Cyprinotus cassidula, Smith & Chang, 2020

Smith, Robin James & Chang, Cheon Young, 2020, Taxonomic assessments of some Cyprinotinae Bronstein, 1947 species (Crustacea: Ostracoda) from Japanese and Korean rice fields, including (re-) descriptions of six species and a review of the type species of the subfamily, Zootaxa 4795 (1), pp. 1-69 : 5-18

Cyprinotus cassidula sp. nov.

( Figs 1–4A & B , 5 , 6 , 7 A–F)

1974 Cyprinotus uenoi Brehm, 1936 —Okubo: 58, 63–66, fig. 3.

1977 Cyprinotus uenoi Brehm, 1936 —Hanai et al.: 21

? 1988 Cyprinotus uenoi —Broodbakker: 7.

1989 Cyprinotus uenoi Brehm—Okubo & Ida : 106, pl. 3a–d, pl. 4m & n.

? 1991 Cyprinotus uenoi Brehm, 1936 —Kim & Min: 83–87, figs 2 & 3.

2004 Cyprinotus uenoi Brehm, 1936 —Okubo: 23, figs 1, 2, 3j, 7a–f.

? 2007 Cyprinotus uenoi Brehm, 1936 —Ikuta et al.: 906–912, figs 1–5.

2009 Cyprinotus uenoi Brehm, 1936 —Hayashi et al.: 77.

2012 Cyprinotus uenoi Brehm, 1936 —Chang et al.: 9, table 1.

2012 Cyprinotus uenoi Brehm, 1936 —Hayashi et al.: 61.

2016b Cyprinotus uenoi —Smith et al.: 10, 11, figs 3b & 9, appendix S1.

2018 Cyprinotus uenoi Brehm, 1936 —Smith et al.: 9, 10, appendix, in part.

Etymology. From the Latin cassidula , diminutive form of cassida, which means helmet. This refers to the relatively small dorsal ridge on the right valve, which in left lateral view of the carapace is reminiscent of a small helmet. The name is a noun in apposition.

Diagnosis. Left valve overlaps right along ventral margin. In lateral view, right valve distinctly higher than left valve and projecting above with elongate, curved ridge or protuberance from about mid-length to posterior margin. Surface of valves smooth in central area, but with small shallow pits in areas towards valve margins, in particular towards anterior and posterior margins. Right valve with denticles running along anterior and posterior-ventral margins; denticles absent only in short middle section of central ventral margin. Left valve with well-developed marginal sockets on calcified inner lamella corresponding to marginal denticles on right valve. Ventral margin of left valve with shallow groove fading out at each end where marginal sockets appear. Aesthetasc Y ca. 19% length of dorsal sclerotised margin of first antennal endopodal segment. Swimming setae long, reaching beyond ends of claws. Male antennal claw Gm short, ca. 37% length of GM. Gamma seta of mandible short and relatively thin, with main body not reaching to end of last segment, and with long setules distally. Third endite of maxillula with strongly serrated Zahnborsten (tooth bristles). Seta h1 of sixth limb long, over one-third length of claw h2. Caudal ramus sexually dimorphic: ramus more or less straight in female, distinctly curved in male. Hemipenis medial shield roughly quadrate, with distal margin straight, and broadly curving at edges to lateral margins. Lateral shield bootshaped, with distal part elongate and with almost parallel sides. Distal end rounded point. Zenker organ with 27 to 32 internal whorls. Females noticeably larger than males.

Type locality. Rice fields in the vicinity of the Tomecho, Nagahama, Shiga Prefecture, Japan, 35.4387º N, 136.3264º E ( Table 1, sample 4) .

Material examined. Holotype. JAPAN • 1 ♂, with soft parts dissected in glycerine and sealed in a slide, valves stored dry in a micropalaeontological slide; Shiga Prefecture, Nagahama, Tomecho ; 35.4387º N, 136.3264º E; alt. 145 m; 24 May 2009; Robin J. Smith leg.; rice field; LBM 1430009503 .

