Ilyocryptus raridentatus Smirnov 1989
Creators: name: Dadykin, Ivan A.
name: Ð ịnh, Cù Nguyên
name: Shiel, Russell J.
name: Kotov, Alexey A.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Branchiopoda
Diplostraca
Ilyocryptidae
Ilyocryptus
Ilyocryptus raridentatus

description: Ilyocryptus raridentatus Smirnov, 1989
(Figs. 1–7)
Synonymy. Smirnov 1989: 58, pl. 4, figs 1–6 (Ilyocryptus raridentatus); Kotov & Štifter 2006: 117–118, fig. 58 (Ilyocryptus raridentatus); 123 (Ilyocryptus cf. sarsi); Kotov et al. 2011a: 135–136, Fig. 33 (Ilyocryptus cf. raridentatus); Kotov et al. 2012: 63–64 (Ilyocryptus cf. raridentatus); Korovchinsky & Kotov 2021: 201–202, fig. 60 (Ilyocryptus cf. raridentatus); Dadykin et al. 2023: 11, 13, fig. 6A–D (Ilyocryptus cf. raridentatus).
Holotype. Parthenogenetic female, AM P37010, Australian Museum, Sydney, Australia.
Type locality. An unnamed swamp near Yarragooly Claypan, via Derby, Western Australia, Australia (17.37°S, 123.75°E).
Material examined here. See a short summary of the material from Australia, Vietnam Thailand, China, Japan, South Korea, Far East of Russia in the Table 1, full information is given at Open Science Framework portal (DOI 10.17605/OSF.IO/GD9JK).
Diagnosis. Adult parthenogenetic female. Body small (length 0.40–0.60 mm), ovoid, relatively high (height 0.33–0.55 mm), very slightly compressed laterally. Dorsal margin slightly convex, with a shallow depression between head and valves. Postero-dorsal angle rounded, dorsal keel rudimentary. Moulting incomplete, valves with a hexagonal reticulation. Head relatively large, with prominent fornices; head shield rounded or slightly angulate anteriorly, reticulated. Dorsal head pore split-like, located in a low transverse projection. Valves with 48–60 setae along ventral and posterior margins; anterior four setae short, the next 20–21 setae long, densely feathered, setae of posterior margin with a single spine-like basalmost setule and very thin distal setulae. Abdominal projection relatively short, acute apically. Postabdomen large, with a maximum height in its medial part; anus located in the medial part of the postabdomen, distinct anal notch. Preanal portion shorter than postanal portion; preanal margin with 5–8 (most usually, 6–7) large teeth of similar length and thickness, oriented perpendicularly to postanal margin, teeth at proximal margin portion located usually more sparsely as compared to more distal teeth; groups of small spinulae near their bases. Anal margin with a row of thick spinulae near anus. Postanal margin with 11–13 paired spines continuing along anal margin and 5–7 lateral setae, which are slightly longer than marginal spines; the basalmost seta is relatively close to anal portion. Postabdominal claw relatively short and thick, with two basal spines of similar length and thickness. Ventral claw margin with a group of 3–4 short denticles in its distal half. Setulae ventrally at base of postabdominal claw relatively long, the largest one as long as the width of the claw base or slightly longer. Ventral margin of postanal portion with a row of 6–8 short setulae, continuing towards the claw base. Postabdominal setae long. Antenna I relatively short, bisegmented; proximal segment with two blunt spines distally, distal segment smooth. A group of nine aesthetascs situated apically, two of them are 1.5 times longer and thicker than the rest; large aesthetascs equal or subequal in their length, twice shorter than distal antennule segment. Antenna II relatively short. Distal burrowing spine short, distal sensory seta relatively long. Apical spines of exopod and endopod of similar size. All three apical swimming setae on both branches of different length and thickness; lateral seta of endopod segment 1 shorter and thinner than that of segment 2. All swimming setae unilaterally armed with short setulae of similar size. Limb I lacking a large seta near base of ejector hooks. P6 subtriangular, with obscure groups of long setulae.
Ephippial female. Body length is about 0.42 mm, body height is about 0.39 mm. Dorsal margin hump-like, a depression between head and valves well expressed. Valves ornamented with stump-like tubercles, ephippium with 1 resting egg parallel to longitudinal body axis.
Redescription. Adult parthenogenetic female. General morphology. Body ovoid in both juveniles and adults (Figs. 1A, 4A), high (BH/BL=0.75–0.85), with a maximum height in middle of carapace. Body slightly laterally compressed (BW/BH=0.65–0.75), with a maximum width at dorsal portion of carapace, median dorsal keel rudimentary (Figs. 1B, 4B). Dorsal margin with a shallow depression between head and valves. Postero-dorsal angle smooth. Moulting incomplete, valves and head with uniform hexagonal reticulation. In live individuals, carapace usually covered with detritus particles.
