Anthalona obtusa, 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 : 32-36

Anthalona obtusa n. sp.

( Figs 16–17 )

Alona verrucosa Sars, 1901 in Johnson (1956a: Fig. 6 ).

nec Biapertura pseudoverrucosa verrucosa ( Sars, 1901) in Dumont & Van De Velde (1977).

Material examined. Holotype. One adult parthenogenetic female mounted in glass slide labelled “ Anthalona obtusa n. sp. holotype ”; from pool at the Palangka Raya University Campus, Borneo, 4.III.2007, Leg. H.J. Dumont.

Paratypes. Three slides with respectively one and two complete females and one dissected female labelled “ Anthalona obtusa n. sp. paratypes ” same slide and data as holotype. Tube containing eight females from type locality. All material deposited at the Royal Belgian Institute for Natural Sciences , Brussels ( RBIN) under accession numbers RBIN IG 31782 INV 96737 -96742.

Additional (paratypes): five adult parthenogenetic females from type locality, UG Collection.

Description. Adult parthenogenetic female. Habitus ( Figs 16A–B ). Small, 0.3–0.35 mm, average length 0.31mm (n=10). Transparent and colourless. Body length 1.5–1.57 times height. Dorsum moderately convex, highest point near middle; posterior margin angular, with posteriorly expanded lower portion ( Fig. 16B ). Ventral extent of rostral tip not reaching carapace margin ( Fig. 16A ). Ventral carapace margin straight or deepest point just before middle ( Fig. 16A ). Posteroventral corner round, with notch ( Fig. 16D ).

Head. Ocellus smaller than eye (diameter of eye is 1.3–1.5 times that of ocellus) ( Fig. 16A ). Well developed rostrum, obtuse. Aesthetascs of antennules projecting laterally from rostrum, antennular corm almost half its length from rostral tip ( Fig. 16A ). Two main head pores ( Fig. 16C ), interpore distance long, three to four times the diameter of one main pore. PP distance short, one third of IP distance, lateral pores at one IP distance from midline and situated posterior to main pores, at a distance of half IP distance from the posterior pore ( Fig. 16C ). Sacks under small pores with diameter similar to that of a main pore or little larger ( Fig. 16C ). These sacks always eight-shaped, but comparably small. Posterior margin of head shield not strongly subdivided ( Fig. 16C ).

Carapace ( Figs 16A–B ). Ornamentation with lines and tubercles arranged in lines, evenly spaced and small ( Fig. 16B ). Tubercles more common in upper half of body, lines in lower half. Marginal setae 24–35 ( Fig. 16A ), differentiated into three groups, anterior group longest, median group shortest, posterior group intermediate in length. Setae not strongly decreasing in size towards the posteroventral corner but ending more abruptly and followed by fine setules ( Fig. 16D ). These setules of similar size, reaching beyond carapace margin in posteroventral corner and continuing in a posterior row of fine long setules ( Fig. 16D ).

Labrum ( Fig. 16G ). Labral keel with moderately convex margin in ventral half and a clear ventral notch ( Fig. 16G ). One proximal denticle on labral keel, not strongly developed. The denticle may be blunt and obscure ( Fig. 16G ).

First Antennae or antennules ( Fig. 16E ). About two times as long as wide, sensory seta implanted at one third of antennular corm. Three to four groups of short denticles on margin. Aesthetascs of similar size, longest about as long as antennular body.

Second antennae ( Fig. 16F ). Basal spine short. Formula as for genus ( Fig. 16F ). First exopod seta on antenna narrow ( Fig. 16G ), reaching beyond ultimate exopod segment; second exopod seta two times as long as previous; on external side of second exopod segment, three to four strong spines ( Fig. 16G ). True spine on first endopod segment reaching just beyond end of second segment; main terminal spines on endo- and exopod well developed, each as long as their apical segment ( Fig. 16G ). Terminal setae on antennal exopod as for endopod and with long setules.

