Ilyocypris dentifera Sars, 1903

Smith, Robin James, Zhai, Dayou & Chang, Cheon Young, 2019, Ilyocypris (Crustacea: Ostracoda) species in North East Asian rice fields description of one new species, and redescriptions of Ilyocypris dentifera Sars 1903 and Ilyocypris japonica Okubo, 1990, Zootaxa 4652 (1), pp. 56-92 : 56-92

Ilyocypris dentifera Sars, 1903

( Figs 5D , 6B , 10 , 11 A–C, 12, 13A-I & 17)

1903 Ilyocypris dentifera, G. O. Sars , n. sp. —Sars: 38–39, pl. 4, figs 8a–c.

1912 I. dentifera O. Sars 1903 —Müller: 155.

1926 I. dentifera—Klie: 37.

1928 I. dentifera G. O. Sars—Gauthier: 309.

1967 I. dentifera SARS, 1903 —Kempf: 70.

1967 Ilyocypris dentifera Sars, 1903 —Klassen et al.: 440.

? 1970 Ilyocypris dentifera —Delorme : 1251, 1252, plate 1, 13 & 14, herein.

? 1973 Ilyocypris dentifera Sars, 1903 —Kaiser et al.: 340, 344, fig. 7, Tafel. XI, Photos 1–4, herein.

1974 I. dentifera Sars, 1903 —Okubo: 49 & 50.

1980 Ilyocypris dentifera sars, 1903 [sic]—Victor & Fernando: 958, table 1.

1981 Ilyocypris dentifera Sars, 1903 —Victor & Fernando: 1103–1104, 1106, 1110, figs 1–22.

non 1981 Ilyocypris dentifera form angulata —Victor & Fernando : figs 23–38, fide Karanovic & Lee 2013.

1982 Ilyocypris dentifera G. O. Sars—Chen : 50, unnumbered fig. 1–3.

? 1986 I. dentifera—Huang: 9, herein.

1987 I. dentifera Sars, 1903 —Forró et al.: 56.

1988 Ilyocypris dentifera —Broodbakker : 15.

1990 Ilyocypris dentifera Sars, 1903 —Okubo: 39, figs 1a–e.

1991 Ilyocypris dentifera —Martens : 57.

non 1991a Ilyocypris dentifera Sars, 1903 —Kim & Min: 317–321, figs 8 & 9, fide Karanovic & Lee 2013.

1992 I. dentifera Sars, 1903 —Martens et al.: 101.

1997 Ilyocypris dentifera, G. O. Sars, 1903 —Yin & Martens: 12.

2000 Ilyocypris dentifera Sars, 1903 —Lee et al.: 443.

? non 2002 Ilyocypris dentifera Sars, 1903 —Nakao & Tsukagoshi: 71, figs 2a–d, tables 2–5, herein.

2004 Ilyocypris nipponica sp. nov. —Okubo: 17, figs 4r–v, synonymy herein.

non 2004 Ilyocypris dentifera Sars, 1903 —Okubo: 16–17, figs 4m–q, herein.

2004 Ilyocypris dentifera —Victor : Fig. 13 c–i.

2006a Ilyocypris dentifera— Sánchez-Bayo & Goka: 1680, 1683.

2006b Ilyocypris dentifera— Sánchez-Bayo & Goka: 263, fig. 1, tables 1, 2, & 4.

? non 2008 Ilyocypris dentifera Sars, 1903 —Nakao & Tsukagoshi: 251, 263, plate 1a–d, tables 1, 12–14, herein.

*non 2006 [Ji Lie Ni Jie Chong]—Huang et al.: 134, unnumbered figure a–e, herein.

2009 Ilyocypris dentifera Sars, 1903 —Hayashi et al.: 77.

2009 I. dentifera Sars, 1903 b—Yu et al.: 38.

2009 Ilyocypris dentifera Sars, 1903 —Wrozyna et al.: 12.

2011 Ilyocypris dentifera —Churchel et al. : Table 1 .

2011 Ilyocypris nipponica Okubo, 2004 —Martens & Savatenalinton: 49.

2011 Ilyocypris dentifera Sars, 1903 —Martens & Savatenalinton: 49.

2011 Ilyocypris dentifera— Shuhaimi-Othman et al.: 2.

non 2012 Ilyocypris dentifera Sars, 1903 —Chang et al.: Table 1 (referring to Kim & Min 1991a).

