(Crustacea: Ostracoda: Cytheruridae: Cytherurinae): a New Species

JapaneseJapaneseSociety Society ofSystematicof Systematic Zoology

Species Diversity, 2011, 16, 49-63

First Report of Em Interstitial Semiaytherura (Crustacea: Ostracoda: Cytheruridae: Cytherurinae): a New Species

from Central Japan

Shinnosuke Yamadai and Hayato Tanaka2

iGeoBio-Cleinter, Luelwig Mctximilians []niversity ofit4tinich, Rtehard VVIxgner Street la 8a333 Mtznich, Germaay E-mail:[email protected] 2Grctduate Schoot ofScience and fl3chnoipgy, Shizuoha [hziversity, bya El3a Suruga-ku, Shizuokq 422-8529 Jictpan

(Received 11 May 2010; Accepted 6 October 2010)

A new species of ostracod, Senitqytherura scrgittijbrmis sp. nov., is described from a sandy beach in Shizueka Prefecture, centrai Japan. It lives in pore-waters of marine sandy sedirnents and is eeologically associated with other interstitial ostracods (e,g., Parmpolycope and Microloxoconcha). Semi- qytherura sagittijbrmis is one of the smallest species in the genus Semi- cytherura, and its carapace size is comparable witih those of some large interstitial ostracods. This fact suggests that a small carapace is the most impor-

tant charaeter for adaptation of ostracods to an interstitial environment,

Key Words: Crustacea, Ostracoda, Semiq)?therura, new species, interstitial

fauna, Japan, taxonomy, carapace size,

Introduction

Podocopid ostracods are small crustaceans furnished with a calcified bivalved carapace. They !ive in various aquatic habitats and their carapaces are often found in sedimentary strata as microfossils. Many taxonomic papers concerning epibenthic ostracods have been published, and a few authors have described the small os- "interstitial tracods living in the pore-water of sandy sediments, the so-called species" (Hiruta 1989; Watanabe et at. 2008; Higashi and Tsukagoshi 2008). interstitial ostracods often show specialised features, such as small carapace size, translucent colour, absence of an eye, valves with no omarnentation, and reduction in the number of setae on the appendages (Hartmann 1973; Maddocks 1976), The interstitial ostracod fauna consists mainly of a few specialised taxa (e.g., Microloxoconcha and Cobanoaythere), but some ostracods belonging to families that are mainly composed of epibenthic species have been reported as interstitial species (Danielopol and Hartmann 1986). The body sizes of these latter interstitial species are usually smaller than those of confamilial epibenthic ones, but some of the other specialised characters listed abeve are not found in their carapace and appendages (Danielopol and Bonaduce 1990), T'he genus Semicytherura VVagner, 1957 is defined by the calcified lamella and the tooth arrangement of the hingement. About 30 named species of this genus have been found in various marine habitats in Japan (rocky shore, irmer bay, and

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50 S, Yamada and H, Tanaka

infratidal zone) and some have also been reported as fossils (Yamada and Tsuk- agoshi 2ele). Their body size is usually smaller than that crf mher epibenthic ostracods (about O.3-O.6mm in length), but hitherto no species has been descrlbed as interstitial. in tihe present paper a new interstitial speeies of Semiaytherura is described, and the importance of bDdy size as an adaptation to an interstitial niche is dis- cussed based on a comparison of carapace sizes among species and genera.

Materials anct Methods

The material studied was collected from Miho Masaki Beach, Shizuoka Prefec- ture, Japan (Fig. 1). Sampling was carried out during Iow tide in November, 2009. Sandy sediment from the interstitial zone (20 cm below the sand surface) was taken with a scoop after digging down to seawater level. In the laboratory the secti-

ment samples were washed several times in a bucket of freshwater, and then the supernatant was strained through a 25-"m mesh sieve. The chitinous parts of ostracods thus recevered were dissected with fine needles and mounted on glass slides, and mor[phological observations were carried out under a Iight mieroseope

1300 1400

N ' s /

4oo ...... - -i --

..3oa . 20 km -..--...... epa..r!. .l 1

1 1 el 1 S, 500 km , . ･:?･-l I 1 1 l 1 l : :

Fig. 1. Sampling sites, A, Map of Japan; B, Miho Masaki Beach (arrowhead).

