In Recent Monodonta Labio (LINNAEUS, 1758) (Gastropoda, Trochidae)

NOM No. 12 (March 1984) pp. 51---56 SHORT NOTE Tidal growth patterns in recent Monodonta labio (LINNAEUS, 1758) (Gastropoda, Trochidae) Terufumi OHNO* and Koichi TAKENOUCHI** Shell of the recent bivalves living in intertidal lites and the inner layer is nacreous. The zones show various growth patterns which reflect innermost layer is confined to the region near the characters of tides of their habitats (EvA NS, the margin of the apperture, and is lacking in 1972 ; RICHARDSON et al, 1979 ; OHNO, 1983a, some specimens. There are two components of b), and such patterns are found also in fossil incremental growth (P1. 1, fig. 2) : thinner growth bivalve shells (OHNO, 1984). This article reports, lines (L) and thicker growth increments (I) that also shells of gastropods show tidal growth between growth lines. Growth lines are patterns taking Monodonta labio (LINNAEUS, observed in all of the three layers mentioned 1758) as an example. We express our hearty than above, but most clearly in the outer layer and in as to Dr. Eiji TSUCHIDA of Ocean Research the innermost layer. Institute to the University of Tokyo, who kindly In the shells of specimens from the Palau gave us specimens from Palau Islands. This Islands, there is an alternation of thicker and study is partly supported by the fund for the thinner growth lines both in outer and inner senior author as a postdoctral fellow of the JSPS , most layers (Pl. 1, figs. 2, 4). .The order of the 1983. appearrance of thicker and thinner growth lines Examined specimens came from tidal zones changes also periodically. Therefore, in an of two localities : Near Koror, Palau Islands and arbitrarily numbering, if growth lines with odd Uranouchi Bay, Kochi Prefecture, Japan. Shells numbers are thicker at first, then after an interval, were bedded in plastic and cut along the line A- growth lines with even numbers become thicker. B in Text-fig. 1. They were abraded with carbo- In the samples from Uranouchi Bay (P1. 1, fig. 1), rundom until the grain size of #3000, then there are parts (S) with thicker and thinner polished with diamond paste. The polished growth lines alternating in a similar manner as samples were etched with 0.1 mol HCl for observed in the specimens from Palau • Islands, about 40 seconds. These samples were then which are separated from each other by parts coated with Au and observed under a SEM. with widely spaced growth lines (N). Shell of Monodonta labio is composed of The growth pattern of Monodonta labio of aragonite (TOGO, 1977) and consists of three Palau Islands is quite similar as that seen in the layers (Pl. 1, fig. 3). The outer layer and inner- bivalve shells living in about middle tide line of most layer are composed of fine acicular crystal- 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 IM 0 Text-fig. 1. Orientation of observed sections and retation of outer (0), linner (I), and innermost (IM) layers to each other (right). In bivalve shells of such level, growth lines are about 18 : 00 o'clock). On such a diagramm, the formed at each low tide, when they are emerged. distribution of thick or thinn growth lines will be Because of the difference of activity of bivalbes, confned to a certain time interval of the day, growth lines formed at daytime low tides are when both of the following two conditions are thicker than those at night time low tides. This filled : causes, besides an alternation of thicker and thin- 1) growth lines are formed with 12.4 hours ner growth lines, the change of the order of period, thicker and thinner growth lines with a period of 2) pattern of thicker and thinner growth lines 14. 77 days. Therefore the growth pattern is in is caused by the interference of 12.4 hours this case a result of interferrence of 12.4 hours period of tide and day-night change with a period of low tides and day-night change with period of 24.0 hour. 24.0 hours period (OHNO, 1983b). The plott for the Monodonta specimen is shown To examine, whether the growth pattern of in Text-fig. 2. Thick growth lines are confined Monodonta labio from Palau Islands is formed to the time period between 6 and 18 o'clock and with the same cause as that of bivalves, a the thinner growth lines to the time period between sequence of 102 growth lines of a sample of 18 o'clock and the 6 o'clock. Therefore it is quite Monodonta labio was observed and each line is probable, that the growth pattern of Monodonta classified into three categories ; thick, thinn, and labio from Palau Islands is caused by the inter- not assignable. The designations of the lines are ference of 12.4 hours period of low tides and plotted in a diagramm with 12.4 hours interval, day-night change with 24.0 hours period. which corresponds the period of low tides. The Similar patterns as that of specimens from ordinate of the diagramm represent days before Uranouchi Bay are common in shells of bivalves the collection of the shell, and the abscissa the living between middle tide line and low tide line. In time of the day. (Because the time of collection those bivalve shells parts with alternation of thinner is not known for the specimens from Palau and thicker lines are formed in the same manner Islands, the last low tide was setted arbitrarily at as mentioned above. These parts are separated Tidal patterns in hard tissues of organisms 0 ^ 1 1 24 | | | | could be applied in biology, paleontology, and | -50 - , geology, for example, estimation of growth rate Al__ _^___ with a resolution of 12.4 hours, recognition of ----m-- ___-°_ 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- LI 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 ' m^ the geological time, from the middle of the - Cambrian Period, even before the appearance of '^^ _ I the bivalves. - --=-11---- _ References -i -1 EVANS, J. W. (1972) : Tiadal growth increments in the -10 - .... cockle Clinocardium nutalli. Science, vol. 176, pp. ^r 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 & 0_ SUNDERMANN (eds.) Tidal Friction and the Earth's Rotation II, Springer, Berlin Heideldberg New York, ^ • .---- pp. 222-228. 1 2 3 OHNO, T. (1983b) : Experimentelle Analysen zur Text-fig. 2. Rhythmik des Schalenwachstums einiger ausgewahlter A sequence of 102 growth lines of a Monodonta labio Bivalven (Mollusca). Doctral thesis, Universitat specimen from the vicinity of Koror, Palau Islands, Bonn (MS). OHNO, T. (1984) : Tidal growth patterns in late Pleisto- plotted with an interval of 12.4 hours : ordinate=days before collection of the shell ; abscissa = hours; 1= thick cene bivalves in the boring cores around Osaka Bay , growth line ; 2 = thinn growth line ; 3= line, which is Central Japan, NOM, no. 12, pp. 41-49 not assigned to either category. (in Japanese with English abstract). RICHARDSON, C. A., CRISP, D. J., RUNHAM, N. W. (1979) : Tidally deposited growth bands in the shell from each other by the parts with widely spaced of the common cocle, Cerastoderma edule (L.). growth lines. The latter parts are formed during Malacologia, vol. 18, pp. 227-290. the neap tide, when the shells are always under TOGO, Y. (1977) : The shell structure of the protoconch and the innermost shell layer of the teleoconch in the water for a few tidal cycles. The growth marine prosobranch gastropods. Jour. Geol. Soc. pattern of the shells of specimens from Urano- Japan, vol. 83, pp. 567-573. (in Japanese with English uchi Bay is very probably formed in the same summary). 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. — ~ Explanation of Plate 1 (In all the figures, direction of growth is to the right, scales indicate 0.1 rm.) Monodonta labio (LINNAEUS, 1758) Fig. 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. Figs. 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。.

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