The malacologicalsocietymalacological society of Japan

fi"te VENUS (Jap, Jour. Malac.) - Vul. 56, No. 2 C1997): 79 91

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A New Turbonillid Gastropod (: )

Ectoparasitic on Tridacnid Bivalves

Shigeo HoRI and Takashi OKuTANI

(Tokyo University of Fisheries, 4-5-7, Konan, Minato-ku, Tokyo 108, and College of Bioresource Sciences, Nihon University, 1866 Kameino-eho, Fujisawa City 252)

Abstract: A pyramidellid has been reported to be ectoparasitic on 7)'idocna gigas (Linnaeus, 1758) from Northeastern Australia and. Solomon lslands and on 7: maxima (R6ding, 1798) from Palau Istands, and so on. Later, the same pyramidellid was also found on T)'iddcna crecea Lamarck, 1819, 71 maxima (R6ding, 1798), and 71 squamosa Lamarck, 1819 from Nansei-Shot6 Islands, southwestern Japan. Because detailed merpho- logical investigation on many specimens revealed that this spec{es is not identical to any of hitherto known taxon, this is described as a new species Tlairbonitla cummingi. Main concho]ogical differences of this new species from other similar species of TleirboniUa in the Indo-West Pacific area are, distinct and strictly constricted sutures, slightly iTregu]ar shell appearance, rather high whorls, and smooth interspaces of the longitudinal ribs.

Keywords: Tleirbonilla, new species, 77idocna, ecteparasite

Introduction

The Pyramideltidae, a group of minute gastropods is known to be ectoparasitic on molluscs and polychaetes (Fretter and Graham, 1949; Robertson, 1957; Ankel, 1959; Robertson and Orr, 1961; Scheltema, 1965; Boss and Merrill, 1965; Robertson and Mau-

Lastovicka, 1979), hydroid (Fretter and Graham, 1949), sipunculid (Kristensen, 1970} and other marine inyertebrates. Among bivalve hosts of pyramidellids, orossostrea gigas (Thun- berg, 1793) is relatively well known in Japan and its adjacent waters (Okamura et at., 1987; Ekawa, 1994). Recently, Cumming (1988, 1993) reported a pyrarnidellid species

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ectoparasite on cultured.giant clam, 77idacna gigas (Linnaeus, 1758) in the Solomon lslands and Queensland, and studied feeding, reproductive behavior, and larval development of this pyramidellid. However, in his papers this species was tentatively named Ilyrgiscus sp. or 71trbonilla sp. based on its slender shell with longitudinal ribs. Later, Hori (1995b) reported this species parasitic on T?'idacna maxima (ROding, 1798) from Ngermeyaus Island, Palau Islands. Most recently, Wise (1996) treated this species from Guam Island under the name of 7bthreUa iredaiei Laseron, 1959 in his phylogenic paper. According to him, this species has inadvertently been sent to mariculture facilities in shipments of tridacnid

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j China 3oe N 400 N Nerth Pacific e

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Kasari Bay

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tts ct Oshima 2gON Island 300 N eS 6 East China Sea

'f sse 's"eif ･,2'' N[if Zamami tss " Island n7" 9' 'io .Okinawa : "tSeN'S"CS' Island s T.,.,.a Kerarna 260 N Group 20" N xbo SN> Ami`O" ' S S e

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Iriomote Island

24e N 1240E 1260E 1280E 1300 E

Fig. 1. A mup ef Nansei-Shoto" Islands, M pm' ui'n Et tw pa

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Hori & Okutani: New Turbonillid Gastropod Ectoparasitic on Tridacnici 81

Australia, Philippines, Guam, and the Solomon seeds, throughout the Indo-Pacifi¢ , such as

