A New Species of Semicytherura (Crustacea: Ostracoda: Cytheroidea) from Obitsu River Estuary (Central Japan) and Its Microhabitat

Species Diversity 25: 1–9 Published online 1 January 2020 DOI: 10.12782/specdiv.25.1

Yuriko Nakao1,3 and Akira Tsukagoshi2 1 Department of Earth and Environmental Sciences, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajousui, Setagaya-ku, Tokyo 156-8550, Japan E-mail: [email protected] 2 Department of Geosciences, Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan 3 Corresponding author (Received 17 April 2019; Accepted 16 October 2019)

http://zoobank.org/6B3FBBFD-7DEB-43F7-B2AE-30FE3DD03B5D

A new ostracod species, Semicytherura obitsuensis sp. nov., is described from the intertidal zone of the Obitsu River estuary, Chiba Prefecture, central Japan. As S. obitsuensis sp. nov. individuals were collected from muddy sand bottoms in tidal creeks, possess some carapace-features comparable to those of interstitial and infaunal ostracods, and were observed to crawl in detritus rich fine-grained sediment in the laboratory, we concluded that this new species is an infaunal species. Key Words: Crustacea, Ostracoda, Semicytherura, infauna, new species, Japan, Obitsu River estuary, microhabitat, tidal flat.

divided benthic ostracods into 4 life types based on their Introduction micro habitat: (1) living on tall seagrass, (2) burrowing in sediments, (3) crawling on the sediment surface, and (4) liv- Benthic organisms are generally divided into two groups, ing on low-growing plants such as the holdfasts of algae and i.e., epifauna and infauna. The epifauna includes organisms seaweed and filamentous mats associated with sediments. crawling on the sediment surface or on plant, coral, or other Furthermore, Tanaka (2009) discussed the relationships organisms projecting above the sediment, and some swim- among their carapace morphology, phylogeny, and lifestyle. ming organisms that swim only short distances (Maddocks Though several studies on ostracods microhabitat were 1976). Meanwhile, the infauna includes interstitial organ- carried out, the terminology used in this field of research isms, mobile endobionts, and sedentary endobionts (Mad- has always not been consistent. Therefore, in this study, the docks 1976). Ikeya and Shiozaki (1993) reported that rep- species crawling on sediments, on plants, and on any other resentatives of benthic ostracods living in inner bays mostly substratum on the sediment are defined as epifaunal species. occur in the uppermost 1 cm of the surface sediment, es- Contrastingly, species burrowing/crawling in the uppermost pecially in the uppermost 0.5 cm. They also investigated layer of sediments with or without flocculent layer are de- in detail the surface sediment structure of inner bays as an fined as infaunal species. Furthermore, we distinguish inter- ostracod habitat and divided sediments into three parts, i.e., stitial species, inhabiting “the water-filled cavities between flocculent layer, oxidized layer, and reduced layer, from the the grains of a clastic sediment” (Maddocks 1976: 195), top down. Furthermore, they described three lifestyles in from infaunal species. these microhabitats: walking through the flocculent layer More than 30 species of the genus Semicytherura Wanger, above the poorly sorted silty bottom, crawling on well- 1957 including both living and fossil specimens, have been sorted sandy bottom deposited under the flocculent layer, reported from Japan and its adjacent areas (Yamada and and moving through the spaces in the flocculent layer and Tsukagoshi 2010). Moreover, Yamada and Tanaka (2011, sandy oxidized layer. Jöst et al. (2017) revealed that deep-sea 2013) reported three interstitial species, i.e., S. mukaishi- benthic ostracods mostly live in the uppermost 1 cm of sedi- mensis Okubo, 1980, S. sagittiformis Yamada and Tanaka, ment and are either epifauna or infauna. This vertical distri- 2011, and S. uzushio Yamada and Tanaka, 2013. Yamada and bution of deep-sea ostracods corresponds to that of shallow Tanaka (2011) emphasized the importance of small carapace marine ostracods reported by Ikeya and Shiozaki (1993). size in the genus Semicytherura for adaptation to the inter- Kamiya (1988, 1989) divided ostracod fauna in Zostera stitial environment, and suggested that S. hanaii Ishizaki, beds into phytal species and bottom-dwelling species, and 1981, S. okinawaensis Nohara, 1987, S. polygonoreticulata reported that bottom-dwelling species comprised spe- Ishizaki and Kato, 1976, S. ryukyuensis Nohara, 1987, S. cies crawling on and in the flocculent layer. Tanaka (2009) sabula Frydl, 1982, S. skippa (Hanai, 1957), and S. yajimae

