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Qualitative and quantitative characterization of some common bivalves: Polymesoda bengalensis, Codakia tigerina and Anodontia edentula.

INTRODUCTION

In the study of the biological form of bivalves, shells are traditionally used in classifications and taxonomic descriptions. The external form of the shell was the principal character used in molluscan species-level taxonomy including diverse groups. Since shell morphometry and sculpture are regarded as essential for species discrimination [2], a comparative study on three species of bivalves inhabiting different ecological environments was done. These species are Bengali geloina (Polymesoda bengalensis) that live in mud flats and estuaries of mangrove areas, and occurring in the Indo-West Pacific from India to Thailand and Celebes, and from the Philippines to northern Australia [3], the pacific tiger lucine (Codakia tigerina) commonly known as "bakalan" which are buried in sandy bottoms, often in coral reef areas, from shallow sub littoral waters to a depth of 20 m. and the toothless lucine (Anodontia edentula) commonly known as "imbao" which are abundantly distributed in the Indo-West Pacific, from East and South Africa, including Madagascar and the Red Sea, to eastern Polynesia; north to southern Japan and Hawaii, and south to New South Wales [1]. All the three species are locally exploited in the Philippines where the shells are used for decorative crafts or to make lime, and the meat is eaten or chewed with betel nut to make the teeth strong [20]. Since these three species are almost having similar external shell shapes, it is important to have a good qualitative and quantitative measure of the nature of variability in the shell structure. For many years, the study of biological form progressed from qualitative to quantitative. While evaluation of characters is sometimes based on qualitative descriptions of the biological structure [10], a more advanced and recent methodology to effectively quantify shell morphometry is the application of Geometric Morphometric (GM) methods. GM has been successfully applied to distinguish between similar species of bivalves, between wild and aquaculture stocks and between fossil and modern taxa, and also to detect ontogenetic shape changes and to analyze geographic variation in shape [11] thus was applied in the current study.

This study described and analyzed the internal anatomical patterns of the bivalve shell and to explain morphological differences in relation to its adaptation providing analytical explanations of bivalve shell patterns that could offer additional records in understanding the nature of morphological variability of the bivalve shells.

MATERIALS AND METHODS

Specimen Collection and Preparation of Samples:

The samples were taken from the marshes of Tubod, Lanao del Norte, Philippines. Ninety-one (91) individuals were used for morphometric analyses: 31 specimens of Polymesoda bengalensis, 30 specimens of Codakia tigerina and 30 specimens of Anodontia edentula. Samples were cleaned of their soft tissue before the shells were sun-dried (Figure 1).

Qualitative and Quantitative Descriptions:

The shells were described based on the following characteristics: shell shape, umbo, ligament position, ligament location, ligament type, hinge line, dentition, musculature, pallial line, and pallial sinus. Qualitative descriptions were then used to correlate the numerical data obtained from GM analysis. To quantify the shell morphometry, a digital image of internal part of the left and right valve of each specimen was taken in a dorso-ventral orientation. On each image, ten landmark points (Figure 2) were marked using tpsDig freeware version 2.2. The number of landmarks was determined by inspection, covering the necessary anatomical points of a typical bivalve shell (Table 1).

The different coordinates produce by tpsDig v.2.2 were subjected to the program tpsRelw freeware version 1.46 [10, 17] which this program shows the Relative Warps among this three specimens. Relative warp (RW) analysis using all shape variables were used to provide an ordination of all the specimens in a morphological space [11]. All relative warp scores were subjected to Paleontological Statistics (PAST) software version 1.91 [5] for further analysis. Canonical Variance Analysis (CVA) was used for scatter plot elucidation to compare patterns of population variation. Kruskal-Wallis Test was then used to determine if there were significant differences on the anatomical structures/landmarks. Other graphical presentation including box plots and histograms were also incorporated to provide a compact view of where the different populations are centered and how they are distributed over the range of the variable. Lastly, correlation analysis was employed to determine whether morphological descriptions and the shapes of the shell are significantly correlated or not.

