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Hes VENUS (Jap. Jour. Malac) VoL 46, No. 4 (1987):lg2-193

4xSMXk 5e R o ma ma ur ut tbu ssA- ll .

paimEpt 1- )lf v v 7 7t if I o:Ex . a> pt .

v i X reEk J6ft as *H *t pteft

bl A \･th az ± fis (YL{･1･1]k\X"taiftEXwtnt)

Studies on the Biology and Eeology of the Intertidal

Animals of Chiehijima Island in the

Ogasawara (Bonin) Islands-II.

Description, Distribution, Size Strueture in the Population,

and Allometric Growth of the Limpet,

Notoacmea schrenckii boninensis n. subsp."

Akira AsAKuRA and Shiro NIsHIHAMA

(Amakusa Marine Biologieal Laboratory, Kyushu University, Tomioka,

Reihoku, Amakusa-gun, Kumamoto-ken, Japan, 863-25)

Abstract: A new subspecies of Acmaeidae, Notoacmea sehrenekii boninensis,

is des¢ ribed, and general biology of this limpet is observed. At Chiehijima Island of the Ogasawara Islands, this limpet was colleeted from underside ef boulders in the intertidal zone of the wave-exposed beaches. The shell size is smaller

than that of N. schrenckii sehrenckii (Lischke) from Japanese temperate region, The shell is green color with radially seattered lines and V-shape patteTn, and is wider and the apex situated more anteriorly than that of IV. sehrenehii schrenckii. They mainly inhabit the rniddle intertidal zone and were also distri-

buted in lower number in the lower intertidal zone, No individual was found

in a sheltered boulder beach, rock platforms, or tide pools.

Introduction

Noteacmea schrenckii (Lischke) is a small limpet common to the intertidal zones of roeky shores in Japan, Formosa, and China (Habe and Okutani, 1975;

Habe and Kosuge, 1967; Nakamura, 1986). Two subspecies have been discrimi-

nated in this , a typical Notoacmea schrenckii schrenckii (Lischke) and

"'Contribution No.320 from Amakusa Marine Biological Laboratory, Kyushu University

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Asakura . Nishihama : Biology of Netoacmea schrencleii boninensis n. subsp. 183

a pink colered Notoacmea schTenckii gloriosa Habe (Habe and Okutani, 1975;

Habe and Kosuge, 1967). The latter was first described as an independent

speeies, Notoacmea gloriosa Habe (Habe, 1944), and some recent authors, such as Nakamura (1986), have adopted this classification. N. sch･renckii schreneicii has a green shell and inhabits a wide range from the middle to lower intertidal

zones in roeky or boulder shores. In contTast, N, schrenckii gloriosa has a pink

shell and its habitat is restricted to the lower intertidal zone (Habe and Oku-

tani, 1975; Habe and Kosuge, 1976; Wada et aL, 1983).

In April 1986, we visited Chichijima Is]and in the Ogasawara Islands, whieh

35-

30.

25.

Z25. I30. 13S. :40.E'

Fig･ L Localities of sampling sites; Chichijima Island in the

Ogasawara Islands and Amakusa, northwest Kyushu. at tcte : INsuaxdeop se kt fL"[･ldk ggzzoiJ( g.

ra SHkH

Yagy

Fig.3. Measurements of the

shelL L: shell length,

W: shell width, and A: length from the apex to -Location the posterior end of the

Fig. 2. of sampling $ites on shell.

the west coast of Chichijima Mi]fiMt"1 L:&ft W

Island in the Ogasawara Islands. : rviPM. A : reMh4bfi 2krkttt}iiesVe6ecfitw.ei, rvK%t ℃ ofts

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184 VENUS: Vol. 46, No.4(1987)

are subtropical oceanie is}ands with several endemic species living in their en-

vironrnents (Habe et al., 1978). The purpose of the visit is to study biological and

ecological aspects of invertebrates inhabiting intertidal hard substrata, inelud-

ing roeky shores, rock platforms, and boulder beaehes. The papers of the results

aTe on the way of publications (Asakura and Nishihama, 1987 and under re-

view). In some boulder beaches, we found N. schrenckii of a new type of color

pattern. This new type of limpet resembles N. schrenckii schrenckii more closely

than N. schrenchii gloriosa, because it has a green-colored shell. In this paper,

we describe this new subspecies and report on the spatial distributien, size struc-

ture and allometrie growth, in comparison with those of typieal N. sehreneleii

frern Amakusa, northwest Kyushu.