Allotype. JAPAN • 1 ♀, with soft parts dissected in glycerine and sealed in a slide, valves stored dry in a mi- cropalaeontological cavity slide; same collecting data as for holotype; LBM 1430009505 .

Paratypes. JAPAN • 3 ♂♂, with soft parts dissected in glycerine and sealed in slides, valves stored dry in mi- cropalaeontological cavity slides; same collecting data as for holotype; LBM 1430009496 , LBM 1430009502 , LBM 1430009504 . • 2 ♂♂, whole, stored dry in micropalaeontological cavity slides; same collecting data as for holotype; LBM 1430009500 , LBM 1430009501 . • 1 ♀, with soft parts dissected in glycerine and sealed in a slide, valves stored dry in a micropalaeontological cavity slide; same collecting data as for holotype; LBM 1430009506 . • 2 ♀♀, whole, stored dry in micropalaeontological cavity slides; same collecting data as for holotype; LBM 1430009498 , LBM 1430009499 .

Other figured material. JAPAN • 1 ♀, whole, stored dry in a micropalaeontological cavity slide; Shiga Pre- fecture, Kusatsu, Oroshimo, Lake Biwa Museum ; 35.07464º N, 135.93402º E; alt. 90 m; 22 May 2009; Robin J. Smith leg.; rice field; LBM 1430009495 . • 1 ♀, whole, stored dry in a micropalaeontological cavity slide; Shiga Prefecture, Moriyama, Hattoricho ; 35.10259º N, 135.99661º E; alt. 91 m; 30 May 2009; Robin J. Smith leg.; rice field; LBM 1430009508 . • 1 ♀, whole, stored dry in a micropalaeontological cavity slide; Shiga Prefecture, Yasu, Inokuchi ; 35.11304º N, 136.00466º E; alt. 84 m; 30 May 2009; Robin J. Smith leg.; rice field; LBM 1430009507 .

KOREA • 1 ♀, whole, stored dry in a micropalaeontological cavity slide; Gyeongsangbuk-do, Gyeongsan-si, Jillyang-eup, Sangrim-ri ; 35.90169º N, 128.83585º E; alt. 62 m; 8 Jun. 2011; Robin J. Smith and Jimin Lee leg.; ditch; LBM 1430009511 . • 1 ♀, whole, stored dry in a micropalaeontological cavity slide; Gyeongsangbuk-do, Gyeongju-si, Bulguk-dong ; 35.78953º N, 129.31646º E; alt. 149 m; 2 Jul. 2011; Cheon Young Chang leg.; rice field; LBM 1430009512 . • 1 ♀, whole, stored dry in a micropalaeontological cavity slide; Gyeongsangbuk-do, Gyeongju-si, Bomun-dong ; 35.83511º N, 129.25050º E; alt. 81 m; 4 Jul. 2011; Cheon Young Chang leg.; rice field; LBM 1430009513 .

Other material. See Table 1.

Description. Female carapace length 1783–1924 µm, height 1027–1153 µm, male carapace length 1479–1550 µm, height 883–934 µm, height / length = 0.57–0.61. Left valve overlaps right along anterior, posterior and ventral margins ( Fig. 1 ). In lateral view, right valve distinctly higher than left valve and projecting above with elongate, curved ridge from about mid-length to posterior margin ( Fig. 1A & B ). Anterior and posterior margins more or less evenly inflated, posterior margin slightly angular at lower third. Ventral margin straight. Dorsal view, maximum width slightly posterior of mid-length, anterior and posterior margins angular, anterior margin slightly ‘beak-shaped’ ( Fig. 1C ). Surface of valves smooth in central area, but with small shallow pits in areas towards valve margins, in particular towards anterior and posterior margins. Right valve with denticles running along anterior and posteriorventral margins; denticles absent only in short middle section of central ventral margin ( Figs 1D , 2C & D , 3A, C & D ). Selvage sub-marginal, displaced further inwards along posterior margin. Anterior calcified lamella with two faint lists with perpendicular, poorly developed striations in-between lists ( Fig. 2C ). Left valve with well-developed marginal sockets on calcified inner lamella corresponding to marginal denticles on right valve (therefore absent long ventral margin) ( Figs 2A & B , E–G). Calcified inner lamella roughened and slightly striated along inner side of marginal sockets. Ventral margin with shallow groove fading out at each end where marginal sockets appear ( Fig. 2G ). Muscle scars typical of family. Colour orangish yellow, darker towards dorsal margin, irregular shaped brownish area behind eye, hepatopancreas greenish-grey in females ( Fig. 4A & B ). Male carapace similar to female, but noticeably smaller ( Figs 1 E–H, 4A & B).