Fig. 1. Sampling site. A, map of Japan; B, location of Obitsu River estuary (arrowhead); C, sampling point (arrowhead) and sediment distribution of the sampling site. [Adopted from Tsukagoshi (1994)]

Ikeya and Zhou, 1992 would be interstitial species based on their small carapace size. Contrastingly, some Semicytherura species were reported as epifaunal species (Tanaka 2009; Ya- Taxonomy mada and Tanaka 2011). Although Semicytherura species have been reported from various environments (e.g., tidal Genus Semicytherura Wagner, 1957 flat, rocky shore, inner bay, estuary, and infralittoral zones), Semicytherura obitsuensis sp. nov. no species have until now been strictly referred to as infau- (Figs 2–5) nal species. This study reports a new Semicytherura species from the Pontocythere sp. 1: Yajima 1982, pl. 10 7–8, text-fig. 13 5–6. Obitsu River estuary, which has a carapace and soft parts that differ in morphology from those of the interstitial and Type series. Holotype: male (SUM-CO-2461; length/ epifaunal Semicytherura species reported previously. height of right valves 0.45/0.17 mm, of left valve 0.45/0.17 mm). Paratypes: 9 males (SUM-CO-2462–2470) and 10 females (SUM-CO-2471–2480). Materials and Methods Type locality. Obitsu River estuary, Tokyo Bay, Chiba Prefecture, Japan (35°25′04.9″N, 139°53′57.8″E). In the present study, the sediment was collected from the Etymology. After the Obitsu River estuary, central intertidal zone of the Obitsu River estuary, Chiba Prefecture, Japan. Japan (Fig. 1). Sampling was carried out during low tide in Diagnosis. Carapace thin, weakly arched cylindroid, March 2016 and 2018. The uppermost layer (approximately and elongated. Carapace surface covered with concentric 1 cm) of muddy sand bottom sediment covered with floc- muri and short muri, forming reticulation in anterior area. culent layer was scooped using a big flat spoon at the tidal Concentric muri in antero-dorsal area showing like broken creek. In the laboratory, samples were washed through a line. Inside valve, depressed triangular lamella of prismatic 63-µm mesh sieve and the carapaces with the chitinous layer in anteroventral area and broad vestibules in anterior parts of ostracods were stored in 70% ethanol. Then, the chi- area in both male and female. Fourth and fifth podomeres of tinous parts were dissected with fine needles and mounted antennule fused. All terminal claws of thoracic legs bearing on glass slides with Neo-Shigaral (Shigakonchu Fukyusha). one small spinous process at 1/3 from proximal end. Male Morphological observations were carried out under a light copulatory organ bearing sub-oval capsule and biramous microscope (Olympus BX51). The uncoated carapaces were distal lobe: one tip sharp and triangular, other one with air-dried and observed under a scanning electron micro- round tip bent at almost right angle. Copulatory duct short scope (HITACHI Microscope TM-1000; SEM). The type se- and coiled. ries is deposited in the collection of the Shizuoka University Description. Carapace (Figs 2, 3, 4A, B). Carapace Museum, Shizuoka, Japan, identified by numbers with the small, thin, weakly arched cylindroid, and more elongated prefix SUM-CO. outline in lateral view in male than female. Greatest height somewhat behind mid-length; dorsal margin gently arched and ventral margin concave anterior mid-length. Ante- rior margin gently tapered-off downward. Posterior margin round without caudal process; lower part of posterior mar- A new species of Semicytherura from Japan 3

Fig. 2. Semicytherura obitsuensis sp. nov. A, male right valve in external lateral view; B, male left valve in external lateral view; C, male left valve in internal lateral view; D, male right valve in internal lateral view; E, female right valve in external lateral view; F, female left valve in external lateral view; G, female left valve in internal lateral view; H, female right valve in internal lateral view; I, male carapace in dorsal view; J, female carapace in dorsal view; K, male carapace in ventral view; L, female carapace in ventral view. A–D, paratype, SUM-CO-3462; E–H, paratype, SUM-CO-2471; I, K, paratype, SUM-CO-2463; J, L, paratype, SUM-CO-2472. 4 Y. Nakao and A. Tsukagoshi

