NOM No. 12 (March 1984) pp. 51---56

SHORT NOTE

Tidal growth patterns

(LINNAEUS, 1758)

in recent Monodonta labio

(Gastropoda, Trochidae)

Terufumi OHNO* and Koichi TAKENOUCHI**

Shell of the recent bivalves living in intertidal

zones show various growth patterns which reflect

the characters of tides of their habitats (EvA NS,

1972 ; RICHARDSON et al, 1979 ; OHNO, 1983a,

b), and such patterns are found also in fossil

bivalve shells (OHNO, 1984). This article reports,

that also shells of gastropods show tidal growth

patterns taking Monodonta labio (LINNAEUS,

1758) as an example. We express our hearty than

as to Dr. Eiji TSUCHIDA of Ocean Research

Institute to the University of Tokyo, who kindly

gave us specimens from Palau Islands. This

study is partly supported by the fund for the

senior author as a postdoctral fellow of the JSPS ,

1983.

Examined specimens came from tidal zones

of two localities : Near Koror, Palau Islands and

Uranouchi Bay, Kochi Prefecture, Japan. Shells

were bedded in plastic and cut along the line A-

B in Text-fig. 1. They were abraded with carbo-

rundom until the grain size of #3000, then

polished with diamond paste. The polished

samples were etched with 0.1 mol HCl for

about 40 seconds. These samples were then

coated with Au and observed under a SEM.

Shell of Monodonta labio is composed of

aragonite (TOGO, 1977) and consists of three

layers (Pl. 1, fig. 3). The outer layer and inner-

most layer are composed of fine acicular crystal-

lites and the inner layer is nacreous. The

innermost layer is confined to the region near

the margin of the apperture, and is lacking in

some specimens. There are two components of

incremental growth (P1. 1, fig. 2) : thinner growth

lines (L) and thicker growth increments (I)

between growth lines. Growth lines are

observed in all of the three layers mentioned

above, but most clearly in the outer layer and in

the innermost layer.

In the shells of specimens from the Palau

Islands, there is an alternation of thicker and

thinner growth lines both in outer and inner

most layers (Pl. 1, figs. 2, 4). .The order of the

appearrance of thicker and thinner growth lines

changes also periodically. Therefore, in an

arbitrarily numbering, if growth lines with odd

numbers are thicker at first, then after an interval,

growth lines with even numbers become thicker.

In the samples from Uranouchi Bay (P1. 1, fig. 1),

there are parts (S) with thicker and thinner

growth lines alternating in a similar manner as

observed in the specimens from Palau • Islands,

which are separated from each other by parts

with widely spaced growth lines (N).

The growth pattern of Monodonta labio of

Palau Islands is quite similar as that seen in the

bivalve shells living in about middle tide line of

intertidal zones in regions of semidiurnal tides.

Department of Geology and Mineralogy, Faculty of Science, Kyoto University, Kyoto 606, Japan

Seto Marine Biological Laboratory, Faculty of Science, Kyoto University, Shirahama, Wakayama 649-22, Japan

Text-fig. 1. Orientation of observed sections

each other (right).

In bivalve shells of such level, growth lines are

formed at each low tide, when they are emerged.

Because of the difference of activity of bivalbes,

growth lines formed at daytime low tides are

thicker than those at night time low tides. This

causes, besides an alternation of thicker and thin-

ner growth lines, the change of the order of

thicker and thinner growth lines with a period of

14. 77 days. Therefore the growth pattern is in

this case a result of interferrence of 12.4 hours

period of low tides and day-night change with

24.0 hours period (OHNO, 1983b).

To examine, whether the growth pattern of

Monodonta labio from Palau Islands is formed

with the same cause as that of bivalves, a

sequence of 102 growth lines of a sample of

Monodonta labio was observed and each line is

classified into three categories ; thick, thinn, and

not assignable. The designations of the lines are

plotted in a diagramm with 12.4 hours interval,

which corresponds the period of low tides. The

ordinate of the diagramm represent days before

the collection of the shell, and the abscissa the

time of the day. (Because the time of collection

is not known for the specimens from Palau

Islands, the last low tide was setted arbitrarily at

IM

0

and retation of outer (0), linner (I), and innermost (IM) layers to

about 18 : 00 o'clock). On such a diagramm, the

distribution of thick or thinn growth lines will be

confned to a certain time interval of the day,

when both of the following two conditions are

filled :

1) growth lines are formed with 12.4 hours

period,

2) pattern of thicker and thinner growth lines

is caused by the interference of 12.4 hours

period of tide and day-night change with a

period of 24.0 hour.