? non 2012 Ilyocypris dentifera Sars, 1903 —Sidorov & Semenchenko: 229–230, figs 13–22, table 1, herein.

2012 Ilyocypris dentifera Sars, 1903 —Sari et al.: 490–491, table 2 & 3.

2012 Ilyocypris dentifera —Osterberg et al. : 10, table 2.

2012 Ilyocypris dentifera Sars, 1903 —Hayashi et al.: 61.

2012 I. dentifera Sars 1903 a—Karanovic: 204, 207.

2013 Ilyocypris dentifera Sars, 1903 —Karanovic & Lee: 41–42, 58–59, 63–64, 67, figs 10c–j, 11a, c, f, g, & 14.

2013 I. nipponica Okubo, 2004 —Karanovic & Lee: 41.

2013 Ilyocypris dentifera Sars, 1903 — Martens et al.: no page numbers.

2013 Ilyocypris nipponica Okubo, 2004 — Martens et al.: no page numbers.

2013 I. dentifera—Zhai & Xiao: 468.

2014 Ilyocypris dentifera Sars, 1903 —Karuthapandi et al.: 6579.

2014 Ilyocypris dentifera Sars, 1903 —Shinde et al.: Table 2.

non 2014 Ilyocypris dentifera Sars, 1903 —Smith et al.: 1 (referring to Kim & Min 1991a).

2014 Ilyocypris dentifera Sars, 1903 —Yu: 48–50, figs 21 & 22.

2015 I. dentifera Sars, 1903 —D’Ambrosio et al.: 65.

2015 Ilyocypris dentifera Sars, 1903 —Kulkarni et al.: Image 5c, table 2.

2015 Ilyocypris dentifera Sars, 1903 —Tabuki & Tsuhako: 211–213, figs 3 & 4, table 1.

2015 Ilyocypris dentifera Sars, 1903 —Tanaka et al.: 37, figs 2m, 4i & j, & 5l.

2016b Ilyocypris nipponica Okubo, 2004 nomen nudum —Smith et al.: Appendix S1 (online supporting information).

2017 Ilyocypris dentifera Sars, 1903 —Karuthapandi & Rao: 261.

2018 Ilyocypris dentifera Sars, 1903 —Smith et al.: Appendix.

2018 Ilyocypris dentifera —Chandran et al. : 574.

2018 Ilyocypris dentifera —Ma & Yu : 1861, table 2.

2019 Ilyocypris dentifera Sars, 1903 —Meisch et al.: 71.

* Only the Chinese species name, in Chinese characters, was given in this publication.

Diagnosis. Carapace quadrate in lateral view, covered in small pits, and approximately six to eight tiny spines near posterior margin. Anterior inner calcified lamellae of both valves with lists. With or without tubercles on carapace. Swimming setae of antenna very long, extending significantly beyond end of claws. Palp of female fifth limb with three segments. Sixth limb with four segments (second endopodal segment undivided). Seventh limb with two setae on third segment (= second endopodal segment). Anterior end of Zenker organ small, slightly wider than central tube. Inner lobe of hemipenis short and stocky, slightly longer than outer lobe, no overlap between middle and outer lobe, with clear gap between them, copulatory process distally widened and striated.

Type locality. Not designated. The material that Sars (1903) examined was from ‘ Puching‘ , China, which probably refers to Pucheng County, Fujian Province in southeast China. Approximate coordinates 27.92º N, 118.54 E .

Type material. Lectotype (female) F12245 a, b, paralectotype (male) F12245 d, e (as designated by Victor & Fernando 1981), stored at the Zoologisk Museum, University of Oslo, Norway. This material has been studied and figured by Victor & Fernando (1981) and Karanovic & Lee (2013). The type material was not reexamined for this study.