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Interstitial Semiqytherura from Japan 51

(OLYMPUS BX-50). The carapaces were air-dried, coated with osmtum

right valve.

Taxonomy

Genus Semiaytherura Wagner, 1957 Semiqytherura sagittijbrmis sp. nov. (Figs 2-8)

Semdytherara? sp. B: Ikeya et al. 1985, pl. 6, fig. 9

Type series. Holotype: male (SUM-CO-1912; length LVIRV = O.34/O.35mm, height LV/RV=O.1610.16mm). Paratypes: 7 males (SUM-CO-1913-1915, 1919, 1920, 1923, 1924> and 7 females (SUM-CO-1916-1918, 1921, 1922, 1925, 1941). Type locality. Miho Masaki Beach, Suruga Bay, Shizuoka Prefecture, Japan (35aOl,13rN, 138e31.07rE). Etymology. Named after its arrowhead-shaped outline in dorsal view, an ad- jective derived from the Latin sagitta (arrow) andforma (shape). Diagnosis. Carapace with 3 sman spines along anteroverMral margin, and oblong or sub-trapezoid in lateral view. Short, upward-bent caudal process at mid- height of carapace. Carapace sur face covered with distinct reticulation. Prominent ridge running from anterocentral margin, descending in posterior direction, and "iamella fbrming posteroventral ala. Sixty pore systems per valve. inside valve, of prismatic layer" (as described by Yamada et al, 2004) well developed, a little broader in male than in female. Male copulatory organ bearing sub-oval basal capsule and biramous distal lobe covered with thin membrane, Two clasping apparatuses long, foliated with blunt top, Copulatory duct short, coiled, Description, Carapace (Ftgs 2, 3) small and thin, oblong or sub-trapezoid in lateral view (Fig. 2A, B, E, F), arrowhead-shaped in dersal view (Fig. 3A, C). Alae well developed in both valves, together fomiing nearly circular shape in ventral view (Fig, 3B, D). Anterior margin with 3 smal[L spines, and arched in lower halfl Caudal process short and upwardly bent, located at mid-height on both valves, Dorsal margin straight, running parailel with ventral margin. Sexual dimorphism not pronounced. Carapace ornamentation as in Fig. 2A, B, E, F, One prominent ridge running from anterocentral margin, descending in posterior direction, and forming posteroventral ala. Strengly developed reticulation and numerous fine pits scattered all over carapace surface, Muscle sears as in Fig. 3E, F. Vertical row of 4 adductor scars in ventromedian area. Uppermost and lowermost scars semi-circular, 2 middle scars elongated. Frontal scar sub-triangular, in front of upper 2 adductor scars, At least 5 dorsal

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52 S. Yamada and H. Tanaka

Fig. 2, Semiaytherura sagittijbrrnis sp. nov. A, B, External lateral views of male LV and RV,

respectively (paratype, SUM-CO-1913); C, D, internal lateral views of male LV (paratype, SUM-CO-1914) and RV (paratype, SUM-CO-1915), respectively; E, F, external lateral views of female LV and RV, respectively (paratype, SUM-CO-1916); G, H, inteunal lateral views ef female LV (paratype, SUM-CO-191D and RV (paratype, SUM-CO-1918), respeetively. Arrows in-

dicate eye tubercles,

scars in upper half of valve. Mandibular scars obscure in both male and female. Hingement (Fig. 3G, H) straight, consisting of 15 fine crenulations in each valve.

sp. nov. view Ftg. 3. Semiq);tlzerura.sngittijbrmis A, Male in dorsal

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54 S. Yamada and H. Tanaka

50 pmm

Fig. 4, Distribution of pore systems ef Semiqytherura scrgittijbrmis sp. nov, A, Male LV in external lateral view; B, male LV in ventrai view; C, male LV in posterior view. Solid circles indicate the positions of pore systems on tihe visible surtiace, and epen circles show those on hSdden sur:faces. Grey ovals indicate the sites of muscle scars internally. A B

Ftg, 5, Semicu,therura sngittijbrmis sp. nev. A, B, Internal views of male LV and RV, respec- ttvely (paratype, SUM-CO-1924).