The plott for the Monodonta specimen is shown

in Text-fig. 2. Thick growth lines are confined

to the time period between 6 and 18 o'clock and

the thinner growth lines to the time period between

18 o'clock and the 6 o'clock. Therefore it is quite

probable, that the growth pattern of Monodonta

labio from Palau Islands is caused by the inter-

ference of 12.4 hours period of low tides and

day-night change with 24.0 hours period.

Similar patterns as that of specimens from

Uranouchi Bay are common in shells of bivalves

living between middle tide line and low tide line. In

those bivalve shells parts with alternation of thinner

and thicker lines are formed in the same manner

as mentioned above. These parts are separated

0 | | -50 - ,

^ |

1 |

1

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'^^ _

-10 -

0_

Al__ _^___

----m-- ___-°_

_

-

_

.

'm^

I-

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^r

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-

--=-11----

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Text-fig. 2.

A sequence of 102 growth lines of a Monodonta labio

specimen from the vicinity of Koror, Palau Islands,

plotted with an interval of 12.4 hours : ordinate=days before collection of the shell ; abscissa = hours; 1= thick

growth line ; 2 = thinn growth line ; 3= line, which is not assigned to either category.

from each other by the parts with widely spaced

growth lines. The latter parts are formed during

the neap tide, when the shells are always under

the water for a few tidal cycles. The growth

pattern of the shells of specimens from Urano-

uchi Bay is very probably formed in the same

manner : the S-parts with alternation of thicker

and thinner growth lines are formed during

spring tides and the N-parts are formed during

the neap tides.

Tidal patterns in hard tissues of organisms

could be applied in biology, paleontology, and

geology, for example, estimation of growth rate

with a resolution of 12.4 hours, recognition of

intertidal fauna, reconstruction of patterns of

paleo-tides, past shore lines, etc. Further efforts

should be done to collect more detailed infor-

mations about the manner of growth line forma-

tions of gastropods, because the existance of tidal

patterns in gastropod shells extends the fields of

application enormously. They are very abundant

not only in the present sea but also throughout

the geological time, from the middle of the

Cambrian Period, even before the appearance of

the bivalves.

References

EVANS, J. W. (1972) : Tiadal growth increments in the

cockle Clinocardium nutalli. Science, vol. 176, pp.

416-417.

OHNO, T. (1983a) : A note on the variability of growth

increment formation in the shell of the common

cockle Cerastoderma edule. In : BROSCHE &

SUNDERMANN (eds.) Tidal Friction and the Earth's

Rotation II, Springer, Berlin Heideldberg New York,

pp. 222-228.

OHNO, T. (1983b) : Experimentelle Analysen zur

Rhythmik des Schalenwachstums einiger ausgewahlter

Bivalven (Mollusca). Doctral thesis, Universitat

Bonn (MS).

OHNO, T. (1984) : Tidal growth patterns in late Pleisto-

cene bivalves in the boring cores around Osaka Bay , Central Japan, NOM, no. 12, pp. 41-49

(in Japanese with English abstract).

RICHARDSON, C. A., CRISP, D. J., RUNHAM, N. W.

(1979) : Tidally deposited growth bands in the shell

of the common cocle, Cerastoderma edule (L.).

Malacologia, vol. 18, pp. 227-290.

TOGO, Y. (1977) : The shell structure of the protoconch

and the innermost shell layer of the teleoconch in

marine prosobranch gastropods. Jour. Geol. Soc.

Japan, vol. 83, pp. 567-573. (in Japanese with English summary).

—

Fig.

Figs.

Explanation of Plate 1

(In all the figures, direction of growth is to the right, scales indicate 0.1 rm.)

Monodonta labio (LINNAEUS, 1758)

1. A specimen from Uranouchi Bay, Kochi Prefecture, Japan. This specimen shows a well defined

tidal pattern in the outer shell layer. S= parts with an alternation of thicker and thinner growth

lines. N = parts with widely distributed growth lines.

2-4. A specimen from the vicinity of Koror, Palau Islands.

2. Alternation of thicker and thinner growth lines in the innermost layer : L=growth lines ; I = a

growth increment.

3. Section of the shell, showing three layers : 0 = oute layer ; I = inner layer ; IM = innermost layer.

Growth lines are clearly visible both in outer and innermost layers.

4. Alternation of thicker and thinner growth lines in the innermost outer layers.

NOM12号(1984年)

短 報

腹 足 類Monodonta labio(LINNAEus ,1758)

の 殻 に見 られ る潮 汐 成 長 パ ター ン

大 野 照 文*・ 竹 之 内 孝 一・**

*京 都大学理学部地質学鉱物学教室

**京 都大学理学部附属瀬戸臨海実験所

(要 旨)

パ ラオ島 と高知県浦之内湾の潮間帯か ら得 られたMonodonta labioの 殻 から

腹足類でははじめて,潮 汐周期 を反映した成長パター ンが見い出された。