RESULTS AND DISCUSSIONS

Qualitative descriptions:

The general phenotypic features of the shell of the three species of bivalves are shown in Table 2. These characters were used to identify the species [7] as employed in taxonomic keys [14].

The shell shape of the three species was observed to be different from each other suggesting distinct morphological adaptations. Since most species of bivalves inhabit the intertidal zone that require high mechanical stability [9, 13], the differences in the shell outline could be an effective adaptation for such type of habitat. Aside from being adapted to intertidal zones, most bivalves are also burrowers [21], those with more streamlined shapes dig deeper. However, the umbo in P. bengalensis is orthogyrous, an uncommon feature among other burrowing bivalves where typically the beaks are pointed towards the anterior of the shell [12] as evident in C. tigerina and A. edentula suggesting that the differences can be genetic in nature. Examination of the lunule, a heart shaped impression on the external side of the hinge that is anterior to the umbo, was found to be depressed in the three species. The depressed lunule is not involved in the burrowing but it is important in taking the weight away from the front and shifting the center of the gravity backward and making assymetric rocking motion of bivalves more effective [15]. Its presence in the three species may suggest shaking of their shells to loosen the sand and to ease their movement through the sediment while burrowing. The valves of the three species were similar being an equivalve held together by an elastic ligament leaving a scar on the hinge. The ligaments were also similar for the three species being opisthodethic and parivincular indicating external development [13]. The same observation was also true to the hinge line of the three species which is arched. The hinge was found to have interlocking ridges called the dentition and was found to differ in the three species. The individual ridges or teeth of P. bengalensis and C. tigerina are heterodont having cardinal teeth and lateral teeth either in front and/or behind beak, while A. edentula is desmodont usually lacking well defined teeth [8]. The two valves were observed to be articulated to the soft body by adductor muscles that produce a scar on the interior surface. The three species are dimyarian having two scars on each valve [19]. The three species are integripalliate since they don't have a pallial sinus [4].

Quantitative Descriptions:

CVA scatter plots of the three bivalve species were clustered from different quadrants (Figure 3) indicating the shapes of the shells were significantly different. The clustering of the individual samples is evidently consistent in both the left and right internal valves. Pairwise comparisons between species are shown in Table 3 indicating the differences observed among the three species were significant.

The variations observed within and between species using the method of relative warps [14] demonstrate five and four significant relative warp scores for the left and right internal shells respectively. The variations are shown in the form of plots and histograms for the left (Figure 4A) and right (Figure 4B) valves. Variation percentage and detailed differences in morphological variations on different axes of the significant warps are discussed in Table 4 and Table 5.

Relative Warp (RW) 1 of the left interior valve is bimodal, this means having two peaks at the positive and negative values. The range of P. bengalensis spreads along the positive values of the axis, suggesting that the sample reflects the morphologies explained in the positive plane of the RW. While the ranges of C. tigerina and A. edentula are on the negative values of the axis, implying that these species resemble the morphologies of the negative axis of RW1. Box plot of RW2 shows that the range of C. tigerina is situated in the positive axis but also extends slightly to the negative axis while the other two is almost uniformly distributed towards zero suggesting a much closer resemblance to the mean shape. The RW3 to RW5 box plot graphs for the three species are relatively similar in distribution that the three population fall in the consensus morphology, which further indicates that most individuals have morphologies identical or similar to the consensus.