Head relatively large (HL/ BL =0.27–0.35), wide (HW / BW =0.56–0.61) with prominent triangular-rounded fornices, headshield wide (HW /HL=0.92–0.97), triangular-ovoid to almost rounded in dorsal view (Figs. 2A–D, 5A). Dorsal margin slightly convex, ventral margin almost straight; antenna I base at low prominence (Figs. 1D, 4D). A single split-like dorsal head pore, situated on top of a low transverse projection (Figs. 2C, 5B). Head shield with distinct concentric lines (Figs. 2A–B, D; Fig. 5A, arrows) and hexagonal reticulation (Fig. 2C), a semilunar arch visible in anteriormost portion of the head in some specimens (Fig. 2D, arrow). Compound eye relatively large (0.020 –0.028 mm in large females), situated in the middle of distance between tip of the head and antenna I base. Ocellus small, situated near base of antenna I (Figs. 1A, 4A).
Labrum wide, subrectangular in ventral view, with prominent lateral bulges, separated by a fold from head ventral margin; labral keel very low, almost straight, with a slightly prominent to smooth antero-dorsal angle (Figs. 1D, 4D). Distal labral plate rounded, smooth.
Valves relatively large (VL/BL=0.65–0.73), ovoid. Dorsal margin of valves smooth, slightly convex, not forming large brooding chamber (Figs. 1A, 4A). Both postero-ventral and antero-ventral angles smooth. Valve surface with distinct polygonal reticulation, not reaching the valve margin. Free margin with a row of multiple (up to 60) setae: four anterior setae short, armed with thin setulae; next 20–21 setae long, equal in size, densely feathered; setae of posterior margin with a single thick spine-like setule (very rarely two setules), a fine basalmost setule and very thin distal setulae (Figs. 1C, 4C); length of posterior setae gradually decreases towards dorsal direction.
Thorax lacks a segmentation, bears six pairs of differentiated limbs.
Abdomen shorter than thorax and postabdomen, with a single process at its anterior part that is relatively short for representative of the genus (APL/APW=2.2–2.4), triangular, acute, slightly curved anteriorly (Fig. 4E). Dorsal surface of both abdomen and abdominal process bears transverse rows of long setulae decreasing in size towards process tip. Rows of short dense setulae laterally continue rows of long setulae at posterior abdomen margin.
Postabdomen large (PL/BL=0.45–0.55), laterally compressed, semi-circular in lateral view, with a maximum height in distal part of preanal margin or proximal part of postanal margin (Figs. 1E, 4E). Preanal margin shorter than postanal margin, slightly arched, armed with a row of 5–8 (usually 6–7) teeth (Figs. 1E, 4E, arrows), oriented perpendicularly to the preanal margin; teeth almost equal in size (Fig. 4E) or slightly decreasing distally (Fig. 1E). Usually preanal teeth somewhat sparsely located in proximal portion of preanal margin as compared to its distal portion. The distal most tooth situated at edge of anal margin, usually it is strongly reduced. Rarely, preanal teeth surrounded with concentric rows of thin setulae. Rows of short spinulae near base of preanal teeth. Few clusters of 4–6 spinulae at lateral surface of preanal portion.
Anal depression distinct. Anus with a row of 9–11 thick spinulae on its internal wall; size of these spinulae might vary between individuals (Figs. 1G, 4G, H, see also Fig. 7); also, 2–3 postanal lateral teeth opposite to anal opening, one-two anterior teeth situated in the center of anal margin varying in their length; the posterior one located at the posterior edge of the anal margin and usually has a length similar to that of the next tooth in the row.
Postanal portion 1.5 times longer than preanal portion, postanal margin evenly arched, with a paired row of 9–13 marginal teeth continuing on anal margin; they gradually increase in length towards posterior end, but the posteriormost tooth usually short and closely located to penultimate one. A row of 5–7 spaced lateral setae along the lateral surface of postanal portion; each seta slightly longer than neighboring marginal tooth but their thickness similar to the latter; base of each seta inflated.The proximalmost seta usually situated posteriorly to anus opening, not reaching anal margin (Figs. 1E, 4E). A cluster of long setulae at base of each lateral seta. Distal part of postabdomen with highly variable armature; usually, this region bears two rows of 6–11 thick spinulae near claw base and 2–3 rudimentary lateral setae situated more basally; also, 2–3 transverse rows of short setulae located anteriorly to claw base (Figs. 1F, 7A, C, F, H, J). Setae ventrally at base of postabdominal claw relatively long (VSL/CW=1.0–1.3), thin; a series of 6–8 short setulae along ventral margin of the postabdomen.
