Coronatella Dybowski & Grochowski, 1894

Damme, Kay Van & Dumont, Henri J., 2008, Further division of Alona Baird, 1843: separation and position of Coronatella Dybowski & Grochowski and Ovalona gen. n. (Crustacea: Cladocera), Zootaxa 1960 (1), pp. 1-44 : 9

Genus Coronatella Dybowski & Grochowski, 1894

Type species. Alona coronata Kurz, 1875 . Subspecies of rectangula as Smirnov (1971) suggested or synonym of Alona rectangula according to Flössner (2000). Position of coronata left undecided here, the C. rectangulacomplex may still have several subspecies in Western Europe. Original locality of A. coronata is in Bohemia ( Kurz 1875).

Diagnosis. Coronatella consists of small to medium-sized alonines with rectangular body, posteroventral notch on valves, three main head pores and simple small pores, labrum relatively small and rounded with naked labral keel (no ventral setules), S-shaped postabdomen with long, unmerged marginal denticles. Five pairs of limbs. P1 with IDL with two setae, reduced anterior elements and anterior setule row decreasing in size and number ventrally, P2 with long exopodite seta (not C. holdeni ) and heterogenous scrapers, no additional soft setae, P3 with six setae in exopodite of which third longest, P4 with six exopodite setae, P5 with four exopodite setae, oval-round inner lobe and reduced gnathobase (0–1 setae).

Description. Adult parthenogenetic female. Body rectangular in lateral view, with straight ventral margin; small to medium-sized animals (0.23–0.6 mm), in life translucid to faintly yellow. Intestine long, with two loops. Head with short blunt rostrum, three main head pores and two small pores lacking additional structures. Carapace lacking a dorsal keel, ornamentation consisting of wide lines, sometimes verrucae but no fine striation; posteroventral corner with notch; marginal setae in posteroventral portion followed by fine spinules, not arranged in groups. Postabdomen two to three times as long as wide, ventral and dorsal margins relatively straight and parallel, postanal little larger than anal portion and well developed sharp preanal angle; postanal margin straight to convex and anal margin straight to concave, in general a moderately S-shaped postabdomen (less pronounced than in Karualona and A. verrucosa -group); marginal denticles consisting of unmerged groups of relatively large teeth (may consist of single spines distally; holdeni ); lateral fascicles slender spines, of which posteriormost may be longer and thicker (in rectangula ). Terminal claw about as long as anal margin, basal spine as long as claw width at base ( holdeni ) up to 1.5–2 times this length (in bukobensis ). First antenna about two times as long as wide, with sensory seta implanted between 1/3–1/2d from apex; nine apical aesthetascs varying in length, about as long as antennular corm (shorter in holdeni and rectangula ). Second antenna with spinal formula 001/101 (these spines strongly developed) and setal formula 113/003 (013/003 in holdeni ). First endopod seta on antenna relatively short and narrow (absent in holdeni ); on external side of second exopod segment, group of narrow spinules to few long spines. Labrum relatively short and round, with straight to wavy labral keel and roundly obtuse ventral tip; lateral bulges at base; keel naked, lacking ventral setules. First maxilla with two setulated setae. Five pairs of limbs. First limb. First endite with three marginal setae, second endite with three setae of which two longer, third endite with four setae; anterior elements on en1–2 strongly reduced to absent. ODL with one slender seta, IDL with two setae, third seta reduced to absent; armature of IDL setae serrate to few strong spines. Accessory seta present. Anteriorly on corm, six to seven setule groups with more than three strong setules in each group; setules in each group decrease in size ventrally. Ejector hooks relatively small and subequal; epipodite round, with or without long projection. Gnathobase a single setulated projection. Second limb. Exopodite with one well developed seta (absent in holdeni ); endites with eight scrapers of which first two long and slender, last three much shorter and with relatively stronger denticles; gnathobasic ‘brush’ short round, gnathobase with a sensillum and three elements, filter comb with seven setae of which the first two to three setae are much shorter and first thicker, brushlike. Third limb. Exopodite with rectangular corm and six long setae in 2+4 arrangement; third exopodite seta longest, fourth may vary in size between species (long or short), sixth seta with non-plumose setulation. External endite with three setae (1’–3’) of which first two scraper-like and with minute element in between; four well developed plumose setae on inner side (1”–4”); one element and four small setae on internal endite preceding gnathobase; gnathobase with a bottle-shaped sensillum and large plumose seta with two naked setae at its base. Filter comb with seven long setae. Fourth limb. Epipodite oval-round, with or without short projection. Exopodite square, with six plumose setae of which third relatively longest and fifth and sixth setae relatively narrower than others. Endite with marginal row of four setae, first short and scraper-like, following three flaming torch setae about as thick as wide and all of similar size, and one marginal round naked sensillum; gnathobase with one long setae, bent over endite and two reduced naked elements; on inner side, three well developed plumose setae and a filter comb with five setae. Fifth limb. Epipodite oval round, with or without short projection. Exopodite shape oval, without deep incisions in margin between setae three and four; four exopodite setae, of which first longest, about two times as long as exopodite itself and oriented dorsally; fourth exopodite seta well developed; inner lobe elongated oval, with long terminal setules; two slender endite setae (1’–2’) of which first little longer than second and bent over inner lobe; behind second endite seta, an elongated element; gnV with 0–1 seta. Adult male with clear sexual dimorphic postabdomen with gonopores opening ventrally, subapical to terminal claw; marginal denticles consisting of unmerged groups of setules. Male IDL with three setae; thick copulatory hook with terminal rugae. Ephippium with dark center; remains attached to the body for a long time ( Frey, 1988).