Anthalona, Van Damme, Sinev & Dumont, 2011

DAMME, KAY VAN, SINEV, ARTEM YU & DUMONT, HENRI J., 2011, Separation of Anthalona gen. n. from Alona Baird, 1843 (Branchiopoda: Cladocera: Anomopoda): morphology and evolution of scraping stenothermic alonines, Zootaxa 2875 (1), pp. 1-64 : 5-7

Genus Anthalona gen.nov.

Gen.Nov. 1 in Van Damme et al. 2010

Type species. Anthalona verrucosa ( Sars, 1901) = Alona verrucosa Sars, 1901

Derivatio nominis. Anthalona (from “anthos”, Greek for “flower” and - Alona ) refers to the peculiar structures under the lateral head pores, typical for the genus.

Description of the genus. Adult parthenogenetic female. Small to medium sized Aloninae , 0.3–0.5 mm. Animals transparent to yellow-brown. Body length 1.5–1.7 times height. Dorsum moderately to strongly convex, highest point near middle; posterior margin round to angular, with expanded lower portion. Hind valve margin with most posterior point at middle of body, or in ventral quarter. In the latter case, the margin forms an angle of up to 20° posteriorly from an imaginary ventro-dorsal axis through the posterodorsal valve corner. Head low and rostrum bent downwards, maximal ventral extent of rostral tip may reach about ventral maximum of carapace margin. Ventral carapace margin straight to moderately convex. Posteroventral corner round, usually without notch (not in A. obtusa n. sp.).

Head. Ocellus smaller than eye (not A. mediterranea ). Well-developed rostrum, obtuse. Aesthetascs of antennules projecting laterally from rostrum, antennular body not reaching apex of rostrum. Two main head pores, connected. Small pores with structures (“ cosmaria ”) underneath, sacks, which may be subdivided into 8-shaped structures.

Carapace. Ornamentation of different types, from fine to wide striations, smooth or with verrucae. Marginal setae differentiated into two to three groups, posterior group always well pronounced. Setae followed by setules of

Labrum. Labral keel “axe-shaped”, rather angular and with straight to moderately convex margin. No ventral setules on labral keel. One or more proximal denticles, none in simplex .

Antennules. Two to three times as long as wide, sensory seta implanted at between half and one third from apex of antennular corm. Three to four groups of denticles on antennular margin. Aesthetascs in two size groups, maximally half size of corm and none strongly elongate.

Second antennae. Anterior spine on basal segment conical. Spinal formula (exo/endo) 001/101, setal formula 113/003. First exopod seta on antenna narrow; on external side of second exopod segment, setules spine-like and modified, into few (three-four) strong ‘spines’. True spine on first endopod segment well developed, reaching end of second segment or beyond; main terminal spines on endo- and exopod well developed, each at least as long as their apical segments. Terminal setae on antennal exopod of similar morphology as those of endopod and with long setules (setae modified in A. acuta n. sp.).

Postabdomen. Short, between two and three times as long as wide, with a rather sinusoidal (S-shaped) dorsal margin. Relatively widest at preanal angle and with rounded dorso-distal margin. Postanal, anal and preanal margins of similar dimensions. Anal margin straight to slightly concave, postanal margin stronger curved, convex. Distal embayment (dorsal to basal claw) present, maximally as deep as claw width at base. Preanal corner moderately developed, rarely protruding beyond maximal dorsal point of postanal margin. Six to seven groups of postanal marginal teeth. Each distal tooth with few adjacent smaller marginal elements on anterior side, unmerged or partially merged. Five to six groups of lateral setae (in fascicles) in postanal portion, consisting of four to eight elements in each group, parallel to each other. Distalmost lateral element always longer and thicker than others per fascicle and protruding beyond dorsal margin of postabdomen. Three to four clusters of long marginal elements, and three to four fascicles in anal portion.

Terminal claw. Longer than anal margin, moderately curved, adorned with setules along dorsal side. Proximal pecten may end in longer spine. Basal spine short, between one to two times width at base and maximally one third of claw length, never up to half claw length. A group of basal spinules accompanies the basal spine.

First maxilla with two setulated setae.

Five pairs of limbs. First limb. Epipodite round, sometimes with a projection reaching beyond limb corm. First endite with one dorsal and two marginal setae; the dorsal seta well developed, as long as the other setae in this first endite and plumose in distal half; second endite with three setae of which two longer (lengths may differ strongly), with thick teeth on anterior side and fine setules on the other side; third seta short, maximally half to one third of the previous. Third endite with four setae of similar length; anterior elements on en1–2 present but strongly reduced. ODL with one slender seta, maximally as long as largest IDL seta and with short fine setules in distal half; two setae in IDL, thickened at base, with modified and chitinized distal spines and reduced beyond (not A. simplex n. sp.). Third seta in IDL strongly reduced to absent, and mostly not visible. Accessory seta present. Four to five anterior setule groups with up to five setules in each group, mostly decreasing in size ventrally. Ejector hooks unequal in size and gnathobase with setulated apex.

