Coronatella (Coronatella) acuticostata (Sars, 1903)

Sinev, Artem Y., Dadykin, Ivan A., Umi, Wahidah A. D. & Yusoff, Fatimah M., 2025, New data on Cladocera (Crustacea: Branchiopoda) of Peninsular Malaysia, Zootaxa 5604 (3), pp. 255-284 : 265-270

Coronatella (Coronatella) acuticostata (Sars, 1903)

Figs. 7–9 , 10A–G

Sars 1903a: 15, pl. I, Figs. 5, 5a–c ( Alona ); Stingelin 1905: 349–350, Taf. 12, Figs. 18–19 ( Alona acuticostata var. tridentata ); Idris & Fernando 1981a: 250, Figs. 67–71 ( Alona monacantha ); Idris 1983: 117, Fig. 35. ( Alona monacantha ); Sinev & Yusoff 2015: 585–586, Figs.1F–G ; Sinev 2016: 467, Figs. 9A–D .

Material examined: several parthenogenetic females from Bukit Merah reservoir, Perak (4.9852° N, 100.6787° E), 26.01.2018 ; 11 parthenogenetic females from Putrajaya Wetland (02.97552° N, 101.70250° E), 3.09.2022 ; parthenogenetic female from Chini Lake , Pahang (03.42484° N, 102.90849° E), 5.09.2022 ; over 30 parthenogenetic females from a roadside pond, Pahang (03.45092° N, 102.86503° E), 6.09.2022 ; several parthenogenetic females from Mentiga Lake , Pahang (03.41537° N, 103.00976° E), 6.09.2022 ; parthenogenetic female from a roadside pond, Pahang (03.56735° N, 102.710508° E), 6.09.2022 .

The species was never fully described, so we provide a complete description for Malaysian populations.

Parthenogenetic female. In lateral view, body ovoid, compressed laterally, low in juveniles ( Fig. 7A ), moderately low in adults ( Figs. 7B , 8A–F ). Maximum height at mid-body or slightly before, height-to-length ratio around 0.6 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 ( Figs. 7C , 8G ) with 30–35 setae. About 8 anterior setae longer than others, next 10 setae short; setae in posterior half of the valve of moderate length. Postero-ventral angle ( Figs. 7D , 8I–H ) with one–four (in most specimens two) denticles, followed by about 20 setulae not organized into groups, the length of the denticle is less than the width of its base, distances between denticles approximately two widths of the base of the denticles. The same specimen can have different number of denticles on left and right valve. Valves in most specimens with a sculpture of well-developed narrow longitudinal lines ( Figs. 8A, C, G ). In some specimens, the valve lines are broad, and consist of overlapping tubercles ( Fig. 8B ).

Head relatively small, triangular-rounded in lateral view, rostrum short, pointing downwards ( Fig. 9A ). Compound eye larger than ocellus. Distance from tip of rostrum to ocellus 1.5 times longer than that between ocellus and eye.

Head shield with a maximum width behind mandibular articulation, with weakly developed tubercules ( Fig. 7E ). Rostrum short, broadly rounded, and posterior margin broadly rounded, slightly wavy. Three narrowly connected major head pores ( Fig. 7F , 9B ), median pore smaller than the others, located medially between the others. PP less than 0.5 IP. Lateral head pores located at less 1 IP distance from midline, at the level of anterior major head pore. Frontal head pore elongated, located between the bases of the antennules.

Labrum relatively large ( Fig. 7G–I . 9C–D ). Labral keel of moderate width (height/width ratio about 1.5), with a rounded or blunt apex. Anterior margin of keel convex, in some specimens with a pronounced blunt prominence in the upper portion, posterior margin without groups of setules.

Thorax twice as long as the abdomen. Dorsal surface of abdominal segments not saddle-shaped. Any abdominal projection absent.

Postabdomen ( Fig. 7J–K , 9E–F ) relatively short, subrectangular, moderately wide, weak narrowing in postanal portion. Length approximately 2.5 heights. Ventral margin almost straight to slightly convex. Distal margin convex, distal angle broadly rounded. The dorsal margin convex in postanal portion and concave in anal one, with distal part about 1.5 times longer than preanal one, anal and postanal portions of similar size. Preanal angle well-defined, soft postanal angle. Postanal margin with 2–3 large distal compound denticles followed by 3–4 groups of 2–4 small sharp denticles; length of longest denticles 1.5 times greater than width of the base of postabdominal claw. Anal portion with 2–3 broad groups of setulae. Postanal portion with 4–5 broad lateral groups of setulae, posteriormost setulae of each group of similar length with longest marginal denticles. Postabdominal claw ( Fig. 8L ) of moderate length, slightly shorter than preanal margin of postabdomen. Basal spine long, slender, about 0.35–0.5 times the length of the claw, a long setula located at its base.