Postabdomen ( Fig. 16H ). Relatively widest at preanal angle; rounded dorso-distal margin. About two times as long as wide. Ventral margin shorter than anal and postanal margin together. Postanal and anal margins of similar length and shorter than preanal margin ( Fig. 16H ). Anal margin straight to slightly concave, postanal margin straight and tapering distally or more convex ( Fig. 16H ). Distal embayment (dorsal to basal claw) about half of claw width at base. Preanal corner protruding beyond dorsal point of postanal margin ( Fig. 16H ). Marginal postanal teeth five to six. Each distal marginal tooth with one to two adjacent smaller elements on anterior side, not merged. These marginal teeth rather long, about two times as long as wide (at base) ( Fig. 16J ). Lateral fascicles five to six groups in postanal portion, consisting of four to six elements per group, parallel to each other. Distalmost lateral element spiniform, long and thick, protruding half of its length beyond dorsal margin of postabdomen ( Fig. 16K ). Distalmost lateral spines in postanal portion reaching beyond marginal teeth ( Fig. 16K ). Second element per fascicle at least half as long as distalmost element in each group. Two to three clusters of long marginal teeth, and three to four fascicles in anal portion.

Terminal claw ( Figs 16H–I ). Longer than anal margin ( Fig. 16H ), moderately curved, implanted with setules along dorsal side. Proximal pecten ending in spine about half as long as width of claw at this point and at about half D. Smallest IDL seta. E. Second limb. F. Idem, sixth scraper (enlarged). G. Third limb, exopodite, setules omitted. H. Idem, with setules. I. Idem, endopodite. J. Idem, inner endite setae. K. Idem, gnathobase. L. Fourth limb (partim). M. Idem, endopodite. N. Fifth limb.

First maxilla not seen.

Five pairs of limbs. First limb ( Figs 17A–C ). Epipodite round with long projection, reaching beyond limb corm. First to third endites as for genus. Longest seta in second endite with few teeth (five), and shortest seta in the same endite is long, half of previous seta. Anterior elements strongly reduced ( Fig. 17B ). ODL with one slender seta, as long as or just longer than largest IDL seta and with short fine setules in distal half ( Fig. 17C ); two setae in IDL, modified ( Fig. 17C ). One large spine followed by reduced distal part ( Fig. 17C ) on largest IDL seta; spine in longest IDL seta is shorter than distal part beyond it. On shortest IDL seta ( Fig. 17D ), two long spines of which proximal is shorter and both shorter than distal part of this seta. Accessory seta present, half of IDL seta ( Fig. 17C , as). Four to five anterior setule groups with two to three setules in each group, decreasing in size ventrally ( Fig. 17A ). Ejector hooks unequal, relatively small for genus ( Fig. 17A ).

Second limb ( Figs 17E ). Exopodite ( Fig. 17E ) elongate, two times as long as wide, with short seta reaching just beyond exopodite apex; tuft of hairs on exopodite apex; endites with eight scrapers gradually decreasing in size towards gnathobase, eight scraper shortest ( Fig. 17E ). First two scrapers relatively slender and finely setulated, about as long as third scraper. Third not modified and intermediate in size between scrapers two and four. Scrapers four and five similar, with fine denticles, scraper six ( Fig. 17F ) shorter by half and with 11–13 thick teeth; final two scrapers decreasing in size towards gnathobase, scraper eight not strongly reduced, with fine denticles. Gnathobasic ‘brush’ short and round, implanted with short denticles. Gnathobase as for genus; filter comb ( Fig. 17E ) with seven setae of which first two shorter, third intermediate between these two and fourth filter seta.

Third limb ( Figs 17G–K ). Epipodite round with projection longer than exopodite corm; exopodite ( Figs 17G– H ) as for genus, with six setae; first exopodite seta twice as long as second and thicker; third exopodite seta twice as long than fifth exopodite seta, fourth seta just shorter than fifth seta and three times as long as sixth seta ( Fig. 17G ). Endite ( Figs 17I–K ) as for genus, but with strongly developed denticles in setae 1’–2’ ( Fig. 17I ), long setae in internal endite ( Fig. 17J ) preceding gnathobase and filter comb setae about as long as last seta on inner side (4”) ( Fig. 17I ).