Lamella of prisrnatic layer (Fig. 2C, D, G, H), broad in both anterior and posterior portion, slightly narrower in posterior ponion of female. Eye present, with obscure tubercle on carapace sux:faee (Fig. 2A, B, E, F). Pore systems as in Figs 4, 5. Sixty pore systems per valve (Fig. 4). Long mar- ginal pore canals developed between outer lamella cuticle and lamella of prtsmatic layer (Fig. 5). Antennule (Fig. 6A) with 6 articulated podomeres. Second podomere with 1 setuleus seta on middle of posterior margin and numerous hairs on anterior margin. Third podomere with 1 setulous seta at anterior distal end. Fourth podomere with 1 medium-long and 1 short seta at anterior dista1 end, 1 short seta at posterior dis-

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Fig, 6. Se7niqytherura scrgittdermis sp. nov, A, Male antemiule

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56 S. Yamada and H, Tanaka

tal end. Fifth podomere with 2 long setae at anterior distal end. Sixth podomere with 3 long and 1 spatulate setae at distal end. Antenna (Fig. 6B) with 5 articulated podomeres. First podomere with long, stout, 2-segmented exopodite (i:spinneret seta) at anterior distal end, Second podomere with 1 short, setulous seta and 1 short, stout seta at posterior dista1 end, Third podomere with 2 short, setulous setae at posterior distal end. Fourth podomere with 1 long, setulous seta near proximal end of anterior margin, 1 short, simple seta in middle of anterior margin, and 1 short, setulous seta at posterior distal end. Fifth podomere witih 1 short, claw-like seta on ledge of posterior margin, and 1 stout, claw-1ike seta and 1 very thin, simple seta at distal end. Mandibula (Fig. 6C) consisting of 5 podomeres. Basal podomere (coxa, first podomere of protopodite) with 5 or 6 teeth on distal end, anterior teuminal tooth es- peciany well developed, and 1 short, sirnple seta at about 1/4 distance from dorsal distal end. Second podomere of protopodite (basis) with medium-long, setuleus seta at ventral distal end, and exopodite reduced to long, stout seta. Third podomere (first podomere of endopodite) wiih 1 medium-leng seta at dorsal distal end, 1 long seta at ventral distal end, and 2 medium-Iong setae near ventral distal end, all setae setulous. Fourth podomere (second podomere of endopodite) with 3 simple, medium-long setae at dorsal dtstal end and 1 medium-long, simple seta and 1 short, simple seta at ventral distal end. Fifth podomere (third pedomere of endopodite) with 2 medium-!ong setae and 1 short, simple seta at distal end. Maxll1ula (Fig. 7A) with extremely thin branchial plate (exopodite) bearing 10 plumose setae and 2 long, reflexed setae. Basal padomere bearing palp and 3 masticatory processes. Lowermost masticatory process witih 3 rather small setae at distal end. Each of other 2 masticatery processes with 4 setae at distal end. Palp consisting of 2 articulated podomeres; first podomere with 2 setae at dorsodistal end, 1 seta at ventrodistal end; second podomere with 2 setae at distal end. Fifth limb (Fig. 7B) consisting of 4 articulated podomeres. First podomere with 2 leng setae near ventral proximal end, 1 long seta at middle of anterior margin, and 2 short setae at anterior distal end, all setae setuleus. Second podomere with 1 short, setulous seta at anterior distal end and hairs along anterior margin. Third podomere with hairs along anterior margin. Fourth podornere with hairs along anterior distal margin and stout claw bearing serrations at distal end. Sixth limb (Fig. 7C) consisting of 4 articulated podomeres. First podomere with 2 long, setulous setae on anterior margin, 1 medium-long setulous seta and 1 very short seta near ventral proximal end, and1 short, setulous seta at distal end. Sec- ond podomere with 1 setulous seta at distal end. Fourth podomere with stout claw with semrations at distai end. Hairs on anterior distal margins of 2nd to 4th podomeres. Seventh 1imb (Fig. 7D) with 4 artieulated podomeres, First podomere with 1 shert, setulous seta at anterior distal end. Second podomere with 1 setulous seta at distal end. Stout claw with serrations at distal end of fourth podomere, Hairs on anterior distal margins of 2nd to 4th podomeres. Male copulatory organ as in Fig, 8A-E. Basal capsule sub-oval (Fig. 8A). Two clasping apparatuses (Fig. 8B, C) both long, foliated with blunt top. Distal lobe with biramous distal end (Fig. 8D, E) covered with thin membrane: one tip bent and sub- reetangular, the other with pistol-g]rip shape, Copulatory duct short, coiled. Caudal part of female as in Fig, 8F. Copulatoivy organ consisting of rectangular

