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R# VENUS {Jap. Jour. Malac.) Vol. 40, No. 4 <19S2}: 203-223

t- p tzi v ff-ivec Drmpella cDtw ifiOL' .El6thL6

=2k tt ue ks ik as ? o 5> nc ijE ts nt ma 3'

Jes M 3i£ [':.

(taEiJc\[Ftlzaunta$ua.Fiff)

On the Secondary Sexual Characters Found in the

Dimorphic Radula of ( : )

with Reference to its Taxonomic Revision*･"

Yoshimi FuJIoKA

(Mukaishima Marine Biologieal Station of Hiroshima University, Mukaishima, Hiroshima Pref, 722)

Abstract

The present paper deals with the seeondary sexual eharacters observed in the dimorphic radulae of the genus DfnLpella by scanning electron microseope

with a taxonomie revision of this characteristie group based on the samples

collected from the Okinawan waters. The radulae of D. coonzus (R6ding), D. fraga (Blainville), D. deatbata (Reeve) and D. conc:atenata (Lamarck)

were revealed to undergo sexually dimorphism in adult stage. The rachidian

teeth of the males are larger in size, thicker, more massive in shape and darker in eolor than those of the females of the same , as was first described by Arakawa (1958a) on two species. On the other hand, it was shown that the

juveniles exhibit no radular sexual dimorphisrn, having thin and fragile

raehidians as the adult females. In the present study it was also demon- strated that the male radular charaeters are acquired as the secondary sexual eharacters at eertain growth stages, muinly in one of the four species, D. fraga.

Introduction

The genus Drzcpelta was established by [I]hiele (1925), based on its aberrant

characters of the radula with slender reed-shaped laterals, quite unlike those of

the other murieids. Drupella is also peculiar in having the radula that the laterals

on eaeh side outnumber the rachidians.

' Contribution from th'e''Mukaishima MtiII'ne Biological Statien, No, 186. ** Contribution from the Sesoko Marine Science Laboratory. No. 73.

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204 VENUS: Vol. 40, No.4(1982)

The radulae of Drupelta have been reported by some former workers, e.g.

Cooke (1895, 1919), Thiele (1925, 1929) and by Peile (1939), eaeh of them giving "same a different illustration of rachidian tooth of the species". Their reports

have caused many taxonomic eonfusions on this group, In 1958, Arakawa made

it elear that these diserepaneies may have been due to sexual dimorphism in the

radula, peculiar to the genus Drupetta. However, Cernohorsky (1969) suggested,

based upon extensive studies of Muricidae from Fiji, that sexual dimorphism

was nQt evident in the radulae of four species of Dru･petla. Before elueidating

such dimorphism, it seems to be quite important to reconsider the taxonomie

problems of this group. The members of Drupetea oecur restrieted within the tropieal to subtropical

shallow waters in the Indo-Paeifia regions, living ehiefly attached to scleTaetinian

corals. I had frequent opportunities to eollect a good number of samples in

Okinawa, the Ryukyu Arehipelago. As a result of the morphological studies of

shells and radulae, I was able to solve some taxonomic problems of this muricid

and reveal the proeess of formation of the seeondary sexual eharacters in the

dimorphic radulae.

Materials and Methods

A total of 667 specimens used here were colleeted mainly from Sesoko Island,

during the years 1978-79. The island is situated off the northwestern coast of

Okinawa Island and surreunded with well-developed fringing reefs. After shell

features were eheeked carefully, the radulae of approximately 170 specimens

were extracted and mounted for observation under light and scanning eleetron

mlcroscopes.

I refer to the ratio of the number of the rows of laterals to that of the

"L-R rows of rachidians as the (lateral to raehidian) row ratio". The term

"adult" is referred to the shell with a thiek outer lips and the moderately

"juvenile" sized denticles irrespective of gonad maturation, while the term

is referred to the shell with a thin outer lip. I also would like to refer to

"M-type the radula of adult male as the radula", and that of adult female as the

"F-type radula" for reasons of eonvenience. The M-type radulae represent those

having thiek and massive raehidians, while the F-type those having thin and

fragile ones.

Sex of the was checked earefully by means of the presence of a penis.

In or-der to ascertain that the penis ean be used to discriminate the male animal

of Drupuella, seminal duct and/or prostate gland of male and capsule gland of

female were checked beforehand on 7 males and 8 females of D. cornus and 13

males and 5 females of D. fraga. The results have shown that the penis is one

of the reliable sex-characters for discriminating the male from the female

of Drupella, though it was regarded as insignifieant in some muricid speeies

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Fujioka: Dimorphic Radulae of Drupetla 205

(Nakano and Nagoshi, 198e, Nishiwaki, personal communieation)".

Taxonomic Reyisions

Genus DruPella Thiele, 1925 Drupella cornus (ROding, 1798) (Pl. 1, figs. 1, 13; PL 2, figs. 1-2; Pl. 3, fig. 1)

1798. Drvop- cornus R6ding, Mus. Bolten., p. 56, no. 704.

1832. Purpzt･ra etata Blainville, Nouv. Ann. Mus. Hist. Nat., 1, p. 207, pl. 11, fig. 1. 1838. Pzarpmra etata Blainv.: Kiener, LC., Spee. G6n. Iconog. Coq. Viva., 2, p.45, pl. 10, fig. 27.

1846. Rin'n?/,la spectrttm Reeve, Conch. Icon., 3, pl. 3, sp. 19. 1880. Ricinu,la (Sistrum) ochrosto'nza (Blainv.) : Tryon, G. W., Man. Coneh. 2, p. 187, pl. 57, figs. 223-224.