Materials and Metheds

The collections were made at three localities on the west coast of Chichijima

Island, namely, Okumura, Sakai-ura and Yagyu-san. (Figs. 1 and 2). In these

sites, a quadrat (1m × 1m) was placed at fouT to six points from the middle to lower intertidal zone, eolleeting all by hand in the quadrat, and fixed

in a 10% formalin so]ution. The limpets weTe dried at 600C for 72 hours and

weighed. In all of the individuals, the shell length(L), the shell width(W) and

the length frem the apex to the pesterior end of the shell CA) (Fig, 3) were

measured with an ocular micrometer under a stereoscopic microscope.

Wave Index(WI) was defined as an indicator ef the degree of wave ex-

posure at each sampling site. Heights of the highest and lowest levels of waves were measured ten times over a period of few minutes using a vertieally stood

ruler. Then, mean values of the both heights were caleulated, and WI was repre- sented by the difference between them. All of the measurements were done at each sampling site at noon on April 12. The weather was sunny and very ealm, and no large atmespheric depressions er cold fronts occurred areund the islands. Thus, the values of WI eould be considered to represent the general degree of

wave exposure at each site. For comparison, specimens of N. schrencicii schrenckii were randomly eol- 'n'. -{' Figl 4s-g. Nbtoacmea schrenckii boninensis subsp. th"tt v i 7 ]i] ab d (MMZg) a-c: Holotype specimen, IesJkeedy d: Paratype specimen No. 1 fftllecrk･eeAS 1 e: Paratype specimen No, 2 l'Uecrkeclt 2 f: Paratype specimen No. 3 rtllffSlen zts 3 g: Enlarged surface of NL schrenckii boninensis rvtcntlJk pt a-g: From Yagyu-san, Chichijima Isl., the Ogasawara Islands. 4NftXMmakt3(reff"pL[aj h-j: N. schrenckii schrenckii CLischke) 7tth't 'V'P77tjb'I k: N. schrenckii gloriosa Habe h-k: From Shiraiwa-zaki, Amakusa, northwest Kyushu ･ JLV･1･NtasgK ･ ie AXI]fire [Vertical bars indicate 10mm.]

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. Asakura Nishihama :Biology ofNetoacmea schrenckiiboninensisn. subsp. 185

a b c

d e f

g

h jt k

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186 VENUS: Vol. 46, No.4(1987)

lected from the lower intertidal zone of a boulder beach of Amakusa, north-

west Kyushu (Fig. 1). The specimens were fixed in a 10% formalin solution and the shells (L, W, A) were measured with the mierometer under the micro- seope.

A linear regression model (Y=ax+b, where a, b: constant) of the allometric growth was fitted for all sets of data.

Taxonomy

Family ACMAEIDAE

Genus Notoacmea Iredale, 1915

Notoacmea schrenckii bortinensis n. subsp.

(Fig. 4a-g)

Description: view. ' Shell patelliferm, depressed conieal and elliptic in apical Apex situated at about nine-tenth anteriorly. Exterior surfaee smooth except

weak growth lines and weak radial ribs, and irregularly and radially scattered

with fine greenish brown lines, whieh sometimes form V-shape pattern, en pale

green baek greund. Inner side of the shell framed with a narrow dark brown

fringe. Callus b]uish white with the horse-shoe shaped muscle scar of the dark

green color.