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Interstitial Semiaytherura from Japan 57

Ftg. 7. Semiaytherura sagittij?)rmis sp. nov. A, Female maxillula (paratype, SUM-CO-1925); B, male fifth 1imb (holotype, SUM-CO-1912); C, rnale sixth 1imb (holotype, SUM-CO-1912); D, male seventh limb (holotype, SUM-CO-1912).

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20 pm-A-E

, E dl F/ + dl

50 pm -

in1) ' F

Ftg, 8. Setnicytherura sagittijiormis sp, nov. A, Male copulatory organ; B, C, clasping apparatus; D, E, distal lobe; F, caudal part of female. A-E, Holotype, male, SUM-CO-1912; F, paratype, female, SUM-CO-1941. Abbreviations: ca, clasping apparatus; dc, copulatory duct; dl, distal IQbe.

structure on posterior end of body. Circular organ connecting to copulatory organ via narrow duct. Caudal process hairy, with spine on distal end. Dimensions. See Table 1. Remarks. Semicytherura sagittijiormts sp. nov. Iives in pore-waters of marine sandy sediments and is associated with other interstitial ostracods (e.g., Parmpoly- cQpe and Microloscococha). A fossil specirnen of this species has evidently been reported from the Pleistocene Furuya Formation, since the carapace ornamenta-

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Table 1, Dimensions of valves of Senziqytherura sagittijbrrnts sp. nov, from the type locality.

Length (mm) Height (mm) Width (mm)

AV OR nAV OR nAV OR n

Male RVLVRVLVO,35O.34O.34O.34O.32-O.36 13111010O,15O.15O.14O.15O,14-O,16 121099O.23 O.22-O.24 5 O.31-O.35 O.13-O.17 Female O.31-0,36 O,14-O.16 O.23 O.22-O.24 5 O.32-O,35 O.1an.16

Abbreviations: AV, mean; OR, range: n, number of specimens.

tions and the distributional pattern of lateral pore systems completely correspond between the present species and Semic),therura? sp. B of lkeya et al. (1985). This new species resembles S. hanaii Ishizaki, 1981 frem the East China Sea in the morphology of the carapace and size, but differences between the two species are clearly evident, Semicytherura sagittijbrmis has a strongty developed ala on each valve and distinct reticulation developed all over the carapace surface whereas S. hanaii has no ala on either valve, and regular reticulation only in the posterior half of the carapace surface. Semiqytherura acutteostata

Discussion

Representatives of about 15 podocopid families living in pore-waters of sandy sediments have been reported. Some of these families also contain many epibenthic species while others consist of only interstitial species (Danielopol and Hart- mann 1986; Watanabe et al, 2008), Hartmann (1973) described some specialised characters of interstitial estracods, such as small body size, absence of an eye, a translucent body, and reduction in the number of appendage setae, as a result of

their adaptation to the interstitial environment. These characters are often appli- "true" cable to the interstitial taxa, which are composed of exclusively interstitial species (e.g,, 1lficroloxoconcha, (iobanoaythere, Parvoaythere, and ethers), but a small body size is the only common character amongst all the interstitial ostracods. The new species, Semiqytherura sagittVZ)rmis, is one of the smallest in the genus Semic),therura from Japan (Figs 9, 10). The carapace of S. sagittijbrnzts (O.34 mm in length and O.15mm in height on average) is smaller than those of other epibenthic Semiaytherura (O.44mm in lengtli and e.23mm in height on average) and is comparable with those of some large interstitial ostracods (e.g., Microtoxo- concha schomikovi Higashi and Tsukagoshi, 2008 of O.33 mm in length and O.15mm

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6e S. Yamada and H. Tanaka

Semicythefura eMnis CSers, ri 866) . S, deishakeenst's Tabuki, 1986 o S. furuyoensis (lshiraki end Kate, 1976) o S. hanaii lshlzaki, 19Ba . S.hentyhoweiHanaiandlkeya,t977 ..