Material examined. See Table 1 .

Description. Male carapace length 778–807 µm, height 414–436 µm, height/length 0.53–0.55. Female carapace length 750–933 µm, height 403–504 µm, height/length 0.54–0.56. Sub-quadrate in lateral view, anterior margin slightly more inflated than posterior margin ( Fig. 10 ). Dorsal margin almost straight, sloping down posteriorly, maximum height anterior of muscle scars. Ventral margin concave. Well-defined bifurcated sulcus near dorsal margin above and slightly anterior of adductor muscle scars, which form small rounded depression below posterior part of sulcus. Adductor muscle scars numbering six. With slight comma-shaped depression on central-anterior to antero-ventral region of both valves (position indicated on Fig. 10B with white dotted line). Surface of valves densely covered with many small pits, slightly better defined towards valve margins. Posterior margin with six to eight tiny spines. Both valves with outer lists running near ventral margins ( Fig. 10K & L ). Tubercles present in some specimens, one each side of sulcus (posterior one lateral tubercle of some authors), one in mid position of sulcus, and two tubercles in central ventral region ( Fig. 11 A–C). Anterior inner calcified lamellae of both valves with lists. Inner side of lists uneven and with striae. Postero-ventral region of calcified inner lamella of left valve with shallow depression, internally roughened, and with 1–5 poorly defined marginal ripplets ( Fig. 10E ). Dorsal view oval, with posterior margin slightly more rounded than anterior margin. Specimens with tubercles with irregular outline.

Antennule with seven articulated segments ( Fig. 12A ). First segment with two long sub-apical setae on ventral margin and one medium-length, stout seta on dorsal margin. Second segment with relatively long apical-dorsal seta. Third segment with one short apical-dorsal seta and one short apical-ventral seta. Fourth segment with two long apical-dorsal setae, and two shorter apical-ventral setae. Fifth segment with two long apical-dorsal setae, and two shorter apical-ventral setae. Sixth segment with four long setae and relatively long alpha seta. Terminal segment apically with two short setae, one long seta and relatively short aesthetasc ya.

Male antennae with fourth segment undivided ( Figs 12B & 13A ). Swimming setae very long, extending considerably beyond end of claws; shorter accompanying seta also long reaching to mid-point of claws. G3 reduced to short seta, but extending beyond end of terminal segment. Claw z1 small and slender, not reaching to end of claw G2. Female antenna with G2 claw as long or slightly longer than claws G1 and G3. Seta z1 stout, claw-like, shorter than setae z2 and z3, longer than half length of G2.

Mandibular coxa small, with well-developed teeth on endite ( Fig. 12D ). Mandibular palp four-segmented ( Fig. 12C ). S1 seta on first segment longer than S2, alpha seta small and slender. Second segment with two setae on outer edge, and 3+1+beta setae on inner edge. Beta seta short, stubby and hirsute. Third segment with four setae on outer apical corner, three setae on inner apical corner, and one apical seta between other two groups. Terminal segment with three stout apical setae, two thinner and shorter apical setae and one seta protruding from area proximal of segment mid-length, towards outer edge.

Maxillula palp first segment with three sub-equal medium-length setae on outer apical corner, one shorter seta positioned on apical edge offset from apical corner, and one sub-apical setae in mid-width position ( Fig. 12E ). Second segment wider than long, apically with three claw-like setae and three shorter setae.

Fifth limb with two a-setae on dorsal margin, and approximately 15 setae along dorsal and anterior edge of basis ( Fig. 12F ). Branchial plate with six rays. Palp (endopodite) of female three-segmented ( Fig. 12G ), terminating with three setae of differing lengths. Palps of male symmetrical, with slender elongate hooks ( Fig. 13C ).

Sixth limb, four-segmented ( Fig. 12H ). First segment (= protopodite) with short d1 seta. Second segment (= first endopodal segment) with short e seta. Third segment (= second endopodal segment) with short f seta protruding from mid-length and apical short g seta. Terminal segment (= third endopodal segment) with relatively long h1 seta, short h3 and well-developed h2 claw, 1.8x length of anterior sclerotized margin of first endopodal segment (indicated with black triangle on Fig. 12H ).

