VENUS 61 (3 4): 193-202, 2002

Cη1ptomyα（lセnαtomya)truncat1α（Bivalvia: Myidae):

Association with Thalassinidean Shrimp Burrows and Morphometric

Variation in Japanese Waters

Gyo Itani 1 and Mako to Kato2

1 Seto Marine Biological Laboratoη，Kyoto University, 2 Shirahama, Wakayama 649-2211, Japan; gyo@seto.わ1oto-u.ac.jpGraduate School of Human and Environmental Studies，めotoUniversity,

ゐshid，ルNihonmatsu-cho，おわ10初，めoto606-8501, Japan

Abstract: The symbiotic association of the myid bivalve Cη1ptomya (Venatomya) truncata

with thalassinidean shrimps was investigated together with morphometric variation on tidal flats in w巴stemJapan, including the Nansei Islands. Sev巴ralspecimens of C. truncata were found buried v巴ryclose to the burrows of Upogebia major, U. yokoyai, U. carinicauda and Callianassa japonica. In each cas巴 th巴 bivalvewas found with its posterior end facing the burrow tunnel at about 5 -20 cm deep in th巴sediment,suggesting that the bivalve was a filter feeder using the shrimp burrow as an extended siphon. Cryptomya truncata was also found in sediments with abundant burrows of U. issaeffi, U. narutensis and U. pugnax, although direct evid巴nceof a symbiotic association was not obtained. Morphometric analyses showed that C. truncata grew taller and thicker in shape ontogenetically, probably as a result of its symbiotic lifestyle with a reduced need to use its long siphons. Cryptomya truncata from Amami-Oshima Is. were smaller and thicker than those from Honshu, Okinawa Is. and Ishigaki Is.

Keywords: Cηptomya, burrows, commensalism, Thalassinidea, Upogebia, shell morphometry

Introduction

Invertebrat巴 burrowsare common in marine sediments and they provide habitats for symbiotic

animals (we will use the term“symbiotic”literally in th巴 senseof “living together”in this

paper following Ross (1983)). A variety of bivalves live within these burrows, attached by a

byssus to the burrow wall or to the body of the burrow owner (Boss, 1965). Some gastropods

also inhabit crustacean burrows or live on the host bodies (Rosewater, 1969; Bieler & Mikkelsen,

1988).

An unusual type of association between molluscs and invertebrate burrows is displayed by

the burrowing bivalve Cryptomya californicα（Conrad, 1837), whose short siphons open into the

burrows of other invertebrates. This bivalve is distributed along the Pacific coast of the Americas

from Alaska to Peru, and the host burrowing species compris巴 thalassinideanshrimps, annelids

and echiurans (MacGinitie, 1934ヲ 1935;Yong巳， 1951;Peterson, 1977; Wicksten, 1978; Lawry,

1987). cηptomya is unique in having very short siphons, in contrast with the closely related Mya

which lives buried deep in the sediment with long siphons extending to the sediment surface.

Although species of Cηptomya are known from the Indo-West Pacific region, their association

with the burrows of other invertebrates has not yet been investigated (Lamprell et al., 1998). Here

we investigated occuπences of Cryptomya （陪natomya)truncata (Gould, 1861) on tidal flats in

western Japan including the Nansei Islands. This species is distributed from Ise Bay to the East

China Sea (Okutani, 2000). We describe its association with burrows of thalassinidean shrimps for

the first time from Japan. We also describe the ontogenetic chang巴sin shell morphology of the

bivalve and analyze morphome仕icvariation between localities.

194 G. Itani & M. Kato

Materials and Methods

During 1994 and 2001 we sampled Cηptomya （恰natomya)truncata living in deep sediments

on tidal flats at various localities in western Japan. At the study sites, deep sediment, rich in白eburrows of thalassinidean shrimps, was carefully dug to a depth of about 40 cm and checked

for the presence or absence and posture of C. truncata. Gravelly sediment where thalassinidean shrimps were not present at白eHaneji-okawa River, Okinawa Prefecture, and sediment rich in the

burrows of the holothurian Patinapta ooplax in Kabira Bay, Okinawa Prefecture, were surveyed in

2001, to determine whether c. truncata, plentiful in those localities, was distributed in sediment without thalassinids.