1925.

1939, Drupetla eor7zus (R6ding): Peile, A.J,, Proc. Malac. Soe. London, 23, p. 273, p.275, fig. 41 (F-type radula). 1939. Drupella ochrosto'ma (Blainv.): Peile, A.J., Ibid., p.273, p.275, fig. 42 (M-type radula).

1958. Dru･pella cornus (R6ding): Arakawa, K.Y,, Venus, 19, p.207, pl. 6, figs. 6-15 (F- and M-type radulae). 1964. Dmu/,pella manc･inella (L.) : Habe, T., Shells Western Paeifie in Coleur, 2, p. 52, pl. 26, fig. 15.

1967. Drupa (Drupella) corveus (R6ding) : Maes, V. O., Proc. Aead. Nat. Sci. Phila., 119, p.130, pL 11, fig. L 1969. Pentpella cof-}nts (R6ding): Cernohorsky, W.O., Veliger, 11, p. 304, p. 305, fig.8 (F-type radula), pl.48, fig. 12 nen 12a and 12b.

Shell large in size for the genus, 21.4-34.6 mm in shell length of adult speci- mens. Pure white in color. Sculptured with 8 axial ribs per whorl, whieh are

erossed by regular 4 spiral ribs of prominent nodes on the last whorl, with 3 or 4

fine cords between each rib; little variation from juvenile to aduit. In adult, interior of outer lip has 6 or 7 moderately sized denticles, the upper one larger

than the lower; eolumellar lip has 2 to 4 folds. Soft parts of the female usually

green in color, while those of the male brown.

Common in Okinawa. Lives assoeiated with living scleraetinian eorals, par- ttt

* Nakano and Nagoshi (1980) mentioned that every animal of Thais clavigera has

a penis regardless of the sex. Prof. S. Nishiwaki (The University of Tsukuba) kindly

informed me that sueh phenomena are also recegnized in Thais bronni and probably in

Rapana thomasinna.

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206 VENUS: VoL 40, No.4(1982)

tieularly with and Montipo7'a or sometimes with some other genera

of eorals. RaduLa (Aduet): Sexual dimorphism is clearly observed in shape and in color of the rachidian teeth CPI. 2, figs. 1-2). The rachidians of the male are larger and thieker than those of the female and have thick central cusps, massive bases and relatively small denticles unlike those of the fernale. No sexual dimor- at the phism is observed with laterals, which are long and slender, and serrated 3, fig.1). inner part of the base, Tip of laterals is either bifurcated or simple (Pl. Male radula is brown in color, female one light brown to translucent. RemaTks : Drupetta co7veus has often been identified as Purpura och7'ostoma Blainville, 1832 by some I)redecessors; Cernohorsky (1976), however, demon- strated that the eharacteristics of radular dentition in ochi'ostoma show no sign of those of Drupetta･ but those of Cronia greup. Purpura elata Blainville, 1832 may be is a synonym for Ricinula spectrum Reeve, 1846. These two species synonymous with Drupa, cornus R6ding, 1798 as has been pointed out. Though Cernohorsky (1969) suggested that D･?'upella cornus shows sexual 48, figs, 12a and dimorphism of the shell, he erroneously identified D. fraga (,Pl. 12b in his paper) as a male of D. eorn?m$. It is quite impossible to discriminate male from female, based exelusively upun shell features. On the other hand, it is evident that D. comus has sexually dimorphie radulae as demonstrated by Arakawa (1958a). There is an agreement between his results and those of the present study with an exception of some minor points.

Drmpella fraga (Blainville, 1832) (Pl, 1, figs. 2-3, 14; Pl, 2, figs. 3-4; Pl. 3, figs. 2, 4-7) 4. 1832. I'urpicr{t t'ragu,"H･ Blainville, Nouv. Ann. Mus. Hist. Nat., 1, p. 203, pl. 9, fig. 1895. Sistru.m spectrum (Reeve): Cooke, H.A,, Cambridge Nat. Hist., 3, p.222,

fig. 124 (F-type rudula). 1918. DTitpa. vitie?lsis Pilsbry & Bryan, Nautilus, 31, pl. 9, fig, 5. 1921. Sistantm vitiense Pilsbry, Proc. Acad. Nat. Sci. Phila., 72, p, 319. 208, 6, figs.1-5 1958. Dr-u,pellcr, frag･u,m (Blainv.): Arakawa, K. Y., Venus, 19, p. pl. (F- and M-type radulae), text-figs. 1-2. Sci. Phila., 1967. Drtipa, (Drupelta) chaidea (Duelos) : Maes, V. O., Proc. Aead. Nat. 119, p. 129, pL 11, fig. g. 11, 48, figs, 12n-12b. 1969. Ih'･upella corw,Ls (R6ding) : Cernohorsky, W. O., Veliger, pl. 132. 1974. Mor'ala fraguwt (Blainv.): Dance, P., The Eneyclepedia of shells, p.

Shell rather ovoidal in shape, small in size for the genus, 14.5 to 26.6 mm in brown in the length of adult speeimens. White in eoler, nodules oceasionally juvenile stage, Seulptured vLrith 10 to 12 axial ribs per whorl, which are crossed 2 to 4 spiral cords by 4 to 7 spiral ribs of light nodes on the last whorl, with between eaeh rib. Aperture ovate in shape, white to creamy-white in eolor, outer

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Fujioka: Dimorphic Radulaeiof DruPelta 207

lip with 5 to 7 dentieles, columellar lip with 3 or 4 folds. Adult shell usually

obseured its charaeters by calcareous inerustation, Soft parts of the female green to yellow in eolor, while those of the male brown. Common in Okinawa. Lives assoeiated with living scleractinian corals, par- ticularly with the arboreseent forms of Acropora-, Montipon and Po7'-ites.