For the right valve, a bimodal RW 1 distribution of the population in the first relative warp strongly suggests two separate normally distributed populations. P. bengalensis draw towards the positive axis, while C. tigerina on the negative but slightly deviates to the positive axis, and A. edentula lies along point zero. Histogram for RW2 is unimodal which shows that the range of P. bengalensis is almost uniformly distributed in the mean or zero value of the horizontal plane. Furthermore, the range of C. tigerina, as shown in the boxplot, is found lying on the negative axis but slightly deviates to the the positive values of the axis. While, the range of A. edentula is located in the positive values. Like RW2, histograms of RW3 and RW4 are both unimodal which shows that both are uniformly distributed in the negative and positive values, with most individuals positioned at zero value. Pairwise comparison of the morphological differences in shell shapes between the three species as shown by the significant relative warps were tested using Kruskal-Wallis test (Table 6). For the left shell, all the variations observed between P. bengalensis and C. tigerina, and P. bengalensis and A. edentula in RW1 are highly significant but not between C. tigerina and A. edentula. For RW2, all the variations observed in the three species are significant. For the right valve, variations in shell shapes between species described in RWs 1 and 2 are significantly different.

Correlation analysis of the morphological characters and shapes of the bivalve shells are negatively correlated (Table 7). It has been accounted that characterization of the internal shells can be strengthened using geometric morphometric analysis. Results of the descriptions of the morphology of the shells of the three species obtained from the significant RWs are summarized in Table 8.

Results show that the differences are focused on the hinge plate formation, muscle scar position and distance of the pallial line. Differences in the hinge plate are due to dentition. Dentition in P. bengalensis and C. tigerina is heterodont with two to three wedge-shaped cardinal teeth set in the center near the umbones. While desmodont dentition, very small or completely absent teeth, in A. edentula. This could be the possible reason for the existence of pronouncedly curved hinge plate of P. bengalensis and slight curved hinged for both C. tigerina and A. edentula. In connection with dentition, the adductor muscle also help the shell to close more efficiently. A system of paired adductor muscles, one at the anterior end and the other at the posterior, is best suited. Sometimes, this muscle leaves a distinctive scar on the internal surface of the shell [16]. Accordingly, differences in the orientation and position of the muscle scar could be affected by the adductor muscles. The larger the muscle scar the larger the adductor muscle attached to it. In majority of bivalves, the posterior portion of the body shell are bigger than the anterior. As a result, the posterior muscle requires to pull stronger and so must be bigger [16]. The same condition is also observed in C. tigerina wherein enlargement of the adductor scar is evident. In addition, the pallial line is a mark on the inner surface of a bivalve shell more or less parallel with the margin caused by the attachment of the mantle [6]. Thus, differences in the pallial line could be attributed to the attachment of the mantle into the bivalve shell. In deep burrowers, the pallial line show a pallial sinus in order to lengthen the muscles of a retractable siphon [18]. Since the three bivalves do not have pallial sinus, this may imply that they live just under the surface of the substrate. This is also supported by the moderately rounded or circular shell outline of the three species.

Conclusions and recommendations:

Based from the results, differences in the hinge plate, pallial line, and muscle scar are found to be significant. It has been found that differences in the hinge plate is affected by dentition, while muscle scar is associated with the adductor muscles attaching to it, and the pallial line is attributed to attachment of the mantle into the bivalve shell. These features are usually affected by habits and habitats of the particular species. Furthermore, to fully understand the mechanism of differences observed in the present study, it is highly recommended to conduct research on functional morphological analysis of bivalves. The ecological parameters and habitat of the bivalves should also be noted to effectively explain the reason behind the variability.

REFERENCES

[1] Bouchet, P., G. Rosenberg, 2015. Anodontia edentula (Linnaeus, 1758). Accessed through: Odido, M.; Appeltans, W.; BelHassen, M.; Mussai, P.; Nsiangango, S.E.; Vandepitte, L.; Wambiji, N.; Zamouri, N. Jiddou, A.M. (Eds) (2015) African Register of Marine Species at http://www.marinespecies.org/afremas/aphia.php?p=taxdetails&id=605402 on 2015-04-03

[2] Dame, R.F., 2012. Ecology of marine bivalves: An ecosystem approach. Boca Raton: CRC Press. Chicago.

[3] Do, V., P.B. Budha, B.A. Daniel, 2012. Polymesoda bengalensis. The IUCN Red List of Threatened Species. Version 2014.3. Accessed at www.iucnredlist.org

[4] Fish, J.D. and S. Fish, 2011. A student's guide to the Seashore. University of Wales, Aberystwyth. ISBN 9780521720595, pp:250-251.