S. hjbema Okubo, Gg80

S, mainensis HaleT and Vatemtine, t969 .

S. minaminipponica lshizaki, 19Bl . S. miurensis {Henai, 1 957] . S. mukeishimensis ekubo, ri 9BO . S.neosubundete(lshizaki,A966) . S, okinawaensis Nohars, ri9B7 o S. pe4igonoreticulata lshizaki and Kato, ri 976 oo. S, rytityuensis Nohara, ri987

S. sabuJe Frydl, rt982 . S, skt'ppa (Hanai, rt957) S. subundata (Hanai, ag57) o S. fetragone (HanaL, ri957) . S. undata (Sars, a866) . S. uakamurasekiYajima, d982 o S. yeiJmee lkeya end Zhou, d992 . S. sfiicrperi Yamada et ai., 2005 S. fteiahene Yarnada et eL, 2005 e S. sasameyuld Yamada et aL, 2005 .. S.maximeYamatifiandTsukageshi,2e1O e S. ikeyoi Yamada end TsukagoshL 20"O .o S. robustundate O!avva and Kemiye, 200B o S, subslpperi Ozavve and KamLya, 2008 S. ieptosuhunaata Oiawa and Kemtya, 200S o

S. teninrurei Ozawa and Kamiya, 2008 o S. pseudeundata 1rizuki and Yamada, 2eU4 o

S. sagntliomrts sp. nev. MicroloxooonchaikeyaiWatanabeetal.,200B @ AL schomikovi Higashi and Tsukagoshi, 200S @ M. kikaijimaensis Higashl and Tsukagoshi, 2008 @ M. kushireensis Hiruta, ri 989 @@ CobaneqytherelaponicaSchomikov,t975 C. toldakeiCSchomikov, t975) @ PervecytherejapenicaWatanabeetaL,2008 @ PsammeqvthereevifornTisHiruta,ri991 @ fenestrfcytherepreboscidsHirutaetat.,2OD7 @

o 200 3eo 400 soe 600 (pm}

Carapace length of holotype

Fig, 9. Cavapace lengths tn hoLotypes of Semiaytherura species and other interstitlal ostra- ceds reported from Japan. Salid circles pertain to recent species, and open circles to fossil speeies, Double circles indicate the values for interstitial ostracods other than

Semiaytherura, [Vhe black bar is the observed range of carapace length of Semiqytherura sngit- tijbrntis. Data compiled from Sars (1866), Hanai (1957), Ishizaki (1966, 1981), Hazel and Valen- tine (1969), Schorriikev (1975), Ishizaki and Kato (1976), Hanai et al, (1977), Okubo (1980), Frydl (1982), Yajima (1982), Tabuki (1986), Nohara (1987), Hiruta (1989, 1991), lkeya et al. <1992), Irizuki et al. (2004), Yamada et al. (2005), Hir'uta et al, (2007), Higashi and Tsukagoshi <2e08), Ozawa and Kamiya (2008), Watanabe et al. (2008), and Yamada and Tsukagoshi (2010).

in height on average). This suggests that the miniaturisation of body (carapace) size is a particularly efficient adaptation to the interstitial environment, compared to other specialised charaeters, since S, s(ugittijbrmis is similar in both carapace

and appendage morphology to other species of Semiaytherura apart from its small carapace size (especially height). Danielopol and Bonaduce (1990) emphasised that

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Interstitial Semicytherura from Japan 61

Semicytherura armis CSars, ri 866) . S, deishekeensis Tabuki, 1986 o S. innLyaensis (lshizaki and Kato, 1976) o S. hanaii lshizakL 1981 . S, hent]thovvei Hafiai end lkeya, a977 . S. hiberna Okubo, t980 . S. mainensls Hezel afid Vatentine, i969 . S. minamlnipponica lshizaki, f9el .. S, miurensis {Henai, 1957) S. mukaishimensis Okubo, 1980 .o