Raduta (Adutt): Sexual dimorphism is evident (.Pl. 2, figs. 3-4; Pl. 3, figs. 4-5) . The rachidians of the male become eonspieuously large in size for the genus.

They have fairly thick central eusps, massive bases and indistinet lateral cusps

and denticles. The raehidians of the female are roughly triangular in outline with distinct lateral cusps and denticles. Laterals show no sexual dimorphism (Pl. 3, fig. 2), which is eompletely similar to those of D. cornus. Male radula brown

in color, female one light brown to translucent. Remarks: Purpura fragum Blainville, 1832 has been erroneously considered as a synonym for Murex eoneatenatics Lamarck, 1822. Drupetta fraga is more bulbous in appearanee than D. concateuata and has a whitish aperture. The shell

illustrated by Blainville (l832) demonstrates a typical form of this species. Al-

though this speeies sometimes erroneously listed as Murex rugosus Born, 1778, the radular eharacters of this species differ quite from those of D. 7'ugosa figured by Cernohorsky (1969). Adult specimens of D. fraga show a Temarkable radular sexual dimorphism as demonstrated by Arakawa (1958a). The greater part of his descriptions

agrees with my observation. The charaeteristics of the female rachidians of

D. fraga and D. cornus are similar in appearance with each other, except that

those of the former speeies have broader base and thinner central cusp than those of the latter.

DrmpeUa dealbata (Reeve, 1846) (PL 1, figs. 4-6, 15; Pl. 2, figs, 5-6; Pl. 3, fig. 3) 1846. Ricinula dealbata Reeve, Conch. Icon., 3, pl. 4, sp. 26 (juvenile shell), 1846. Ricinula elata (Blainv.): Reeve, L. A., Ibid., 3, pl. 4, sp. 27. 1880. Ricinula (Sistrum) ochrostom(t (B]ainv.) : Tryon, G. W., Man. Conch., 2, p. 187, pl. 57, fig. 230, pl. 58, figs. 231-234. 1925. DavLpa (Dintpetta) sl)ectru"'c (Reeve): Thie]e, J,, Tiefsee-Exp., 17, p. 171, fig. 4 (M-type radula). 1929. Drzapa (Drz{petla) spectTum (Reeve) : Thiele, J., Handb. Syst, Weicht,, p. 295, fig. 321

1939. Drupella sp. Peile, Ibid., p.275, sp. 5 (M-type radula). 1957. Mofntlnc etatct (BIainv,): Demond, J., Pac. Sci., 11, p. 311, fig. 19.

Shell of moderate size, 20.1 to 30,1 mm in length, biconical in shape, and white in eolor. Sculptured with 9 to 11 axial ribs per whorl, whieh are crossed

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208 VENUS: VoL 40, No.4(1982)

by 2 to 4 strong spiral ribs on the last whorl and their interstiees are ornamented

with several spiral cords, In juvenile shells, prominent thin brown lines are

arranged intermittently on the spiral ribs. Aperture white to ereamy-white in

color, euter Iip with 7 denticles and eolumella with 3 or 4 folds. Siphonal eanal

relatively long for the genus. The adult shell features are frequently obseured

with caleareous incrustation. Soft parts of the female green to yellow in eolor,

while those of the male brown.

Moderately eommon in Okinawa. Lives assoeiated with living scleractinian

eorals, exelusively with the arboreseent forms of Acropora, MontipoTa and .

Rndula (Adult): Sexually dimorphic (Pl. 2, fig. 5-6). The raehidians

of the male have only massive and smooth central cusps, and lack lateral cusps

and denticles. The raehidians ef the female have smooth eentral and lateral

cusps, and laek any dentieles. Outline of laterals in both male and female re-

sembles eaeh other. There are no serrations on the inner margin of the base,

the edge of which is pointed. Tips of lnterals are either bifureated or sirnple (Pl. 3, fig. 3). Male radula brown in color, female one translucent. Remarles: Ricinuta etata figured by Reeve (1846) has been regarded as a synonym for Drupetta cornus (R6ding) (=Purpura elata Blainville, 1832).

Reeve's speeies, however, eould not be identical with Blainville's elata because

the former species has irregular spiral ribs and 9 or more axial ribs. Ricinula

deaebata Reeve, 1846 is a juvenile specimen beeause thin intermittent lines are

arranged on the spiral ribs. This speeies is a synonym for Reeve's etata.

The radulae of Drupa (Drupetlct) spectrzam figured by Thiele (1925, 1929)

completely agree with those of D. dealbata from the Okinawan waters. From this

it is evident that his identification was not correet.

Drupetla concatenata (Lamarck, 1822) (PL 1, figs. 7-12, 16; Pl. 4, figs. 1-6)

1822. Mu.Tex coneateotatus Lamarck, Anim, sans. vert., 7, p. 176.

1832. PuTpu･ra concatenata (Lamk.): Blainville, H.H.D., Nouv. Ann. Mus. Hist,

Nat., 1, p. 204. 1838. Pwrpura eoncatenata BIainv.: Kiener, L.C., Spec. G6n. !eonog. Coq. Viva,, 2,

p.32, pL 8, fig. 20. 1838. Pzarpura fragum Blainv.: Kiener, L.C., Ibid., p.35, pL 8, fig. 21. 1843. Murex concntenatus Lamk,: Lamarek, J.B.P. A., Anim. sans. Vert. (2nd ed.),

9, p.599. 1846. Ricinuta eoncatenata

fig. 269. 1934. concatenata (Lamk.): Hirase, S., A eolleetion of Japanese Shells, pl.