Fig. 3. Semicytherura obitsuensis sp. nov. A, male carapace in anterior view; B, male carapace in posterior view; C, female carapace in anterior view; D, female carapace in posterior view; E, adductor muscle scar of male right valve (arrow indicating anterior); F, adductor muscle scar of female right valve (arrow indicating anterior); G, hingement of male right valve; H, hingement of male left valve; I, hingement of female right valve; J, hingement of female left valve. A, B, paratype, SUM-CO-2463; C, D, paratype, SUM-CO-2472; E, G, H, paratype, SUM- CO-2462; F, I, J, paratype, SUM-CO-2471. Arrowheads indicate mandibular scars. gin straight more prominently in male. Carapace surface male. Lower 3 somewhat large; upper one elongate; middle with reticulation composed of concentric and short muri one square; lower one semi-circular. Large circular fulcral in anterior area; obscure reticulation in mid-lateral area; al- point in front of row of adductor muscle scars. Two large most smooth in dorsal and posterior area. Concentric muri frontal scars in front of fulcral point; anterior one circular in antero-dorsal area showing like broken line. Sixty-three and posterior one kidney-shaped. Two obscure mandibular pore systems per valve. Eyes present without tubercle. scars on lamella of prismatic layer. Lamella of prismatic layer, depressed triangular shape Hingement (Fig. 3G–J). Lophodont. Hinge line weakly with cleaved sides in antero-ventral area in both male and arched. Groove and weakly developed terminal teeth in female; broad in posterior area in male. Vestibules devel- right valve. Bar and terminal socket in left valve. oped in anterior, slightly narrow from ventro-median to Antennule (Fig. 4C). Six articulated podomeres, with 4th posterior area in both male and female. and 5th podomeres fused. First podomere with minor as- Muscle scar (Fig. 3E, F). Vertical row of 4 adductor scars semblage of setulae on anterior-distal and distal margin. in ventro-median area. Uppermost circular; obscure in fe- Second podomere with 1 very long setulose seta at middle A new species of Semicytherura from Japan 5

Fig. 4. Semicytherura obitsuensis sp. nov., valves and appendages. A, internal view of male right valve; B, internal view of female right valve; C, antennule; D, antenna of male; E, antenna of female; F, mandibule. A, C, D, F, holotype, SUM-CO-2461; B, paratype, SUM-CO-2471; E, paratype, SUM-CO-2473. of posterior side, assemblage of short setae on proximal and end. Sixth podomere with 2 long, 1 medium, and 1 spatulate distal area, and setulae along distal half of anterior margin. setae on distal end. Third podomere with 1 medium setulose seta on near dis- Antenna (Figs 4D, E). Five articulated podomeres. First tal end, one assemblage of short setae at middle, and setulae podomere with 1 long stout exopodite (= spinneret seta) along anterior margin. Fourth and 5th podomeres almost and assemblage of short setae on anterior-distal end. Nu- fused. Fourth podomere with 2 long simple setae and 1 merous rows of setulae on outer lateral side. Second podo- medium setulose seta on distal end, and row of numerous mere with 1 setulose and 1 simple short setae on postero- short setulae on anterior side. Fifth podomere with 2 setu- distal end, assemblage of short setae on antero-proximal end lose stout setae, 1 thin short and 1 simple setae on distal and on outer lateral side, and setulae along anterior margin. 6 Y. Nakao and A. Tsukagoshi

Fig. 5. Semicytherura obitsuensis sp. nov., appendages. A, maxillule; B, fifth limb; C, sixth limb; D, seventh limb; E, male copulatory organ. A–E, holotype, SUM-CO-2461.