[5] Hammer, O., D.A.T. Harper, P.D. Ryan, 2001 PAST version 1.91: Paleontological statistical software package for education and data analysis. Palaeontologia Electronica, 4(1): 9.

[6] Huber, Markus, 2010. Compendium of Bivalves. A Full-color Guide to 3'300 of the World's Marine Bivalves. A Status on Bivalvia after 250 Years of Research. Hackenheim. ISBN 978-3-939767-28-2, at, p: 57.

[7] Kozloff, Eugene, N., 1987. Marine Invertebrates of the Pacific Northwest. University of Washington Press, Seattle, WA. ISBN 0-295-96530-4, pp: 511.

[8] Leal, J.H., 2002. Bivalves. Bailey-Matthews Shell Museum, Florida, USA.

[9] Moneva, C.S.O., P.M.L. Baquiano, J.O. Blasco, K.M.E. Borlaza, D.M.E. Burias, K. Flores, G.R.E.. Fuentes, A.G.E. Pancho and R.R. Sanchez, 2014. Comparative morphological descriptions of interior shell patterns of the Venerid bivalves: Merytrixlyrata (Sowerby, 1851), Mercenariamercenaria (Linnaueus, 1758) and Venerupisphilippinarum (Adams and Reeve, 1850) using Landmark-based Geometric Morphmetric Analysis.

[10] Moneva C.S.O., M.A.J. Torres, T. Wada, R. Joshi, C.G. Demayo, 2012 Relative warp and correlation analysis based on distances of the morphological shell shape patterns of Pomaceacanaliculata Lamarck from Japan and the Philippines. Advances in Environmental Sciences, 4(1): 12-21.

[11] Morais, P., M.M. Rufino, J. Reis, E. Dias, R. Sousa, 2013. Assessing the morphological variability of Uniodelphinus Spengler, 1783 (Bivalvia: Unionidae) using geometric morphometry. Journal of Molluscan Studies, 80(1): 17-23.

[12] Morton, Brian, 1987. The functional morphology of Neotrigonia margaritacea (Bivalvia: Trigoniacea), with a discussion of phylogenetic affinities. Records of the Australian Museum, 39(6): 339-354.

[13] Neubauer, T.A., M. Harzhauser, O. Mandic, 2013. Phenotypic evolution in a venerid bivalve species lineage from the late Middle Miocene Central Paratethys Sea: a multi-approach morphometric analysis. Biological Journal of the Linnean Society, 110(2): 320-334.

[14] Ortega, P. Eduardo, Demayo, G. Cesar, Torres, J. Mark Anthony, Adamat, A. Liza, Tabugo, M. Sharon Rose, Olowa, F. Lilybeth, E.Manting Muhmin Michael and Moneva, O. Carlo Stephen, 2013. Bio 105.2 Systematics Laboratory Manual. Department of Biological Sciences, College of Science and Mathematics, MSU-Iligan Institute of Technology.

[15] Prothero, Donald, R., 2013. Bringing Fossils to Life. An Introduction to Paleobiology. Third Edition. Columbia University Press. New York, USA.

[16] Ray, A.K., 2008, Fossils in Earth Sciences, 1st Edn., Prentice Hall, India, pp: 444.

[17] Rohlf, J.F., 2008. Relative Warps version 1.46. Ecology and Evolution, SUNY at Stony Brook.

[18] Seilacher, Adolf and Gishlick, D. Alan, 2014. Morphodynamics. Taylor and Francis Group. ISBN 9781482221183, pp: 551.

[19] Shanmugam, A. and S. Vairamani, 1994. Molluscs in Mangroves: A Case Study, Centre of Advance Study in Marine Biology Annamalai University.