Shell length (antero-posterior), shell height (ventro司dorsal)of the left valve, and shell width (left-right) of the valves were measured to 0.01 mm using vernier calipers (see Lamprell &

Stanisic, 1998 for details of shell measurement). Ontogenetic changes in the ratio of shell height

and shell width against shell length were analyzed. Allometric equations were computed from log transformed data as ordinaηleast-squares (OLS) linear regression and comparisons were made

among samples from the mainland of Japan, Amami-Oshima Is., Okinawa Is. and Ishigaki Is. (subsequently referred to as Honshu, Amami, Okinawa and Ishigaki, respectively) using analysis

of covariance (ANCOVA) and Tukey multiple companson test (Z訂， 1999).

Results

Associations with thalassinidean shrimp burrows Specimens of Cryptomya （怯natomya)truncata were collected from 15 localities with

sediment rich in the burrows of thalassinidean shrimps (Fig. 1). The shrimps comprised two

families and seven species; Upogebia carinicauda, U. issa々が， ιmのor，ι narutensis,U. pugnax and U. yokoyai [Upogebiidae], and Callianassa japonica (= Nihonotηpaea japonica)

[Callianassidae]. The localities of these specimens and the owners of the burrows are listed in Table 1.

In many cases burrows collapsed while digging, and it was not possible to determine the

posture of bivalves. But in some cases, the bivalves were found buried in the sediment within a few millimeters of the tunnels of thalassinidean shrimp burrows with their posterior ends facing

the tunnel (Fig. 2). At the Chigusa River, a specimen of C. truncata was found near a burrow of U. yakο＇yai at about 10 cm deep. At Tsubuta, Mukaishima Is., two specimens of C. truncata were

150。

Tanaka River Chigusa River Yorishima Mukaishima Is. Iwashishima Is.

Fig. 1. Localities of Cη1ptomya （防natomyα）truncata coll巴ctedin this study.

Symbiotic Bivalve with Shrimp Burrows

Table 1. Collection data for Cη1ptomya （防natomya)truncata.

Honshu

Ise Bay

Locality*

Tanaka River, Kawage, Mie Pref.

Seto Inland Sea

Chigusa River, Ako, Hyogo Pref.

Osa, Yorishima, Okayama Pref.

Tachibana, Mukaishima Is., Mukaishima, Hiroshima Pref.

Tsubuta, Mukaishima Is., Mukaishima, Hiroshima Pref.

Iwashishima Is., Mukaishima, Hiroshima Pref.

Yamaguchi Bay, Yamaguchi, Yamaguchi Pref.

Ariho River, Onoda, Yamaguchi Pref.

N ansei Islands

Amami Oshima Is.

Dat巴N Shell length

0・ （range)

May 1997 3 10.2-14.6

Oct 1994 5 11.3-17.2

Jul 1996 2 19.5-21.5

Jun 1998 1 9.9

Feb 1999 11 6.8-17.6

May 1998 2 8.4-15.1

乱fay1998 18 6.9-18.5

Apr 1994 2 no data

乱fay1999 5.0

Aug 1997 11.5

195

Burrow owner(s）キ＊

U. yokoyai, C. japonica

U. yokoyai, U. major

U. major

U. major

U. narutensis、U.issaeffi

U.rr凶rjor

U. narut

U. major

U. major

C.faponicα

Yanyu, Tatsugo, Kagoshima Pref.

Tatsugo Bay, Tatsugo, Kagoshima Pref.

Ashiken, Uken, Kagoshima Pref.

Jun 1997 16 4.8-12.4 U. carinicauda, U. yokoyai

N出kai,Sumiyo, Kagoshima Pref.

Okinawa Is.

Han吋i-okawaRiver, Nago, Okinawa Pref.

Ishigaki Is.

Kabira Bay, Ishigaki, Okinawa Pref.

Iriomote Is.

Funaura Bay, Taketomi, Okinawa Pref.

*localities征ein the order of longitude, from east to west キキU.:Upogebia, C.: Calliαnassa

Jun 1997 7 5.4伊 12.2 U. carinic倒~da

Jun 1997 25 4.0-12.8 U. carinicauda

Jun 1997 1 7.9 U.pugnax

Jul 2001 70 5.8 14.7 C.1apomca

Jun 2001 68 4.5-16.8 U. yokoyai

Jun 2000 5 9.4-15.8 U. yokoyai

Table 2. Results of regression analyses, ANCOVAs and Tukey tests. In the Tukey tests, elevations not

underscored by the sam巴line訂Edi百巴rentat白巴 0.05level.

