Coronatella (Coronatella) jejuana, Sinev & Lee & Kotov, 2022

Sinev, Artem Y., Lee, Wonchoel & Kotov, Alexey A., 2022, A new species of Coronatella Dybowski & Grochowski, 1984 (Cladocera: Chydoridae) endemic to Jeju Island (Republic of Korea), Zootaxa 5159 (4), pp. 571-582 : 572-578

Coronatella (Coronatella) jejuana sp. nov.

Kotov et al. 2017: 242–243, Fig. 10 ( Coronatella trachystriata )

Etymology. The taxon is named after its type locality, Jeju Island.

Type locality. Sangdoekcheon Gyocharo , a small pond with Utricularia sp. (33.48265 N, 126.7456 E), Jeju-do, Republic of Korea. The type series was collected on 13.02.2012 by H.G. Jeong .

Holotype. A parthenogenetic female from type locality, MGU Ml 245 .

Paratypes. All samples are from Jeju-do. Two parthenogenetic females from Yongsuji Reservoir ( N 33,317 52, E 126,1892), coll. on 15.02.2012 by H.G. Jeong, NIBRIV 0000812490; 12 parthenogenetic females from type locality, MGU Ml 246; 10 parthenogenetic females a pond in Dream forest 1 ( N 33,487 19, E 126,7031), 12.06.2018, coll. A.A. Kotov, H.M. Yang & C.W. Lee AAK M-4155; 7 parthenogenetic females from Yongsuji Reservoir ( N 33,317 52, E 126,1892), 15.02.2012, coll. H.G. Jeong, AAK M 2368, 2369 .

Description. Parthenogenetic female. In lateral view, body ovoid, compressed laterally, low in juveniles ( Fig. 1A ), moderately low in adults ( Figs. 1B , 2A–E ). Maximum height at middle of body, height-length ratio about 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 ( Fig. 1C ) with 30–40 setae. About 10 anterior setae longer than others. Postero-ventral angle ( Fig. 1D ) with over 60 setules not organized into groups. Valves with a sculpture of sparsely spaced longitudinal lines, but in some specimens antero-dorsal portion of valves oblique.

Head relatively small, triangular-rounded in lateral view, rostrum short, pointing downward. Compound eye larger than ocellus. Distance from tip of rostrum to ocellus 1.5 times greater than that between ocellus and eye.

Head shield with maximum width behind mandibular articulation, oblique ( Fig. 2F ). Head shield with a short, broadly rounded rostrum and broadly rounded posterior margin ( Figs. 1E–F ). Three narrowly connected major head pores ( Figs. 1E–F , 2G–H ); middle pore smaller than others, located medially between the others. PP about 0.5–0.7 IP. Lateral head pores located at less 1 IP distance from midline, at the level of middle major head pore.

Labrum relatively large ( Fig. 1G ). Labral keel of moderate width (height/width ratio about 1.5), with a rounded apex. Anterior margin of keel convex; posterior margin without clusters of setules.

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

Postabdomen ( Fig. 1H ) relatively short, moderately wide, with almost parallel dorsal and ventral margins in postanal portion. Length about two heights. Ventral margin almost straight to very slightly convex. Distal margin convex, distal angle broadly rounded. 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, postanal angle smooth. Postanal margin with 5–6 clusters of 2–6 small sharp denticles; length of longest denticles slightly smaller than the diameter of postabdominal claw at its base. Postanal portion with 4–5 broad lateral fascicles of setules; posteriormost setule of each fascicle as thin as other, two times longer than neighbouring marginal denticles. Postabdominal claw of moderate length, shorter than preanal margin of postabdomen. Basal spine of moderate length, slender, about 0.2 length of the claw, a group of thin setules near it.

Antennule ( Fig. 1I ) comparatively large, its tip almost reaching tip of rostrum, with two clusters of long setules at anterior face. Length/width ratio about 2.5. Antennular sensory seta slender, two times shorter than antennule, arising at about 2/3 distance from the base. Nine aesthetascs, three longest about 2/3 length of antennule.

Antenna s hort ( Figs. 1J–K , 3A–B ). Antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Basal segment robust, branches short and stout. Coxal portion with two short setae. Basal segments of both branches almost two times longer than middle and apical segments. Seta arising from basal segment of endopod thin, reaching end of the latter. Seta arising from middle segment of endopod shorter than apical setae. Both apical segments with three setae of similar thickness. Spine on basal segment of exopod extremely long, 1.5 times longer than middle segment. Spines from apical segments extremely long, 1.5 times longer than apical segments.