Islands including areas where tridacnid species in question does not naturally occur. Conse- to quently, as he stated, the original geographical distribution of this species is difficult determine at present. In Nansei-Shot6 Island, southwestern Japan, one of the authors, (S. H.) found the same species parasitic on 71ridacna maxima (ROding, 1798) in Furuzamami, Zamami Island, Kerama Group and Kasari Bay, Amami-Oshima Island, and on T, erocea Lamarck, 1819 in Amitori Bay, Iriomote Island. Further, Mr. Shin'ichi Ikebe provided us several specirnens by of this species parasitic on 7: squamosa Lamarck, 1819 collected from Ishigaki Island Mr. Osamu Masuda. As mentioned above, this species was once identified as 7bthreUa iredalei Laseron, 1959 by Wise (1996). However, our examination on the holotype specimen of 71athretla iredalei revealed that Wise's (1996) identification was inadequate, Further investigation on shell and soft part of this species comparing with many similar-looking species in the Indo-West Paeific clearly demonstrated that this species should be a new species, which we describe

in the following lines.

Matedals and methods

' After observation of head-foot characters in living condition, all of the specimens were were dissolved by preserved in 70(Vb alcohol. The shells of all specimens for dissection a solution of diluted hydrochloric acid. All soft part anatomy was accomplished under a stereomicrescope and a biological microscope, but not by sectioned material at all. Definition of each organ, arrangement, and terminology adopts Hori & Okutani (1995) and Hori & Tsuchida (l995). Abbreviations used in this paper are as follows: AMS = Australian Museum, Sydney,

NSMT-Mo = National Science Museum, Tokyo, Division of . In the descriptions, rhe abbreviations of anatomical terminology, which is all common to Figs, 17-23 will be arbitrarily inserted in the text to help for referring textfigures.

Taxonomy

Family PYRAMIDELLIDAE Gray, 1840 Subfamily Turbonillinae Bronn, 1849

Genus 7leirbonilla Risso, 1826

7)irbonilla cummingi n. sp.

(Figs 2-13, 17-24)

Islands]. Ryrgiscus sp.: Cumming, 1988, pp. 231-236 [Solomon TZirboniUa sp.: Cumming, 1993, pp. 760-771 [Queensland, Australia]; Hori, 1995, pp. S6-57, pl, 1, fig. 1 [Ngermeyaus Island, Palau Islands]. 7kethrelta iredalei Laseron, 1959: Wise, 1996, pp. 504-50S, figs 11G, 21D, 22D, 26C 29A-H [Guam Island].

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Hors & Okutani; New Turbonillid Gastropod Ectoparasitic on Tridacnid 83

Materiats emamined: 100 specimens frem Furuzamami, Zamami Island, Kerama Group, Nansei-Shot6 Islands (Fig. 1), depth of 3-S m, collected by S. Hori, on March 30, 1992; Five specimens from Ngermeyaus Island, Palau Islands, depth of 1 m, collected by S. Hori,

on August 21, 1994; 50 specimens from Kurasaki, Kasari Bay, Amami-Oshima Island, Nansei-Shot6 Islands (Fig. 1), depth of 5 m, collected by S. Hori, on July 4, 1996, all attached on the shell of 7-1"idacna maxima 1798); 20 specirnens from Amitori (ROding, ' Bay, Iriomote lsland, Nansei-Shot6 Islands (Fig. 1), depth of 1 m, collected by S. Hori, on December 17, 1995, attached on the shell of 77idacna crocea Lamarck, 1819; Five specimens from Ishigaki Island, Nansei-Shot6 Islands (Fig. 1), coltected by O. Masuda, on February 20, 1996, attached on the shell of 77idacna squamosa Lamarck, 1819.