110, fig. 18. 1939. Df'ttpelta sp. Peile, Proc. Malac. Soc. London, 23, p.274, p.275, sp. 2, fig.44

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Fujioka: Dirnorphic Radulae of Drupella 209

M-type radula). 1957. Mornta concatenctta (Lamk.); Demond, J., Pae. Sci., 11, p. 311. 1966. Morzcla concatena.ta (Lamk.) ; Habe, T., Shells of the World in Color, 2, p. 54, pl. 20, fig. 7. 1969. Drupelta ochrostowta (Blainv.): Cernohorsky, W.O., Veliger, 11, p.305, fig. 9 (F-type radula), pl. 48, figs. 14 and 14a,

Shell 13.4 to 26.4 mm in length, varies in shape, white in eolor, and nedules oecasionally brown. Sculptured with 9 to 13 axial ribs per whorl, whieh are crossed by 4 or 5 spiral ribs of prominent nodules on the last whorl, nodules

oeeasionally conneeted by fine eords. Adult shell characters are frequently ob-

seured by ealcareous inerustation. Aperture with 6 or 7 dentieles on the inside of outer lip and eolumellar lip with 2 or 3 folds. Color of aperture varies among

light-pink, reddish-orange, yellow, light-violet, creamy-white, white and so en. Soft parts of both female and male are green te yellow in eole!'. Moderately common in Okinawa. Lives assQciated with living seleractinian corals, particularly with the arboreseent Acropora. Raelula (Adutt): Widely varied in the shape of raehidians

female. The laterals of both sexes have no serration and the inner margin of

their bases are angular and not pointed. This is one of the most important

eharacters of D. concatena･ta. Tips of Iaterals are not bifurcated but simple, while

the inner part near their distal ends are oceasionally beset with several aceessory

projections (Pl, 4, fig. 6). Male radula light brown to translueent in color, that

of fernale translucent. '

Remarks: Drupella concateuata is easily distinguishable from the other

species described above by the color of the shell aperture and by the eharaeter-

isties of radula. Although variation in morphology among different specimens is very large, it is quite natural te consider that they are eonspecifie beeause

of the elose agreement ef the pattern of lateral teeth and of the continuity of morphological variation of raehidian teeth and shells. ' The radula of Drupelta rugosa figured by Cernohorsky (1969, fig. 10 in his paper) differs from that of the present species in having pointed inner margin on the base of the laterals as D. dealbata. Although Cernohorsky also figured

the radula of D. ochrostoma in the same paper, he eorrected his ochrostoma "the as orange-mouthed male eolor-form of the highly variable D. cornus"

(Cernohorsky, 1976) after that. His descriptions and figure of the radula of D.

ochrostoma in fig. 9 agree well with those of D. concatenata from Okinawa.

The Change of Radular Types with Growth

In order to make clear the growth processes of the radula, the radular char-

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210 VENUS: VoL 40, No. 4 (1982)

Juvenile Adult

E-typeradula F-typeradula \ . F-type radula/x s-typeradula M-typeradula 8 .

Dr"petla Fig. 1. Diagram showing the change of radular types of with growth. The radulae of the female show F-type through life, while those of the male show the change from F-type in the juvenile stage to M-type in the adult stage through S-type. Stft tr= ec ts -. ( uaifi a.)Urk i' Sit L(vN < : b SL Ef .Jk-;' pa .t. me t･t -( LkIE ig jM L; F Jti). de ;[l- fr (, oO l,:L ktt 1., rel･X F mp- S ev-MJi[l E! ait:L'(Li<.

aeters were compared between the juvenile and adult stages mainly in Dru-peUa･ fraga. It was found that the sexual dimorphism found in the adult radula (Pl 3, figs. 4-5) was not recognized in the radula of the juvenile. No radular dimer-

phism in size, in shape and in color was found in all of the 63 juvenile specimens of Drupelta examined. The radulae of the juveniles possess thin and fragile raehidians just like those of the adult females do. The number of the outer dentieles of rachidians and the value of L-R row ratio inerease with the growth -hence with the increase in the length-of the shell, whereas there is no essential difference in the form between the adult females and juveniles. That is to say,

every individual regardless of the sex has the F-type radula in the juvenile stage. These facts suggest that the female raehidian does not ehange the shape

throughout life, while the male one ehanges with growth, I was able to obtain six specimens of D. fraga and one of D. concatenata･ which were exaetly in the transitional stage of male (Pl. 3, figs. 6-7), During this stage, the raehidian

transforms clearly on a series of radular ribbon; that is to say, the F-type radulae

are localized in the anterior part of the ribbon and the M-type radulae in the posterior part near the odontoblasts. I would like to refer this radula as the

``SCShift)-type radula". Then the change of radular types with growth can be

expressed as Fig. 1. Although the proeess of transformation is gradual, the

replacement from the F-type to M-type must occur with the forvLrard rnovement

of the radula as growth proeeeds. The shell length of six males of D. fraga in the intermediate stage were 17.0, 17.7, 18.4, 20.0, 20.1 and 21.7mm, whieh were

larger in size arnong the juveniles having thin euter lips. Since the lateral teeth are not sexually dimorphic, the L-R row ratios are

different among the F-, M- and S-type radulae. This is clear from Fig. 2, which

shows the relatienship betwee] breadth of rachidians and the L-R row ratio in O.13 mm D. fraga. In the case of males, the juvenile with rachidians up to about in breadth has the F-type radula, in. which the L-R row ratio ranges fi-om 1.04