Antennule with seven articulated segments ( Fig. 5A ). First segment with tiny Wouters organ and seta on dorsal margin, and two long sub-apical setae on ventral margin. Second segment with small Rome organ, and apical-dorsal seta. Third segment with one apical-dorsal seta and one apical-ventral seta. Fourth segment with two long apicaldorsal setae, and two short apical-ventral setae. Fifth segment with two long apical-dorsal seta, and two apical-ventral setae. Sixth segment with four long and one very short (alpha) setae; alpha seta 1.7 times length of dorsal margin of terminal segment. Terminal segment apically with one stout, short seta, two long setae and aesthetasc ya.

Male antenna, exopodite with longest seta reaching to end of first endopodal segment, medium-length seta ca. one-quarter length of longest seta ( Fig. 5B ). Aesthetasc Y 19% length of dorsal sclerotised margin of first endopodal segment (marked with dotted arrowed line on Fig. 5B ). Swimming setae long, reaching beyond ends of claws. Claw G1 short and slightly sinuous, ca. 42% length of claw G2 ( Fig. 6A ). Z1 claw long and robust, slightly longer than claw G2. Claw z2 slender, 80% length of z1. Seta z3 reaching to ca. end of claw G2. Claw Gm slender, slightly sinuous and short, ca. 37% length of GM. Female antenna with short G2 claw, ca. half length of G1 ( Fig. 6B ). Claw Gm very slender, half length of claw GM. Setae z2 and z3 not reaching to end of claws, seta z1 shorter.

Mandible palp, first segment with small, slender alpha seta, tapering distally to setule-like distal end ( Fig. 5C & D ). Second segment 3+1+beta setae on inner edge, and three setae on outer edge. Beta seta setulous, slightly longer than alpha. Third segment with group of four sub-apical setae on outer edge, gamma + 3 setae along distal edge, one long and one very short setae on inner sub-apical edge. Gamma seta short and relatively thin, with main body not reaching to end of last segment, and with long setules distally. Terminal segment with three stout claw-like setae and three thinner setae. Mandibular coxa robust, with ca. seven teeth of various sizes ( Fig. 5E ).

Rake-shaped organ with 8–9 teeth distally.

Maxillula palp, first segment with group of five setae on outer apical edge, all of varying lengths, and two sub-apical setae, one of which long, located on outer edge, and other, much shorter seta displaced inwards ( Fig. 5F ). Second segment elongate, apically with three claw-like robust setae, and three smaller setae. Third endite with strongly serrated Zahnborsten.

Fifth limb (maxilliped) basis with two a setae, and medium-length d and b setae; c seta missing, typical of subfamily ( Fig. 6C ). Endite with ca. 14 apical setae. Exopodite (branchial plate) with six rays. Male palps asymmetrical, right palp with broad, curved hook, inner edge almost straight ( Fig. 5H ), left hook much thinner than right, tightly curved proximally, distal half almost straight ( Fig. 5G ). Female palp with one long apical seta, and two shorter apical setae of similar lengths ( Fig. 6C ).

Sixth limb (walking leg) robust with five articulated segments ( Fig. 6D & E ). First segment with short d1 seta. Second segment with e seta reaching beyond end of third segment. Third segment with f seta reaching to beyond end of fourth segment. Fourth segment with one long and one short g setae. Fifth segment with very long h1 seta, over one-third length of claw h2, much shorter h3 seta, and robust, long h2 claw with well-developed serration. Male with proportionally shorter claw G2 than female, and with stronger developed serration.