Seventh limb with four segments ( Fig. 13D ). First segment with seta d1. Second segment with seta e reaching to approximately mid-length of third segment. Fourth segment with two setae on anterior edge (f and g), distal most one longest. Fourth segment small and elongate, supporting equally long h1 and h3 setae and short h2 seta.

Caudal ramus typical of genus, ramus distinctly curved at mid-length ( Fig. 13E ). Claw Gp slightly longer than Ga, seta sp long.

Female reproductive organ with large, rounded genital lobe anteriorly, and smaller rounded lobe posteriorly, just anterior of base of caudal ramus ( Fig. 13F ). Organ delicate and easily distorted or damaged during dissections.

Hemipenes, outer lobe rounded distally, with clear gap between it and middle lobe ( Figs 5D , 13G ; black triangle indicates gap, 13I). Middle lobe triangular, inner corner sharply angled, outer edge slightly less angled. Inner lobe slightly longer than outer lobe, distally rounded on outer edge, slightly angled on inner apical edge; with distal folded protrusion (seen by focussing through specimen). Copulatory process well developed, distally widened, with sinuous distal edge, and large rounded, striated protrusion on lower edge ( Fig. 13H ).

Zenker organ with 16–21 internal rosettes ( Fig. 6B ). Proximal end oval and small, slightly wider than central tube. Spermatozoa lengths ranges from 862 to 911 µm, with a mean of 889 µm ( Smith et al. 2016b).

Intraspecific variation. 11.1% of specimens studied have tubercles on the carapace ( Table 1 ), varying from slightly to strongly developed ( Fig. 11 A–C). Tuberculated males have a hemipenis morphology strongly resembling that of non-tuberculated forms, and so they are considered to be conspecific. The number of marginal ripplets var- ies between specimens, ranging from one to five. The ripplets are rather poorly defined, and grade to a roughened surface towards the posterior margin ( Fig. 10E ).

Remarks. Sars (1903) described Ilyocypris dentifera (males and females) and Ilyocypris angulata Sars, 1903 (females only) from specimens raised from Chinese mud. He opined that I. angulata may be a variety of I. dentifera , the two species differing only by the presence of tubercles on the former. Kaiser et al. (1973) considered that both forms were variations of the same species, and used the name I. dentifera , but a year later Okubo (1974) reported I. angulata from Japan, including males. Victor and Fernando (1981), after examination of type material, concluded that the two species names are synonyms, and retained the name I. dentifera . Victor and Fernando’s (1981) synonymy of the two species names was followed by some authors (e.g. Martens 1991; Okubo 2004; Sari et al. 2012; Sidorov & Semenchenko 2014), but not by others (e.g. Chen 1990; Kim & Min 1991a; Yu et al. 2009; Martens & Savatenalinton 2011). After Victor and Fernando’s (1981) revision, Chen (1990) figured I. angulata from China, including the male hemipenis, but this was quite different to that figured by Okubo (1974) for I. angulata in Japan. Karanovic and Lee (2013), again after examining Sars’ material, considered both I. dentifera and I. angulata as valid species based on the discovery of males of I. angulata in lectotype material. They partly figured the male of I. angulata and noted that it resembled the species figured by Chen (1990). They therefore judged Okubo’s (1974) record of I. angulata as incorrect, and also noted that I. dentifera reported from Korea by Kim & Min (1991a) was also likely a different species. A possible third species was also identified in Sars’ material by Karanovic and Lee (2013), called by them as Ilyocypris cf. angulata , which varied in the shape of the inner lobe of the hemipenis.

