Ilyocypris incus, Smith & Zhai & Chang, 2019

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 incus sp. nov.

( Figs 5F , 6C , 14–17 )

1974 Ilyocypris angulata Sars, 1903 —Okubo: 46–50, fig. 1a–v.

? 1991a Ilyocypris dentifera Sars, 1903 —Kim & Min: 317–321, figs 8 & 9.

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

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

2013 Ilyocypris angulata Sars, 1903 —Karanovic & Lee: 41, 55, 59, 64, fig. 14 (in part, referring to Okubo 1975 [sic]).

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

Etymology. From the Latin ‘incus’ meaning anvil and referring to the shape of the copulatory process of the hemipenis (treated as a noun in apposition).

Diagnosis. Carapace quadrate in lateral view, covered in small pits, and approximately seven 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. 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 longer than outer lobe, touching or slightly overlapping middle lobe, with bulbous end. Outer lobe nearly touching to slightly overlapping middle lobe, copulatory process well developed, with large, roughly triangular distal end with uneven distal edge.

Type locality. Rice fields in Bomun-dong, Gyeongju-si, Gyeongsangbuk-do, South Korea, 35.8364º N, 129.2483º E, altitude 73m.

Type material. Holotype: Male ( LBM 1430009132 ), dissected with appendages sealed in a glass slide and valves stored dry in a micropalaeontological cavity slide.

Allotype: Female ( LBM 1430009134 ), dissected with appendages sealed in a glass slide and valves stored dry in a micropalaeontological cavity slide.

Paratypes: Males ( LBM 1430009131 and DB40054), dissected with appendages sealed in glass slides and valves stored dry in micropalaeontological cavity slides. Male ( LBM 1430009138 ) whole carapace, stored dry in a micropalaeontological cavity slide .

Females ( LBM 1430009136 and DB40055), dissected with appendages sealed in glass slides and valves stored dry in micropalaeontological cavity slides. Female ( LBM 1430009137), whole carapace, stored dry in a micropalaeontological cavity slide.

All type material collected from the type locality on 4 July 2011.

Other material. Okubo (1974) stated that some specimens of the Japanese “ I. angulata ” he studied would be deposited in the collections of the National Science Museum, Tokyo, but enquiries revealed that the specimens are not in their collections.

Description. Male carapace length 746–797 µm, height 404–436 µm, height/length 0.53–0.55. Female carapace length 827–910 µm, height 463–504 µm, height/length 0.55–0.57. Anterior margin more inflated than posterior margin ( Fig. 14 ). Dorsal margin almost straight, sloping down posteriorly, maximum height anterior of muscle scars. Ventral margin strongly concave. Well-defined bifurcated sulcus near dorsal margin just anterior of adductor muscle scars, which form small rounded depression below posterior part of sulcus. Surface of valves densely covered with many small pits. Area near posterior margin with about seven tiny spines. Both valves with faint outer lists running near ventral margins ( Fig. 14J & K ). Tubercles present in some specimens, one each side of sulcus (posterior one more developed), one slight one in mid position of sulcus, one in postero-ventral region and one in central ventral region. Inner calcified lamella narrow, especially posteriorly. Anterior inner calcified lamellae of both valves with lists. Postero-ventral region of calcified inner lamella of left valve with shallow depression containing 2–3 marginal ripplets ( Fig. 14E ). Adductor muscle scars obscured. Dorsal view oval, with posterior margin more rounded than anterior margin.

Antennule with seven articulated segments ( Fig. 15A ). 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 ( Fig. 15B & 16B ). 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, extending to distal end of terminal segment. Claw z1 small and slender, not reaching to end of claw G2. Female antenna with G2 claw as long as claws G1 and G3 ( Fig. 16A ). Seta z1 stout, claw-like, shorter than setae z2 and z3, approximately half length of G2.

Mandibular coxa small, with well-developed teeth on endite ( Fig. 15D ). Mandibular palp four-segmented ( Fig. 15 C ). Alpha seta on first segment 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 seta and one seta protruding from area proximal of mid-length, towards outer edge.

Maxillula palp first segment with three sub-equal medium-length setae on outer apical corner, one mediumlength seta positioned on apical edge offset from apical corner, and one sub-apical setae in mid-width position ( Fig. 15E ). Second segment wider than long, apically with three claw-like setae and three shorter setae.