Shetl (Figs 2-13): The shell is slenderly conic (L/W = 2.0-3.2), thin, polished, and translucent white. The protoconch is helicoid, 1200 heterostrophy, smooth, and about 1/3

of it is obliquely immersed in the first whorl of teleoconch (Figs 13a, b). The whorls

ot' the teleoconch are seven to eight in number, with walls that swell especially in abapi- cal part, separated by distinct and constricted sutures. Surface is marked by longitudinal ribs which are nearly straight or feebly flexuous. The number of the ribs reaches to 28

on the . The interspaces of the longitudinal ribs are smooth, and as wide as the width of the ribs. The body whorl occupies 40-60q7b of the shell length, and its periph-

ery is rounded. The longitudinal ribs terminate at the periphery, and the base is sculptured only by growth lines. In some specimens longitudinal ribs become weaker towards the periphery of the body whorl, but they are gradually extended to the umbilical region not

J(' 't iJ 't iJ 'f = Figs. 2-13. Tttrhonilla cttmtnittgi, n. sp. ii ;] ti' it F }- " tr ?' ff , Sl.=shelL length, SW shell width. 2-7, Apertural view of shcll of speeimens from Furuzamami. Zamnmi Ts]and, Kerama Group, mpRma:'gU ptnvEkEdiwtmaEKgmaptcDNttvaiAi

= 3.Juvenile, SI. = 2. Juvenile, SL = 1,9 mrn, SW O.8 mm (PllraLype specimcn No. 1: NSMT-Mo 70749);

= 3.4 mm, SW = 2.0 mm. SW = O.9 mm {Puratype spccimen Ne. 2: AMS C203189); 4. Subadult, SL

= = 1.3 rnm CParutype speeirncn: No, 3 NSMT-Mo 70750); 5. Adult, SL 4.0 mm. SW 1.3 mm {Paratype

specimcn No, 4: NSMT-Mc) 7U751)/ 6. Adult, SL = 3.9 mm, SW = 1.4 mm {Parntype spccimen No, 5: 'J!=' AMS C 20:l190); 7, Adult, SL = 4.2 mm. SW ; 1.3 mm cHolotypc spccimen/ NSMT-Mo 70748), ffj)t ee2ts, 8-12. Apertural yie"' ef shelj of speclmens frem Kurasaki. Kasuri Bay, Amami-Oshima Island. hieeXms V$il ifi fi th5 rk ma Mg a) H tu' ]fi 1fi i 8. Adult, SL = 4,7 rmn, SW = 1.5 mm

= = 1.8 mm (Paratype specimen Ne, 9: NSMT-Me 7{)754); IZ, Abnormal form of adult, SL 4,8 inm, SW (Paratype specimen No. 10: AMS C203192).

iPI = 13. Protoconch of the holotype specimen, fler)S ee C() thrc. Scale 100 um, a, Abaperturul view; b. Umbilical view.

Figs, 14-16. Holotypc speeimen of 7bthreUa iredalei Lascren, 1959 (AMS CI05285). SL = shell length, SW = shell

width.

14. Protoconch. Scalc= ]OO pt m. a. Abapertural view; b. Umbilical view; IS. Narrow spira[ groove on the reurth and fifth whorls

= = = I.7 mm, {lndicated by arrows). Scale 5UO g m; 16. Apertural view of shell. SL 3.9 mm, SW

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terminating at the periphery. There is no umbilicus. Aperture is oval, and occupies 24-38% of the shell length. The is slightly concave, widens abapically. Since the adapicalmost part of the columella is involute into inside of the shell, this part barely creates a columellar fold. The inner wall is not covered by callus. The outer lip is thin, often slightly concave at its adapical end, where pTesent a small sinus. Inner surface of the whorls is smooth. Opercutum (Fig. 18): The operculum is somewhat thick, and oblong ovate in shape with more or less coarse growth lines and no sculpture on the inner side. The color is translucent pale yellow, but becomes gradually paler toward the margin. Head:fbot (Figs 17, 19): The exposed part is translucent white in living specimens. But the middle part of the mentum is often rongitudinally colored by dark brown color. The area between the eyes and parts of the mantle is occasionally stained by the same color. The cephalic tentacles (ct) are slenderly triangular. The eyes (e) are set moderately close to each other. The mentum (m) is rectangular, but its anterior left and right corners conspicuously protrude antero-laterally. The distal ends of these projections are s]ightly