We concur with previous studies that I. dentifera and I. angulata should be treated as separate species based on the morphology of the hemipenes (as figured in Chen 1990; Karanovic & Lee 2013; Zhai & Zhao 2014). However, I. dentifera can have well-developed angular tubercles, similar to I. angulata . Yu (2014) figured specimens with a hemipenis resembling that of I. dentifera , but with tubercles on the carapace, similar to those of I. angulata . This study also found specimens that have tuberculated carapaces similar to I. angulata (i.e. with angular tubercles), but with a hemipenis morphology that concurs with I. dentifera . This indicates that like other Ilyocypris species, (e.g. Ilyocypris gibba ( Ramdohr, 1808) , the type species of the genus, and Ilyocypris decipiens Masi, 1905 ), tuberculated and non-tuberculated forms of I. dentifera exist. Ilyocypris dentifera and I. angulata cannot therefore be discriminated on the presence or absence of tubercles alone, but the dorsal views of the carapace, and hemipenis morphology are sufficiently different to distinguish the two species. The dorsal view of I. angulata has more compressed anterior and posterior regions ( Fig. 11 D–F) than that of I. dentifera ( Fig. 11 A–C), producing a less rounded outline. Ilyocypris angulata also has larger spines along the anterior and posterior margins of the valves compared with those in I. dentifera . The inner lobe of the hemipenis is long and hook shaped in I. angulata ( Figs 5E & 13J ), whereas it is shorter and stubbier in I. dentifera . Ilyocypris angulata also lacks the inflated end to the copulatory process as seen in I. dentifera ( Figs 13H & K ), and the outer lobe of the hemipenis overlaps the middle lobe, in contrast to the gap between these lobes in I. dentifera .

Ilyocypris nipponica was very briefly described by Okubo (2004), who figured photographs of the male valves, the sixth limb, hemipenis and Zenker organ. As there was no explicit designation of type material, and no information as to where the specimens are deposited (contravening sections 16.4.1 and 16.4.2 of the ICZN code), the original description did not erect a valid species. For this study, numerous specimens of I. dentifera collected in the vicinity of Lake Biwa (the locality given by Okubo (2004) for I. nipponica ) were examined by one of us (RJS). These specimens correspond very closely with the photographs of I. nipponica provided by Okubo (2004), and the drawings of the paralectotypes of I. dentifera given by Karanovic & Lee (2013). We therefore conclude that I. nipponica is a junior synonym of I. dentifera . The specimen labelled as I. dentifera in Okubo (2004) , however, has a differently shaped inner lobe of the hemipenis, and we consider this to be conspecific with Ilyocypris incus sp. nov. (see Remarks section of Ilyocypris incus sp. nov. below). This confusion of the identity of I. dentifera in Okubo (2004) may relate to the previous confused synonymy of these two species by Victor & Fernando (1981). Okubo (2004) followed this synonymy, considering I. angulata to be a junior synonym of I. dentifera , but later authors have treated the two species separately (see first paragraph of this section). The previous record of I. dentifera by Okubo (1990) is probably correct, as the drawing of the hemipenis is similar to our material and that of I. nipponica in Okubo (2004) . The species figured as I. angulata in Okubo (1974) is considered to be Ilyocypris incus sp. nov. (see Remarks section of Ilyocypris incus sp. nov. below).

The figures of the carapace of I. dentifera from the Far East of Russia ( Sidorov & Semenchenko 2012) are most similar to I. angulata , but the hemipenis is not figured for this occurrence so cannot be confirmed. Nakao & Tsukagoshi (2002; 2008) reported I. dentifera from the Obitsu River Estuary, Japan, but the figured carapace and valves look more similar to I. japonica , in particular the lateral view of the carapace and the relatively large pits on the carapace surface.

Huang et al. (2006) reported I. dentifera from Sichuan, China, but the accompanying figures of the appendages include a five-segmented walking leg and antennal swimming setae only reaching to the end of the claws, so is clearly a misidentification. An earlier record of I. dentifera from Sichuan by Huang (1986) cannot be confirmed due to lack of figures, but this too could be a misidentification.

While similar in general outline, Canadian Pleistocene specimens of I. dentifera figured by Delorme (1970) are more elongate than Asian I. dentifera . The Pleistocene record from Syria reported by Kaiser et al. (1973) is also slightly different to Asian specimens in that the calcified inner lamella on the left valve is wider and the right valve is more rounded posteriorly in the Syrian fossils.

