Anthalona spinifera, Tiang-Nga, Supatra, Sinev, Artem Y. & Sanoamuang, La-Orsri, 2016

Tiang-Nga, Supatra, Sinev, Artem Y. & Sanoamuang, La-Orsri, 2016, A new species of the genus Anthalona Van Damme, Sinev & Dumont, 2011 (Cladocera: Anomopoda: Chydoridae) from North-East Thailand, Zootaxa 4150 (1), pp. 93-100 : 94-99

Anthalona spinifera sp. nov.

( Figs. 1–3 )

Etymology. species name derived from Latin “spina” (spine) and “ferre” (“to carry”) after its main diagnostic feature, long spines on IDL setae.

Type locality. Bang Bat river , Bueng Kan province, Thailand, 18°14᾿12.83᾿᾿N, 103° 51᾿37.32᾿᾿E, 155 m. a.s.l., 24.03.2014, coll. Supatra Tiang-nga. At time of sampling, characteristics of water were: temperature 27.2°C ; pH, 6.98; electrical conductivity, 31 µS cm -1; total dissolved solids, 15 ppt; and dissolved oxygen, 6.5 mg L -1.

Type material. Holotype: parthenogenetic female from the type locality, Zoological Museum of M.V. Lomonosov Moscow State University, Ml-150.

Paratypes: 6 parthenogenetic females from the type locality, Zoological Museum of M.V. Lomonosov Moscow State University, Ml-151.

Other material studied. Six more females from the type locality were dissected for the analysis of appendages or used for SEM studies. Two parthenogenetic females from Lake Kud-Thing, Bueng Kan province, Thailand, 18° 19᾿03.77’’ N, 103° 40᾿37.37᾿᾿, 20.07.2014, coll. Supatra Tiang-nga . At time of sampling, characteristics of water were: temperature 35,9°C; pH, 6.58; electrical conductivity, 8 µS cm -1; total dissolved solids, 4 ppt; and dissolved oxygen, 8.4 mg L -1. Specimens used for analysis of appendages.

Description. Parthenogenetic female. Habitus. In lateral view, body oval, low in juveniles ( Fig. 1 A), moderately high in adults ( Fig. 1 C, 2A–C), maximum height at the middle of the body. Height-length ratio 0.65– 0.7 in adults. Dorsal margin convex, postero-dorsal and postero-ventral angles broadly rounded. Posterior margin convex, ventral margin almost straight, antero-ventral angle rounded. Ventral margin ( Fig. 1 D) with 35–40 setae.

About 20 anterior setae short, thin, naked, posterior setae longer and thicker, plumose. Postero-ventral angle with about 60 setulae not organized into groups. Carapace and headshield covered by tubercles.

Head relatively small, triangle-round in lateral view. In lateral view rostrum protruding downwards. Ocellus smaller than eye. Distance from tip of rostrum to ocellus about 1.5 times of that between ocellus and eye. Headshield shape typical for genus (Fig. 2D). Rostrum short and rounded. Posterior margin notched. Two main headpores with a narrow connection between them ( Fig. 1 B, E, 2E), PP less than 0.6 IP. Lateral headpores located with bilobed or trilobed asymmetric cosmaria, at about 1 IP distance from midline, at level before anterior main head pore.

Labrum of moderate size, without lateral projections ( Fig. 1 F–G). Labral keel wide, height only slightly exceeding width, with lateral indentations. Anterior margin of keel convex, with small blunt denticle in the upper third, apex rounded, posterior margin convex, without setulae.

Thorax two times longer than abdomen. Dorsal surface of abdominal segments not saddle-shaped.