Seventh limb (cleaning limb) with seta d1 on first segment shorter than d2 and dp of same segment ( Fig. 6F ). Second segment with relatively long e seta. Third segment with f seta at mid-length, almost reaching to end of segment. Terminal segment part of pincer structure typical of the family.

Male caudal ramus slender and curved. Claw Ga long, ca. 65% length of caudal ramus ( Fig. 7A ). Claw Gp noticeably smaller, about 63% length of Ga. Seta sp long, but shorter than claw Gp. Seta sa relatively long, about 38% length of Ga. Female caudal ramus straighter than that of male ( Fig. 7B ). Caudal ramus attachment single branch, curved towards dorsal third ( Fig. 7C ).

Hemipenis medial shield roughly quadrate, with distal margin straight, and broadly curving at edges to lateral margins ( Fig. 7D ). Lateral shield boot-shaped, with distal part elongate and with almost parallel sides. Distal end rounded point. Lateral shield distally ranging from pointed to rounded, and sometimes with small protrusion on outer corner (‘heel of boot’) ( Fig. 7E ).

Zenker organ with 27 to 32 internal whorls. Spermatozoa range from 1059 to 1109 µm in length, with mean of 1080 µm (Online Supplementary Appendix of Smith et al. 2016a, as Cyprintous uenoi ).

Remarks. This species was first reported from Japan as Cyprinotus uenoi Brehm, 1936 by Okubo (1974), but the Japanese specimens are different to the original description of C. uenoi in the following ways: Even allowing for a large margin of error in the drawings, the valves depicted by Brehm (1936) are significantly different in shape to those of the Japanese specimens ( Fig. 7F & G ). Brehm (op. cit.) noted that in lateral view the right valve overlaps the left dorsally (typical of Cyprinotus ), and the left valve overlaps the right, particularly in the posterior area (shown to be a considerable overlap on Brehm’s Fig. 1 ). While the left valve overlaps the right in the posterior area in Japanese specimens, it is only very slight compared to Brehm’s description. The right valve overlap of Japanese specimens starts just anterior of maximum height of the left valve and extends down the posterior dorsal margin, in contrast with that of C. uenoi , which is entirely anterior of the point of maximum height of the left valve ( Fig. 7F & G ). Brehm (1936) also did not mention the sexual dimorphism in carapace size for C. uenoi that is seen in the Japanese specimens. Based on these features, it is highly unlikely that the Japanese species is conspecific with the Chinese species. Brehm’s specimens of C. uenoi were collected from a “swamp with luxurious growth of vegetation” in “Tsitsikar in Mandschuko”, present day Qiqihar in Heilongjiang Province, China. However, Brehm did not designate type specimens of C. uenoi , and the location of his collection is currently unknown ( Nagler et al. 2014).

Of the seven other species in the genus Cyprinotus , most have a different shape in lateral view compared with Cyprinotus cassidula sp. nov. The closest is the Australian species Cyprinotus dahli Sars, 1896 , but Cyprinotus cassidula sp. nov. is more rounded anteriorly and has a straighter ventral margin. Other differences include the caudal ramus (setae sa and sp are much longer in Cyprinotus cassidula sp. nov.), and hemipenis (the lateral shield is more elongate and thinner in Cyprinotus cassidula sp. nov.). Other features of C. dahli remain unknown hindering further comparisons.

Kim & Min (1991) reported Cyprinotus uenoi from various localities in South Korea. Their figures mostly correspond with the Japanese species, although the right valve is noticeably higher, the lobe of the male sexual organ is shorter and some aspect of the chaetotaxy are different (e.g. no Rome organ on the antennule, additional setae on the terminal segment of the antenna, five setae on the terminal segment of the mandibular palp, eight setae on the first segment of the maxillular palp, and no d1 seta on the sixth limb). It is unclear if these are true differences between the Korean and Japanese populations as some are highly unusual for the whole family, such as the extra setae on the antenna. The specimens collected for this study from South Korea are very similar to those from Japan, and so the records of Kim & Min (1991) are possibly conspecific.