Fourth limb ( Figs 17L–M ). Epipodite oval with long projection ( Fig. 17L ) reaching by almost half its length beyond exopodite margin. Exopodite with six marginal plumose setae; first three exopodite setae longer, third longest of the three (one sixth longer than second seta), fourth seta two thirds length of preceding seta; fifth and sixth setae narrow ( Fig. 17L ). Both these setae shorter than the fourth, fifth just longer than sixth ( Fig. 17L ). Endite ( Fig. 17M ) as for genus.

Fifth limb ( Fig. 17N ). Epipodite oval with long projection reaching half its length beyond exopodite margin. Exopodite ( Fig. 17N ) shape broadly oval, about 1.5–two times as long as wide, with straight margin between setae three and four; four exopodite setae, first (dorsal) two longest, oriented dorsally, longer by one third of exopodite width; third shorter than second exopodite seta, fourth exopodite seta half as long as third seta; inner portion of limb ( Fig. 17N ) with broad oval inner lobe and long apical setules; two endite setae (1’–2’) of which first longer; this seta just reaching apex of inner lobe; second endite seta shorter by a fourth of latter. Gnathobase as for genus.

Differential diagnosis. A. obtusa n. sp. is another relatively small species (0.31mm) of the A. verrucosa- complex, with tubercles arranged in (10–12) rows; sometimes only striae present. Body shape as in A. verrucosa , with posterior valve margin not straight or round but expanded in ventral part. Anthalona obtusa n. sp. has a notch in the posterior margin of the valves ( Fig. 16D ) and the labrum has a clear ventral notch ( Fig. 16G ). Proximal labral denticle blunt (in most specimens), a very clear feature ( Fig. 16G , arrow). The postabdomen has a relatively long basal spine ( Fig. 16H ), about one third of the length of the basal claw, with short basal spinules; marginal teeth on the postabdomen are relatively long in A. obtusa n. sp., twice as long as wide. For limbs, scrapers on second limb are not strongly modified as in majority of Anthalona and sixth scraper bears relatively many (11) teeth.

Distribution and ecology. Borneo and, likely, Sumatra. Its wider distribution in South-East Asia, particularly Indonesia is unknown, but could be expected throughout the region. We consider it most likely identical to Alona verrucosa from Sumatra in Johnson (1956a), who describes the typical blunt denticle (on labrum). Nayar (1971) mentions an A. verrucosa from Rajasthan, India, with indistinct denticle on the labrum and notes that it corresponds closest in postabdomen to the animal of Johnson (1956a); these populations should be checked. All records of Alona verrucosa from South East Asia (e.g., Idris & Fernando 1981) need revision and it is not unlikely that more cryptic species of the A. verrucosa- complex may be found here. An incertae sedis in the near vicinity is seem to have a blunt denticle. A. obtusa n. sp. was found in a small permanent pond, between Utricularia , together with the Anomopoda Euryalona Sars, 1901 , Ephemeroporus Frey, 1982 , Alonella Sars, 1862, Notoalona Rajapaksa & Fernando, 1987 , Macrothrix Baird, 1843 and Acroperus Baird, 1843 .

Figures

FIGURE 6. Anthalona acuta n. sp., males from the Lençóis Maranhenses, Brazil. Leg. K. Van Damme. A. Habitus. B-C. Postabdomen. D. Detail first limb, with copulatory hook or clasper. Abbreviations: ch, copulatory hook, IDL, inner distal lobe, ODL, outer distal lobe.

FIGURE 16. Alona obtusa n. sp. Parthenogenetic females from pond at Palangka Raya University Campus, Borneo. A. Habitus. B. Body outline. C. Head shield, posterior margin with head pores. D. Posteroventral corner of valves (with ventral notch);

FIGURE 17. Alona obtusa n. sp. Parthenogenetic females from pond at Palangka Raya University Campus, Borneo. A. First limb, anterior view, IDL and ODL omitted. B. Idem, anterior view (to show soft setae). C. Idem, IDL, ODL and accessory seta.