Site N Equation R2 Allometry ANCOVA and Tukey t巴st

Shell height (SH) based on shell len酔（SL)

df F p

Honshu 38 log SH＝ー0.272+ 1.096 log SL 0.990 positive Slope 3, 215 0.783 0.505

Amami 47 log SH＝ー0.259+ 1.078 log SL 0.983 positive El巴vation 3, 218 3.081 0.028

Okinawa 70 log SH= 0.286 + 1.116 log SL 0.986 positive Tukey multiple comparison test among elevations

Ishig紘i 68 log SH＝ー0.261+ 1.086 log SL 0.986 positive Okinawa Ishigaki Honshu Amami

Shell width (SW) based on shell length (SL)

df F p

Honshu 27 log SW = -0.582 + 1.149 log SL 0.989 positive Slope 3, 204 2.538 0.058

Amami 47 log SW= -0.553 + 1.135 log SL 0.975 positive Elevation 3,207 9.261 0.000

Okinawa 70 log SW = -0.646 + 1.121 log SL 0.963 positive Tukey multiple comparison test among elevations

Ishigaki 68 log SW＝ー0.563+ 1.125 log SL O目963 positive Amami Okinawa Honshu Ishig法i

196 G. Itani & M. Kato

I I

I I

I I

I I

1, I

F ’ 幽司 陣ー ー『 制 m - ・由巳 輸町 Ii 1

Fig. 2. Posture of Cryptomya (Venatomya) truncata associated with an Upogebia carinicauda burrow (drawn from a photograph taken at Ashiken, AmamトOshimaIs.). The bivalve was at about 15 cm deep in the sediment. Scale bar = 10 mm.

found around burrows of U. major at about 10 and 20 cm deep. At Ashiken, Amami-Oshima Is.,

a specimen of C. truncata was found close to a burrow of U. carinicauda at about 15 cm deep (Fig. 2). At Haneji-okawa River, two specimens of C. truncata were found close to burrows of

Callianassa japonica at about 5 and 10 cm deep. Although 70 specimens of C. truncata were collected from an area of sediment of ca. 2.25 m三

rich in the burrows of callianassids, at Han吋i-okawaRiver, no specimen was obtained from ca 1.25 m2 of sediment without callianassid burrows. In Kabira Bay, no specimen of this bivalve was

obtained from ca. 1.25 m2 of sediment, rich in the burrows of the burrowing holothurian Patinapta ooplax, whereas 68 specimens of白ebivalves were collected from of ca. 5m2 of sediment, rich in the burrows of U. yokoyai.

A specimen of Cη1ptomya busoensis Yokoyama, 1922 (shell Ieng白 7.9 mm) was obtained from Fujimae tidal flat, Nagoya, Aichi Pref., located at the innermost part of Ise Bay. Although this specimen was collected from sediment rich in burrows of U. major, we did not obtain any evidence of a symbiotic association.

Morphology

Cryptomya truncata has short siphons and a large mascular foot (Fig. 3). The surface sculpture

of th巴 specimenscollected in this study (Figs. 2, 3, 4) is slightly different from the figure (plate 59, figs. 1, 2) of Venatomya truncata in Rabe (1977). Whereas the latter have radial ribs on all

over the surface, the present material lacks the ribs on the anterior third and posterior marginal

regions (Fig. 3). The characters of the shell surface of our specimens closely matched the description of Gould (1859-1861) and the figure in Okutani (2000: pl. 508，自g.5). Specimens

from all localities and of all sizes in this study were almost the same in shell surface characters.

Morphometric analyses

Specimens of Cη>ptomya truncata collected in this study differed greatly in size between

localities. Mean shell lengths of Honshu, Amami, Okinawa and Ishigaki populations were 12.92

Symbiotic Bivalv巴 withShrimp Burrows 197

Fig. 3. A live specimen of Cηptomya （除問tomya)truncatαcollected at Haneji okawa River, Okinawa Is., Okinawa Pref. Note the short siphons (arrow) at th巴 posterior巴ndand large foot. Scale bar = 10 mm.