Third podomere with 2 short setulose setae on postero-dis- claw-like seta on ledge of posterior margin, 1 short thin seta, tal end, setulae along anterior margin, and short setae along and 1 claw-like seta possessing spinous process on distal proximal half of anterior margin. Fourth podomere with 1 end. Serrations along distal part of both of claw-like setae. long curved spatulate seta more developed in male near Mandibula (Fig. 4F). Five articulated podomeres, with proximal end on outer lateral side, 1 thin seta at middle of 2nd to 5th podomeres fused. First podomere (coxa) with anterior margin, 1 stout setulose seta on postero-distal end, several stout irregular teeth on anterior margin and setu- and setulae along posterior margin. Fifth podomere with 1 lose seta at about 1/3 from dorso-distal end. Second podo- A new species of Semicytherura from Japan 7 mere (basis) with bunch of short setae at middle of ventral podomere with one short setulose seta on antero-distal end, margin, 1 long setulose seta on distal end, and exopodite setulae along anterior margin, and assemblage of setulae on reduced to 1 stout setulose seta. Third podomere (1st podo- postero-proximal area. Second podomere with 1 long setu- mere of endopodite) with 1 long seta on dorso-distal end, lose seta on anterto-distal end and setulae along distal half 1 long seta on ventro-distal end, and 2 long setae on near of anterior margin and distal margin. Third podomere with ventral distal end, all setae setulose; fine setulae along dorsal setulae along distal half of anterior margin and distal mar- margin. Fourth podomere (2nd podomere of endopodite), gin. Fourth podomere with setulae on distal half of anterior with 2 medium simple setae and 2 long simple setae on margin and distal margin and 1 large terminal claw bearing ledge at middle of dorsal margin, 1 stout setulose seta, and 1 serrations; on anterior margin of claw, one small spinious simple seta on ventro-distal end. Fifth podomere (3rd podo- process at 1/3 from proximal end. mere of endopodite) with 1 claw-like seta, 2 rather short Male copulatory organ (Fig. 5E). Basal capsule sub-oval. claw-like setae, and 1 fine short simple seta on distal end. One clasping apparatus, thin and broad with round top. Dis- Maxillula (Fig. 5A). Extremely thin branchial plate (exop- tal lobe with biramous structure on distal end: one tip sharp odite) consisting of 14 simple setae and 2 long reflexed and triangular, other one with round tip bent at almost right setae. Basal podomere bearing palp (endopodite) and 3 en- angle. Pectinate structure and parallel lines on proximal area dites. Palp consisting of 2 podomeres; first podomere with of distal lobe. Copulatory duct short and coiled. 4 long setae at dorso-distal end; second podomere with Dimensions. See Table 1. 4 setae on distal end and 1 short seta on middle of ventral Remarks. In the morphology of soft part, the present margin. Each of three endites with 5 setae on distal end. new species is appropriately assigned to the genus Semicy- Brush-shaped organ. Not found. therura. Semicytherura obitsuensis sp. nov. is distinguished Fifth limb (Fig. 5B). Four articulated podomeres. Costae from other Semicytherura species based on its carapace (frame of podomere) especially developed along anterior morphology, i.e., relatively smooth surface with weak reticu- and posterior margins of second podomere. First podomere lation, elongated outline, the round posterior part without with 1 seta at middle of anterior margin, 2 long setae on an- caudal process, and broad vestibules in the anterior area. tero-distal end, and 2 setae on near postero-proximal end; Semicytherura obitsuensis sp. nov. resembles S. sabula from all setae setulose. Second podomere with 1 long setulose Tateyama Bay. However, S. obitsuensis sp. nov. has more seta on antero-distal end and setulae along distal half of an- tapered anterior and posterior margins and shows a much terior margin and distal margin. Third podomere with set- clearer reticular ornamentation. Moreover, only males of ulae along distal half of anterior margin and distal margin. S. obitsuensis sp. nov. have developed “lamella of prismatic Fourth podomere with setulae along distal half of anterior layer” (Yamada et al. 2004: 384) in the posterior and ventral margin and distal margin and 1 large terminal claw bearing areas, whereas in S. sabula both males and females have it. serrations; on anterior margin of claw, one small spinous Their carapace size is also different: S. obitsuensis sp. nov. process at 1/3 of from proximal end. (0.45–0.48 mm male length) is more extensive than S. sab- Sixth limb (Fig. 5C). Four articulated podomeres. Costae ula (0.31–0.33 mm male length, Frydl 1982). Semicytherura (frame of podomere) especially developed along anterior obitsuensis sp. nov. also resembles S. hiberna Okubo, 1980 and posterior margins of second podomere. First podomere from Seto Inland Sea. However, S. obitsuensis sp. nov. has with 2 setae on anterior margin, 1 seta on antero-distal end, a broad vestibule in anterior area whereas S. hiberna has a and 1 seta on near postero-proximal end; all setae setulose. broad lamella of prismatic layer in that area. Moreover, the Second podomere with 1 long setulose seta on antero-dis- shape of the male copulatory organ is different, and the 4th tal end and setulae along distal half of anterior margin and and 5th podomeres of antennule are not fused in S. hiberna. distal margin. Third podomere with setulae along distal half The carapace morphology and size of S. obitsuensis sp. of anterior margin and distal end. Fourth podomere with nov. are similar to Pontocythere sp. 1 reported by Yajima setulae along anterior margin and distal margin and 1 large (1982) (0.43/0.16 mm, length/height). Based sp. nov. on car- terminal claw bearing serrations; on anterior margin of claw, apace morphology, Pontocythere sp. 1 seen in SEM images one small spinous process at 1/3 of from proximal end. of Yajima (1982) are male specimens. They differ from the Seventh limb (Fig. 5D). Four articulated podomeres. First new species by the absence of the lamella of prismatic layer.