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Fujioka: Dimorphic Radulae of Drupella 211

5 O M-TYPE RADULA AS.TYPE RAeULA - F-TYPE RADULA 94 3

cr

1 o.s

O O.1 O.2 O.3 O O.1 O.2

BREADTH OF RACHIDIAN (mm)

Fig. 2. Relationships between breadth of rachidian and the L-R (lateral to rachidian) row ratie in 30 males (left) and 25 females (right) of DruPella fraga. ･f L .x v n v v pt'- va) esklfi o,= ms [･t6 pAlkrta t tsit;UJ.'tO oufi1c

to 1.20. In the intermediate stage with the S-type radula, the L-R row ratio

increases at high rates as the raehidians beeome larger. The adults with the

rachidians measuring more than O.13 mm in breadth has the M-type radula, whose L-R row ratio has a high value and increases gradually. On the other hand all

the females have the F-type radula, in whieh the L-R row ratio increases gently from approximately 1.00 to 1.12 with the individual values scattering little around the regression line. It should be pointed out, at this stage, that the L-R row

ratio varies net only, with the type of radula but also with the size of rachidians

within each type.

Fig, 3 indieates the relationship between the shell length and the breadth of raehidians in the F- and M-type radulae of D. fraga. Close correlation can be recognized between the two I)arameters in eaeh radular type, respectively, The

rate of inerease in the breadth of the raehidians relative to shell length is much

higher for the former than the latter type. This suggests that the rachidians of the former type grows more rapidly than those of the latter type. The broadest raehidian in the M-type radula reaehes O.30 mm, which is obtained from a speei-

men with a 25.8 mm Iong shell. In the F-type radula, the raehidian never exceed

O.14mm in breadth.

The number of outer dentieles on the rachidians are not always alike. The outer dentieles of the rachidians increase in number with growth in the F-t,ype radula, while in the M-type radula these tend to become traces. Even a single

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212 VENUS:Vol. 40, No. 4 (1982)

O.3

AEEvzg

o.2g8g6l2

o.iNm

O 10 20 30 SHELL LENGTH (mm)

Fig. 3. Relationships between the shell length and the breadth of rachidian in DruPella fraga. The rachidian of M-type (regression line : N = 18, Br ='. O.OI07Ls+O.O0370, r= O. 7355) grows more rapidly than that of F-type (N==33, Br=: O. O0519Ls+O. O179, r=O. 9362). lt 1 z;f p tzf i)/ ptTi ti L' 2ts H"6meftEtlirk,ptM'oma en. Mav cD ii:ueotFlt!:epasphtstr=ntftt6ctSffiL(uNts.

radula does not possess a constant number. A raehidian of the F-type radula

usually has a single inner denticles on each side of the central cusp with the

variation from zero to two number. This variation, however, fails to be

dependent on shell length.in

Discussion

Drupetla from Okinawa were examined on the hasis ef the shell and radular

features and identified into four speeies, i.e. cornus, fraga, eleatbata and con-

cateuata, as summarized in Table 1. Sinee these species resemble each other

in shell charaeters, studies on the radular eharacters may also become necessary

for identification,

My observation indicates that the radulae of these four species tend to be sexually dimorphie as compared in Table 2. Arakawa (1958a) first revealed these facts in D. comus and D, frncga, and described that there were great differenees between males and females in the ferm of the vachidians, in the L-R row ratio, in proportion of length of the laterals to breadth of the rachidians, as well as in the color of radula. My results agree well with the findings of Arakawa. It

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Fujioka: Dimorphic Radulae of DrntPella 213

Table 1. Comparisons of shell characters among four species of Drupella used here. DruP.e.ILa-4 ptOec0meSa) J:tK.

S:o,e i Na./:is,a.Oif species sggNc,:tr.,Oe,`n,s sNp//,ta.Oi` .,C.Oo.if,O.r,. ll..ft･/.i"".i.tt.h "4

D.D.D.D. cornus 137(20.5%') 21.4-34.6 8 white fraga 452(67.8%) 14.5--26.6 10-12 4-7 white to creamy-white dealbata 56( 8. 4%) 20. 1-30.1 9- 11 2-4 white to creamy-white concatenata 22( 3.3%) 13. 4-26.4 9-13 4-5 pink, orange, yellow, violet, white, etc.

Table 2. Comparative measurements of sexually dimorphic raclulae in the abult stage ef four species of DrupeJla. ". lik C) O 4 ; bt) Drupelta H deiil MUrets Llawt. as#IMIelj ilmb.pats 5 2L 6 .

No. of Length Breadth radttlae No. ofrows L'Rrow of ofrachidian Species Sex mounted of radula 'ratlo (juveniles rachidian (mm) in brackets) (mm)

D, cornus Female 40 (20) 5.4- 9.1 e,11-O,14 242-298 1. 07-1. 14

Male 24(4) 7. 7-10. 0 O. 16-O. 24 98-147 1. 86-2. 72

D. fraga Female 28 (13) 4. 9- 6,7 O, 11- O. 14 182-277 1. 02-1. 12

Male 37 (18) 7. 3- 9. 5 O. 13-O. 30 62- 103 2. 59-4. 54

D, dealbata Female 4(1) 4. 9- 7. 0 O. 07-O. 09 172-226 1. 15--1. 17

Male 11(2) 6. 7-10, 1 O. 15-O, 24 76-113 2. 26-3. 23

D. concatenata Female 8(2) 4. 5- 8.1 O. 07-O, 13 162-223 1. 04-L 23

Male 7( 3) 6. 3- 8, 9 O. 08-O. 15 112--200 1.l5-2..13 . .