Fig. 4. Variation in shell thickness of Cryptomya (i令natomya)trunca的 collectedat Han吋i-okawa River, Okinawa Is., Okinawa Pref. A. A specimen in shell length 12. l mm, shell width 4.5 mm. B. A specimen in shell length 12.2 mm, sh巴11width 5.5 mm. Scales are 1 mm intervals.

mm, 8.71 mm, 10.13 mm and 10.11 mm, respectively. A Kruskal-Wallis test showed that the

diff1巴rencewas significant (He = 33.64, df = 3, p < 0.0001: Dunn’s multiple comparison test,

Honshu> Okinawa= Ishigaki > Amami).

Results of the allometric equations and ANCOVAs are listed in Table 2. When shell height

was regress巴dagainst shell length on logarithmic scales, the slopes were significantly higher

than 1 for all the populations (t-tests, p < 0.001 for each population) showing positive allometry. ANCOVA showed no difference between populations in the slopes of the allometric equations,

but showed that the elevations (the 叫ustedmean) were significantly different among populations

(pく 0.05).Tukey test showed that the bivalves from Okinawa were significantly taller than those

from Amarni.

When shell width was regressed against shell length on logarithmic scales, the slopes were

also significantly higher than 1 for all the populations (t-tests, p < 0.0001 for each population) showing positive allometry. ANCOVA showed no difference between populations in the slopes

of the allometric equations, but showed that the elevations were significantly different among

populations (pく 0.0001).Tukey test showed that bivalves from Amami were significantly thicker

白anthose from Honshu, Okinawa and Ishigaki.

The ratio of shell height to shell length and that of shell width to shell l巴ngthwere plotted

against shell length (Fig. 5). As predicted from allometric equations, Cη>ptomya truncata became

taller and thicker ontogenetically. Variation of the ratios not related to shell length was high

within a population (Fig. 4) and the ratios of each population overlapped considerably with each

other (Fig. 5).

198 G. Itani & M. Kato

昏.80

＠

ハ＠ ＋

4ト

,..,• －・よ命 ..... +

j自由語~ 0.70 t 、J ． J、、唱込ζPや《曙弘一 bl"＜ト +

、、、

i o.65 ．草壁塁毛で~.，，.... +" +

警~ 。

。＋． ． 0.6母 ． ＠

．

0.55 2 4 6 事 10 12 14 16 18 2轟 22

尊.45r ＠ ＠

+ ． 。 ＋ ．

"' や + ．

ト。［ • • I.・.＇語＠ a・ 4砂・＠噂・ ＠ 令。

窓d司冨ヨ．、、

-..砂 13・＇..！匂》 Illt:f:. e’ u 下六 ＋

－義 0.35t ． 4ト．

し二。＠ ＠

2 4 6 事 10 12 14 16 18 20 22

Shell length (mm)

Fig. 5. Shell proportions of Cη'Pfomya (Venatomya) truncata. Specimens were grouped in four regions, Honshu, Amami-Oshima Is., Okinawa Is. and Ishigaki Is.

Discussion

Inv巴stigationof Cη1ptomya （持natomya)truncata living in association with tunnels of

thalassinidean shrimp burrows suggests that the bivalve lives in a similar symbiotic relationship

to that of C. californica, a filter feeder that uses invertebrate burrows as an extension for its siphon (MacGinitie, 1934; Yonge, 1951; Lawry, 1987). Cηptomya californica has a large foot

and slender valves that enable it to move relatively rapidly in sediments in order to maintain the association with burrows (Yonge, 1951; Lawry, 1987).

Host shrimp species that we confirmed as having direct associations with C. truncata comprise Upogebia major, U. yo此oyai,U. carinicauda and Callianassa japonica. Although we could not

observe direct evidence of an association, burrows of U. narutensis, U. issa々が andU. pugn仰

may also be utilized by C. truncata, since the bivalves were collected in sediment containing

Symbiotic Bivalve with Shrimp Burrows 199

burrows of these shrimp. Cηptomya calif omica uses burrows of the thalassinidean shrimps, C.

californiensis and U. pugettensis, as well as those of the annelid Arenicola brasiliensis and the echiurid Urechius caupo (MacGinitie, 1934, 1935; Yonge, 1951; Peterson, 1977; Wicksten, 1978;

Lawry, 1987). In this study, however, it could not be determined whether C. truncata also uses other invertebrate burrows.