Table 1. Dimensions (mm) of Semicytherura obitsuensis sp. nov.

Length Height Width Object Av OR n Av OR n Av OR n Male RV 0.46 0.45–0.48 5 0.18 0.17–0.18 5 LV 0.47 0.45–0.48 5 0.18 0.17–0.18 5 C 0.16 0.15–0.17 2 Female RV 0.45 0.43–0.48 4 0.19 0.18–0.21 4 LV 0.45 0.43–0.48 4 0.19 0.18–0.21 4 C 0.18 0.16–0.19 6 Abbreviations: Av, average; C, carapace; LV, left valve; n, number of specimens; OR, observed range; RV, right valve. 8 Y. Nakao and A. Tsukagoshi

However, the lamella of prismatic layer was not observed tial lifestyles with most ostracod sampling methods, and or was unclear in some male specimens of S. obitsuensis sp. that the exact ostracod life mode can be determined only nov. on microscopic observation. Moreover, it was some- by direct observation of living specimens or by functional times destroyed after washing our specimens with sodium morphologic analysis of carapace and appendages. Living hypochlorite in preparation for SEM observation. Given individuals of S. obitsuensis sp. nov. were observed to crawl those situations, it is reasonable to assume that the lamella in detritus rich fine-grained sediment in a petri dish under of prismatic layer was not preserved in the fossil specimen microscopic observation during this study. And, although of Yajima (1982). Thus, we conclude that Pontocythere sp. 1 the carapace of S. obitsuensis sp. nov. is small, elongated, should be recognized as a Pleistocene fossil record of S. obit- translucent, and weakly ornamented (those features are con- suensis sp. nov. from the Boso Peninsula, central Japan. sidered as adaptations to the interstitial life; Hartman 1973; Nakao and Tsukagoshi (2002) reported 21 species belong- Maddocks 1976), unlike interstitial Semicytherura species ing to 17 genera from the Obitsu River estuary intertidal (see above), the carapace and appendage morphology of S. zone. This new Semicytherura species is the twenty-second obitsuensis sp. nov. is not similar to that of epibenthic non- species reported from the area. interstitial species. Considering its morphology, behavior, and also habitat, we concluded that S. obitsuensis sp. nov. is an infaunal species. Jöst et al. (2017) reported that infaunal Discussion ostracod species living in fine-grained sediment of the deep- sea ocean has a smooth and elongated carapace; the smooth Yamada and Tanaka (2011) reported Semicytherura sag- and elongated carapace of S. obitsuensis sp. nov. could be ittiformis as the first interstitial Semicytherura species from adaptations to the infaunal environment. Other morpho- Japan. Besides the small carapace size, both carapace and logical features of S. obitsuensis sp. nov. (i.e., the fusion of appendage morphology of S. sagittiformis resembles that of antennal 4th and 5th podomeres, small spinous process on other, non-interstitial Semicytherura species. The authors the terminal claw of walking legs, and long seta on walking claimed that the miniaturization of carapace is an efficient legs), which are unique among congeners, may also be adap- adaptation to the interstitial environment in this genus. tations to infaunal habitats. However, it remains as a matter Moreover, they suggested a possibility that some Semicy- to be discussed further. therura species with small carapace are interstitial species as Yamada et al. (2005) and Yamada and