Measzarement :

Holotype CNSMT-Mo 64445): Length 13,60mm, width 10.25mm, height

2.65 mm

Paratype No. 1 (NSMT-Mo 64446) : length 12,85 mrn, width 9.35mm, height ' 2.15 mm

Paratype No. 2 (NSMT-Mo 64447) : length 11.45 mm, width 8.15 mm, height

2.05 mm

Paratype No. 3 (NSMT-Mo 64448) : ]ength 11.35 mm, width 8.10 mm, height

2.00 mm

Type locatity: Yagyu-san, Chichijima Island, the Ogasawara Islands (under

the boulders in the intertidal zone)

Distribution: Okumura, Sakai-ura, and Yagyu-san, Chichijima IsL, Oga-

sawara Isls.

Comparison: Radula of N. schrenekM boninensis differs from N. schrenckii

schrenckii: A larger cusp in the bieuspid tooth of lateral teeth is rounder in

boninensis than in schrenckii (Fig. 5).

Differences in the shell allometory between N. schTencloii schrenekii and N. schrencleii boninensis are illustrated in Fig. 6 (IrW relation) and Fig. 7

(L-A relation). Parameters of eaeh regression are shown in Table 1. Highly

significant correlations were found in all cases by analysis of variance (Table 1). Only a slight difference eould be detected between the regression of boninens･is and that of sehrenckii in both eases, although they showed a statistically sig-

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Asakura ・Nishihama ：Biology of 1＞oteacmea sc 宛プ6 η o 肋 うo η 豌 召η s ’s n ． subsp ． 187

Table 1． Regression analysis of allometric growth of N ． schrenckii boninensis and N ，schrenckii schrencleii ．オ ガ サ ワ ラ ア オ ガ イ と ア オ ガ イ の 相 対成 長 式

Regression

Y ；aX 十 b

where ， X ： shell length in mm ［L ］ and “ ” Y ： shell width in mm ［W ］ or length A in mm （in Fig．3） ［A ］

Relation of of variance

shell Subspeciesn Slope Intercept rAnalvsis − meaSUrement （a ） （b） F value P − 一 L W わonin 召 nsis 60 O．7930 〇．9934 O，9934 4528．6 ＜ 0．001 − s σん7 召π o 虍露 72 ．72550 0 ，2434 0．9909 3803 ．4 く O． OOI − ’ − L A うo η わzθπ s 露s 60 ．90640 0，0793 0．9967 8633．8 く O． OOI

schren ‘々齬 72 ．8708 0．0359 0，9943 6063．2 く 0 ，001

1 2

Fig．5． Radulae of N ． schrenckii schrenckii （1）and N ， schrenckii

boninensis ， Horizontal bar indicates O， lmm ． ア オ ガ イ （1 ）と オ ガ サ ワ ラ ア オ ガ イ （2）の 歯 舌

Table 2． Analysis of covariance for the difference in the regression lines of

allometric growth between N ． schrenckii boninensis and N ． sehrenckii schrenckii ． Abbreviations of shell measurement as in Fig ．3， オ ガ サ ワ ラ ア オ ガ イ と ア オ ガ イ の 相対 成長 式 の 共分 散 分析

Relation of Analysis of covariance bodymeasurement

F −value Probabi1ity − L W slope 4，894094 O．025 く p ＜ 0 ．05 Y −intercept ，6355 p ＜ 0．001 − L A slopeY ．675029 0．01く p ＜ 0．025

・intercept ．006 p く O． OO1

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188 VENUS: Vol.46, No. 4 (1987)

- - 16aEv e16 H v

}2=-Q-)B = 12 <

= =8 p aAhl o z 4=ca -4

A

o 4 S l2 l6 20 O 4 S 12 16 20

SHELL LENGTH (mm) SHELL LENGTH(mm)

Fig.6. Relationship between shell length and Fig. 7. Relationship between shell length and shell width ef N schrencki･i boninens･is the length from the apex to posterior

"A" (B) and N, schrencleii schrenckii (S), end of the shell (length in Fig, 3)

Values of constants of each regression of IVL schrenckii beninensis (B) and IV. in Table 1. schrencleii schrencleii (S). Values of con-

1- b'Hb il 7 7 1- th' ij E 7 t h' ti Orvft stants of each regression in Table 1. -meptMuaesa)Lktt. ,7 Nrati wa o ts c･: t h'V 7 7 i- th'l }. 7 fr h' ( as esft -"A" Table 1 $.H,ll,,. ftcaesa)Lkut. A a･tnttathliB 'tra) fircth%' st ftS (Fig. 3 tsP,B). PllfifftiMOmaX Table 1 #P,e,.