Peterson (1977) showed a positive correlation between densities of C. californicαand the

callianassid shrimp C. califomiensis. He also found that C. californica died out about a ye紅 aftera removal experiment of C. californiensis and concluded that the association represented obligate

commensalism. Benefits from th巴 shrimpburrow association for C. truncata include access to

the burrow water that is rich in food and dissolved oxygen (also suggested for C. californica). Upogebiid and callianassid shrimps are deep burrowers (Griffis & Suchanek, 1991; Nickell &

Atkinson, 1995; Tamaki & Ueno 1998), and their ventilation activities maintain a relatively high dissolved oxygen content in their burrows (Koike & Mukai, 1983; Astall et al., 1997). Burrowing

in deeper sediment reduces the risk of predation, comp巴titionfor space and the chance of

desiccation (Peterson, 1977) as long as food and oxg巴n-richwater is available. Significantly, short siphoned small bivalves like C. truncata could not live in th巴 sandy-mudsediment as deep as 20

cm found in this study without access to invertebrate burrows. Morphom巴tricanalyses showed that C. truncata becomes taller and thicker as it grows (Table

2, Fig. 5). This allom巴tricgrowth might b巴 relatedto their symbiotic lifestyle in which they do not need to elongate their siphons and consequently their shells. Newell & Hidu (1982) analyzed

shell length-shell height and shell length-shell depth (width) regressions in Mya arenaria, which has a long siphon, and concluded that these equations showed isometry, which is not the case in C. truncata.

Many authors have demonstrated phenotypic plasticity in bivalve shell growth or form (S田 d,

1968; Newell & Hidu, 1982; Hinch et al., 1986; Richardson et al., 1995; Cigarria & Perna ndez, 1998). In myids Newell & Hidu (1982) showed that Mya arenaria grown in different sediments displayed slower growth rat巴sand a more globose form in gravel than in sand or

mud. Furthermore they found that clams in sand were longer and n紅rowerthan those in mud. Latitudinal gradient of body size may also play a role in non-selectional shell shape variation

of several bivalves (Vermeij, 1978), although such gradients were not obs巴rvedin the case of C. truncata. On the other hand, Soares et al. (1998) claimed that differences in the shell shape of

Donax serra from two di百erentregions in South Africa were白巴 resultsof directional selection maintained by geographic isolation.

The difference in the growth patterns of C. truncata among localities may be due to

differences in sediment type and/or population subdivision. Alternatively, environmental differences in different host shrimp burrows and host shrimp behavior may also cause plastic or

genetic changes in shell morphology. Upogebiid shrimps are principally filter feeders, whereas callianassid shrimps are deposit f巴巴ders(Dworschak, 1987; Griffis & Suchanek, 1991; Nickell

& Atkinson, 1995; Pinn et al., 1998; Stamhuis et al., 1998; Coelho etαl., 2000). Although the

pumping rates of upogebiids are high and plenty of nutritious overlying water will enter the burrows (Dworschak, 1981), C. truncata and upogebiids may compete for suspended matter, as suggested for C. calゆmicaby MacGinitie (1935). Applying an empirical rule that slower-

growing bivalves are usually more globose than faster growing members of the same species

(Choe & Ohshima, 1958; S巴ed,1968; Newell & Hidu, 1982) to this study, growth rate of bivalves in Amami Is. might be slower than that in oth巴rlocalities. Thus, it might be possible

that bivalves in Amarni Is., symbiotic with U. carinicauda, compete more severely with the host shrimp than those in Okinawa Is. that are symbiotic with callianassid shrimp. Morphometric

difference between bivalves in Amami Is. and those in Honshu and Ishigaki Is. might be due to different host Upogebia species. It is known that U. carinicauda, a small-sized species, harbors an

200 G. Itani & M. Kato

ectosymbiotic galeommatid bivalve Peregrinamor gastrochaenans, whereas larger-sized speci回 of

Upogebia harbor P ohshimai (Kato & Itani, 2000). However, great overlaps in shell shape (Fig.

5) and similar shell surface sculpture show白atthe four regional populations (Honshu, Amami

Is., Okinawa Is., and Ishigaki Is.) are not morphologically differentiated, at least in the characters

we used in this study. It is interesting to speculate whether behavior and巴cologyof C. truncata

differentiate or not with association with different thalassinidean shrimp species, which are also

diverse in their burrow structures, habitats and behaviors.