Second limb. Exopodite oval round, with short seta, maximally reaching exopodite apex; minute setules on exopodite apex; endites with eight scrapers decreasing in size towards gnathobase, eighth scraper shortest. First two scrapers relatively slender and finely setulated, third modified and shorter than two and four (not in A. simplex n. sp.), with stronger denticles than scrapers one to five. Scrapers four and five similar, with fine denticles. Scraper six modified, bearing strongest teeth of all scrapers (not A. simplex n. sp.). Final two scrapers decreasing in size towards gnathobase, scraper eight typically shortest. Gnathobasic ‘brush’ short and round (not simplex ), implanted with short denticles. Gnathobase with a sensillum and three elements, one short seta, one plump seta with small denticles in distal half and again a short seta; filter comb with seven setae of which the first two half as long as the last four, and the third one intermediate in length between setae two and four (same length in A. harti occidentalis ssp. n.). Second limb with reduced soft setae, though some remnants may be present at base of first scraper or between third and fourth scrapers.

Third limb. Pre-epipodite round, epipodite oval to round, in some species with long projection; exopodite with quadrangular corm and six long setae in 2+4 arrangement; first exopodite seta as long as second or longer; third exopodite seta longest, fourth seta of similar size of fifth seta (or slightly shorter), sixth seta shortest, maximally half size of fifth. All these setae strongly plumose, except for fifth and sixth, which may be plumose only in distal ules; four well developed plumose setae on inner side (1”–4”) of similar length; one naked element and four small naked setae on internal endite preceding gnathobase; the latter with a bottle-shaped sensillum and large bent plumose seta with two naked elements at its base. Filter comb with seven setae.

Fourth limb. Pre-epipodite round, epipodite oval to round, occasionally with long digitiform projection. Exopodite round to square, with six marginal plumose setae; first three exopodite setae long, fourth shorter than preceding seta; fifth and sixth setae narrower than first four. Endite with marginal row of four setae, first thickened and longer than flaming torch setae, following three setae with cylindrical base, decreasing in size towards gnathobase, and one round marginal sensillum; the last two flaming torch setae are half as thick as the first one and have less setules. Gnathobase with one long seta, bent over endite and basal reduced naked elements; on inner side, three long plumose setae (1”–3”) gradually increasing in size towards gnathobase and a filter comb with five relatively short setae, as long as or just longer than inner plumose seta (3”).

Fifth limb. Pre-epipodite oval to round and implanted with long setules; epipodite oval to round, may bear long projection. Exopodite shape broadly oval, about two times as long as wide, with expanded margin between setae three and four; four exopodite setae, first (dorsal) two longest, oriented dorsally; third shorter than second exopodite seta, fourth exopodite seta shorter than other setae by one third to a half; inner portion of limb with broad inner lobe with round to triangular apex and long apical setules; two thick endite setae (1’–2’) of which first longer as long as or reaching over inner lobe; second endite seta between half and two thirds of latter. Gnathobase with one setulated round hillock and small naked projection, no filter comb. Sixth limb absent.

Diagnosis. Anthalona consists of small to medium sized Aloninae (0.3–0.5 mm) with oval body, moderately arched, posteroventral notch on valves may be present and carapace expanded posteriorly, two main head pores and small pores with round sacks below, short labrum with denticle (absent in some species), first antenna without projection, second antenna with strong spines (not in all species). Postabdomen relatively short, S-shaped with deep concave anal margin and convex postanal margin, unmerged marginal denticles and lateral fascicles with long distal spines. Five pairs of limbs. P1 with reduced anterior elements and IDL with two setae, strongly modified and spiniform armature (not all species), dorsal seta in first endite present, P2 with exopodite seta reduced to absent, third and sixth scraper with stronger denticles (not A. simplex n. sp.), fcII with seven setae of which first two markedly shorter, no additional soft setae near scraper 1, P3 with six setae in exopodite of which third longest, fcIII with seven setae, P4 with six exopodite setae of which last two narrowed, enIV with three flaming torch setae (reduced in A. brandorffi ), fcIV with five long setae, P5 with four exopodite setae, oval inner lobe, two inner setae and reduced gnathobase (0 setae).

Differential diagnosis. Anthalona gen. n. is externally most similar to Coronatella Dybowski & Grochowski, 1894 in dimensions of body and postabdomen. In general, the body is less rectangular in Anthalona gen. n. than in Coronatella . In the latter, the posterior margin of the valves is straight, not expanded posteriorly in its ventral part like in most Anthalona gen. n. These are subtle differences, best seen when the two are viewed together. Anthalona gen. n. differs from Coronatella in having a shorter basal spine on the terminal claw, which is much longer in Coronatella and directly related taxa ( A. monacantha group, A. dentifera group and Leberis ), the presence of two main head pores (three in Coronatella ) and sacks below small pores (absent in Coronatella ). Also, Anthalona gen. n. has a denticle on the labrum (not A. simplex n. sp. or A. brandorffi ), first limb with modified IDL setae and sixth scraper of P2 (not A. simplex n. sp.). In Coronatella , the labrum has no denticle (except Alona monacantha group, which belongs to this genus). On P2, the first two filter setae in gnathobase are shorter than the following. It differs from Karualona in shape of the body and postabdomen and presence of cosmaria; also, the latter has denticles in the posteroventral valve corner, completely absent in Anthalona gen. n.