Two other species of Ilyocypris are very similar to tuberculated forms of I. dentifera : Ilyocypris hanguk Karanovic & Lee, 2013 and Ilyocypris dui Ma & Yu, 2018 . Ilyocypris hanguk was described from two adult males and some juveniles collected from a stream on an island off the south west coast of South Korea ( Karanovic & Lee 2013). The carapace morphology of the adult female remains unknown, but the male carapace is very similar to that of male I. dentifera in lateral outline. Ilyocypris dui was described from one male and two females collected from a stream in Ningbo, Zhejiang Province, China ( Ma & Yu 2018). Again, the carapace is very similar to that of I. dentifera , and it is not possible to discriminate it from I. dentifera on the carapace features alone. Discrimination of I. dentifera , I. hanguk and I. dui can only reliably be conducted on the male hemipenes ( Fig. 17 ).

Yin & Martens (1997) listed Ilyocypris echinata Huang, 1979 as a possible synonym of I. dentifera , but this synonymy has not been followed by other authors (e.g. Mischke et al. 2003; 2006; Yu et al. 2009; Yu 2014). Ilyocypris echinata has an overall different lateral view to I. dentifera , with the posterior end less inflated, and the surface highly uneven with many small tubercles. It also has several large, laterally protruding spines on each valve, so far not recorded in I. dentifera . Herein, this species is treated as distinct from I. dentifera .

Distribution. The distribution of this species is uncertain due to the confused synonymy with I. angulata , and possible misidentifications. Confirmed reports are from China (Fujian Province and Shanghai) ( Sars 1903; Yu 2014), Korea (Gyeongsangnam-do and Gyeongsangbuk-do Provinces) (herein), and Japan (Shiga, Shizuoka, Fukuoka, Tokushima and Okinawa Prefectures) ( Okubo 1990; 2004 (as I. nipponica ); herein) ( Fig. 9 ). Although not figured, the reports of I. dentifera from Ibaraki Prefecture, Japan ( Sánchez-Bayo & Goka 2006a; 2006b) were based on specimens checked by one of us ( RJS). Other reports from Okinawa and Shizuoka, Japan ( Tabuki & Tsuhako 2015; Tanaka et al. 2015), China ( Chen 1982) and India ( Kulkarni et al. 2015) are not accompanied with figures of the hemipenes (the most reliable character for identification), but the carapace figures generally concur with I. dentifera . Reports with no figures, such as Philippine, Taiwanese and other Japanese and Indian reports (e.g. Victor & Fernando 1980; Broodbakker 1988; Yu et al. 2009 citing grey literature; Shinde et al. 2014), cannot be confirmed. Ilyocypris dentifera was reported from various places throughout South Korea by Kim & Min (1991a), although these records at least in part probably refer to Ilyocypris incus sp. nov. (see Remarks section of Ilyocypris incus sp. nov. below). This study confirms that I. dentifera is present in Korea, in parts of Gyeongsangnam-do and Gyeongsangbuk-do Provinces in the south east of the country. Most occurrences of I. dentifera fall into the temperate, without dry season, hot summer Köppen climatic zone (Cfa), while Philippine and Indian reports are from the tropical monsoon zone (Am) and tropical savannah zone (Aw) ( Peel et al. 2007) ( Fig. 9 ). Ilyocypris dentifera has been reported from Pleistocene deposits in Manitoba, Canada, and the Damascus Basin, Syria ( Klassen et al. 1967; Delorme 1970; Kaiser et al. 1973), but there are some morphological differences compared with Asian specimens (see Remarks section above).

Ecology. Ilyocypris dentifera is a typical inhabitant of rice fields in East Asia. In Japanese and Korean rice fields we have found it with two other Ilyocypris species, I. japonica and Ilyocypris incus sp. nov. Its ecology is poorly known, but it can be found in the top few mm of mud in the oxidised zone of rice fields. We have collected it from the end of May through to mid July in Japan, after which rice fields are usually allowed to dry out prior to harvesting.