s

17.7)4rboniUa =T it .r Fig. cummtngi. n, sp, S. it ff ft' FV F )b tr F'J 7V' l , ,

shell removcd. ;1 nc de ty l) waLi fo wttsgts. Scale = O.5 rnm. ag, albumen gland. di [ilwa ; ct, cephalic tentac]e, ca'suStwM ; dcs, dorsal ciliated strip. 7?ou twEdi ; dg, digestive gland. ewIltwa l e, eye. ilN; k, kidney. Wwr ; m, mentuin. I]1vakiSt ; mg, mucous gland, tstaM ; op, operculum. en ; opp, opening of posterior peda] muceus gland. thfifiIil*hta wa maMpt ; pmo, pigmcntcd mantle organ. di#Sf･geee ; se, sole, emim.

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85 Hori & Okutani: New Turbonillid Gastropod Ecteparasitic on Tridacnid

widened. The dorsal surface of the mentum is lined by median longitudinal groove. The mentum. The proboscis pore

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reaching to lhe style bulb. tn this region, these ducts run independently from any part of the alimentary canal, bur in parallel to the buccal pump I, The proboscis retractor muscle (prm) runs from the posterior end of the proboscis sheath to the columelLar muscle. About anterior 114 of this muscle is wide, reaching about O.3 mm in width, but divided into two filaments, The posterior end of this diyided part is attached by the junction

' 19 ststt/ttt

,Xi! sb 'J/tt''t'L/ 't ･s sd -/ 'i' /. rm "-',,i ' ttt t/tt ttt .t.ttt . ao 'i' /:tttl / ./t /tt:tl tt t '-1"['/ '.i'';･･, /,11,･ .,･.l･･ l･.tt.t.t".' '..1., sg ps "t' ･,･. sgr

:' 'li '

, po ' ' sg ..ttt.tt.tt./ ttttttttttt/tttttttttt Xt..r "crv - vd 21 - 22 tt' " tttttttttttt-tt

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87 Hori ＆ Okutani ： New Turbonillid Gastropod Ectoparasitic on Tridacnid

of the anterior and posterior oesophagi and the bu ｛：cal ganglia （bg ）・ Oenitat system （Figs 17 ，22 ，23） （ln specimen of 4 ．6 mm in shell length and L5 m 皿 2 ．5 mm in in shell width ．） The albumen gland （ag ）is opaque white ， and reaches about length and about O5 mm in width ． A sing 且e mucous g且and （mg ）is translucently grayish ．17 ． white ， about 1／20f the a 置bumen gland in length and about 4／50f it is width （Fig ） about ． mm and connected with The seminal receptacle （sr） is globular， O 1 in diameter， the fertilization pocket by a narrow duct which is about three times as long as the dia皿 eter duct of the seminal receptacle ． The fertilization pocket is followed by the common genital which runs along the right wall of the rnantle cavity ． A 且most all the way of the common genital duct in the mantlc cavity is surrounded by common genital gland which consists white about 3／5 of conspicuously swollen mucous gland ， which is translucently grayish ， on 0f the albumen gland in width ． The anterior distal part of the common genital duct

the common aperture opens in this the right side of propodium is muscular ， and genital to the cephalic haemocoel the area ． In the area close to the common genital aperture ， slender ， saccular bursa copulatrix （bc） with muscular wall lies． The width of the bursa copulatrix reaches about O ．1 mm （Fig ．20 ）． The copulatory apparatus accords with the through penis housed in the penial sheath ， which is located in the cephalic haemocoel passing the circumoesophageal nerve ring and opening to the area beneath the mentum ． The penis

mm in width ．It tapers （pe）is very long and slender ，1．7 mm in length and O．04 gradually distany and possesses a thin and shallow groove on its dorsal surface for its Iotal length．