[20] Taylor, J., 2014. Codakia tigerina. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=215835 on 2015-03-02

[21] Trueman, E.R., A.R. Brand and P. Davis, 1965. The Dynamics of Burrowing of some common Littoral Bivalves. J. Exp. Biol., 44: 469-492.

Katherine S. Tan, Carlo Stephen O. Moneva, Christina A. Barazona, Kimverly Hazel I. Coronel and Cesar G. Demayo

Department of Biological Sciences, MSU-Iligan Institute of Technology, Iligan City, Philippines

ARTICLE INFO

Article history:

Received 23 June 2015

Accepted 25 July 2015

Available online 30 August 2015

Corresponding Author: Carlo Stephen O. Moneva, MSU-Iligan Institute of Technology, Department of Biological Sciences, 9200, Iligan City, Philippines

Tel: +639358375916 E-mail: carlox.xia@gmail.com

Table 1: Descriptions and types of anatomical landmarks used to
describe the three species of bivalve in terms of left valve and
right valve internal morphology.

Anatomical                        Configuration
Landmarks

1                                     Umbo
2                      Ventral anterior end of hinge plate
3                     Ventral posterior end of hinge plate
4             Dorsal tip of anterior adductor-retractor muscle scar
5            Ventral tip of anterior adductor-retractor muscle scar
6                       Anterior end of the pallial line
7                         Deepest point of pallial line
8                       Posterior end of the pallial line
9            Ventral tip of posterior adductor-retractor muscle scar
10             Dorsal tip of the posterior adductor-retractor scar

Table 2: Characters described of the shells of three bivalve species.

Characteristics       Polymesoda        Codakia         Anodontia
                     bengalensis       tigerina         edentula

Shell Shape         Subtrigonal to    Subcircular        Rounded
                       rounded

Umbo                 Orthogyrous      Prosogyrous      Prosogyrous

Lunule                  Small,          Small,         Moderately
                      depressed        depressed     large, slightly
                                                        depressed

Ligament Position      External        External         External

Ligament location    Opisthodetic    Opisthodetic     Opisthodetic

Ligament Type        Parivincular    Parivincular     Parivincular

Hinge line              Arched          Arched           Arched

Dentition            Heterodont,      Heterodont,      Desmodont,
                    with cardinal    with cardinal    without teeth
                     and lateral      and lateral
                        teeth            teeth

Musculature          Anisomyarian    Anisomyarian     Anisomyarian

Pallial line           Present          Present          Present

Pallila sinus           Absent          Absent           Absent

Table 3: Pairwise comparison of the three species multivariate
analysis of variance (MANOVA) for the three bivalve species.

Left interior    P. bengalensis    C. tigerina     A. edentula
valve

P. bengalensis         --         1.08287E-23 *   4.48528E-40 *
C. tigerina      3.24861E-23 *         --         2.85416E-18 *
A. edentula      1.34559E-39 *    8.56249E-18 *        --

Right interior   P. bengalensis    C. tigerina     A. edentula
valve

P. bengalensis         --         1.8447E-26 *    5.08511E-30 *
C. tigerina       5.5341E-26 *         --         1.27838E-16 *
A. edentula      1.52553E-29 *    3.83514E-16 *        --

Legend: * significant value(s), Bonferroni corrected
(lower values)\uncorrected (upper values)

Table 4: Left internal valve percentage variance and over all
morphological variation of the three species as explained by
significant relative warps.

Relative warps   Negative axis          Positive axis

RW 1 (51.36%)    * The distance         * The
                 between the            ventral-anterior tip
                 dorso-anterior         of the
                 adductor-retractor     adductor-retractor
                 muscle scar away       muscle scar joins
                 from the anterior      together with the
                 end of the pallial     anterior end of the
                 line.                  pallial line.

                 * The ventral tip of   * Deepest point of
                 the anterior           the pallial line has
                 adductor-retractor     shorter distance
                 muscle scar closer     with the posterior
                 to the deepest point   end of the pallial
                 of the pallial line.   line.

