Karualona arcana, Tiang-Nga & Sinev & Sanoamuang, 2021

Tiang-Nga, Supatra, Sinev, Artem Y. & Sanoamuang, Laorsri, 2021, A new species of Karualona Dumont & Silva-Briano, 2000 (Cladocera: Anomopoda Chydoridae: Aloninae) from Northeast Thailand, Zootaxa 5057 (2), pp. 285-294 : 287-288

publication ID	https://doi.org/ 10.11646/zootaxa.5057.2.8
publication LSID	lsid:zoobank.org:pub:1AEA85F2-A937-4679-BE9A-044098FECE88
DOI	https://doi.org/10.5281/zenodo.5592758
persistent identifier	https://treatment.plazi.org/id/03F58789-B051-FFAD-AEFD-FF30CC0CF9DB
treatment provided by	Plazi
scientific name	Karualona arcana
status	sp. nov.

Treatment

Karualona arcana sp. nov.

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Etymology. The species name “ arcana ” (Latin for “ mysterious ”) refers to both its rarity and its unclear taxonomic status.

Type locality. A rice field in Seka District , Bueng Kan Province, Thailand, 18°09᾿34.04” N, 103°53᾿58.85” E, 155 m. a.s.l. The animals were collected by S. Tiang-nga on 24 June 2012 .

Holotype. A parthenogenetic female from the type locality, deposited in the collection of ZMMU, accession number Ml–249.

Paratypes. Four parthenogenetic females from the type locality, deposited in the collection of ZMMU, accession number Ml–250 .

Seven parthenogenetic females from the type locality were dissected for the analysis of appendages or used for SEM studies.

Description. Parthenogenetic female. In lateral view, body moderately compressed laterally, low oval in juveniles ( Fig. 1A–B View FIGURE 1 ) and moderately high oval in adults ( Figs. 1C–D View FIGURE 1 , 2A–B View FIGURE 2 ). Maximum height at middle of body. Dorsal margin convex, posterodorsal and posteroventral angles broadly rounded. Posterior margin convex, ventral margin almost straight, anteroventral angle rounded. Ventral margin ( Fig. 1E View FIGURE 1 ) with about 40 setae, 10 anterior setae long, next 10 setae very short, posterior 20 setae of moderate length, increasing in length posteriorly. Posteroventral angle ( Figs. 1F View FIGURE 1 , 2C View FIGURE 2 ) with 3–4 denticles with wide bases, width of denticle base greater than its length, distance between denticles 3 times greater than the width of denticle base. A row of about 70 short setules on inner side of carapace along posterior margin. Carapace covered by moderately thick, sparsely spaced longitudinal lines.

Head relatively small, triangle-round in lateral view; rostrum short, pointing downward. Eye larger than ocellus. Distance from the tip of rostrum to the ocellus 1.5 times greater than that between the ocellus and the eye.

Head shield with maximum width behind mandibular articulation, with tubercular sculpture. Rostrum short, broadly rounded ( Fig. 2E View FIGURE 2 ). Posterior margin of head shield straight. Two narrowly connected main head pores ( Fig. 2F View FIGURE 2 ), PP about 1.5 IP. Lateral head pores located at about 0.5 IP distance from midline, at the level of anterior and middle main head pore. Dorsal midline of valves behind the head shield with dorsal pore in shape of two apertures in a small depression, located at about 0.5 IP from midline ( Fig. 2G View FIGURE 2 ).

Labrum relatively large ( Figs. 1G–H View FIGURE 1 , 2D–E View FIGURE 2 ). Labral keel of moderate width (height/width ratio about 1.5), with a rounded or blunt apex, with well-developed lateral indentations. Anterior margin of keel convex, with about 10 very short setules in upper third ( Fig. 2E View FIGURE 2 ), posterior margin without clusters of setules.

Thorax two times longer than abdomen. Dorsal surface of abdominal segments not saddle-shaped. No abdominal projections.

Postabdomen ( Figs. 1I–K View FIGURE 1 , 3C–F View FIGURE 3 ) short, of moderate width, with strongly convex postanal margin, strongly concave anal margin, and distal angle broadly rounded. Maximum height at middle of postanal portion. Length about 2.2–2.4 height. Ventral margin convex. Basis of claws bordered from distal margin by clear incision. Distal margin convex. Dorsal margin with distal part about 1.5 times longer than preanal one; postanal and anal portions of similar length. Preanal angle well defined, postanal angle not defined ( Fig. 3E View FIGURE 3 ). Preanal margin sigmoid. Postabdomen with 7–8 groups of short elementary denticles; distal 3–4 groups consisting of single denticle only, in other groups 2–4 denticles, followed by 3–4 clusters of setules ( Fig. 1J View FIGURE 1 ). Length of marginal denticles decreasing in size distally; denticles at preanal angle being longest, of about width of postabdominal claw base. About 10 lateral groups of setules; in 5–6 postanal groups distalmost setules with very long and thick, much thicker than others, 2–2.5 times longer than marginal denticles. Number of setules in group increases from 3–4 in distalmost groups to 10–12 in anal ones. Postabdominal claw ( Figs. 1K View FIGURE 1 , 3F View FIGURE 3 ) weakly curved, of moderate length, slightly shorter than preanal portion of postabdomen. Basal spine short, straight, and thin, about 0.15 length of claw. Some specimens with two very small spinules between basal spine and base of claw.