Antennule ( Fig. 7M , 9C ) comparatively large, its tip almost reaching tip of rostrum, with three clusters of short setulae at anterior face. Length/width ratio c.a. 2.5. Antennular sensory seta slender, two times shorter than antennule, arising at about 2/3 distance from the base. Nine aesthetascs, two longest almost as long as antennule itself.

Antenna short ( Fig. 7N , 9G ). Antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Basal segment robust, branches short and robust. Coxal portion with two long setae. Basal segments of both branches almost two times longer than middle and apical segments. Seta arising from basal segment of endopod thin, reaching the end of the apical segment. Seta arising from middle segment of endopod shorter than apical setae. Both apical segments with three setae of similar thickness, one of them much shorter than two others. Spine on basal segment of exopodite longer than middle segment. Spines on apical segments slightly longer than respective segment.

Thoracic limbs: five pairs.

Limb I ( Figs. 10 A-C) of moderate size. Epipodite oval, with a curved process longer than epipodite itself. Accessory seta short, about 1/3 length of ODL seta. IDL ( Fig. 10B–C ) with rudimentary seta 1 at its base. Seta 3 as long as ODL seta, seta 2 slightly shorter than seta 3. Seta 2 armed with large spines at the middle, seta 3 with single large spine, distal portion of both setae longer than mentioned spines. Endite 3 with four setae, inner seta (1) shorter than other setae (a–c). Endite 2 with seta d as long as setae a–c of endite 3, seta e long, almost as long as limb itself, seta f about 3/4 length of seta e. Endite 1 with two distally setulated 2-segmented setae (g–h) and a long flat seta (i) much longer than setae of endite 3. No naked inner setae (2–3) and sensillae on endites 1 and 2. Five–six rows of thin long setules on ventral face of limb. Two ejector hooks of unequal size. Maxillar process with a single seta.

Limb II ( Fig. 10 D,E ). Exopodite elongated, with a single seta twice as short as itself. Eight scraping spines armed with thin spinules: scrapers 1–5 long, increasing in length distally, scraper 3 slightly thicker than scrapers 2 and 4; scrapers 6–8 short, of similar size. Distal armature of gnathobase with four elements. Filter plate with seven setae, the two posterior ones considerably shorter.

Limb III ( Fig. 10F ). Epipodite oval, with a process as long as epipodite itself. Exopodite subrectangular, with six setae. Seta 3 being longest, seta 5 about 1/3 length of seta 3, seta 4 about 1/4 length of seta 3. Setae 1–4 plumose, seta 5 armed with thick setules in distal portion, seta 6 naked. Morphology of inner portion of the limb typical for the subgenus Coronatella (Coronatella) .

Limb IV ( Fig. 10G ). Preepipodite setulated; epipodite oval, with a process longer than epipodite itself. Exopodite rounded, with six setae. Seta 3 longest, setae 1 and 2 about 4/5 length of seta 3, seta 5 about 1/3 length of seta 3, setae 4 and 6 short. Setae 1–4 flattened, plumose, setae 5 and 6 slender, without setulae. Morphology of inner portion of the limb typical for the subgenus C. ( Coronatella ).

Limb V ( Fig. 10H ). Preepipodite setulated, epipodite oval, with a process 1.5 times longer than exopodite. Exopodite oval, slightly bilobed, with four plumose setae, evenly decreasing in size basally, seta 4 four times shorter than seta 1. Inner limb portion as broad rounded lobe, with setulated inner margin.At inner face, two short setae, one 1.5 times longer than another. Filter plate absent.

Ephippial female, male. Unknown.

Size. In studied material, juvenile female II length 0.19–0.21 mm, height 0.12–0.13 mm; adult parthenogenetic female length 0.24–0.31 mm, height 0.15–0.19 mm.

Differential diagnosis. Coronatella (C.) acuticostata belongs to the monacantha -clade of C. ( Coronatella ), and shares main character of the group, presence of denticles on posteroventral margin of valves ( Sinev 2020). Known species of the group include Neotropical C. (C.) monacantha (Sars, 1901) and C. (C.) undata Sousa, Elmoor-Loureiro & Santos, 2015 , and African C. (C.) hardingi (Brehm, 1957) . Coronatella (C.) acuticostata differs from both Neotropical species in a variable number of denticles on the posteroventral angle of valves – C. (C.) monacantha always has a single denticle, while C. (C.) undata always has two denticles spaced very close to each other (see Sousa et al. 2015). Coronatella (C.) hardingi (see Van Damme 2016) has uniformly convex, not wavy posterior margin of valves, shorter basal spine of postabdomen, and 1 or 2 narrower denticles on posteroventral angle of valves (if there are two denticles, they are spaced very close to each other), and longer antennal spines, spine of basal segment of exopodite reach to the middle of apical segment, and apical spines 1.5 times longer, than apical segments.