is reeognized in each of four species that there is a general trend for the male

raehidians to be larger in size, broader thicker in shape and darker in color

than those of female. There is also tendeney for the male radula to be J longer than the female one. In the present study, lt was found that such dimor-

limited phism is to the adult stage; every juvenile has the F-type radula as adult female does, It can be consi dered these diserepancies may be due to the

secondary sexual eharacter as Arakawa (1969) predicted. The important prob-

Iem, how are the sexual dimorphism anda secondary sexual eharacter related to

their feeding habits, is a subject for future study. . Cernohorsky (,1969) suggested that sexual d]morphism of the radula of

Drupellnc was not evident and explained the diserepancies between Arakawa's

and his findings may be due to Arakawa's misidentification or regionality in sampling. It is inferred that Cernohorsky's erroneous suggestion might have been eaused by a possibility that he might have examined only juvenile speeimens. It is assumed from the studies of Arakawa and the results of the present study

that radular the sexual dimorphism and secondary sexual character may be reeog- nizable among other species of this genus. D. rugosa and D. ef. angutata de-

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214 VENUS: VoL 40, No.4(1982)

seribed by Cernohorsky (1.c.) require a re-examination.

It is needless to say that the size of radula and the number of rows increase ontogenetically. Drupella is a peculiar group in having fewer rows of raehidian

than those of laterals. Peile (1939) first notieed this faet in D. coo-nus and

suggested that its L-R row ratio shows the value of 1.1. Arakawa (1958a)

mentioned that the L-R row ratio of the females of D. cornus and D, f･raga

showed a constant value of 1.1, while that of the male of D. cornus 5.0 and that

of the male of D. fraga 3.0. However, these figures give only the means of

some values which would be dependent upon the growth and sex of the rnollusks, The growth rate of the rachidians is quite independent of that of the laterals,

From this, it is eonsidered that functional differentiation has oecurred between

the rachidians and the laterals of the teeth, Aberrant reed-shaped laterals may

be adapted to sweep up the tissues on the coral skeleton effeetively or may play

a signifieant role in defending against nematocysts,

The members of the genus Drupetla is distributed throughout the tropical

to subtropieal shallow waters in the Indo-Paeifie, their assoeiation being limited

to the seleractinian eorals (Demond, 1957, Maes, 1967 and Taylor, 1971). Like-

wise, in the vicinity of Okinawa they oecur exclusively on the seleraetinian corals,

most frequently on aeroporid corals, and feecl on eoral tissues. Aceording to

Cernohorsky (1969) and Robertson (1970) they live not only on the corals but

also on some other habitats, e.g. under the rocks, in the erevices of reefs, under

trufs of green algae, and so on.

A few workers have figured the radulae based on rather small number uf speeimens. This may possibly, be one of the reasons why in Drupella

have become eonfused. To some extent this problem was solved in this paper.

Reeently, PurpzaTa elata Blainville, 1832 was designated as the type species of

Drupetta by the use of the plenary powers of the International Commission on

Zoological Nomenclature (ICZN, 1980). It would have been better to have chosen

Drupa eo7'nu-y R6ding, 1798 as Dr. Sabrosky pointed out in that paper because

t,he available evidenee suggests that D. elata (Blainville) is a synonym or at

least subspeeies for D. cornus (ROding).

Sinee the study of Arakawa (1958a) the sexually dimorphic radulae of gastropods were reported by some authors. Arakawa (1958b) also found that the

raehidians of male were larger than that of the female in Mancineela echinutata･.

Furthermore, Arakawa (1964) discussed that the remarkable variation found in

the radula of Vexilta, previously reported by Cooke (1919) and Peile (1936),

might have been resulted from differences in the feeding habits or in sex. In

the radulae of Nassa francolina and N. serta sexual dimorphism was recognizable both in size and in shape CMaes, 1966), although not so great as those of Drupella.

Cernohorsky C1971) reported the sexual dimorphism of P･isania tuctuo$a. The

above-mentioned examples are all limited to the neogastropod families Muricidae

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Fujioka ： Dimorphic Raduiae of Drupetla 215

and Buccinidae ． But Robertson （1971 ） found the dimorphic radulae in an

archaeogastropod species 7 幅 oo 地 （Hilot”） 膿 γ Zα b覦 8 ， in which the male had the

smaller numbcr of marginals and the narrower cusps of rachidian and 且aterals

than the female ， Nevertheless it is regretful that in spite of much attention ， ，

to the dimorphic shells ， only a few studies on the dimorphic radu 且ae have been

done ． Future study would reveal that many species show sexual dimorphism of

the radulae ．

− I would like to extend my thanks to Prof ． A ． Inaba Hiroshima Acknowtedgements ，

study and to ． （． ． University ，for his guidance throughout the present ， Dr 1 Y Arakawa ，

Hiroshima Prefectural OMce ， for his fruitful discussions ． Thanks are also due to − Prof K ， Yamazato University of the Ryukyus for his kind criticism on 七he manu ， ， ，

Prof T Habe Tokai University for his kindness in me valuable script ， to ． ． ， ， giving

information to Mr ． K Sakai for his assist in collecting specimens under study ． ， and ．

要 約

荒 川 （1958a ） は DruPella に お い て 歯舌 に 性 的 二 形 の あ る こ と を 初 め て 閉 ら か に し，歯 舌 の 形 質

い い の に こ っ は 種 や 属 に よ っ て 変 わ らな と う従 来 か ら 考 え を 改 め た が ，中 は れ を 否 定 す る 見 解 も あ 一． ： こ た 。 し か し 著 者 は 今 回 ，荒 川 の 報 告 し た 2 種 を 含 め 同 属 の 4 種 で 性 的 形 が 存 在 す る とを 確 認 し ，