Ilyocypris dentifera was one of three species of rice field ostracods (the other two being Cypridopsis vidua (O. F. Müller, 1776) and Cypretta seurati Gauthier, 1929 ) used for testing the toxicity of imidacloprid, a pesticide widely used in rice fields, on micro-crustaceans by Sánchez-Bayo & Goka (2006a; 2006b). They found that all three species of ostracods tested, including I. dentifera , are very susceptible to imidacloprid, with a range of 301–715 g /L for 48-h LC50, 200 times lower than that for cladocerans. The use of this pesticide therefore probably dramatically impacts the ecological role of I. dentifera in rice fields. Such impacts remain largely unrecognised however, as the environmental assessments of imidacloprid are based on toxicity values of tolerant cladoceran species (Sánchez- Bayo & Goka 2006b).

In addition to rice fields, I. dentifera has been reported from an ‘ikuza’ field, and ponds, one of which was partially dried, on Okinoerabu Island, Japan ( Broodbakker 1988). Indian reports are from a seasonal pond in an abandoned quarry, and in (seasonal?) small pools on the plateaus of the North Western Ghats, India ( Shinde et al. 2014; Kulkarni et al. 2015).

Figures

FIGURE 5. Light microscopy photographs of Ilyocypris hemipenes. A, Ilyocypris japonica Okubo, 1990 (LBM 1430009150, sample 18; see Table 1). B, Ilyocypris japonica Okubo, 1990 (LBM 1430009151, sample 18). C, Ilyocypris mongolica Martens, 1991 (LBM 1430009161, sample 17). D, Ilyocypris dentifera Sars, 1903 (LBM 1430009119, sample 6). E, Ilyocypris angulata Sars, 1903 (LBM 1430009112, sample 20). F, Ilyocypris incus sp. nov. (DB40054, sample 14). E has been reflected on the vertical axis to facilitate comparisons.

FIGURE 6. Light microscopy photographs of Ilyocypris Zenker organs. Black triangles mark the anterior ends. A, Ilyocypris japonica Okubo, 1990 (LBM 1430009144, sample 9; see Table 1). B, Ilyocypris dentifera Sars, 1903 (LBM 1430009119, sam- ple 6). C, Ilyocypris incus sp. nov. (LBM 1430009131, sample 14).

FIGURE 9. Distribution maps of Ilyocypris dentifera, I. angulata, I. japonica, I. mongolica, and Ilyocypris incus sp. nov. One additional fossil record of I. dentifera exists from Manitoba, Canada (Klassen et al. 1967), but is not shown on the map. As the records of Ilyocypris dentifera of Kim & Min (1991) probably at least in part refer to different species, their records are not plotted on the map. Records of I. dentifera by Huang (1986) and Huang et al. (2006) are also not plotted as they are likely to also be misidentifications. Other reports with no figures cannot be confirmed but are plotted (see text for more details).? indicates uncertain records. Abbreviations and colours of points refer to Köppen climatic zones, following Peel et al. (2007). Data from: 1, Kaiser et al. (1973). 2, Shinde et al. (2014). 3, Kulkarni et al. (2015). 4, Zhai & Zhao (2014). 5, Chen (1982; 1990). 6, Sars (1903), Chen (1982). 7, Yu et al. (2005). 8, Ma & Yu (2018). 9, Yu (2014). 10, Yu et al. (2009). 11, Victor & Fernando (1980). 12, Zenina & Schornikov (2008). 13, Sidorov & Semenchenko (2012). 14, Lee et al. (2000). 15, This study. 16, Tabuki & Tsuhako (2015). 17, Okubo (1990). 18, Broodbakker (1988). 19, Okubo (2004), this study. 20, Tanaka et al. (2015). 21, Sánchez-Bayo & Goka (2006a; 2006b). 22, Van der Meeren et al. (2010). 23, Martens (1991). 24, Zhai & Zhao (2014). 25, This study. 26, Okubo & Terauchi (1992). 27, This study. 28, Okubo (1990). 29, Nakao & Tsukagoshi (2002; 2008). 30, This study. 31, Okubo (1974).