Taxonomic notes. Coronatella (Coronatella) acuticostata was described from Sumatra ( Sars 1903a) as Alona acuticostata . Later, Stingelin (1905) described Thailand populations with three denticles on the posteroventral angle of valves as a special variety, Alona acuticostata var. tridentata . During the XXth century, this taxon was accepted as a synonym of Alona monacantha Sars, 1901 ( Smirnov 1971; Idris 1983; Maiphae et al. 2008). However, recent studies of the monacantha -group ( Sinev 2004; Sousa et al. 2015; Van Damme 2016) led to a re-evaluation of the status of Neotropical and African species of this group. Our data fully confirms the independent status of C. (C.) acuticostata , suggested during previous studies of Indo-Malaysian fauna ( Sinev & Yusoff 2015; Sinev 2016).

Detailed morphological study of Coronatella (Coronatella) acuticostata is conducted for the first time. The species was described from Sumatra, so the studied populations are distributed quite close to the type locality. Our data confirm both an independent status of the species and its position within the monacantha -clade. The monacantha -group is distributed in Neotropical, Afrotropical and Indo-Malaysian Provinces. Recent revisions of the monacantha -group ( Sousa et al. 2015; Van Damme 2016) and our data once again fully confirm the “Frey’s non-cosmopolitanism paradigm” ( Frey 1982, 1987b) for Chydoridae . Taxonomic status of the monacantha -clade populations recorded from India and Sri Lanka is unclear at the moment, but they probably belong to Coronatella (Coronatella) acuticostata as well. Interestingly, the most widely distributed tropical Aloninae clades are also present in Australia, but not the monacantha -group ( Smirnov & Timms 1983). The only Australian species of C. ( Coronatella ) is C. (C.) novaezealandiae ( Sars, 1904) (Sinev 2022) .

Distribution and ecology. Coronatella acuticostata is a littoral species, associated with vegetation, distributed in Indo-Malaysian region. Our data suggests that all earlier records of Alona monacantha from South-East Asia (see Koronchinsky 2013) refer to С (С.) acuticostata . Taxonomic status of monacantha -group populations from India remains unclear, as the level of present descriptions is not sufficient to clarify the taxonomic status of local populations.

Figures

FIGURE 1. Simocephalus (Echinocaudus) exspinosus (De Geer, 1778) from pond at Permai Lake, Ipoh, Perak, Malaysia, parthenogenetic female. A, lateral view. B, postabdomen, С, postabdominal claw from outer side. D, basal portion of postabdominal claw from outer side. E, group of pigmented hypoderm cells on valves. Simocephalus (Simocephalus) mixtus Sars, 1903 pond at the Permai Lake, Ipoh, Perak, Malaysia, F, lateral view. G, head. H, posteroventral angle of valves. I, postabdomen. J, basal portion of postabdominal claw from outer side.

FIGURE 5. Acroperus africanus Neretina & Kotov, 2015 from Chini Lake, Pahang, Malaysia.A–D, parthenogenetic female.A, lateral view. B, posteroventral angle of valves. C, postabdomen. D, antenna. E–J, adult male. E, lateral view. F, postabdomen. G, antenna. H, antennule. I, ODL, copulatory hook and IDL of thoracic limb I. J, frontal side and endite 3 of thoracic limb I.

FIGURE 7. Coronatella (Coronatella) acuticostata (Sars, 1903) from roadside pond, Pahang, Malaysia. A. juvenile female of instar II. B, adult parthenogenetic female, lateral view. C, ventral margin of valves. D, postero-ventral angle of valves. E, head shield. F, head pores. G–I, labrum. J–K, postabdomen. L, postabdominal claw. M, antennule. N, antenna.

FIGURE 8. Coronatella (Coronatella) acuticostata (Sars, 1903) from roadside pond, Pahang, Malaysia, parthenogenetic female. A–C, lateral view, D–E, dorsal view. F, ventral view. G, postero-ventral portion of valves. H–I, postro-ventral angle of valves.

FIGURE 9. Coronatella (Coronatella) acuticostata (Sars, 1903) from a roadside pond, Pahang, Malaysia, parthenogenetic female. A, rostrum and labrum. B, head pores. C, labrum and thoracic limb I. D, frontal head pore (indicated by arrow). E–F, postabdomen. G, antenna.

FIGURE 10. Coronatella (Coronatella) acuticostata (Sars, 1903) from a roadside pond, Pahang, Malaysia, thoracic limbs of parthenogenetic female. A, limb I. B–C, IDL and ODL of limb I. D–E, inner and outer parts of limb II. F, exopodite of limb III. G, exopodite of limb IV. H, limb V (inner setae not shown). Karualona serrulata Van Damme, Maiphae & Sa-adrit, 2013 from from a lake at Paya Indah Wetland, Selangor, parthenogenetic female. I, lateral view. J, posteroventral angle of valves, K, labrum. L, postabdomen.