Postabdominal claw relatively short (CL/PL=0.42–0.51), slightly bent distally (Figs. 1E, 4E). Three pectens of thin setulae along lateral side of claw: the proximal pecten short, close to basal spines; the medial one reaches a third of claw length; the distal one continues towards distal end of claw. A series of 3–4 spines ventrally at distal part of claw. Basal spines long (BSL/CL=0.32–0.35), subequal in length.
Postabdominal seta long (PSL/PL=1.23–1.25), bisegmented, distal segment somewhat shorter than proximal one (DL/PRL=0.67–0.90); proximal segment naked; distal segment feathered with long setulae (Fig. 1E).
Antenna I bisegmented, relatively short (AL/BL=0.16–0.18). Proximal segment large (PRL/AL=0.20–0.24), cylindrical; anterior surface bears two blunt spines subapically (Figs. 2E, F, 5D). Distal segment with a maximum width in its medial part, without spinules or setulae. Distal segment with nine terminal aesthetascs (Figs. 2E, F, 5D, E). Two aesthetascs are much longer and thicker than the rest (0.5–0.6 of distal segment length); largest aesthetascs equal or subequal in length (L1/L2=0.8–1.0).
Antenna II relatively short, stout (ANL/BL=0.42–0.48); coxa folded, inner surface with transverse rows of long setulae and few series of denticles (Figs. 2G, 5F); outer surface armed with rows of denticles (Figs. 2H, 5G); two sensory setae, first one 1.5–2 times longer than other, both setae feathered. No projection at base of sensory setae. Basal segment as long as endopod; outer surface of basal segment bears few rows of denticles. Distal sensory seta relatively long, located on inner surface of basal segment (Figs. 2G, 5F). Distal burrowing spine relatively long, setulated, located on outer surface of basal segment, far from its distal extremity.
Antennal branches short, a distal end of each segment armed with a row of denticles; also, transverse rows of denticles present in outer surface of both branches (Figs. 2G, 5F). Endopod 3-segmented (EN/ANL=0.31–0.35). Proximal segments short, distal segment elongate. Exopod 4-segmented, longer than endopod (EN/EX=0.65–0.75); all segments subequal in length; proximal segment wide; distal segments progressively narrowing towards the tip of exopod (Fig. 2I, arrow).
Antennal formula 0-0-0-3/1-1-3, spines 0-1-0-1/0-0-1. Lateral setae of endopod bisegmented, seta of proximal endopod segment distinctly shorter than seta of segment 2 (S1/S2=0.75–0.80); distal segments of lateral setae with unilateral short setulae; no hooks at tips of lateral setae. All three apical setae of both branches differ in size and thickness: the longest one far exceeds the length of its branch (EN/ AS =0.30–0.39), (EX/ AS =0.38–0.50); the shortest one much shorter (EN/ AS =0.88–0.95), (EX/ AS =0.53–0.58). All apical setae with uniform bilateral short setulation. Apical spines equal in size, slightly bent, covered with fine setulae; both spines exceed distal segment lengths. Spine on second exopod segment short, about 0.60–0.65 of third exopod segment length (Figs. 2H, 5G).
Mandibles robust, subrectangular in anterior view, slightly compressed laterally, with an incurvation at their distal part. Gnathal plate with two rows of 9–10 incurved serrate denticles (Figs. 2J, 5C). Maxillulae strongly reduced, spatulate. Maxillae absent.
Thoracic limbs: six pairs differing in size and structure (Figs. 3, 6).
Limb I (Figs. 3A, B, 6A, B): epipodite small, limb corm covered by numerous long setulae. Outer distal lobe elongate, bottle-shaped, bearing distally two setae: seta b short and thin, naked; seta c long, uniformly feathered by long setulae; a transverse row of short setulae near base of seta b. A relatively long feathered seta (seta a) at base of DL, with a long feather-like setulation. Two ejector hooks (ejh) at anterior side of limb I; hooks equal in size, bent distally, unilaterally armed with short sparse setulae. A large seta near ejector hooks absent. Inner margin of limb with four setae: setae 1 and 2 long, equal in size; setae 3 and 4 short, setae 1–3 bisegmented, with sparse bilateral setulation of distal segment; seta 4 non-segmented, densely feathered by long setulae. A small naked seta 5 near the base of seta 4. Two sensory elements: a large one near base of setae 1 and 2, and smaller one between ejector hooks and seta 1.