nificant difference by analysis of covarianee CTable 2). IV. schrenckii bontnensis 'the has a wider shell than N. schrenckii schrenckii, and especially in adult shells, " apex of boninensis is situated at a more antemor position than that of schrenckii, ' Color pattern of N. sclbrenckii boninenszs differs from that of N. sehrenekii

schrencleii and N. schrenckii gloTiosa･ in having the radially scattered brown fine

lines and V-shape pattern on the surface, In eontrast, N. schrencleii schrenckii

has a green shell with numereus yellow and dark patehes superfieially (Fig. 4h-:')

and N. schrenckii glorios- has a pink shell with numerous white patches with red

outline and a few red patehes (Fig. 4k) '

The radial ribs on the exterior surfaee of N. schTencicii sehTenekii and

N. schrenekii gtoriosa are granulose, whereas that of N. schrencicii boninensis

has weak radial ribs without granules.

N. schrenckii boninensisis distinguished from N. concinna concinna (Lischke),

N, coneinna nigrans Kira, 2V. concinna radicla Kira, N. concinna tera･machii Kira

and N. eonci･nna f･useoviridis Teramachi by both color pattern of the exterior surfaee and shell morphology. Although these subspeeies were first deseribed as independent species (Terarnachi, 1949; Kira, 1961), recent authors do not agree with those classification (e.g. Habe and Okutani, 1975). N. eoncinna eon-

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Asakura.Nishiharna:Biology of Nbtoacmea schrencleii beninensis n. subsp. 189

cinna is uniform greenish brown eolor, N. concinna radula is scattered with man'y white patches on the dark green surfaee, nigrans has two symmetrical

broad white bands from the apex to the both lateral sides, teTamachii has obvious

many yellow radial striae, and fuscoviridis is maculated by yellow spots on the

green surface. The apex is less anterioTly situated in these subspecies than that

in N. schrenekii boninensis; at about one-sixth anteriorly ill nigrans and one-

seventh in raduta, terqmachii, ftescoviTidis and concinna. Their shells are less

depressed than that ef N. schTencicii boninensis and have distinct radial ribs

with many minute granules on the surfaee.

Biology

The density of N. schrencleii boninensis in three sampling sites is shown in

Table 3. All specimens were found from the boulder beaches except the she]tered

Kiyose beach, where WI was 2.8cm, and also no individual was found on the

rock platforms or in the tide pools at any of the sampling sites. They showed

the greatest abundanee at the wave-exposed boulder beach in Yagyu-san.

Table 3. Density of N, sehrenckii boninensis in three sampling sites on the

west coast of Chichijima Island. See the text for the definition of WI (Wave Index), indicating clegree of wave expesure. .3CndiJ"r"'l- T7 'i rtifet6 7 t h'( o fifii"ff,,.ma, W I-t･.mE?RollutLtts.itWliva. 1"'t - Site WI(cm) No. ofquadrat Total no, Meandensity(ind,,!mP)s. d.

collected

okumulh' IL4 6 1 O. 17 O. 37

Sakai-ura 12,7 5 3 O. 60 O, 80 Yagyu-san 4 1.23 39.71 ..-f2.7 . . - tt.75 .

Fig. 8 shows the relationship betweell shell length and dry body weight with

she]1 of N. schrenchii boninensis, presenting a highly significant correlation be-

tween them.

Fig. 9 shows size-frequency histograms of N. schrencleii boninensis collected

from the Yagyu-san boulder beach. Density was the highest at point B in the

middleand intertidal zone. Small individuals were distributed mainly at the points A

B in the rniddle intertidal zone. Larger ones were found both from the

middle and lower intertidal zones.

