dumont, 2009 , another genus related to the Hexalona-branch, in the shape and armament of the postabdomen, in a present IDL seta 1, and in an exopodite III with seven setae.