Limb II (Figs. 3C, D, 6C, D): epipodite ovoid. Distal lobe elongate, bearing two large setae (a and b) subequal in size; both setae feathered with long setulae from base to top (this setulation is not illustrated in Fig. 3C); groups of setulae at anterior part of distal lobe. Inner margin spatulate, with four bisegmented setae, slightly decreasing in length towards gnathobase, feathered from base to top. Two small sensory elements between setae 1 and 2, and 2 and 3. Inner portion strongly projected, with an ovoid sensillum at its base. A single bisegmented seta unilaterally armed with short setulae in middle part of inner portion. Ventral margin of gnathobase with a group of long setulae and a row of 5 bilaterally feathered setae: seta α short, bearing short setulae, setae β–ε subequal in size, or seta β the longest. Filtering plate of five similar setae; a cluster of setulae ventrally to filtering plate.
Limb III (Figs. 3E, F, 6E, F): epipodite ovoid (it is not illustrated in Fig. 3E). Exopodite with five terminal (d–h) and three lateral (a–c) setae of different size and armature: seta d short, naked; seta e and g large, bisegmented, distal segment feathered with long setulae; seta f the thickest, as long as setae e and g or slightly longer, covered by very long setulae from base to top; seta h as long as seta 4, naked. Lateral setae of exopod (a–c) increasing in size and thickness proximally: the proximalmost one (seta a) as long as seta f. A transverse row of setulae near base of setae d and e. Inner margin with a lobe bearing five setae: setae 1 and 2 short, seta 2 slightly longer than seta 1; setae 3–5 long, densely feathered from base to top, seta 4 the longest, seta 3 and 5 of similar length. A sensory element near base of setae 3 and 4. Basal endite with a row of four soft setae (setae 6–9) similar in size to setae 3 and 5 of inner limb portion; a small sensory element between setae 6 and 7. Gnathobase with four elements: setae α and 4 short, thin, naked; seta β slightly longer, with widened base, armed with short setulae distally; seta γ long, with a bottle-shaped base and long feather-like distal setulation. Filtering plate of 8 similar setae.
Limb IV (Figs. 3G, H, 6G, H): preepipodite large, setulated; epipodite relatively small (they are not represented in Fig. 3H). Exopodite large, ovoid, with eight feathered setae (a–h) with unclear subdivision into proximal and distal segments; exopodite outer margin setulated in spaces between setae a–e. Setae b–h subequal in size, seta a twice shorter and closely spaced to seta b. Distal margin of inner lobe with four setae with unilateral armature (setae 1–4) and five uniform long setae with distal segments densely feathered (setae 5–9). Gnathobase with three elements: seta α thick, hook-like, fringed with a row of setulae; seta β long, bisegmented, bent in the middle, with distal segment asymmetrically setulated; seta γ relatively short, bisegmented, with a row of setulae; a cluster of long setulae at base of long seta. Filtering plate of eight setae, no distinct border between filtering plate and inner lobe.
Limb V (Figs. 3J, 6I, J): preepipodite large, setulated; epipodite relatively small. Exopodite large, ovoid, armed with seven setae subequal in length, feathered from base to top. Outer margin in spaces between setae c–g setulated. Inner portion flattened, forming a large elongate lobe with distal and outer margins densely setulated. Two feathered setae at base of the lobe: seta 1 thick, far exceeding the length of the lobe; seta 2 relatively thin, as long as the lobe. Gnathobase with four elements: a short thin seta α; a long seta β, feathered from base to top; two spines γ and δ of different length. Filtering plate of three similar setae.
Limb VI (Figs. 3K, 6K) elongate, flattened, subtriangular, inner margin convex, bearing 5–6 clusters of long setulae, with small gaps between the former.
Ephippial female. Body rounded in lateral view (BL/BH=1.07), with a wide depression between head and valves (Fig. 1H); middle part of dorsal margin hump-like; body width and keel as in parthenogenetic female (Fig. 1I). Dorsal and lateral regions of valves strongly chitinized, ornamented with sparse stump-like tubercles. No ventral margin of ephippium visible. Ventral and anterior regions of valves not modified. In general, morphology conforms to that of parthenogenetic female. Ephippium with a single longitudinally oriented egg.
Pre-ephippial female fits to the description of the parthenogenetic female, but ephippium formation can be observed beneath the valves.
Male. unknown
Size: adult parthenogenetic females 0.40–0.60 mm, ephippial female 0.42 mm.