Thoracic limbs: five pairs.

Limb I ( Figs. 4A, B ) of moderate size. Epipodite oval, with a finger-like process longer than epipodite itself.Accessory seta short, about 1/3 length of ODL seta; IDL with two setae, seta 1 absent. Seta 3 as long as ODL seta; seta 2 slightly shorter than seta 2. Setae 2 armed with robust spinules of similar size; seta 3 with well-developed spine at the middle, its size varies, distal portion of seta 3 always longer than the spine. Endite 3 with four setae; inner seta (1) much shorter than other setae (a–c). Endite 2 with seta d as long as setae a-c of endite 3, seta e very long, as long as limb itself, seta f about 2/3 length of seta e. Endite 1 with two distally setulated 2-segmented setae (g–h) and a long flat seta (i) as long as setae a-d. No naked 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 unequal size. Maxillar process with a single seta.

Limb II ( Figs. 4C–D ). Exopodite elongated, with a single seta as long as exopodite. Eight scraping spines armed with thin setules: scrapers 1–5 long, of similar thickness, increasing in length distally; scrapers 6-8 short, of similar size. Small sensillum located near the base of scraper 1. Distal armature of gnathobase with four setae. Filter plate with seven setae, two posteriormost setae considerably shorter than others.

Limb III ( Figs. 4E–G ). Epipodite oval, without a process. Exopodite subrectangular, with six setae. Seta 3 being longest, seta 5 about 1/3 length of seta 3, seta 1 about 1/5 length of seta 3, other setae very short. Setae 1–4 plumose, seta 5 armed with thick setules in distal portion, seta 6 naked. Distal endite with three setae, two distalmost setae (1– 2) slender, sharp, of similar length, with long denticles in distal part; basalmost seta (3) two times shorter, flattened and setulated. Basal endite with four outer setae (a–d) slightly increasing in length basally. Gnathobase not clearly separated from basal endite. Four inner setae (4–7) slightly increasing in size basally; a sensillum near the base of distalmost seta. Distal armature of gnathobase with four elements; the first one an elongated, cylindrical sensillum; the second a geniculated seta; two others are short spines with fused bases. Filter plate with seven setae.

Limb IV ( Figs. 4H–J ). Preepipodite setulated; epipodite oval, with short process. Exopodite rounded, with six setae. Seta 3 longest; setae 1 and 2 about 4/5 length of seta 3; seta 5 about 2/3 length of seta 3; setae 4 and 6 short. Setae 1–4 flattened, plumose; setae 5 and 6 slender, with short setules in distal portion. Inner lobe of limb IV with four setae ( Figs. 4I, J ). Scraping seta (1) slender, sharp; distalmost flaming-torch seta (2) large, with broad basal portion, armed with 7–8 thick long setulae; two other flaming-torch setae (3–4) much smaller, with narrow basal portion, armed with thin short setulae. Sensillum of irregular shape. Three outer setae (a–c) slightly increasing in size basally. Gnathobase with a short 2-segmented seta, and a small hillock distally. Filter plate with five setae.

Limb V ( Figs. 4K–L ). Preepipodite setulated, epipodite oval, 1.5 times shorter than exopodite. Exopodite oval, not divided into two lobes, with four plumose setae, evenly decreasing in size basally; seta 4 three 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, and large cylindrical sensilla, as long as shorter seta. Filter plate absent.

Ephippial female, male. Unknown.

Size. Juvenile female II length 0.34–0.36 mm, height 0.19–0.2 mm; adult parthenogentic female length 0.39– 0.44 mm, height 0.22–0.25 mm.

Differential diagnosis. Coronatella (Coronatella) jejuana sp. nov. shares main diagnostic characters of the subgenus C. ( Coronatella ), including: (1) small body size; (2) a short and thin seta on basal segment of the antennal endopod; (3) a short accessory seta of limb I; (4) exopod II bearing a long seta (see Sinev 2020). C. (C.) rectangula (Sars, 1862) , is also present in Jeju Island, but it has (1) a slightly higher body ( Fig. 1L ); (2) thinner connections between major head pores ( Fig. 1M ); (3) postabdomen with several distal marginal denticles being composite and lateral groups of setules with distalmost setulae much thicker than other ( Fig. 1N ); (4) postabdominal claw with a longer and more slender basal spine; (5) a shorter spine on proximal segment of the antennal exopod ( Fig. 1O ); and (6) seta 2 of IDL armed with two large spines ( Fig. 4N ). C. (C.) jejuana sp. nov. differs from another East Asian endemic species, C. (C.) trachystriata (see Kotov et al. 2011), in (1) presence of a seta on proximal segment of the antennal endopod, (2) a short, not truncated rostrum, and (3) presence of a strong spine on IDL seta 3 of limb I.