Aparedsize-frequeney histograms of all specimens collected from Yagyu-san is com- with that of N. sehTenckii schrencleii from Amakusa (Fig. 10). Mean size

of N. sehTenck ii boninensis was significantly smaller than that of N. schrencicii

sehrenekii (p

Discussion

N. schrenck ii boninensis is living mainly under boulders in the wave-exposed

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190 VENUS ： VoL 46， No ．4 （1987）

＝ 6 Log Y 3 ，32S8 Log X 一 正．6999 n 日 7 る （ n ＝ 34

u 。 2A r z O ，9899 E 500 》 0 2 4 6 8 lO 匚2 14 16 18 20 ト 200IOO5020Io5212SHELL5 20220B エ O ロ n ＝ 83 冖 ∈ 丶 ハ 国 ． b412hO5 ℃

OOO ｝

【 ← ◎

10 20 一 ら a LENGTH 〔mml mz 20

Fig ．8． Relationship between the shell length 42C of n ＝ 19 and dry body weight （with shel1 ） 国

N ．sch7 θnchii boninensis a 一 オ ガ サ ワ ラ ア オ ガ イ の 殻 長 乾 重量 の 02 DO n ＝ 4 関係 ：： ． ］ − rP − 一 一 P b 1 2 ら 6 8 塵0 且2 1ら 16 且820

SHELL LENGTH 〔m 皿 ） MHWS （ 00 匚 ∈ ）り

ト

の ＝ ’ 2昌 N ． 3chrenckdi boninensi3 Oh 腕 ー く ° m 2 ら n ＝123 05 ） 翠 A B 目 凵 凾 20

＝ こ ー 巳16 犁 」 」幽儚層 日 12 ン． こ 舗 U MLWS −0 一9 ！ Fig ．9 ． Size−frequency histograms of N ． sch − 〇 Z 4 6 3 LO l2 匸る 16 1820 2Z 24 renckii boninensis in the Yagyu ・san N ． 5 ⊂ぬ re 月 cktt 5chr2 昂 cki ゴ 凱6 n ＝ 124 boulder beach in Chichijima Island． i ： ご Profi且e of the beach and locations of the sampling are also shown ． 箋 ・ Points 野 羊 山近 くの 転 石 海 岸 に お け る オ ガ サ 襃 。 2 も 58IOI2 ［ら 161820222 ら ワ ラ ア オ ガ イ の 潮 位 ご と の サ イ ズ 組 成 SHELLLENGTH lmm ｝

Fig．10． Size−frequency histograms of total individuals collected from Yagyu ． san in Chichijima Island （upPer ： N ，schrenckii boninensis， mean ＝ 8，31

（3，15s．d．） mm ） and from Amakura − Kyushu （lower ： N ． schrencleii schren ckii ， mean ・＝ 11．71 （4，65s．d ．） mm ）． 父 島 の オ ガ サ ワ ラ ア オ ガ イ と 天 草 の ア オ ガ イ の サ イ ズ 組 成 の 比 較。

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Asakura.Nishihama:Biology of Notoacmea schrenckii boninensis n, subsp, 191

roeky shores. This habitat is quite similar to that of N. schrenckii schrenckii

(Wada et al. 1983).

Mean size of N. sc]be"encleii boninensis is smaller than that of N. schrencicii

schrenckii. The maximum size of N. schrenckii schrenckii collected in this study

was 20.55 mm in shell length. Adult sizes of this limpet have been reported by

different authers; 30mm in Habe and Okutani (1975), 22mm in Habe and Kosuge (1967), and 20mm in Nakamura (1986). The latter two values are

in good agreement with our values. However, informations on the seasonal vari-

ations in size structure of the populations of both N, schrencicii schrenckii and

N. sehrenckii boninensis have never been available. Thus, further observatien

on specimens from various seasons is needed.

It is knoNsTn in some gastropods in the noTthern hemisphare that individuals in the southern population are smaller thall those in the northern population

(Tissot, 1984; Brock, 1980; Smith and Breyer, 1983; Frank, 1975; Lewis et al.,

1982), and sometimes this has been considered to be caused by higher water

temperatures in southern habitat (but the physiological mechanism is unknewn).

Thus, one possibility in preducing smaller size of N. schrenchii boninensis may

be higher water temperature in the Ogasawara Islands, but the other possibilities,

such as higher predation pressure in tropieal waters (Frank, 1975), must be

also considered and tested in the future study.