Antennule ( Figs. 1L View FIGURE 1 , 2E View FIGURE 2 ) of moderate size. Length/width ratio about 3. Antennular sensory seta slender, 2.5 times shorter than antennule, arising at about 2/3 distance from base. Nine terminal aesthetascs ( Fig. 2E View FIGURE 2 ).

Antenna ( Figs. 1M View FIGURE 1 , 3A–B View FIGURE 3 ) short. Antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Basipodite robust, branches short and stout. Basal segments of both branches 1.5 times longer than middle and apical segments. Seta arising from basal segment of endopodite thin, shorter than endopodite. Seta arising from middle segment of endopodite of same size with shortest apical setae. Both apical segments with one shorter and two longer setae of similar thickness. Spine on basal segment of exopodite of similar length with middle segment. Spine from apical segments longer than apical segments.

Maxilla process with single seta.

Thoracic limbs: five pairs ( Figs. 1N–T View FIGURE 1 , 3G View FIGURE 3 ).

Limb I ( Fig. 1N–O View FIGURE 1 ) of moderate size. Epipodite oval, with long process two times longer than epipodite itself. Accessory seta short, about 1/3 length of ODL seta. IDL with two setae, seta 1 not found. Seta 3 as long as ODL seta, seta 2 1.5 times shorter than seta 3, both armed with long thick setules, evenly decreasing in size posteriorly. Endite 3 with four setae, inner seta (1) much smaller than setae a–c. Endite 2 with seta d as long as setae of endite 3, seta e long, almost as long as limb itself, seta f about 2/3 length of seta e. Endite 1 with three setae. No inner setae (2–3) and sensillae on endites 1 and 2. Five rows of thin long setules on ventral face of limb. Two ejector hooks of similar size.

Limb II ( Fig. 1P View FIGURE 1 ). Exopodite elongated, without seta. Eight scraping spines armed with thin setules, decreasing in length basally. Distal armature of gnathobase with four elements. Filter plate with seven setae.

Limb III ( Fig. 1Q View FIGURE 1 ). Epipodite oval, without process. Exopodite subrectangular, with 6 setae. Seta 3 being longest, setae 4 and 5 of moderate length, seta 5 longer than seta 4, setae 1, 2, and 6 short. Setae 1–3 plumose; seta 4 in basal portion unilaterally armed with very long setules, in distal portion plumose; seta 5 bilaterally armed with thick long setules in distal portion; seta 6 naked. Inner portion of the limb not studied.

Limb IV ( Fig. 1R–S View FIGURE 1 ). Preepipodite setulated; epipodite oval, with process as long as epipodite itself. Exopodite irregularly rounded, with 6 setae. Seta 1–3 long; seta 5 about 1/2 length of seta 1; seta 4 about 1/3 length of seta 1; seta 6 extremely short. Setae 1–4 flattened, plumose; seta 5 unilaterally armed with long setules in distal portion; seta 6 naked. Inner lobe of limb IV with 3 setae ( Fig. 1S View FIGURE 1 ). Distalmost seta (1) slender, sharp; flaming-torch setae (2–3) with broad basal portion, armed with 6–7 thin setules each. Sensillum slightly small. Three soft setae (a–c) increasing in size basally. Gnathobase with 2-segmented seta, and a small hillock distally. Filter plate with 5 setae.

Limb V ( Fig. 1T View FIGURE 1 ). Preepipodite setulated, epipodite oval with process longer than epipodite itself. Exopodite oval, not divided into two lobes, with four plumose setae; setae decreasing in size basally. Inner limb portion as a rounded lobe, with setulated inner margin. At inner face, two setae. Filter plate not found.

Ephippial female and male. Unknown.

Size. In juvenile females, length 0.22–0.30 mm, height 0.13–0.20 mm. In adult females, length 0.35–0.41 mm, height 0.22–0.25 mm. Height/length ratio 0.6–0.65 in adults.

Differential diagnosis. Karualona arcana sp. nov. differs from all other species of the genus in the absence of IDL seta 1, in the shape of the postabdomen, in the apical setae of the antenna endopodite being of equal thickness, in the presence of setules on the anterior margin of the labral keel, and in reduced seta 6 on the exopodite of limb IV. These characteristics are summarized in Table 1 View TABLE 1 .

Distribution and ecology. Karualona arcana sp. nov. has so far only been found in Thailand. This species was collected from a single locality, a rice field in Bueng Kan Province, Thailand during the rainy season. The water’s properties at the time of sampling were as follows: temperature, 26 °C; pH, 5.64; electrical conductivity, 87 µS cm-1; total dissolved solids, 42 mg L- 1; and dissolved oxygen, 7.2 mg L- 1. We also found common species of Aloninae in the region, e.g., K. cf. karua (King, 1853) , Coronatella acuticostata (Sars, 1903) , Anthalona harti harti Van Damme, Sinev & Dumont, 2011 , Ovalona cambouei (Guerne & Richard, 1893) and Leberis diaphanus (King, 1853) .