Cyprinotus cingalensis Brady, 1886 reported from China ( Yu 2014) is considered herein to be a misidentification as the carapace differs from figures in Neale (1979). The Chinese species is close to Cyprinotus cassidula sp. nov. but differences include the length of the antennal G2 claw in females (much longer in the Chinese species), the length of the h1 seta on the sixth limb (much longer in Cyprinotus cassidula sp. nov.) and the dorsal view of the carapace (right valve with a posterior indentation in the Chinese species). This Chinese species is also different to Brehm’s (1936) original description of C. uenoi in the lateral view of the carapace, especially the left valve, and may represent an undescribed species. Victor & Fernando’s (1981) record of C. uenoi from the Philippines is also different from Brehm’s (1936) species in lateral view. It is also smaller than the Japanese species, and has a more prominent dorsal ridge on the right valve, producing a concave antero-dorsal margin.

A second much smaller Cyprinotus species has been reported from Japanese rice fields on Shikoku Island, and in Okinawa and Okayama Prefectures, identified as Cyprinotus kimberleyensis McKenzie, 1966 and/or Cyprinotus setoensis Okubo, 1990 ( Okubo 1974; 1990; 2004). It has a noticeably lower height than C. kimberleyensis as figured by McKenzie (1966), and it is not clear if it is conspecific. Further analysis of this species is hindered by lack of specimens as well as the incomplete description of C. kimberleyensis .

It has been reported that the size of the dorsal ridge on the right valve is highly variable in Cyprinotus kimberleyensis McKenzie, 1966 (e.g. Okubo 1990; Karanovic 2008), although it is not clear if all reports are accurate identifications (see above; Martens et al. 2019). This feature in Cyprinotus cassidula sp. nov. does not show any significant variation in size ( Fig. 3 E–J), although it is slightly relatively larger in males compared to females ( Fig. 1A & E ).

Distribution and ecology. This study can confirm that this species is present in Japan and South Korea. Kim & Min’s (1991) records of C. uenoi , which may be the same species, are from various localities in South Korea. Chang et al. (2012) reported this species as C. uneoi from Gyeongsangbuk-do, South Korea. Other reports of C. uenoi are not accompanied by figures so cannot be assessed, but probably all Japanese records of C. uenoi are erroneous and represent Cyprinotus cassidula sp. nov. Specimens examined for this study were mostly collected from rice fields, but also a ditch next to a rice field ( Table 1). We have collected it from the end of May through to early July. Nothing else is known about its ecology in rice fields.

Figures

FIGURE 1. Cyprinotus cassidula sp. nov. A, whole carapace, left view, female (LBM 1430009498). B, whole carapace, right view, female (LBM 1430009499). C, whole carapace, dorsal view, female, anterior to left (LBM 1430009498). D, right valve, internal view, female (LBM 1430009506). E, whole carapace, left view, male (LBM 1430009500). F, whole carapace, right view, male (LBM 1430009501). G, whole carapace, dorsal view, male, anterior to left (LBM 1430009500). H, right valve, internal view, male (LBM 1430009496). All specimens from type locality (Table 1, sample 4). Scale bar = 500 µm.

FIGURE 2. Cyprinotus cassidula sp. nov. A, left valve, internal view, female (LBM 1430009506). B, left valve, internal view, male (LBM 1430009496). C, right valve, internal view, female, detail of antero-ventral area (LBM 1430009506). D, right valve, internal view, female, detail of postero-ventral area (LBM 1430009506). E, left valve, internal view, female, detail of posteroventral area (LBM 1430009506). F, left valve, internal view, female, detail of antero-ventral area (LBM 1430009506). G, right valve, internal view, female, detail of central ventral area (LBM 1430009506).All specimens from type locality (Table 1, sample 4). Scale bar = 500 µm for A & B, 108 µm for C–G.

