Ilyocryptus yooni, Jeong, Hyun Gi, Kotov, Alexey A. & Lee, Wonchoel, 2012

Jeong, Hyun Gi, Kotov, Alexey A. & Lee, Wonchoel, 2012, A new species of the genus Ilyocryptus Sars, 1862 (Cladocera: Anomopoda: Ilyocryptidae) from the East Asian Palaearctic, Zootaxa 3475, pp. 36-44 : 37-42

Ilyocryptus yooni sp. nov.

Ilyocryptus agilis Kurz in Yoon & Kim 1987, p. 195, Fig. 9d–g; Yoon 2010, p. 101–102, Fig. 51; Kotov et al. 2011, p. 405. Not Ilyocryptus agilis Kurz in Kim 1988, p. 58, Figs 45–46; Chen 1993, p. 9–10, Figs 1 –4.

Etymology. The species is dedicated to Dr. Seong Myeong Yoon, who was the senior author of the paper where this taxon was described and illustrated for the first time as I. agilis from Korea ( Yoon & Kim 1987).

Type locality. An un-named lake in Bak Sil Ji (= Paksil-chi) wetland near Hapcheon town, Gyeongsangnamdo, southern portion of Republic of Korea. Geographic coordinates: 35.5419ºN; 128.1209ºE. The type series was collected in 16.v.2010 by H.G. Jeong.

Type material. Holotype. Parthenogenetic female in 95% alcohol, NIBRIV0 0 0 0 247617 Paratypes. Five females from the type locality in 95% alcohol, NIBRIV0 0 0 0 247618.

Other material studied. 4 females from a small backwater in the mouth of Tom' River, Amur Area, Russia, coll. in 25.viii.2006 by N.G. Sheveleva, AAK 2009-001 (51.0356ºN; 127.8895ºE); 6 females from Lake Khanka, Primorski Territory, Russia, coll. in 11.07.1990 by E. I. Shornikov, AAK 1999-001 (44,8ºN; 132,6ºE); 2 female from Touro-ko (Lake), Hokkaido Island, Japan, coll. in 27.xi.2006 by S. Ishida, AAK M-0295 (43,1539ºN; 144,5080ºE).

Diagnosis. Parthenogenetic female. Body high, dorsum of valves moderately convex. Body moderately compressed laterally, with a relatively sharp dorsal keel. Moulting complete. Setae of postero-ventral portion of valves short. Each of seta on posterior margin with a thick basal part, armed with a single, stout, spine-like setule. Abdominal projection long. Postabdomen with anus opening somewhat closer to base than to distal extremity, few spinules on its internal wall. Preanal teeth single, no denticles or setae near them. Submarginal spines small, their row continues on the anal margin. Large lateral setae 8–9, relatively long, proximalmost one located on postanal margin, at a small distance from anus. Postabdominal claw with 6–8 denticles in its ventral distal portion, no additional denticles in medium part of claw. Distal spine on base of postabdominal claw longer and stouter than proximal one. Setules ventrally on claw basal border very short. Antenna I long, although shorter than in I. agilis . Distal segment with 6–8 transverse rows of minute denticles; no hillocks at its distal end. One among two longest aesthetascs located at a distance from the other aesthetascs. Antenna II relatively long for the genus. Distal burrowing spine not projected behind the distal end of basal segment. Apical swimming setae long, somewhat different in size, their distal segments unilaterally armed by minute setules. Proximal and distal lateral swimming setae of similar size, both armed analogously with apical setae, with minute hooks at their tips. Apical spines with similar size in the apical segments, spine on basal segment of exopod as long or shorter than the second segment. Limb I with outer distal lobe bearing a large seta and a small seta, the latter as long as this lobe. No seta near ejector hooks. Gnathobase I completely absent. Beating seta on limb II with short setules. Naked beating seta on limb III. Four setae on inner-distal margin of limb IV of different size and armature, sensillum near base of basalmost member of this row short and straight. Filter plate V with 4 setae. Limb VI with six bunches of long, robust setules. Size up to 1.09 mm. Male and ephippial female unknown.

Description. Parthenogenetic female. Body transparent, widely-triangular in lateral view, specially high for the genus (body height/body length about 0.9–1.0 in adults) ( Fig. 1 A). Dorsal margin with distinct cervical incision, dorsum of valves more convex than in I. agilis , postero-dorsal angle distinct, posterior margin straight to concave.