                 * Longer distance      * The
                 between the            ventral-anterior
                 posterior end of the   adductor-retractor
                 pallial line and       muscle scar has
                 deepest point of the   longer distance to
                 pallial line.          the deepest point of
                                        the pallial line.

                 * The distance         * Posterior end of
                 between the            the pallial line is
                 ventral-posterior      compressed with the
                 adductor-retractor     ventral-posterior
                 muscle scar away       adductor-retractor
                 from the posterior     muscle scar.
                 end of the pallial
                 line.                  * The over all hinge
                                        plate pronouncely
                 * The over all hinge   curved.
                 plate is slightly
                 curved.                * The distance
                                        between dorsal tip
                 * The umbo is          of anterior
                 depressed.             adductor-retractor
                                        muscle scar and
                 * The distance         ventral tip of
                 between dorsal tip     anterior
                 of anterior            adductor-retractor
                 adductor-retractor     muscle scar is
                 muscle scar and        shorter.
                 ventral tip of
                 anterior adductor-
                 retractor muscle
                 scar is longer.

RW 2 (16.82%)    * Closer distance      * Ventral posterior
                 between posterior      end of the hinge
                 end of the pallial     plate joins together
                 line and ventral tip   with the dorsal tip
                 of posterior           of the posterior
                 adductor-retractor     adductor-retractor
                 muscle scar.           muscle scar.

                 * The ventral tip of   * The ventral
                 anterior               anterior end of the
                 adductor-retractor     hinge plate is
                 muscle scar moves      compressed with the
                 away from the          dorsal tip of
                 anterior end of the    anterior
                 pallial line.          adductor-retractor
                                        muscle scar.
                 * The ventral
                 posterior end of the   * Ventral tip of
                 hinge plate and        anterior
                 ventral tip of the     adductor-retractor
                 posterior              muscle scar is
                 adductor-retractor     compressed with the
                 scar moves apart       anterior end of the
                 from each other.       pallial line.

RW3 (7.57%)      * Ventral and          * The distance
                 posterior hinge        between the ventral
                 plate are closer       posterior end of the
                 together.              hinge plate is
                                        closer to the tip of
                 * Umbo is              the posterior
                 depressed.             adductor-retractor
                                        muscle scar.

                                        * Ventral tip of
                                        posterior
                                        adductor-retractor
                                        muscle scar closer
                                        to both posterior
                                        end of the pallial
                                        line and tip of the
                                        posterior
                                        adductor-retractor
                                        muscle scar.

RW4 (5.17%)      * The distance         * Distance of the
                 between the dorsal     ventral posterior
                 and ventral tip of     end of hinge plate
                 anterior               is closer to the tip
                 adductor-retractor     of the posterior
                 muscle scar is         adductor-retractor
                 closer.                muscle scar.

                 * Ventral posterior    * Ventral tip of
                 end of the hinge       anterior
                 plate away from the    adductor-retractor
                 tip of the posterior   muscle scar has
                 adductor-retractor     closer distance with
                 scar.                  anterior end of the
                                        pallial line.

RW5 (5.09%)      * Closer distance      * The anteriro end
                 between posterior      of the pallial line
                 end of the pallial     moves closer to both
                 line and ventral tip   dorsal and ventral
                 of posterior           anterior
                 adductor-retractor     adductor-retractor
                 muscle scar.           muscle scar.

                 * The ventral          * The distance
                 posterior end of       between posterior
                 hinge plate and the    end of the pallial
                 tip of the posterior   line apart from that
                 adductor-retractor     of the ventral tip
                 muscle scar away       of posterior
                 from each other.       adductor-retractor
                                        muscle scar.
                 * The umbo is
                 slightly depressed.    * The anterior
                                        margin is
                                        compressed.

Table 5: Right internal valve percentage variance and over
all morphological variation of the three species as
explained by significant relative warps.