FIGURE 10. Ilyocypris dentifera Sars, 1903. A, female left valve, external view (LBM 1430009124, sample 6; see Table 1). B, female right valve, external view. White dotted line marks comma-shaped depression (LBM 1430009124, sample 6). C, female left valve, internal view (LBM 1430009124, sample 6). D, female right valve, internal view (LBM 1430009124, sample 6). E, female left valve, internal view, detail of postero-ventral margin (LBM 1430009124, sample 6). F, female right valve, internal view, detail of antero-ventral margin (LBM 1430009124, sample 6). G, female left valve, internal view, muscle scars (LBM 1430009124, sample 6). H, male right valve, external view (LBM 1430009122, sample 6). I, female carapace, dorsal view, anterior to right (LBM 1430009123, sample 6). J, male carapace, dorsal view, anterior to right (LBM 1430009130, sample 25). K, male right valve, ventral view (LBM 1430009122, sample 6). L, male right valve, detail of ventral margin (LBM 1430009122, sample 6). Scale bar = 500 µm for A–D, H–K, 174 µm for E–G, 151 µm for L.

FIGURE 11.A–C, Ilyocypris dentifera Sars, 1903, tuberculated form.A, female carapace, right lateral view (LBM 1430009129, sample 23; see Table 1). B, female carapace, dorsal view, anterior to right (LBM 1430009129, sample 23). C, male carapace, dorsal view, anterior to right (LBM 1430009126, sample 16). D–F, Ilyocypris angulata Sars, 1903. D, female right valve, external view (LBM 1430009113, sample 20). E, female carapace, dorsal view, anterior to right (LBM 1430009115 sample 20). F, male carapace, dorsal view, anterior to right (LBM 1430009114, sample 20). Scale bar = 500 µm

FIGURE 12. Ilyocypris dentifera Sars, 1903. A, antennule, male (LBM 1430009119). B, antenna, male (LBM 1430009119). C, mandibular palp, female (LBM 1430009120). D, mandibular coxa, male (LBM 1430009119). E, maxillula palp and endites (setae on endites not drawn), male (LBM 1430009119). F, fifth limb, female (LBM 1430009125). G, fifth limb palp, female (LBM 1430009121). H, sixth limb, male (LBM 1430009119), arrow and dashed line indicate length of first endopodal segment. All specimens from sample 6; see Table 1.

FIGURE 13. A–H, Ilyocypris dentifera Sars, 1903. A, detail of male antenna (LBM 1430009119, sample 6; see Table 1). B, detail of female antenna (LBM 1430009124, sample 6). C, fifth limb palps, male (LBM 1430009119, sample 6). D, seventh limb, male (LBM 1430009119, sample 6). E, caudal ramus, male (LBM 1430009119, sample 6). F, outline of female reproductive organ, arrow indicates anterior (LBM 1430009127, sample 18). G, hemipenis (LBM 1430009119). H, copulatory process of hemipenis (LBM 1430009119, sample 6; see Table 1). I, outlines of the hemipenes of four specimens (clockwise LBM 1430009118, sample 4; LBM 1430009128, sample 21; LBM 1430009117, sample 2; LBM 1430009116, sample 1). J & K Ilyocypris angulata Sars, 1903. J, hemipenis (LBM 1430009112, sample 20). K, copulatory process of hemipenis (LBM 1430009112, sample 20). J & K have been reflected on the vertical axis to facilitate comparisons.

FIGURE 17. Summary of the soft part characters defining the two Ilyocypris groups recognized herein. (1) Only two males of I. bradyi have been reported, but they were not found with any adult females (Karanovic & Lee 2013). (2) Adult females of I. hanguk are unknown (Karanovic & Lee 2013). (3, 4, 8, 9) Outlines drawn from figures in Karanovic & Lee (2013). (5, 6) Outlines drawn from photograph in Zhai & Xiao (2013). (7) Outline drawn from figure in Smith et al. (2011). (10, 11) Outlines drawn from photograph in Ma et al. (2018). * indicates figures reflected on the vertical axis to facilitate comparisons. Not to scale.