In anterior view ( Fig. 1 B), body moderately thick (body width/body length about 0.5); in contrast to more compressed body of I. agilis (see Kotov, 1999), maximum width of body in the dorsal portion of valves, medial dorsal keel low, relatively sharp.

Head in lateral view with ventral margin generally straight, but with a slight prominence (basis for antennae I) in posterior head part ( Fig. 1 C). Head shield subovoid in dorsal view, with prominent fornices, dorsal head pore not found. Compound eye about 0.05 mm; ocellus irregular in shape, with diameter about than half of eye diameter, located closely to bases on antenna I.

Labrum wide, with lateral projections in its middle portion on each side; in posterior (distal) portion, rows of setules on each side. In lateral view, labrum robust, rectangular; with a shallow projection at its postero-ventral angles. Distal labral plate large, boot-shaped ( Fig. 1 C).

Valves large with distinct polygonal reticulation ( Fig. 1 E). Moulting complete. Numerous marginal seta (about 50 in adults). Four anteriormost setae short, relatively sparsely and finely setulated ( Fig.1 A), posterior to these setae, a bunch of closely located long setae, each with slightly inflated base; next setae plumose, regularly distributed along ventral margin ( Fig.1 E). Setae at postero-ventral region and posterior margin relatively short (in contrast to I. agilis ), each with a thick proximal portion armed with a single spine-like setule, and slender distal portion armed with fine setules ( Fig. 1 F).

Abdomen long, with relatively long abdominal projection on the first segment ( Fig. 2 A–B). Dorsal surface of all segments with several transverse rows of setules.

Postabdomen large, high for the genus (postabdomen height/postabdomen length about 0.5), with maximal height in basal region of postanal part ( Fig. 2 A–B). Dorsal margin with distinct anal depression; anus opening somewhat closer to base than to distal extremity due to this preanal margin short (preanal margin length/ postabdomen length about 0.4), slightly convex, with a small base of postabdominal setae posteriorly and a series of 7–9 regularly spaced preanal teeth, which are non-duplicated. The basalmost tooth located closely to base of postabdominal setae. No spinules or denticles near preanal teeth. An oblique row of denticles on lateral faces of postabdomen basally. Anus small, with short denticles on internal wall near the opening ( Fig. 2 C). On each side of distal (anal plus postanal) portion of postabdomen, a row of 12–14 short submarginal spines continues to anal margin, and a row of 8–9 large lateral setae which are noticeably longer than the spines. There is a small gap between basalmost seta and anus. Near claw base, a group of medium-sized lateral setae, and series of rudimentary lateral setae ( Fig. 2 D). Row of fine setules at bases of large, middle-sized and rudimentary lateral setae.

Postabdominal claw relatively short for the genus (claw length/postabdomen length about 0.46), slightly bent in distal half. On outer side, two successive series of thin setules along the dorsal margin and an oblique, short series, at base of claw. About 6–8 additional denticles in distal portion along ventral side; no additional denticles in medium part of claw. A group of short setules immediately on claw base ventrally ( Fig. 2 D–E). Two relatively large spines (so-called basal spines) on base of each claw, distal one longer than basal one. Postabdominal seta markedly shorter than body, but longer than postabdomen; its distal segment regularly feathered by relatively long hairs ( Fig. 2 A).

Antenna I two-segmented, long (antenna I length/body length about 0.3–0.4) but shorter than that in I. agilis ; straight in dorso-ventral plane ( Fig. 1 C). Proximal segment short, with well-developed hillocks and a finger-like projection on anterior face. Distal segment elongated, somewhat extended in the middle part, with 6–8 incisions bearing transverse rows of denticles. Distal end of antenna I truncated, without hillocks, bearing nine aesthetascs, two of them remarkable longer that that the rest; one of them located at a short distance from rest; length of largest aesthetascs more than half the distal segment.