also very thin with no sperm sac ， and its wall The penial sheath （pes ）is long， ， possesses anarrow Vas deferens （vd ）which is about O ．01 mm in width ． The penis and the penial sheath are connected with each other at their proximal ends （Fig．23 ）． The proximal part end of of the penial sheath is connected with the columellar muscle nearby the posterior

by ・h ・ ・t ・・ ・ 且・t。 ・ ・ ・at ・ ・ ret ・a ・t・ ・ m ・ ・cl・ （・a ・）（Fig・ 21）・ th ・ p ・。 b ・ ・ci・ ret ・a ・t・ ・ m ・ ・cl ・ P ；y pP

1 Figs． IS−23 ． Turbonitla cutnntin ，gi， n ． sp ．．シ ャ コ ガ イ ヤ ド リ イ ト カ ケ ギ リ ガ イ − ・ ，Scate 18．lnner side of operculum 、蓋 の 内 面 ， Scaie ＝ 0．3 mm ； 19 ．DQrsa 且view of hcad foot．頭部 腹 足背 画

＝ view ＝ 2 〔｝． Dorsal 、・iew er mantle cavity opened ．切 開 し た 外套 腔背 面 ． Scale 0．2 mm ； 21 ．LateraL 025mm ； ． copulatrix Scalc ＝ O 2 mm ； ef anterior aiimentary canal ．消 化 管 前 部 側 面 ．Sca］e ＝O ．2 rnm ；？2． Bursa ・交 尾 嚢 ・ ・

＝ ・ 23．Coputatery apPuratus ．交接器 ， Scalc O・2 mm ，

； ・ ・ ant ・ ・ ・ ・ … epL ・・ ・ ・ ； bg buccal 】i・m ・冂 部 神 。 nt ，，i。 ・ ・。 ・t・ ． 彳f大 動 脈 ， i ．前 食 道 ， gang 。 。， 前 g ； ・ a ・ ・・ ・ 1・ t・ ・ ・ ・・at ・ s ： ・ ・c ・・ ・ mP ．口 ・ ； b ・ b・ ・ c ・1 ・ac ・” 嚢 ， 経 節 bp ，b 1 P i7irn 引 器 ， P y pP ’ ； cgg common ． 通 生 殖 腺 ； ct ， cephalie retractor musclc ．交 接 器 牽 引 筋 ， gcnitalgtand it ； ； ciiiated strip ． ； e eye ： k kidney ． ． 叫 tcntacle ．頭 部 触 角 dcs，dorsal 、背 側 繊 毛帯 ， ．眼 ， 腎臓

・ d ． 凵 ； ・ t m 、。t。 m ．1 吻 基 板 ； ・ PP ，・ P ・ ni ・ g ・ fp ・ st・ ・i・・ p・d・l mu ・ ・ ul g ］a 後 部足 ＊1臨液 腺 開 部 ，

； ・ ・ni ・ ； ・・ ・ ni ・ 1 ・ heath ・ 茎 ： 。，al t。 b。，H 管 ； P ・ ，． pe・i・ardium ．心 嚢 P ，P ．陰 茎 P ， P 陰 鞘 Pgl・

． ： ・ ・ ・t・・・・・・nd ・ ・・ d … tl・ 。 ・ … 色 素 外 套 器 官 ・ i P lli 1 gl ．外 套 腺 ； pm ， pigmen g P P ； retruc しor muscle 冂 吻 oesophagus ： ．口 開 口 部 ， ． ．後 食道 pp ， proboscis pore 吻 prm preboscis ； sb stylct bulb，吻 針 球 ； sc sucker ．吸 盤 ； sd salivary 牽 引筋 ； ps，proboscis sheath ．ロ 吻鞘 ， ， ，