Many gastropod species closely related to temperate Japan species are

known in the Ogasawara Islands, such as perplexa boninensis (vs.

Monodonta perplexa peTplexa in the main Japan Islands), Cellana enneagona

(vs. Cellanes toTeuma), Monodonta australis (vs. Monodonta tabio), etc. Recently,

Takenouchi (personal communication) found that Monodonta australis from

the Ogasawara Islands shows an obvious morphologica! difference from the

typical M. attstratis such as specimens from South Afriea. He suggested that

the specimens from the Ogasawara Islands should not be identified to true

M. australis but may be an endemic form to the islands.

"speciations" One of the factors causing these ean be considered to be the

geographical isolation of the islands, because the islands are situated about

1000km from the main, tempeTate Japan Islands, 1200km from the Ryukyu

Islands, and 2000 km from China. In several eases of the variations in gastro-

pods shells, the isolation has been considered an important factor (Brock, 1980;

Tissot, 1984). Thus, difference in shell morphology of N. schrenckii boninensis

from N. schTencltii schrencleii may be eaused by a geographical isolation. We believe that present study provides sQme basie information on the origin and

speciation of marine animals in the Ogasawara Islands.

Acknowledgements:-We express our sincere appreciation to Dr. T. Habe, Professor

of Tokai University, and Dr. T. Okutani, Professor of Tokyo University of Fisheries

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192 VENUS ： Vo1 46 No 4 1987 ． ， ． （ ）

for valuable advice and critical reading of the manuscript ． Dr ． B ． D ． Snlith of Guam

University Marine I．aboratory kindly gave us helpful information． Thanks are also

due to Mr ． K ． R ． Nakamura of Amakusa Marine Biological Laboratory for improv − ing’English ．

We also thank Mr ， K ． Nishimura of Ogasawara Fishery Center ， Professor T ． Yana −

of the of gisawa Ogasawara Research Committee Tokyo Metropolitan University， ML Y ． Kurata of Ogasawara Marine Center， Mr ， Y ． Matsumoto of Toba Aquarium

for their valuable suggestions advice and aid survey of ， ， in bibliographical ． Staffs Ogasawara Youth Hostel and T ． Nakajima of Urayasu OMcial kindly assisted us in

our fieldworks．

要 約

小 笠 原 諸 島 父 島 よ り 採 集 し た ア オ ガ イ の 新 亜 種 ，オ ガ サ ワ ラ ア オ ガ イ Notoacmea schrenckii boni・

べ nensis の 記載 を し 生 息状 況 を 調 た D ’ オ ガ サ ワ ラ ア オ ガ イ の 殻 は 楕 円 形 ，偏 ドな 円 錐 状 を な す が ア オ ガ イ 1＞btoaemea sehrencbii よ り 丸

く 腰 高 で あ る 。殻 頂 は ア オ ガ イ よ で の の に ・ で い り前 寄 り 全 長 約 妬 所 あ る 。 殻表 は F滑 薄 緑地 に 短 か 茶

．こ 褐 色 線 を 不 規則 な放射 状 ； 散 らす 。部位 に よ っ て は こ の 2 本 の 線 の 片 側 の 端 点 が 付 い て V 字 模 様 と な

る 。内而 周 縁 は 茶 色 に 狹 く縁 取 られ る 。滑1曽は 灰 青 色 で 中．央 の 緑 褐色 班 は 明瞭 で あ る 。 ． ・ ・ ． ． 本 種 ぱ 父 島 西 海 岸 に あ る 奥村 境 浦 野 羊 山 付近 の 転 イ」 海 岸 に そ の 生 息 を 確認 し た が ，特 に 波 浪 の ’ 強 い 野 羊 山 の 海 岸 で 密 度 が 高 く，潮 閲 帯 の 巾部 を 中 心 に ト部 ま で 分布 が 認 め ら れ た 。 岩 盤 上 や タ で ド

プ ー一ル ・ 画 中 力 ら は 見 い 出 →± な 力 つ た o

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[Received: September 21, 1987]

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