Antenna II ( Fig. 2 F) long for the genus (antenna II length/body length about 0.5); coxal part with two short setulated sensory setae ( Fig. 2 F). Basal segment with distal sensory seta and distal burrowing spine sub equal in size ( Fig. 2 F), the spine reaching distal end of basal segment. Antennal branches elongated, on all segments there are well-developed denticles around distal segment ends, and rows of few similar denticles in middle part; exopod longer than endopod. Swimming setae 0-0-0-3/1-1-3, spines 0-1-0-1/0-0-1. Apical swimming setae long (longest seta length/body length about 0.6), somewhat different in size; their distal segments unilaterally setulated with minute setules. Proximal and distal lateral swimming setae of similar size, both armed analogously with apical setae, with minute hooks at their tips. Apical spines with similar size in the apical segments, spine on basal segment of exopod as long or shorter than the second segment.

Limb I ( Fig. 3 A–B). Cylindrical outer distal lobe bears a large seta, unilaterally setulated in basal portion, and bilaterally feathered in distal part (in contrast to I. agilis , see Kotov, 1999), and a second seta which is small (as long as the lobe). A long, bilaterally feathered seta near base of outer distal lobe ( Fig. 3 A, arrow). Two ejector hooks of similar size, no other setae in this region, as in some other species ( Kotov & Štifter 2006). On the inner margin of limb I, there are four large, differently armed setae of different size, and a small rudimentary one. A large receptor ( Fig. 3 B, arrow) between bases of two ventralmost setae; a very small receptor midway between the ejector hooks and ventralmost large seta. No remainder of gnathobase I on limb base.

Limb II ( Fig. 3 C–E). Sub-quadrangular distal lobe bears two long setae of similar size, bilaterally setulated from base to top, a small bud-like element, and two groups of setules on its outer surface. Along inner margin of limb, four bilaterally setulated setae with size somewhat decreasing towards the gnathobase with small receptors near second and third setae of this row ( Fig. 3 C, arrows). Inner portion of limb strongly projected and somewhat inflated; a curved sensillum at the base of this projection. A single bisegmented beating seta armed with short setules in distal part near gnathobase ( Fig. 3 D, arrow). Distal armature of gnathobase with four closely located setae ( Fig. 3 D–E); filter plate with eight short, bisegmented setae.

Limb III ( Fig. 3 F–G). Exopodite with five terminal (armed in a different manner), and three lateral setae. Distal endite with two relatively short feathered setae of different length distally ( Fig. 3 F, arrows); three large setae of different size, bilaterally setulated from base to top, with small receptors near first and second seta ( Fig. 3 G, arrows). Basal endite anteriorly with a row of four soft setae ( Fig. 3 G), more posteriorly with a curved sensillum near border with distal endite, and a single naked beating seta near gnathobase. Four setae in the distal armature of gnathobase. Filter plate with 8 setae.

Limb IV ( Fig. 3 H). Large subovoid exopodite with 8 feathered setae as in I. agilis (not illustrated here). Innerdistal portion of limb forms a flat lobe; near base of flap, two groups of two thin setae, somewhat differently armed ( Fig. 3 H, arrows) (in contrast to I. agilis with uniform armature of these setae); a relatively short, straight sensillum near base of basalmost member of this group. At external side, there are five long setae, bilaterally feathered from base to top. Distal armature of gnathobase with four setae, filter plate with 8 setae, no distinct border between filter plate and row of setae of inner limb face.

Limb VI ( Fig. 3 I). Small triangular plate with inner margin bearing six bunches of few, relatively robust setules, 2–3 setules in each bunch.

Ephippial female, adult male. Unknown

Size. Holotype 0.82 mm, parthenogenetic females 0.59–1.09 mm.

Differential diagnosis. Among the agilis -like species sensu Kotov & Elías-Gutiérrez (2009), I. yooni sp.nov. is unique in absence of any setules or denticles near preanal teeth. It also differs from its closest relative I. agilis Kurz, 1878 in (1) a more sharp dorsal keel; (2) short setae at postero-ventral portion of valve; (3) a long abdominal projection; (4) presence of spinules on internal wall of anus; (5) a shorter antenna I; (6) distal burrowing spine not projected behind distal end on basal segment of antenna II; (7) spine on proximal segment of antennal exopod not longer than the next segment; (8) setae at base of the flap at inner-distal portion of limb III of different size and armature.

Comments. Previously Harada (1943) and Chiag & Du (1979) illustrated an agilis -like taxon, but their drawings and description are not detailed enough for any taxonomic conclusions. No I. agilis- like populations were known from Japan ( Tanaka 2001; Kotov & Štifter 2006).