Relative warps   Negative axis          Positive axis

RW 1 (59.08%)    * The umbo is          * Ventral tip of
                 depressed              anterior
                                        adductor-retractor
                 * Distance between     muscle scar joins
                 the ventral tip of     with the anterior
                 the anterior           end of the pallial
                 adductor-retractor     line.
                 muscle scar and
                 anterior end of the    * The distance
                 pallial line away      between the ventral
                 from each other.       posterior end of
                                        hinge plate and tip
                 * Shorter distance     of the posterior
                 between the ventral    adductor-retractor
                 tip of anterior        muscle scar is
                 adductor-retractor     closer.
                 muscle scar and
                 deepest point of       * The hinge plate is
                 pallial line.          pronouncedly curved.

                 * The distance         * The distance
                 between the ventral    between the ventral
                 tip of posterior       tip of posterior
                 adductor-retractor     adductor-retractor
                 muscle scar and        muscle scar and
                 dorsal tip of the      dorsal tip of the
                 posterior              posterior
                 adductor-retarctor     adductor-retarctor
                 muscle scar is         muscle scar is
                 longer.                shorter.

RW 2 (11.38%)    * Ventral posterior    * Ventral posterior
                 end of the hinge       end of hinge plate
                 plate joins together   and tip of the
                 with the tip of the    posterior
                 posterior              adductor-retractor
                 adductor-retractor     muscle scar away
                 muscle scar.           from each other.

                 * The distance         * Distance of the
                 between the dorsal     ventral tip of
                 tip of anterior        anterior
                 adductor-retractor     adductor-retractor
                 muscle scar is         muscle scar is
                 closer to the          slightly closer with
                 anterior end of the    the deepest point of
                 pallial line.          pallial line.

RW3 (9.25%)      * The distance         * Tip of the
                 between the dorsal     posterior adductor-
                 tip of anterior        retractor muscle
                 adductor-retractor     scar moves closer
                 muscle scar is         to the ventral
                 closer to the          posterior end of
                 anterior end of the    hinge plate and
                 pallial line.          ventral tip of
                                        posterior adductor-
                 * Closer distance      retractor muscle
                 between deepest        scar.
                 point of pallial
                 line and anterior
                 end of pallial line.

RW4 (5.96%)      * Distance of the      * Ventral posterior
                 ventral posterior      end of the hinge
                 end of hinge plate     plate is closer to
                 moves closer to the    the tip of the
                 dorsal tip of          posterior adductor-
                 anterior               retractor muscle
                 adductor-retractor     scar.
                 muscle scar.
                                        * The distance of
                 * Ventral tip of       the ventral tip of
                 anterior               anterior adductor-
                 adductor-retractor     retractor muscle
                 muscle scar and        scar away from the
                 anterior end of the    anterior end of the
                 pallial line closer    pallial line.
                 to each other.
                                        * Dorsal tip of
                 * Distance between     anterior adductor-
                 ventral anterior end   retractor muscle
                 of hinge plate and     scar has closer
                 dorsal tip of          distance with the
                 anterior               anterior end of the
                 adductor-retractor     pallial line.
                 muscle scar are
                 compressed with each
                 other.

Table 6: Results of the Kruskal-Wallis Test for
significant differences in the mean morphologies
of the three species.

Left interior valve

RW1       A            B            C

A        --       2.07E-11 *    2.07E-11 *
B     6.2E-11 *       --          0.1393
C     6.2E-11 *     0.4179          --

RW2       A            B            C

A        --       3.961E-07 *   1.5E-08 *
B     1.2E-06 *       --        3.2E-10 *
C     4.481E *    9.477E-10 *       --

RW3       A            B            C

A        --         0.5398        0.5303
B         1           --          0.7283
C         1            1            --

RW4       A            B            C

A        --         0.6086        0.3987
B         1           --          0.9293
C         1            1            --

RW5       A            B            C

A        --         0.5935        0.3275
B         1           --         0.05188
C      0.09826      0.1556          --

Right interior valve

RW1       A            B            C

A        --       2.07E-11 *    2.0E-11 *
B     6.2E-11*        --        9.8E-06 *
C     6.2E-11*    2.95E-05 *        --