Postabdomen ( Fig. 1 G–H) short and wide, maximum height at preanal angle. Length about 2.3–2.4 height. Ventral margin straight. Basis of claws separated from distal margin by clear incision. Distal margin weakly convex, distal angle rounded. Dorsal margin weakly convex in postanal portion and concave in anal one, distal part 1.5–1.6 times longer than preanal one, postanal portion slightly longer than anal one. Preanal angle well-defined, postanal angle weakly defined. Preanal margin almost straight. Postanal margin with 5–6 well-developed composite denticles of similar length, most with several spinules along anterior margin; length of denticles about the width of postabdominal claw base. Anal margin with 3–4 groups of marginal spinulae and setulae. Ten-eleven lateral fascicles of setulae. In postanal portion fascicles narrow, composed of 3–7 setulae each, distance between fascicles about width of fascicle; posteriormost setula very long and thick, in distalmost groups with length about 2.5 widths of postabdominal claw base. In anal portion fascicles wider and spaced more closely, with shorter distalmost setule. Postabdominal claw slender, of moderate length, shorter than preanal portion of postabdomen. Basal spine short and slender, less than 0.2 of the claw length. A long spinule located near the base of basal spine.

Antennule ( Fig. 1 J) of moderate size, length about three widths, with 5 clusters of short setulae at anterior face. Antennular seta of about half length of antennule, arising at 2/3 distance from the base. Nine terminal aestetascs, longest of them about half length of antennule.

Antenna ( Fig. 1 K, 2F) with antennal formula: setae 0-0-3/1-1-3 and spines 1-0-1/0-0-1. Basal segment robust, with short seta between branches; branches relatively short; basal segments in both branches 1.5 times longer than others. Basal and middle segment of endopodite with clusters of short setulae. Seta arising from basal segment of endopodite reaching after the end of endopodite. Seta arising from middle segment of endopodite of similar size to apical setae. One of apical setae on both branches significantly shorter and thinner than two others. Spine on basal segment of exopodite slightly longer than middle segment. Spines on apical segments slightly longer than apical segments.

Thoracic limbs: five pairs.

Limb I ( Fig.3 A–C). Epipodite oval, with finger-like projection two times longer than epipodite itself. Accessory seta 2.5 times shorter than ODL seta. ODL seta with short setulae in distal portion. IDL with two setae; seta 3 thick, curved, longer than ODL seta, ending in three-four long spines; seta 2 short, more thin, bearing 3 thick spines longer than seta itself. Endite 3 with four short setae, setae 1 and с thick, robust; setae a–b thin. Endite 2 with two long setulated setae (e–f); a shorter seta near their base (d), and a very short inner seta (2) on anterior face of limb; seta e almost as long as limb itself, with long setulae in distal portion; seta f about 2/3 length of seta e. Endite 1 with two long 2-segmented setae of similar size (g–i), setulated in distal part; long flat seta (j) pointed to the limb base; and a very short inner seta (3) on anterior face of limb. Ventral face of limb with 5–6 clusters of long setulae. Two ejector hooks, one of them much larger than other.

Limb II subtriangular ( Fig. 3 D–E). Exopodite elongated, with very short seta. Eight short scraping spines; spines 1–5 long, armed with thin spinules, decreasing in length basally; spine 3 more thick than others; spines 6–8 short, with wide bases and short distal part; spine 7 smaller than two others. Very short denticles observed only on spine 6. Distal armature of gnathobase with four elements. Filter plate II with seven setae.

Limb III ( Fig. 3 F–G). Epipodite rounded. Exopodite subrectangular, with six setae. Seta 3 longest; setae 1, 4 and 5 about 1/4, 1/3 and 1/2 length of seta 3; setae 2 and 6 very short. Setae 1–4 plumose; seta 5 armed bilaterally with short hard setulae; seta 6 naked. Distal endite with 3 setae, two distalmost members slender, with blunt tips, without denticles in distal part, short bottle-shaped sensillum located between their bases. Basal endite and gnathobase typical for the genus.