Female fifth limb with large basis supporting two a-setae and approximately 17 setae of various lengths on inner edge (endite) ( Fig. 15F ). Palp with two segments, terminating with one long and two mid-length setae. Branchial plate obscured, but with at least five rays. Male palp with long, thin proximal segment, supporting distally two setae and large grasping hook. Left and right hooks similar in morphology, gently curved and tapering to sharp tips, with short, distally very fine seta on outer edge ( Fig. 15H ).

Sixth limb four-segmented ( Fig. 15G ). 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 short apical g seta. Terminal segment (= third endopodal segment) with relatively long h1 seta, short h3 seta and well-developed h2 claw, approximately 1.9x length of anterior sclerotized margin of first endopodal segment (marked with black triangle on Fig. 15G ).

Seventh limb with four segments ( Fig. 16C ). 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, with seta h3 slightly longer than h1, and seta h2 short.

Caudal ramus typical of genus, ramus distinctly curved distal of mid-length ( Fig. 16D ). 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. 16E ). Organ delicate and easily distorted or damaged during dissections.

Hemipenes, outer lobe unevenly rounded distally, nearly touching to slightly overlapping middle lobe ( Fig. 5F , 16F & H ). Middle lobe triangular, inner corner sharply angled, outer edge more rounded. Inner lobe longer than outer lobe, with inner edge slightly curving along most of length, before smoothly curving to bulbous distal end; bulbous end projecting towards middle lobe, sometimes slightly overlapping. Copulatory process well developed, with large, roughly triangular distal end with uneven distal edge ( Fig. 16G ).

Zenker organ with 18–19 internal rosettes ( Fig. 6C ). Proximal end oval and small, slightly wider than central tube.

Intraspecific variation. Some specimens have tubercles developed on the carapace to varying degrees, while others have no obvious tubercles. Okubo (1974; as I. angulata ) figured specimens with five tubercles on each valve. Seta sa on the caudal ramus is variable in length, with that of some specimens up to 157% longer compared with the holotype’s. The inner lobe of the hemipenis is rather variable in appearance distally, sometimes with a slight gap between it and the middle lobe, while in other specimens slightly overlapping the middle lobe ( Fig. 16H ).

Remarks. This species is very similar to I. dentifera , I. hanguk , I. dui , and I. gibba . The valves are more round- ed posteriorly than those of I. dentifera , which tends to have a more truncated posterior. The hemipenes demonstrate several differences, including the shapes of the outer and inner lobes, and the copulatory process. Our specimens are a close match to the incorrect records of I. angulata and I. dentifera figured by Okubo (1974; 2004), and we consider them conspecific.

The misidentified Ilyocypris dentifera of Kim & Min (1991a) comes close to this species, but the outer lobe of the hemipenis has a slightly different shape and the claw of their figured sixth limb is robustly serrated. The outer lobe of the hemipenis does vary somewhat in our material, and so the hemipenis morphology recorded by Kim & Min (op. cit.) could represent the same species. The robust serration on the sixth limb is unusual for Ilyocypris species generally, and maybe a result of Kim & Min’s drawing style; other species figured by them also have robust, rather exaggerated serration on the sixth limbs ( Kim & Min 1991a; 1991b). We consider the records of I. dentifera of Kim & Min (1991a) at least in part, as possibly conspecific with Ilyocypris incus sp. nov.

Ilyocypris hanguk is similar to Ilyocypris incus sp. nov., but the posterior margin of the male carapace is more rounded in the latter (adult female morphology of I. hanguk remains unknown). The three lobes on the hemipenis are different in shape compared with those of Ilyocypris incus sp. nov., in particular, the middle lobe of I. hanguk is proximally wider and the copulatory process is missing the large distal projections found in Ilyocypris incus sp. nov. Other features of I. hanguk that are different include the very small h1 seta on the walking leg (note that the h1 and h3 setae of the sixth limbs are mislabelled in Karanovic & Lee 2013), and the large number of rosettes in the Zenker organ (approximately 25 in I. hanguk , 18–19 in Ilyocypris incus sp. nov.).

Similar to I. hanguk , the carapace of I. dui resembles that of I. dentifera more than Ilyocypris incus sp. nov. The middle lobe of the hemipenis of I. dui is most similar to that of I. hanguk in that it is proximally wide, which also distinguishes it from Ilyocypris incus sp. nov. The outer and inner lobes and the copulatory process are also differently shaped than those of Ilyocypris incus sp. nov.