I. agilis from Korea in Kim (1988) is in reality I. spinifer Herrick, 1882 (even Kim 1988 correctly represented the head with traces of incomplete moulting, which is characteristic for I. spinifer , not for I. agilis ). Chen (1993) apparently illustrated just I. agilis s.str., not I. yooni sp. nov., from China. Therefore, both species are present in China, where their exact distribution is unknown.

Distribution. Ilyocryptus yooni sp. nov. is found to date in South Korea, the Far East of Russia, and Japan. It will be apparently found in North Korea and NE China after accurate studies of these regions. The southernmost border of its distribution is unclear.

Ecology. Among four water bodies where the species was found, three are large, permanent lakes having broad, shallow water zones with well-developed littoral vegetation, where I. yooni sp.nov. probably is quite common. In Bak Sil Ji and Khanka Lake these areas were covered by submerged leaves of the water caltrop Trapa sp. But the species was found also in a backwater of small river, so it seems to be distributed in a wide range of permanent water bodies.

The type locality is the richest of species among all water bodies studied in South Korea by Kotov et al. (2012), where 26 other species were found on the same date (listed alphabetically): (1) Alona costata Sars, 1862 ; (2) A. guttata Sars, 1862 ; (3) Bosmina longirostris (O.F. Müller, 1776) ; (4) Ceriodaphnia cornuta Sars, 1885 ; (5) C. cf. pulchella Sars, 1862 ; (6) Chydorus irinae Smirnov & Sheveleva, 2010 ; (7) C. cf. sphaericus (O.F. Müller, 1776) ; (8) Coronatella cf. rectangula (Sars, 1862) ; (9) Daphnia galeata Sars, 1864 ; (10) D. pulex (De Geer, 1778) ; (11) Diaphanosoma macrophtalma Korovchinsky & Mirabdullaev, 1995 ; (12) Disparalona cf. hamata Birge, 1879 ; (13) D. ikarus Kotov & Sinev, 2011 ; (14) Ilyocryptus cuneatus Štifter, 1988 ; (15) I. cf. raridentatus Smirnov, 1989 ; (16) I. spinifer Herrick, 1882 ; (17) Macrothrix pennigera Shen Chia-Jui, Sung Ta-hsiang & Chen Kou-hsiao, 1961; (18) Moina weismanni Ishikawa, 1896 ; (19) Nedorchynchotalona chiangi Kotov & Sinev, 2011 ; (20) Picripleuroxus cf. laevis (Sars, 1862) ; (21) P. cf. denticulatus (Birge, 1879) ; (22) Pseudochydorus cf. globosus (Baird, 1843) ; (23) Scapholeberis cf. kingi Sars, 1903 ; (24) Simocephalus cf. congener (Koch, 1841) ; (25) S. mixtus Sars, 1903 ; (26) S. serrulatus (Koch, 1841) . Note that taxa 6, 11, 13, 17, 19 are members of the Far East endemic complex revealed recently by Kotov et al. (2011, 2012).

Figures

FIGURE 1. Adult parthenogenetic female of Ilyocryptus yooni sp. nov. from an un-named lake in Bak Sil Ji, Republic of Korea, holotype (A – B, E – F) and paratype (C – D). A, lateral view. B, anterior view. C, head, lateral view. D, head shield, dorsal view. E – F, setae at postero-ventral portion of valve. Scale bars 0.1 mm.

FIGURE 2. Adult parthenogenetic female of Ilyocryptus yooni sp. nov. from an un-named lake in Bak Sil Ji, Republic of Korea, paratype. A – B, abdomen and postabdomen. C, anus, inner view. D, distalmost portion of postabdomen with postabdominal claw, lateral view. E, basal portion of postabdominal claws, ventral view. F, antenna II, anterior view. G, tip of lateral setae on antenna II. Scale bars 0.1 mm.

FIGURE 3. Thoracic limbs of adult parthenogenetic female of Ilyocryptus yooni sp. nov. from an un-named lake in Bak Sil Ji, Republic of Korea. A – B, limb I. C, limb II. D, gnathobase of limb II. E, distal armature of gnathobase of limb II. F, limb III. G, inner portion of limb III. H, inner portion of limb IV. I, limb VI.. Scale bars 0.1 mm.