； salivary ・ nd ．唾 液 腺 ； sg ・ ・・ li… ・ nd ・el ・act ・ ・ mu ・cl ・ ・唾 液 腺 牽 引 d ． ct ．唾 液 管 sg ， gl ， y91

； ・r ・・cminal ・eeeptuc ］・ ． 精 嚢 ； stS ・tyl ・t ・h・ ath ・吻針 鞘 ； vC ・，… t・al 筋 ； ，。 ，、。 【， ．蹠 面 ， e ，

： vd vas 輸 精 ciliared strip ．腹 側 繊 毛帯 ， deferens， 管 、

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71ype materials:

Shell length (mm) Shell width (mm} Holotype (NSMT-Mo 70748) (Figs. 7, 13a, b) 4,2 1.3O,8O.91.31.31.41.52.02.31.81,8

Paratype 1 (NSMT-Mo 70749) (Fig. 2) 1.9 Paratype 2 (AMS C203189) (Fig. 3) 2.0 Paratype 3 (NSMT-Mo 70750) (Fig, 4) 3,4 Paratype 4 (NSMT-Mo 70751) (Fig. 5) 4,O Paratype 5 (AMS C203190) (Fig. 6) 3.9 Paratype 6 (NSMT-Mo 70752) (Fig. 8) 4.7 Pararype 7 (AMS C203191) (Fig. 9) 6.0 Paratype 8 (NSMT-Mo 70753) (Fig, 10) 6.0 Paratype 9 (NSMT-Mo 70754) (Fig. 11) 4.6 PaTatype 10 (AMS C203192) (Fig. 12) 4.8 Type tocality: Furuzamami, Zamami lsland, Kcrama Group, Nansei-Shot6 Islands,

Distribution: Amami-Oshima Island (this paper), Zamami Istand, (this paper), Ishigaki and lriomote Isrands, (thispaper), Guam lsland (Wise, 1996), Palau Islands (Hori, 1995b), Philippines 1996), Solomon Isiands (Wise, (Cumming, 1993), and Queensland (Cumming, 1993),

Fig. 24.Two ]iving inclividuulN oVI'urhoftitla citnm'iingi,

n. sp, atutching near the vcntral margin ef the

shell of lis,ing Tridaenct maxitiitt (RUding. 1798)

frQm depth of 3 m, Kujirahama. Kusari Bav, Amiuni-oshima Island, (courtesy I. soyamal 5'y -g-k 7t E ff t di tt a) vatatr < l:I" li 2 ma ts

a)V fi- - h"t fi. F' TJ t Fhe=F iJ h'd

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1996), Habitat: This species is eetoparasitic on 71ridacna maxima (Rbding, 1798) (Hori, T. T. crocea Lamarck, 1819 (this paper), 7L squamosa Lamarck, 1819

Discussion

The conchological characters of the present specimens are identical with those of the soft of the ones reported by Cumming (1988, 1993) and Wise (1996). Anatomy of part Wise except the absence present specimens well accords with what described by (1996>, of a bulbous sperm sac on the unterior portion of the penial shearh. In some pyramidellid vary among individuals as spe ¢ ies, the presence of sperm sac on the penial sheath may in Odostomia hirotamurana Nomura, 1937 (Hori, unpubl.). Wise (1996) identitled this spe- specimen cies with 7bthretta iredaiei Lascron, 1959. However, examination of thc holotype of T. iredatei (Figs 14-l6: AMS CI05285) revclaed that T, iredalei is entirely different on species frQm this species. T, iredatei possesses a narrosN' spiral groove the periphery below of' each whorl (Fig. 15) and cxtremely obscure longitudinal ribs which commence the sutures unlike this species. Further, its taller protoconch (Figs 14a, b) and rounded

teleoconch whorls endorse th ¢ distinction of T, iredatei from this species. for shell length The range of intraspccific variation of shell of this species is large body whorl, and shcll width ratio, grade of swelling of each whorl, proportion of the strength of longitudinal ribs, among others. The she]1 of this species is slenderly conic,