Ilyocypris gibba has a similar outline in lateral view to Ilyocypris incus sp. nov. and overall the differences in carapace morphology are subtle. Ilyocypris gibba has more ripplets (6–10) on the postero-ventral calcified inner lamella of the left valve than Ilyocypris incus sp. nov. (2–3), but the numbers of ripplets are known to vary within species and are not considered to be a reliable taxonomic feature ( Mazzini et al. 2014). The pitting on the carapace is coarser and the postero-dorsal corner more angular in I. gibba compared with Ilyocypris incus sp. nov. The appendages are also very similar in the two species, with only the hemipenes and Zenker organs showing clear differences; the inner lobe of the hemipenis of I. gibba is much shorter and the outer lobe more angular than those of Ilyocypris incus sp. nov. ( Meisch 2000). The shape of the copulatory process of I. gibba remains unknown. The Zenker organ of I. gibba has a more inflated proximal end compared with that of Ilyocypris incus sp. nov.

Several species known from China don’t have appendages described, so comparisons with these species rely solely on the carapace morphology. Ilyocypris xizangensis Yang, 1982 (in Huang et al. 1982) is noticeably more elongate, and Ilyocypris sebeiensis Yang et al., 2004 a lot less elongate compared to Ilyocypris incus sp. nov. Ilyocypris echinata Huang, 1979 has lateral spines on the carapace, not seen in Ilyocypris incus sp. nov. Ilyocypris microspinata Huang, 1982 has a more sloping dorsal margin and a less inflated posterior in lateral view. The Pleistocene Ilyocypris opima Huang, 1982 is much more rounded in lateral view and Ilyocypris crassireticulata Huang, 1982 has much coarser pitting.

Distribution. Currently known from Gyeongsangbuk-do, South Korea, and Okayama Prefecture, Japan ( Fig. 9 , see Table 1 for more details). Both known occurrences of this species fall into the temperate, without dry season, hot summer Köppen climatic zone (Cfa) ( Peel et al. 2007). Kim & Min (1991a) reported “ I. dentifera ”, which possibly represents this species, from various places throughout South Korea. However, considering the close similarity of this species with the true I. dentifera , it is unknown how many of these records potentially refer to Ilyocypris incus sp. nov.

Ecology. Ilyocypris incus sp. nov. was found in a rice field with I. dentifera and I. japonica during early July in Korea. Okubo (1974, as I. angulata ) reported that it is found from spring to summer, sometimes autumn, “creeping” in mud, although the habitat was not mentioned.

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 14. Ilyocypris incus sp. nov. A, female left valve, external view (LBM 1430009136). B, female right valve, external view (LBM 1430009136). C, female left valve, internal view (LBM 1430009136). D, female right valve, internal view (LBM 1430009136). E, female left valve, internal view, detail of postero-ventral margin (LBM 1430009136). F, female right valve, internal view, detail of antero-ventral margin (LBM 1430009136). G, female carapace, dorsal view, anterior to right (LBM 1430009137). H, male right valve, external view (LBM1430009131). I, male carapace, dorsal view, anterior to right (LBM 1430009138). J, male right valve, ventral view (LBM 1430009133). K, male right valve, detail of ventral margin (LBM 1430009133). Scale bar = 500 µm for A–D, G–J, 174 µm for E & F, 135 µm for K. All specimens from sample 14; see Table 1.

FIGURE 15. Ilyocypris incus sp. nov. A, antennule, male (DB40054). B, antenna, male (LBM 1430009132). C, mandibular palp, female (LBM 1430009136). D, mandibular coxa, female (LBM 1430009134). E, maxillula palp and endites (setae on endites not drawn), female (LBM 1430009136). F, fifth limb, female (DB40055). G, sixth limb, male (LBM 1430009132), arrow and dashed line indicate length of first endopodal segment. H, fifth limb palp, male (DB40054). All specimens from sample 14; see Table 1.

FIGURE 16. Ilyocypris incus sp. nov. A, detail of female antenna (LBM 1430009134). B, detail of male antenna (LBM 1430009132). C, seventh limb, male (LBM 1430009132). D, caudal ramus, male (DB40054). E, outline of female reproductive organ, arrow indicates anterior (LBM 1430009134). F, hemipenis (LBM 1430009132). G, copulatory process of hemipenis (LBM 1430009132). H, outlines of the hemipenes of four specimens (left to right LBM 1430009132, LBM 1430009135, LBM 1430009133 (reflected on the vertical axis), DB40054). All specimens from sample 14; see Table 1.

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.