こ の 現 象 が DruPella の 成 只 に ．広 く み ら れ る こ と を 示 し た 。 ． つ で こ れ ら性 的 一二形 は 成 貝 に お い て の み 認 め られ ，幼 貝 で は 雌 雄 共 に 雌型 歯舌 を も 。 また 雄 は 成 貝

に な る の に 前 後 し て ，雌 型 歯舌 か ら 雄 型 歯舌 へ と 形 態 が 著 し く変 化 す る 時則 が 認 め ら れ た 。 こ れ ら の 一 二 の つ で こ と か ら性 的 ．形 は 次 性 徴 ひ と あ る と 考 え ら れ る 。

の ・ ・ の に 二 い か 中 歯 形 態 大 き さ 色 な ど に 顕 著 な 雌 雄差 が み られ る 対 し ， 側 幽は 形 を 示 さ な 。 し も 一 の に る の は 定 せ ， 中 歯 は 側 歯 よ り 急速 に 成 長 す る の で ， 歯 列 比 （側 歯 列 数 中 歯列 数 対 す 比 ） 値 ず 性

て が っ た で 成 さ れ る こ と か ら 機 能 の 分 化 が や 成 長 段 階 に 対応 し 変 動 す る 。 側 歯 中 歯 と異 な 成 長 率 形 ，

の ． 起 こ っ て い る も と 考 え ら れ る 。

歯 舌 の 形 態 の 研 究 を も と に ， こ れ ま で 混 乱 し て い た DruPella 属 の 分類学 的 再 検 討 を 行 い ，沖 繩 産

DruPella を 以 ドの 4 種 に 分 け た 。

Dr “ Pella cornus （R6ding ，1798 ） シ ロ レ イ シ ダ マ シ

D ． fraga （Blainville，1832 ） ヒ メ シ ロ レ イ シ ダ マ シ

D ． dealbata（Reeve ，1846 ） ＝セ シ ロ レ イ シ ダ マ シ （新 称 ）

ク チ ベ ニ レ シ ダ マ シ D ． concatenata （Lamarck ， 1822 ） イ

References ‘‘ ” Arakawa ， K ． Y ．1958a （ 1957 〉． On the remarkable sexual dimorphism of the radula

of ）ruf ）ellα ． ： − ． ． 1 Venus ， 19 206 214 ，pl 6 ・ 1958b notes on the radula of Ptt，rpura eehin ul α tcs Lamarck ． Arakawa ， K ，Y ． ． Some

τ！enus ， 20 ； 69−75 ．

Arakawa K ． Y ．1964 ， A study on the radulae of the Japanese Muricidae 2 ． Vent ’s ， ， （ ） 22 − ： 355 364 ， p1，21 ．

Arakawa K ． Y 1969 ． On some of sexually dimorphic radulae abstract in ， ． problems （

： Japanese ）． Venus ， 28 125，

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216 VENUS: VoL 40, No.4(1982)

Blainville, H. M. D. 1832. Disposition m6thodique des especes reeentes et fossiles des

genres Pourpre, Ricinule, Licorne et Conch61epas de M. de Lamarck, No"v. Ann. Mus. Hist. Nat., PaTis, 1: 189-263, pls. 9-12.

Cernohorsky, W.O. 1969. The Muricidae of Fiji. Part II Subfamily Thaidinue. The Vetiger, 11: 293-315, pls. 47-49, Cernohorsky, W. O. 1971. Indo-Paeifie Pisuniinae (Mo]lusea: Gastropoda) and related

buccinid genera. Res, A-uctela7id Iozst. M'u･s., 8: 137-167.

Cernohorsky, W. O. 1976. The taxonomy of some Indo-Paeific , Part 4. With

descriptions of new taxa and remarks on Nassarius coppix,geri (Smith). Itec. Auckl(mtd Inst. Mus., 13: 111-129. Cooke, A. H. 1919. The radula in Thais, Prupa, MorulQ, Co7tcholepas, Cron'i(z, Jopa･s,

and the allied genera. Prec. Malae. Soc. Londoii, 13: 90-110.

Cooke, A. A., A. E, Shipley and F. R. C, Reed. 1895, Molluses. Cambridge Nat. Hist., 3, Molluscs and Brachiopods. 535 pp. Macmillan & C., London. Demond, J. 1957. Micronesian reef-assoeiated gastropods. Pac. Sci., 11: 275-341.

International (:ommission on Zoological Nomenclature. 1980. 0pinion 1154. Drupelta Thiele, 1925 (Mollusea, Gastropoda): designation of a type speeies by the use of the plenary powers. Bzi.Zl. Zool. Nont･., 37: 85-88. Maes, V.O. 1966. Sexual dimorphism in the radula of the murieid genus Nassa. N(Lutilus, 79: 73-8e. Maes, V.O. 1967. The littora,1 rnarine mollusks of Cocos-Keeling Island (Indian Oeean). Proc. Aead. Nat. Sei. Phila., 119: 93-217. Nakano, D. and M. Nagoshi. 1980. Growth and age of Thais etavigera. (KUster), prosobranch, in tidal zone around Shima Pentnsula, Japan (in Japanese). Publ. 25th Anniv,, Toba aquarium: 87-92.

Peile, A.J. 1!)36. Radula notes I. Pf"oc. Matac. Soe. London, 22: 139-144.

Peile, A.J. 1939. Radula notes VII. PToe. M(Llac. Soc. London, 23: 273-276.