Tsukagoshi (2010) well. Particularly, S. yajimae and S. skippa were considered has reported 4 benthic Semicytherura species. Semicytherura interstitial because, in addition to their small carapace, they sasameyuki Yamada et al., 2005 was collected from the sedi- have been obtained from samples containing other intersti- ment samples of Maizuru Bay, and the other three species, tial ostracods and from coarse-grained sand, respectively. S. slipperi Yamada et al., 2005, S. maxima Yamada and Tsu- Yamada and Tanaka (2013) described carapace and ap- kagoshi, 2010, and S. ikeyai Yamada and Tsukagoshi, 2010, pendage morphology of S. mukaishimensis and S. uzushio, were collected from the dredged samples of Akkeshi Bay. classifying them as interstitial Semicytherura species. Sizes Based on the kind of the samples, it is possible that these (height/width) of S. mukaishimensis, S. sagittiformis, S. species are infaunal. However the authors did not mention uzushio, and S. skippa, are approximately 0.18/0.21 mm, that these species live in sediments strictly. Thus, to the best 0.15/0.23 mm, 0.16/0.11 mm (Yamada and Tanaka 2013), of our knowledge, this is the first report of an infaunal Semi- and 0.14/0.14 mm (Hanai 1957), respectively. Moreover, cytherura species from Japan. the carapace height of S. yajimae is approximately 0.16 mm (Ikeya et al. 1992). Semicytherura obitsuensis sp. nov. has a small carapace (approximately 0.18/0.17 mm), which falls in Acknowledgments the size range of interstitial Semicytherura species. Hartman (1973) noted that marine interstitial ostracods The authors wish to express their sincere thanks to Dr. inhabit 4 types of environments, namely littoral and sublit- Shinnosuke Yamada (International University of Health toral sands, coralline debris, gravel beach, and root tufts of and Welfare, School of Medicine, Japan) and Dr. Iwana the marine grass Posidonia, i.e., wherever the sediment par- Karanovic (Hanyang University, Korea) for their construc- ticles are big enough to form cavities. All reported intersti- tive suggestions that improved the manuscript. We also ap- tial Semicytherura species have been obtained from coarse- preciate Dr. Hayato Tanaka (Tokyo Sea Life Park, Japan) for grained sediment (Okubo 1980; Ikeya et al. 1992; Wilkin- valuable advice and discussion on interstitial species and son and Williams 2004; Yamada and Tanaka 2011, 2013). Semicytherura species. We thank Dr. Hyunsu Yoo (Hanyang However, S. obitsuensis sp. nov. was collected from intertidal University, Korea) for the valuable suggestions on soft part zone sediment samples covering the uppermost 1 cm surface morphology of the new species. We would like to thank of muddy sand sediment covered by flocculent layer. This Editage (www.editage.jp) for English language editing. This mud-rich sediment is different from those deposited in the work was partly supported by Grant-in-Aid for Scientific 4 environments mentioned above and cannot develop cavi- Research (JSPS KAKENHI Grant Number JP18K02990), ties suitable for inhabitation of interstitial species. and Individual Research Expense of Institute of Natural Sci- Maddocks (1976) mentioned that it is difficult to dis- ences at Nihon University for 2016 and 2017. criminate clearly among epifaunal, infaunal, and intersti- A new species of Semicytherura from Japan 9