S, neosubunaata (lshi2akl, t966) . S, okinaweensis Noinera, a9B7

S. poJygonoreticuleta lshizakl and Kato, n976 o S. rvuigtuensis Nohara, ri987 o

S. sahula Frydl, a982 .. S. sklppa (Hanai, a957) S. subundata {Hanai, 1957> o S, tetragena (Hanai, t957) . S, undata (Sars, 186S) . S. wakamurasaldYajima, 1982 o

S. ynyimee 1keya and Zhou, 1992 .

S. slipperi Yamada st ah, 2005 e S. kazehane Yameda et eJ., 2005 . S.sasameyublYamadaetaL,2eD5 S.maximeYamaciaandTsukegoshi,201O .

S. ikeyei Yamada end Tsukagoshi, 20dD .. S, rob"stundata Ozavva and Kamiya, 2008 o S, subslpperi Ozevva e"d Kemiya, 2008 o S, Ieptesubundata Ozawa end Kemlye, 2008 o

S, tanimurai Ozawa end Kemiya, 2008 o S.pseudeundetetriz"kiandYernada,200tL o S. sagtmmlis sp, nov. -@ MicrotoxoconchaikeyeiWs±anabeefaL,2008 M. schomikovi Hlgesh: and Tsukagoshi, 2008 @

M. kOcepmneensis Higashi and Tsukegoshi, 2e08 @

M. kushifoensis Htruta, 19B9 @ CobanocythereJaponiceSdiornikav,ri975 @ C. tokiokai (Schornikov, ri975) @@ PamocytherejaponlcaWatanabeetel,,2008 @ Rssmmoe)ehereeviic"nisHlruta,a99t ferre6triCythereproboscidisHirutaetal.,2007 @

o80 9e 100 200 300 4oe (vm)

Carapace height of holotype

Fig, 10, Carapace heights in holotypes of Semicytherura species and other interstitial species

reported frem Japan, Solid circles pertain to recent species, and open circles to fossil species.

Double circles indicate the values for interstitial ostracods other tihan Semtaytherura. The

black bar is the observed range of carapace height of Semiaytherura sagittijbrmis. Sources of

the compiled data are as given in Fig. 9,

a small carapace size is advantageous for migration into an interstitial habitat, as exemplified by some xestoleberidid ostracods. Semiqytherura hanaii, S. okinawaensts Nohara, 1987, S. polygonoreticulata Ishizaki and Kato, 1976, S, r:yultyuensis Nohara, 1987, S. sabula Fhrydl, 1982, S. skippa (Hanai, 1957), and S. yojimae Ikeya and Zhou, 1992 are as small as S. sngitti- formis in terms of their carapace length and height. Their precise habitats are stM unknown, because S. okinawaensis, S. po()zgonoreticulata, and S. T:J,uityuensis are only known as Pliocene fossils and no living specimens of S. hanaii, S, sabula, S. skippa, and S. yop'imue have yet been described, only dead shells. However, S. yoji-

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62 S. Yamada and H. Tanaka

mae was reported from Otsuchi Bay in northeastern Japan (Ikeya et al, 1992), where its shells were associated with those of the interstitial ostraced

Clobanoqythere at many sampling sites. Ii'urthermore, living specimens of S. skippa are often recovered from coarse-grained sediment trapped in the hol(fflasts of Etse- nia biayclts (Kjellman) Setchell, based on our preliminary field observations. It is, therefore, possible that the smal1 Semiaytherura species mentioned above also have an interstitial life style.

Acknowledgements

The authors express their deep gratitude to Dr Ryouichi Higashi (Shizuoka University) for valuable discussions and also thank Prof. Akira Tsukagoshi (Shizuoka University) for facilities he made available for this work. We also appre- ciate the helpfu1 eomments of two anonymous reviewers. This study was partly funded by a Researeh Fellowship fOr Young Scientists awarded by the Japanese So- ciety for the Promotion of Scienee (to S. Y.).

References

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