-,ith many whorls and longitudinal ribs, and possesses no columellar fold, About 5oo spe- this species cies of the Indo-West Pacific also have such conchological characters. However, sutures, can be distinguished from many of them because of distinct and strictly constricted arrangement of whorls, slightl>, irregular appearance of the shell due to some",hat irregular longitudinal ribs being rather tall whorls, smooth internal spaces of the longitudinal ribs, will be cempared with this species equal to the inter-rib spaces. Some closely related species below. TlirboniUa acosmia Dall & Bartsch, 1906 from Japan is closely sirnilar to this specres whorls and loosely in shell appearance and size, but differs from this species in much taller Bartsch, constricted sutures. Although T, abseida Dall & Bartsch, 1906, T. dunkeri Datt & species in Japan and 1906, and 71 inLfantuta Dall & Bartsch, 1906 seem to be common regularly slender, are also similar to this new species. However, the first specjes has thickeT, ribs conic shetl, with shorter whorls, and the latter two have less number of longitudinal & Mermod, 1924 from and taller whorls compared to this species. T, arianae Hornung the Red Sea can be distinguished from this species by more strictly stTaight longitudinal has lessnumber ribs and small size of the shell. T, similans Smith, 1903 t'rom South Africa Shell of the longitudinal ribs and more regularly set whorls cemparing to this species.

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appearance of 7：∫顔 dθ厂f Hornung ＆ Mermod ，1924 from the Red Sea resembles this species ， the but longitudinal ribs of the Red Sea species are much narrower than their inter−rib spaces ln contrast to those of this species ． In this paper we provisionally placed this species in the subfamily Turbonillinae and the genus Tu ゆ o 躍”ta because of its slenderly conic ， with many whorls bearing many longitu− ribs dinal ， and no columellar fold θ ． ． Laseron 1959 Nordsieck （ g ， ； ， 1972 ； Hamatani ’η Okutani， 1986 etc ．）

Acknowledgments − ： We wish to express our gratitude to Mr ． Isamu Soyama ， for an unusual photo − graph of living condition of this new species ． Special thanks are due to Mr ． Ian Loch and the collection managers of the division of Invertebrate Zoology ， Australian Museum ， for the loan of the holotype specimen of Tath 厂e ’ia ’redalei ． We also wish to thank to Dr ． Winston F ． Ponder， the Australian Museum his encouragement lor and valuaUe comments on parasites on tridacnids， and Dr ． Susumu Segawa Tokyo University of Fisheries for his ， ， obliging advices ． ML Shin ichi Ikebe， Wakayama and Mr ．Osamu Masuda Himeji City Aquarium kindly ， ， provided us some specimens of T． cummingi from Ishigaki Island． Mr ． Taiji Kurozumi Natural History ， Museum and Inst貢utc Chiba，obligingly sent us the literature useful for the present study ．

要 約

・ Trida（ncr gi，gas 〔Linnaeus， 1758 ）オ オ ジ ャ コ ガ イ を は じ め と す る シ ャ コ ガ イ 類 に 寄 生 す る イ ト カ ケ ギ リ ー ・ ガ イ 類 が 過 去 に ソ ロ モ ン 諸 島 ， オ ス ト ラ リ ア ， フ ィ リ ピ ン ， グ ア ム 島， パ ラ オ 諸 島 な ど の イ ン ド

の ． い 太 平 洋 熱 帯 域 か ら 報 告 され て る 。 1司種 を沖 縄 県座 間味 島 占座 間 味 お よ び 鹿児嵩県奄 美 大 島 笠 利 湾

の T．〃 〜α珈 zα R6ding 1798 シ ミ ガ ’ ’ コ （ ， ） ラ ナ イ， 沖 縄 県西 表 騰網 取湾 の 71 c．roc ．ea Lamarck ，1819 ヒ メ ジ ャ ガ イ ， 沖 縄 県 石 垣 島 の 7二 squamosa Lamarck ，1819 ヒ レ ジ ャ コ ガ イ の 殻 L か ら 採集 し 精 査 し た 結 果 ， こ