Acknowledgments

We are grateful to Prof. Y. Shirayama, Seto Marine Biological Laboratory, Kyoto University for giving us consistent help, and the other members of the laboratory for白eldassistance. Thanks are also due to Prof. H. Michibata, Mukaishima Marine Biological Laboratory, Hiroshima University and Mr. K. Yoshimura, Ube College for letting us use the facility. We would like to acknowledge the valuable comments of Dr. K. Iwasaki, Nara University, and anonymous reviewers on this and an earlier versions of the manuscript. This study was paロlysupported by a Grant-in-Aid for Scienti白cRes巴archfrom the Ministry of Education, Culture, Sports, Science and T巴chnology,Japan, and a JSPS F巴llowshipfor Young Scientists.

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(Received August 21, 2001 I Accepted April 12, 2002)

Note Added in Proof

Since this paper was first submitted, F巴ld巴r(2001) has r巴portedthat the lucinid bivalv巴 Phacoidespectinatus is associated with the burrows of th巴 thalassinideanshrimp Axianassaαustralis in巴asternFlorida, in much the same way as Cη1ptomya calif ornica and C. truncata. In addition to the bivalves, Kinoshita (2002) has reported that tubes of the phoronid worm Phoronis pallida were connected to the burrows of Upogebia major in Japan. This worm is a suspension feeder and might share the same nich巴as Cηptomya. From th巴 burrowsof U. major, several other symbionts have b巴巴nr巴ported;th巴 scal巴worm Hesperonoe hwanghaiensis (Sato et al., 2001), the poecilostomatoid copepod Hemicyclops tanakai (Ito & Nishida, 2002), the alpheid shrimp Chelomalheus koreanus (= Cavipelta yamashit，αi) (Hayashi,

202 G. Itani & M. Kato

1998), and the grapsid crab Acmaeopleura toriumii (Itani, 2002).

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Hayashi, K. 1998. A new genus and a new speci巴sof alpheid shrimpのecapoda,Caridea) from Japan. Zoosystema 20: 229-238.

Itani, G. 2002. Two types of symbioses between grapsid crabs and a host thalassinidean shrimp. Publications of the Seto Marine Biological Laboratoy 39: 129-137.

Itoh, H. & Nishida, S. 2002. A new species of Hemicyclops (Copepoda, Poecilostomatoida) from burrows of the mud shrimp Upogebia major in an estuarine mud-flat in Tokyo Bay, Japan. Hydrobiologia 474: 139-146.

Kinoshita, K. 2002. Burrow structure of the mud shrimp Upogebia major (Decapoda: Thalassinidea:Upo gebiidae). Journal of Crustacean Biology 22: 474-480.

Sato, M., Uchida, H., Itani, G. & Yamashita, H. 2001. Taxonomy and life history of the scale worm Hesperonoe hwanghaiensis (Polychaeta: Polynoidae) newly recorded in Japan, with special reference to commensalism to a burrowing shrimp Upogebia major. Zoological Science 18: 981-991.

日本産クシケマスオガイにみられる

アナジャコ下日甲殻類の巣穴への共生と殻形態の変異

伊谷行・加藤真

要約

南西諸島を含む西日本に分布するオオノガイ科二枚貝類のクシケマスオガイについて，アナジャコ

下目甲殻類の巣穴への共生と殻形態の変異を調査した。底質中の正確な位置を確認できた数個体のクシ

ケマスオガイは，アナジャコ，ヨコヤアナジャコ，ミナミアナジャコ，ニホンスナモグリの巣穴の近く

から採集された。その個体は，いずれも水管のある殻後部を巣穴に向けていたこと，堆積物中深くに分

布していたことから，この貝はアナジャコ類の巣穴に水管を閉口する懸濁物食者で、あることが示唆され

た。巣穴への関口は確認できなかったが，クシケマスオガイはパルスアナジャコ，ナルトアナジャコ，

Upogebia pugnaxの巣穴が多く存在する堆積物中からも採集された。殻形態の計測により，クシケマスオ

ガイは成長とともに，殻高／殻長比および殻幅／殻長比が大きくなるように成長することが分かつた。

これはこの貝が共生生活によって長い水管を必要としないことによるものかもしれない。また，奄美大

島産の個体は本州，沖縄本島，石垣島の個体より，サイズが小さく，殻幅が厚い傾向が見られた。