In morphology of IDL setae, C. (C.) jejuana sp. nov. is similar to C. (C.) cf. bukobensis (Weltner, 1897) , C. (C.) begoniae ( Sinev & López-Blanco, 2018) and C. (C.) novae-zealandiae (Sars, 1904) (see Sinev & López-Blanco 2018; Sinev 2020, 2022) but clearly differs from them in a very long spine on the proximal segment of the antennal exopod. C. (C.) jejuana sp. nov. differs from species of the acuticostata -group (Oriental C. (C.) acuticostata (Sars, 1903) , African C. (C.) hardingi (Brehm, 1957) , Neotropical C. (C.) monacantha (Sars, 1901) and C. (C.) undata Sousa, Elmoor-Loureiro & Santos, 2015 (see Sousa et al. 2015; Van Damme 2016; Sinev 2016) in absence of denticles on posteroventral margin of valves, and from species of the circumfimbriata -group (North American C. (C.) circumfimbriata (Megard, 1967) and South American C. (C.) serratalhadensis Sousa, Elmoor-Loureiro & Santos, 2015 (see Sinev 2009b; Sousa et al. 2015) in non-differentiated spinules on posteroventral corner of valves. C. (C.) jejuana sp. nov. differs from South American C. (C.) poppei (Richard, 1897) and C. (C.) paulinae Sousa, ElmoorLoureiro & Santos, 2015 (see Sousa et al. 2015) in a very long spine on proximal segment of the antennal exopod and in presence of a strong spine on IDL seta 3, and from African C. (C.) holdeni (Green, 1952) (see Van Damme & Dumont 2008) in a shorter spine on proximal segment of the antennal exopod (in the latter it is extremely thick and reaching the end of apical segment).

Distribution. To date this species is known from Jeju Island only where it is found in two relatively large reservoirs and two small ponds. Coronatella (C.) jejuana sp. nov. was found mainly in the winter samples, while absent in numerous samples taken during and after the monsoon time.

Figures

FIGURE 1. Coronatella (Coronatella) jejuana sp. nov. from Sangdoekcheon Gyocharo (type locality), Jeju-do, Republic of Korea, parthenogenetic females. A, juvenile female of instar II, lateral view. B, adult, lateral view. C, ventral margin of valves. D, posteroventral angle of valves. E–F, head pores. G, labrum. H, postabdomen. I, antennule. J, antenna. K, antennal exopod, setae not shown. C. (C.) rectangula from a small pond near Jungsanganseo-ro, Jeju-do, Republic of Korea. L, adult, lateral view. M, head pores. N, postabdomen. O, antennal exopod, setae not shown.

FIGURE 2. Coronatella (Coronatella) jejuana sp. nov. from Sangdoekcheon Gyocharo (type locality), Jeju-do, Republic of Korea, parthenogenetic females. A–B, lateral view. C, anterolateral view. D, ventral view. E, dorsal view. F, head shield. G–H, head pores.

FIGURE 3. Coronatella (Coronatella) jejuana sp. nov. from Sangdoekcheon Gyocharo (type locality), Jeju-do, Republic of Korea, parthenogenetic females. A, antenna. B, labral keel.

FIGURE 4. Coronatella (Coronatella) jejuana sp. nov. from Sangdoekcheon Gyocharo (type locality), Jeju-do, Republic of Korea, parthenogenetic females. Parthenogenetic female, thoracic limbs. A, limb I. B, IDL and ODL of limb I. C–D, outer and inner portions of limb II. E, exopodite of limb III. F–G, inner portion of limb III. H, exopodite of limb IV. I–J, inner portion of limb IV. K, exopodite of limb V. L, inner lobe of limb V. Coronatella (Coronatella) jejuana sp. nov. from Yongsuji Reservoir, Jeju-do, Republic of Korea, parthenogenetic female. M, IDL and ODL of limb I. Coronatella (Coronatella) rectangula (Sars, 1862) from a small pond near Jungsanganseo-ro, Jeju-do, Republic of Korea, parthenogenetic female. N, IDL and ODL of limb I.