れ は 未 記 載 種 で あ る こ と が 判 明 し た 。

T “ rhonilta （cummingi ， n ． sp ．シ ャ コ ガ イ ヤ ドリ イ トカ ケ ギ リ ガ イ （新 称 ） ° ． 〜 殻 は 長 円錐 型 で 薄 く， 白色 半透 明 。 胎 殻 は 平 滑 で IZO 異 旋 を示 す 。螺 層 は 7 8 層 に 達 し，各層 の ド方 が 膨 ら み ， 縫 合 は 明 瞭 で 締 め 付 け ら れ る 。殻 表 に は 真 直 ま た は 僅 か に 波 打 っ た 縦 肋 を もち ， そ の い 数 は 体 層 に お て 28 本 を数 え る 。縦 肋 間 は 平 滑 で 肋 と 同 じ 幅 を もつ 。 体 層 の 縦 肋 は 周縁 に お い て 止

ま る が ，不 明 瞭 に 殻 底 に ま で 延 長 す る 。 に よ っ て は は づ つ の 個 体 縦 肋 体 層 周 縁 に 近 く に れ 弱 ま り ， そ

へ い ま ま弱 ま りな が ら臍部 と延 長 す る 。臍孔 は な 。 軸 唇 は 僅 か に 湾 曲 し，上 部 が 内 方 に 巻 き込 ん で 弱

い つ る 襞 を く 。 外 唇 上 部 は 僅 か に 湾 入 す る 。殻 高 4．2rn［n ． 殻 径 1．3mm （完 模 式 標 本 ） 模 式 産 地 ： 沖縄 県 慶 良 間 列 島 座 間 味 鵬古 座 間 味 イ ト カ ケ ギ リ ガ イ属 の 他 の 多 くの 種 は 主 に ，縫 合 が 明 瞭 で 締 め 付 け ら れ る こ と ，殻 形 が や や 不 規 則

で あ る こ と ， 各 層 が 高 い こ と ，縦 肋 間 が 平 滑 で あ る こ と に よ っ て 区 別 で き る 。 Tathretta iredaiei Laseron ，1959 は 各 層 の 膨 ら み が 強 い こ と， 各層 の 周 縁 に 細 い 螺溝 を 巡 ら し ，縦 肋 が 非常 に 弱 く縫 合 の ・ 少 し 下 か ら 生 じ る こ と，そ し て 胎 殻 が や や 高 い こ と に よ っ て 本種 と 区 別 で き る e 本 種 の 亜 科 属 位 に つ い て は の ， 貝 殻 が 長 円 錐 型 で 多 く 螺 層 と縦 肋 を も ち ， 明 瞭 な 軸襞 を も た な い こ と に 基 づ い て ， ・ Turb （）nil 】inac イ 1 カ ケ ギ リ ガ イ 亜 科 の T 〃 rhoniJla イ ト カ ケ ギ リ ガ イ 属 に 置 い た 。

Refe 『ences

Anke1 ，W ．E ．1959 ．Beobachtungen and Pyramidellidcn − des Gullmar Fjordes． Zoo ’．！ lnz．162 ： 1− 21 ． Boss K ．J ．and A ， ． S ． MerriU ，1965 ． Dcgree of host specifity in two species of Odostomia （Pyramidell ト

dae ： ）． Proc ．ハ4〃 々c ．50c ， London 36 ： 349 − 355 ．15． ， ， p1

Cumming ， R ． L ．1988 ． Pyramidellid in clam maricultu 爬 system5 − parasites giant ．pp ．231 236 ． み1 ： 」．W ． Copland and J， S． Lucas （eds ．）Gian【 clams in Asia and 1he Pacific． Australian Centre

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