RW2       A            B            C

A        --       2.85E-06 *    4.9E-11 *
B     8.5E-06 *       --        8.2E-11 *
C     1.5E-10 *   2.44E-10 *        --

RW3       A            B            C

A        --         0.7076        0.4841
B         1           --          0.3403
C         1            1            --

RW4       A            B            C

A        --         0.6443        0.3338
B         1           --          0.9941
C         1            1            --

Legend: *significant value, A--Polymesoda bengalensis,
B--Codakia tigerina, C--Anodontia edentula Bonferroni
corrected (lower values)\uncorrected (upper values)

Table 7: Correlation analysis of the morphological patterns
and quantitative descriptions of the three species of bivalves.

Variables     Left valve               Right valve

               r value     p value     r value     p value

shell shape   -0.85161    1.0663E-26   -0.73073   2.0074E-16
Umbo          -0.94995    9.5159E-47   -0.93855   6.819E-43
Lunule        -0.52536    8.9548E-08   -0.32635   0.0015939
Dentition     -0.523536   8.9548E-08   -0.32635   0.0015939

Table 8: Over-all morphological descriptions of the interior shell
of the three bivalves.

Polymesoda bengalensis

* The over all hinge plate is prouncedly curved.

* The ventral-anterior tip of the adductor-retractor muscle scar
joins together with the anterior end of the pallial line.

* The ventral-anterior adductor-retractor muscle scar has longer
distance to the deepest point of the pallial line.

* Posterior end of the pallial line is compressed with the
ventral-posterior adductor-retractor muscle scar.

* The distance between the ventral posterior end of hinge plate and
dorsal tip of the posterior adductor-retractor muscle scar is
closer.

* The distance between dorsal tip of anterior adductor-retractor
muscle scar and ventral tip of anterior adductor-retractor muscle
scar is shorter.

* The distance between the dorso-anterior adductor-retractor muscle
scar apart from the anterior end of the pallial line.

* Closer distance between posterior end of the pallial line and
ventral tip of posterior adductor-retractor muscle scar.

* The distance between the ventral tip of posterior
adductor-retractor muscle scar and dorsal tip of the posterior
adductor-retarctor muscle scar.

Codakia tigerina

* The over all hinge plate is slightly curved.

* The umbo is depressed, anteriorly pointed.

* The distance between the ventral-posterior adductor-retractor
muscle scar moves away from the posterior end of the pallial line.

* The ventral tip of the anterior adductor-retractor muscle scar
moves closer to the deepest point of the pallial line.

* Longer distance between the posterior end of the pallial line and
deepest point of the pallial line. * The distance between dorsal
tip of anterior adductor-retractor muscle scar and ventral tip of
anterior adductor-retractor muscle scar is longer.

* Ventral posterior end of the hinge plate joins together with the
dorsal tip of the posterior adductor-retractor muscle scar.
Anodontia edentula

* The over all hinge plate is slightly curved.

* The distance between the ventral-posterior adductor-retractor
muscle scar apart from the posterior end of the pallial line.

* Ventral posterior end of hinge plate and dorsal tip of the
posterior adductor-retractor muscle scar away from each other.

* The distance between the ventral-posterior adductor-retractor
muscle scar away from the posterior end of the pallial line.

* The distance between dorsal tip of anterior adductor-retractor
muscle scar and ventral tip of anterior adductor-retractor muscle
scar is longer a

* Ventral posterior end of the hinge plate joins together with the
dorsal tip of the posterior adductor-retractor muscle scar.

* The distance between the ventral tip of posterior
adductor-retractor muscle scar and dorsal tip of the posterior
adductor-retarctor muscle scar is shorter.
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Author:Tan, Katherine S.; Moneva, Carlo Stephen O.; Barazona, Christina A.; Coronel, Kimverly Hazel I.; Dem
Publication:Advances in Environmental Biology
Article Type:Report
Date:Aug 1, 2015
Words:4781
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