Reeve, L.A. 184fi Conehologia Iconica, or i]lustrations of the shells of molluscous animals. Monograph of the genus R'iei7z'ula･. London, pls. 1-6. Robertson, R. 1970. Review of the predators and parasites of stony corals, "'ith spe- cial reference to symbiotic prosobraneh gastropods. Pa･c. Sci., 24: 43-54. Robertson, R. 1971. Sexually dimorphie archaeogastropods and radulae. Aotn. Rep. 1970 Amer. Malac. Un･i., 75-78. Taylor, J.D. 1971. Reef associated molluscan assemblages in the western Indian Ocean. Symp. Zool. Soc. Loozdun, 28: 501-534. Thiele, J. 1925. Gastropoda der Deutschen Tiefsee-Expedition, paTt 2. IViss. Eo'g. I). Tiefsee-Expeditioit, 17: 36-382, pls. 13-46.

Thiele, J. 1929-193i Handb. Syst. Weiehtierkunde, Jena, 1-4: 1-1154. Wu, SrK. 1965. Studies of the radulae of Tai"Jan muricid gastropods. B'ttU. Jnst. Zoel. Acade7n･ia Sinica, 4: 95-106. t -tt tt tt ttt-t ttttt ttttt -ttttt ...Nt PL 1. Shells, (Scale bars=10mm) (Opposite page) 1, 13. DruPelta cornus (R6ding) V'v trf V' pt"" V, 2, 3, 14. D. fraga(Blainville)

u. x tf p v./r "x.pt'v? =-tt rr v., 4-6, 15. D. dealbata (Reeve) t- p L. V. Ji'- V', 7-12, 16. D. concatenata (Lamarck) P, f-'<=- trd ".$'vv

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Pl．2． Scanning electron micrographs of the sexually dimorphic radulae of l）ru − pella． A row of rachidlan and base of laterals are shown ． The lower part of each micrograph leads to the forward direction on an odontophore ．（All ＝ scale bars 130 μ m ） ’ ． 1）ruPella の 二 ． ． の ． 歯舌 性 的 形 。走 査 電 顕 写 真 ，中 歯 と側 歯基 部 ，各写 真 下 側 が 歯 舌 の 前 プ∫。 ． ．’ コ DruPetla （／ornus M −type radula ン ロ レ イ シ ダ ・ シ M 12345n ， ． ， 型 歯舌 。 ． 「 1 − ・ マ コ PPDり （tornus ， F type radula ． シ 「 レ イ シ ．ダ シ ， F 型 歯 舌 。

ひ M −type radula ． ヒ メ シ ロ レ シ ダ マ シ fraga， イ ，M 型 歯 舌 。 − 』 ． ロ ロ fraga， F type rndulu ． ヒ メ シ 卩 レ イ シ ．ダ マ シ ， F 型 歯 舌 。

t ’ コ ρ ロ deatbata M −type radula ． ニ セ シ P レ シ タ v シ ． イ ，M 型 歯舌 。 ー ／ ．． ． ， 』 り 0 dealbata ， F −type radula ． ニ ヒ シ ロ レ イ シ ダ ？ シ ， F 型 歯 舌 。

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P1．3． Scanning electron micrographs of the sexually dimorphic radulae of Dru − ＝ pelta，（All scale bars 130pm ） DruPella 粛 舌 の 性 的 二 形 、，走 査 電 顕 写 真、， ー’ ． 1． Drupelta cornus ． the tlps of laterals． シ ロ レ イ シ タ ・ シ ，側 歯 の 先 端 。

ーe 2 D ナ α ditto ヒ メ シ ロ レ ． シ ダ シ ． ． ノ ， ． イ ， i司 L 。 ・ 3． 1）． dealbata ． ditto． ニ セ シ ロ 」 イ シ ダ マ シ ， 同 上 。

4． 0 ． 8 ，rachidian and laterals on both side of the M ・type radula ． ル ． ． ヒ メ シ ロ レ シ ダ マ シ イ ，M 型 歯舌，中 歯と側 歯 。

’ ．・． 5． D ． ノraga ． ditto， of the F ・type radula ， ヒ メ ゾ μ レ イ ン ．ダ マ シ ， F 型 歯 舌 ， 同 上 ， − − 6 7． D ． fraga， S type radula ． The form of rachidian changes froln − − F type to M type on a series of ribbon ． A considerable change has occured’ at the 102nd row （indicated by an arrow ）． ヒ メ シ ロ レ イ シ ダ マ シ ， S 型 歯舌 。 1 本 の 歯舌 上 で ， F 型 か ら M 型 へ と 中歯 の 形 態 が 変 化 す る 。

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PL 4 ． Scanning electron micrographs of the sexually dimorphic radulae of Dru ． pella concatenata ． Considerable variation can be recognized ．（All scale bars ＝ 130 μ m ） 一 DruPeUa 歯舌 の 性 的 ．形 。走 査雷 顕 写 真，， ク チ ベ ニ レ イ シ ダ マ シ の 歯 舌 は 変 異． が 大 き い 。 − − 1 2 ． Dr “ concatenata ， rachidian and base of laterals of the M type pella 「 ベ ニ マ Ilr radula ． ク チ レ イ シ ダ シ ，M 型 歯 舌 ， 歯 と 側 歯基 部。

− − ベ r ． 3 5． P ． concatenata ． ditto， of the F type radula ． ク チ レ イ シ ダ 『 7 シ ， F 型 粛舌 ， 同 H。

ク チ ベ L ＝レ シ ダ マ シ の 6． D ． concatenata ，tips of laterals． イ ， 側 歯 ．先 端、

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