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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
|
'^^ _
-10 -
0_
Al__ _^___
----m-- ___-°_
_
-
_
.
'm^
I-
_
-i-1
^r
~
LI
-
--=-11----
24
_-
^..^
.
....
• .---- 1 2 3
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。