FIGURE 3. Cyprinotus cassidula sp. nov. A, right valve, ventral view, female (LBM 1430009506, sample 4; see Table 1). B, left valve, ventral view, female (LBM 1430009506, sample 4). C, right valve, ventral view, female, detail of marginal denticles (LBM 1430009506, sample 4). D, right valve, ventral view, female, detail of ventral area (LBM 1430009506, sample 4). E–J, whole carapaces, left views, females, each from different locations, E–G from Japan (LBM 1430009495, sample 3, LBM 1430009508, sample 4, LBM 1430009507, sample 10 respectively), H–J from Korea (LBM 1430009511, sample 22, LBM 1430009512, sample 25, LBM 1430009513, sample 28 respectively). Scale bar = 500 µm for A & B, 28 µm for C, 108 µm for D, 817 µm for E–J.

FIGURE 4. A & B, Cyprinotus cassidula sp. nov. (sample 10; see Table 1).A, left lateral view of whole carapace, female. B, left lateral view of whole carapace, male. C, Hemicypris megalops, whole carapace, right lateral view, female (paralectotype from Sumatra, Indonesia F12292c2, before dissection). D–F, Hemicypris posterotruncata. D & E, left lateral views of whole carapaces, females. F, dorsal view of whole carapace, anterior to left, female. G & H, Hemicypris ovata. G, paralectotype (NHMO F12264c), right view of whole carapace, female (prior to SEM). H, paralectotype (NHMO F12264b), internal view of right valve, female (before dissection). I & J, Hemicypris barbadensis (LBM 1430009514). I, left valve, internal view, female. J, right valve, internal view, female. K & L, Heterocypris savatenalintonae sp. nov. K, left lateral view of whole carapace, female. L, left lateral view of whole carapace, male. M–O, Hemicypris kibiensis (LBM 1430009515). M, left valve, internal view, female. N, right valve, internal view, female. O, high magnification transmitted light microscopy of valves. A–H, K & L, photographed while specimens submerged in water. I, J, M–O, mounted in unknown medium on glass slide.All photographs focussed stacked. Scale bar = 1506 µm for A & B, 1000 µm for C to N, 238 µm for O.

FIGURE 5. Cyprinotus cassidula sp. nov. A, antennule, male (LBM 1430009504). B, antenna, male (LBM 090524-01-014). C, mandibular palp, male (LBM 1430009502). D, alpha, beta and gamma setae of mandibular palp, male (LBM 1430009502). E, mandibular coxa, male (LBM 1430009502). F, maxillula palp and endites (setae on endites not drawn) (LBM 1430009502). G, left fifth limb palp, male (LBM 1430009502). H, right fifth limb palp, male (LBM 1430009502). All specimens from type locality (Table 1, sample 4).

FIGURE 6. Cyprinotus cassidula sp. nov. A, antenna, male, detail of last two segments (LBM 1430009502). B, antenna, female, detail of last two segments (LBM 1430009505). C, fifth limb, female (LBM 1430009505). D, sixth limb, male (LBM 1430009502). E, sixth limb, female (LBM 1430009505). F, seventh limb, male (LBM 1430009502). All specimens from type locality (Table 1, sample 4).

FIGURE 7. A–F, Cyprinotus cassidula sp. nov. A, caudal ramus, male (LBM 1430009503, sample 4; see Table 1). B, caudal ramus, female (LBM 1430009505, sample 4). C, caudal ramus attachment, male (LBM 1430009503, sample 4). D, hemipenis (LBM 1430009503, sample 4). E, outlines of hemipenes (left to right, LBM 1430009509, sample 18, LBM 1430009494, sample 3, LBM 1430009496, sample 4, LBM 1430009497, sample 4, LBM 1430009510, sample 21). Asterisk indicates drawing reflected on the vertical axis to facilitate comparisons. F, outlines of left and right valves, and carapace, not to scale, arrows indicate anterior. G, Cyprinotus uenoi, outlines of left and right valves, and carapace, redrawn from Brehm (1936), not to scale, arrows indicate anterior.