Variability. A slight variability was observed within and between the populations studied. Usually, large aesthetascs are slightly different in size inAustralian individuals, but have a similar length in EastAsian representatives. Also, morphology of anal margin is variable: first postanal tooth is distinctly shorter (LT1/LT2=0.44–0.71) than the second one in most of Australian populations (Figs. 7B, D, E, G); all the Asian individuals have the first postanal tooth similar to the second one or even longer. A small tooth might be present at proximal half of the anal margin (Figs. 7B, D, L). The last preanal tooth (x) might be slightly (Fig. 7I) or strongly (Figs. 7B, E, L) shortened. Spinulae of preanal and anal margin might also differ in their length and thickness. Distal end of postabdomen has a various armature, with one or two distal pectens of long spinulae and 1–4 solitary spines continuing the row of lateral setae (Figs.7 A, C, F, H, J). Sometimes the distalmost pecten might be replaced by a row of short setulae (Fig. 7J). Finally, the elements of limb II gnathobase might vary in their relative length (Figs. 3D, 6D).
Differential diagnosis. Ilyocryptus raridentatus Smirnov, 1989 belongs to the sarsi -group including I. anatolicus Gündüz, 1996, and I. sarsi Stingelin, 1913. All three species share similar traits: 1) incomplete moulting; 2) dorsal keel reduced; 3) long seta located ventrally to postabdominal claw base; 4) medial anal opening; 5) a group of spinulae in the internal wall of anal opening; 6) clusters of short spinulae near preanal teeth base; 7) short first antenna; 8) absence of large seta near ejector hooks base. Furthermore, adult individuals of all three species are somewhat smaller (0.4–0.6 mm) compared to sordidus representatives-group (I. cuneatus Štifter, 1988, I. spinosus Štifter, 1988, I. silvaeducensis Romijn, 1919), having a length 0.57–0.93 mm (Kotov & Stifter 2006; Korovchinsky & Kotov 2021).
I. raridentatus could be differentiated from I. sarsi by having: (1) 5–8 preanal teeth only (10–13 in I. sarsi); (2) proximal segment of first antenna with two subapical spines only (a pair of lateral hillocks in I. sarsi); (3) antennal endopod clearly shorter than the exopod (equally long in I. sars i); (4) ejector hooks of similar length (unequal length in I. sarsi); (5) three setae on the gnathobase of limb IV (four in I. sarsi); (6) a seta of limb IV armed with sparse unilateral setulae (membranous stripe in I. sa rsi); (7) three setae on a filter comb of limb V (four in I. sars i).
I. raridentatus is very similar to I. anatolicus and might be its main synonym. The studied individuals had a relatively greater number of marginal setae (48–60 in I. raridentatus, 43–48 in I. anatolicus). The morphology of the thoracic appendages was not studied for I. anatolicus.
I. raridentatus differs from I. spinosus in medial position of the anal opening (shif ted distall y in I. spinosus) and a fewer number of preanal teeth (17–19 in I. spinosus). Preanal teeth are never doubled in I. raridentatus, in contrast with I. cuneatus and I. sylvaeducensis. Unlike to I sordidus, I. raridentatus has solitary spines at setae of posterior margin, fewer number of preanal teeth (10–15 in I. sordidus) and lacks a long seta near ejector hooks.
Distribution and ecology. Ilyocryptus raridentatus is widely distributed in Australia and East Asia (Fig. 8). The species was recorded in Malaysia (Kotov & Štifter 2006), North Thailand (Maiphae et al. 2008; Choedchim & Maiphae 2023), Vietnam (this study), Central China (Dadykin et al. 2023), Japan (Kotov & Štifter 2006), South Korea (Kotov et al. 2012; Jeong et al. 2014; Kotov et al. 2022), penetrating north to the Far East of Russia (Kotov et al. 2011a; Kotov et al. 2011b). Our study confirms that this species belongs to the southern tropical (ST) faunistic complex according to Kotov (2016).
I. raridentatus inhabits a wide range of lentic and lotic water bodies, including ponds, reservoirs, wetlands, puddles and river floodplains. The lifestyle and ecological preferences of I. raridentatus yet have not been studied.
description: Published as part of Dadykin, Ivan A., Ð ịnh, Cù Nguyên, Shiel, Russell J. & Kotov, Alexey A., 2024, Redescription of Ilyocryptus raridentatus Smirnov, 1989 (Cladocera: Ilyocryptidae), pp. 331-349 in Zootaxa 5468 (2) on pages 334-345, DOI: 10.11646/zootaxa.5468.2.5, http://zenodo.org/record/11616000