Limb IV ( Fig. 3 H–I). Pre-epipodite setulated; epipodite with finger-like process two times longer than epipodite itself; exopodite rounded, with six setae. Setae 1–3 long, of similar length; setae 4–6 about two times shorter. Setae 1–4 flat, plumose; setae 5–6 thin, with short setulae in distal portion. Inner portion of limb IV with four setae and small sensilla. Scraping seta (1) slender, without denticles in distal portion; first flaming-torch seta (2) much wider than two other (3–4). Three soft setae, basalmost seta significantly larger than others. Gnathobase with two-segmented seta and a small hillock distally. Filter plate IV with five setae.

Limb V ( Fig. 3 J). Preepipodite setulated, epipodite oval, with finger-like projection two times longer than epipodite itself. Exopodite oval, with four plumose setae. Seta 1–3 long, subequal in length, seta 4 short, four times shorter than seta 1. Inner lobe rounded. At inner face, two setae, distal seta two times longer than basal one, and a small sensilla. Filter plate V absent.

Ephippial female and male unknown.

Size. In two juvenile females of instar II length was 0.27 mm, height 0.17 and 0.18 mm; in adult female length was 0.31–0.38 mm, height 0.22–0.25 mm.

Differential diagnosis. Anthalona spinifera sp. nov. differs from most species of the genus in IDL setae armed with 3–4 very long spines, and in having very short spines 6–8 in limb II, with shortened distal portion; these characters are shared only by South American Anthalona brandorffi ( Sinev & Hollwedel, 2002) . A. brandorffi differs from A. spinifera sp. nov. in the shape of postabdomen, which is narrowing basally in anal portion; in much longer posterior setae of valves; in posteroventral angle of valves armed with about 25 setulae only; and in shortened setae e–f of limb I, being of same length than seta с. Other differences between these two species are summarized in Table 1 .

Distribution and ecology. Anthalona spinifera sp. nov. so far is known from North-East Thailand, but probably has wider distribution. It was found in localities with abundant submerged macrophytes in a shallow lake and in a river. Water current in riverine sampling sites was very slow to undetectable, and therefore A. spinifera sp. nov. cannot be treated as a specialized rheophile. In both localities, A. spinifera sp. nov. is encountered together with most common Anthalona species of the region, Anthalona harti harti .

Figures

FIGURE 1. Anthalona spinifera sp. nov. from Bang Bat river, Bueng Kan province, Thailand (type locality). A – B, juvenile female of instar II. A, lateral view. B, head pores. C – K, adult parthenogenetic female. C, lateral view. D, ventral margin of valves. E, head pores. F – G, labrum. H – I, postabdomen. J, antennule. K, antenna.

FIGURE 3. Anthalona spinifera sp. nov. from Bang Bat river, Bueng Kan province, Thailand (type locality), thoracic limbs of parthenogenetic female. A, limb I. B, IDL and ODL of limb I. C, IDL of limb I. D – E, inner and outer parts of limb II. F, exopodite of limb III. G, distal endite of limb III. H, exopodite of limb IV. I, inner portion of limb IV (inner setae and gnathobase filter comb not shown). J, limb V.

Tables

TABLE 1. Differences between Anthalona spinifera sp. nov. and Anthalona brandorffi.

Character	A. spinifera sp. nov.	A. brandorffi
Body outline	Oval, maximum height at the middle of the body	Egg-shaped, maximum height after the middle of the body
Ventral setae of valves	Short, posteriormost setae located before posteroventral angle	Long, posteriormost setules located at porteroventral angle
Posteroventral angle of valves	With about 60 setulae	With about 25 setulae
Endite 3 of limb I	Seta 1 thick, as long as others; seta с without denticles	Seta 1 thin, significantly shorter than others; seta с with long denticles.
Endite 2 of limb I	Setae e–f long, 1.5–2 times longer than seta c	Setae e–f short, of similar length with seta c, with reduced distal portion
IDL of limb I	Seta 2 with three spines of similar length	Seta 2 with four spines of different length, basalmost spine 2 times shorter than distalmost one
Limb II	Scraper 7 only slightly smaller than scrapers 6 and 8	Scraper 7 two times shorter than scrapers 6 and 8
Inner portion of limb IV	With three flaming-torch setae	With two flaming-torch setae