cea) from the Obitsu River estuary, central Japan. Species Diver- References sity 7: 67–115. Okubo, I. 1980. Six species of the subfamily Cytherurinae Müller, 1894, in the Inland Sea, Japan (Ostracoda). Publication of the Seto Ma- Frydl, P. M. 1982. Holocene ostracods in the southern Boso Peninsula, rine Biological Labolatory 25: 7–26. The University Museum, The University of Tokyo, Bulletin 20: Tanaka, G. 2009. Adaptive modification of carapace outlines in the 61–140. Cytheroidea (Ostracoda: Crustacea). Biological Journal of the Lin- Hanai, T. 1957. Studies on the Ostracoda from Japan. III. Subfamilies nean Society 97: 810–821. Cytherurinae G. W. Müller (emend. G. O. Sars 1925) and Cyth- Tsukagoshi, A. 1994. Natural history of the brackish-water ostracode eropterinae n. subfam. Journal of the Faculty of Science, The Uni- genus Ishizakiella from East Asia: evidence for heterochrony. Jour- versity of Tokyo, Section 2 11: 11–36. nal of Crustacean Biology 14: 295–313. Hartmam, G. 1973. Zum gegenwästigen Stand der Erforschung der Os- Wagner, C. W. 1957. Sur les Ostracodes du Quaternarie Récent des Pays- tracoden interstitieller Systeme. Annales de Spéléologie 28: 741– Bas et leur Utilisation dans l’Étude Géoloique des Dépôts Holocénes. 752. Mouton, Amsterdam, 259 pp. Ikeya, N. and Shiozaki, M. 1993. Characteristics of the inner bay ostra- Wilkinson, I. P. and Williams, M. 2004. An interstitial Ostracoda from codes around the Japanese islands—The use of ostracodes to re- a beach-sand habitat in Keawéula Bay, northern Hawaii. Revista construct paleoenvironments. Memories of the Geological Society Española de Micropaleontología 36: 109–116. of Japan 39: 15–32. [In Japanese with English abstract] Yajima, M. 1982. Late Pleistocene Ostracoda from the Boso Peninsula, Ikeya, N., Zhou, B.-C., and Sakamoto, J. 1992. Modern ostracode fauna central Japan. The University Museum, The University of Tokyo, from Otsuchi Bay, the Pacific coast of northeastern Japan. Pp. Bulletin 20: 141–227. 339–354. In: Ishizaki, K. and Saito, T. (Eds) Centenary of Japanese Yamada, S. and Tanaka, H. 2011. First report of an interstitial Semicy- Micropaleontology. Terra Scientific, Tokyo. therura (Crustacea: Ostracoda: Cytheruridae: Cytherurinae): a Jöst, A. B., Yasuhara, M., Okahashi, H., Ostmann, A., Arbizu, P. M., and new species from central Japan. Species Diversity 16: 49–63. Brix, S. 2017. Vertical distribution of living ostracods in deep-sea Yamada, S. and Tanaka, H. 2013. Two interstitial species of the genus sediments, North Atlantic Ocean. Deep Sea Research Part I 122: Semicytherura (Crustacea: Ostracoda) from Japan, with notes on 113–121. their microhabitats. Zootaxa 4745: 435–448. Kamiya, T. 1988. Morphological and ethological adaptations of Ostra- Yamada, S. and Tsukagoshi, A. 2010. Two new species of Semicytherura coda to microhabitats in Zostera beds. Pp. 303–318. In: Hanai, T., (Podocopa: Ostracoda) from Akkeshi Bay, Hokkaido, Japan, with Ikeya, N., and Ishizaki, K. (Eds) Evolutionary Biology of Ostracoda comments on their speciation and related species. Zoological Sci- (Proceedings of the 9th International Symposium on Ostracoda). Ko- ence 27: 292–302. dansha, Tokyo. Yamada, S., Tsukagoshi, A., and Ikeya, N. 2004. Ultrastructure of the Kamiya, T. 1989. Functional morphology of Ostracoda in seagrass carapace in some Semicytherura species (Ostracoda: Crustacea). beds—with special reference to the copulatory behavior. Benthos Micropaleontology 50: 381–389. Reserch (35/36): 75–88. [In Japanese with English abstract] Yamada, S., Tsukagoshi, A., and Ikeya, N. 2005. Taxonomy, morphology Maddocks, R. F. 1976. Pussellinae are interstitial Bairdiidae (Ostraco- and speciation of the Semicytherura henryhowei group (Crustacea, da). Micropaleontology 22: 194–214. Ostracoda). Hydrobiologia 538: 243–265. Nakao, Y. and Tsukagoshi, A. 2002. Brackish-water Ostracoda (Crusta-