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The Relationship of Mass and Surface Area of Molluscs retrieved from the Intertidal Zone
of Magellan Bay, Lapu-Lapu City1
Arombo, Julianne Marvin B.
November 2015
1A research paper submitted in partial fulfillment of the requirements in ZOO 111
(Invertebrate Zoology) A.Y. 2015-2016 under Prof. Marjorie D. Delos Angeles and Prof.
Brisneve Edullantes of the BS Biology Program, Sciences Cluster, University of thePhilippines Cebu.
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ABSTRACT
The marine invertebrate molluscs within the intertidal zone are predominantly
comprised of gastropods and bivalves. Both of these classes has the delineating
structure of the number of shells each molluscs synthesize. In investigating the
phenotypic plasticity, a phenomenon which allows diversity of shell morphology,
shell growth is regarded. Shell growth in general affected greatly by two factors-
mass and surface area. These coping mechanisms for growth allows an association
in lieu of correlation. The study aims to answer the problem of the type of
correlation that the aforementioned factors exhibited towards their contributing
scheme. The specificity of mass and surface area was performed with the use of dry
mass and maximum estimated surface area. As these variables treated in equal
matter within a parametric set-up, the morpho-anatomical features of each samples
is also included as supplementary information. With the use of Pearson Product-
Moment Correlation, the investigation turned out that there is a strong positive
relation between the two variables regardless of its effect to one another vis-a-viz.The use of correlation to the study portrayed the effects of phenotypic plasticity due
to the efficiency of shell growth within the various kinds of mollusc regardless of
shell type and number as they enact upon the adaptations of the organisms.
Keywords: Phenotypic plasticity, Shell Mass, Shell Surface Area, Molluscs,
Bivalves, Gastropods.
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INTRODUCTION
Background of the study
The phylum Mollusca is remarkably a diverse taxon group of its own, as it
defies an ideal organism predominantly due to its diversity and phenotypic
plasticity among the species (Pechenik, 2014). A general feature of the
aforementioned phylum is the synthesis of shells yet not referred as a defining
characteristic (Pechenik, 2014). The varied morphological structures of shells
manifests within certain time frames and environmental changes. Shells are indeed
subjected to phenotypic plasticity. Although phenotypic plasticity are remarked to
have ecological and environmental consequences, a possible and relative reason is
due to adaptation which ratifies the benefits within (DeWitt, Sih, & Wilson, 1998).
Moreover, the phenotypic plasticity exhibited by the molluscs is due to increased
environmental tolerance which promotes survival amidst heterogeneous
environments (Via, et al., 1995). In marine gastropods, the existence of various
shell forms allow defense against predation (Palmer, 1979). The molluscan shell
phenotypic variations then allows study of their variation and also their growth
mechanisms and coping factors.
Shells in general are yet to be more than for aesthetic and ornamental
purpose solely, as they provide factual information with their corresponding
organisms with their phenotypic expressions (Rice, 1998). These phenotypic
expressions also adhere to the growth factors not only of the molluscan organism
but also the shell which it manifests. In some studies, it is concluded that the
aperture opening is directly proportional to the body mass which excludes the shell
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(Rice, 1998). Inferences from specific shell factors obtained are indeed highly
essential to the study of relationship or association in two out of the abundant
contributing factors to growth as usual means of correlation. Relationship of factors
are obviously limited to two in order to investigate the ratio and proportion in each
of the quantitative measurements.
Through statistical methods, variables set forth in research studies will
manifest inferential and methodological results. Within the bounds of statistics,
variables of mass and surface area in shell are evaluated in terms of their
association. Hence, a measurement of how two variables are correlated to one
another regardless of the variable affecting another variable as such in controlled
experimentation using linear association denoted by r is obtained through finding
the Pearson product-moment correlation coefficient (Lund & Lund, n.d.).
The shell mass and surface area, with their correlation, will be used to
investigate the functional significance of shell morphology among one-shelled
molluscs (gastropods) and two-shelled molluscs (bivalves) and their delineating
factor of shell numbers or valves.
The assessments of quantitative factors in shell will also be conglomerated
with other biological concepts within the scope of morphology, anatomy, and
taxonomy through identification of the specimens with their contributing factors to
the growth mechanisms of molluscs particularly the gastropods and bivalves with
the primary focal aspect of difference in shell number as secondary to the
adaptations.
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Statement of the problem
This research study answers the association of growth variables in
molluscan shells particularly the gastropods and bivalves with the main tenets of
mass and surface area as two variables associated and compared to one another.
The following sub-questions are sought to be answered:
1. What is the functional significance of shell morphology with regards to one
shelled and two shelled molluscan body type?
2. What are the part and parcel of morphological and anatomical structures
present both in gastropods and bivalves which makes the classes delineated
and innate from one another?
3. What is the importance of obtaining the surface area as a preceding data
before the overall area of the shell?
4. Why is the dry weight of shell considered to be feasible in the correlation
rather than the wet weight of molluscs in general?
Objectives
The general objective of this study seeks to find the correlation of shell dry mass
and maximum estimated surface area in both gastropods and bivalves, with each
variables treated equally. Meanwhile, the following are the specific objectives of
the study:
a) To assess visual comparison of specimens to theoretical and previous
images of molluscan shells in identification of collected organisms through
morphological and anatomical structures.
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b) To evaluate the specific mass and surface area set forth in the study, and
that generalizing the two variables will result to misconceptions and
inaccuracy of data.
c) To study the phenotypic plasticity among gastropods and bivalves and their
relation to the functional significance of their delineation.
Significance of the study
The correlation of dry mass and surface area of shelled marine invertebrates
allows a bridge between the scientific studies of invertebrate zoology and
theoretical mathematics (algebra and calculus). As the two fields of sciences
intertwined together, this will allow a yield of more factual and valid data especially
in research. The study highly manifests interdisciplinary studies which yields
holistic learning ang exploration through heterogeneity of academic parcels without
ostracizing other relevant aspects of various fields of knowledge.
Moreover, obtaining the ratio and proportion of dry mass and maximum
estimated surface area of the shell allows synthesis of formula that can be used for
further study in shell growth and morphology of the molluscan phylum.
The study of shell morphology and anatomy allows training in identifying
organisms which is highly essential in creating taxonomic relationships. In
addition, the study allows cognitive advancements in differentiating and finding
similarities among shell-producing marine invertebrates, with the familiarity of
possible shelled invertebrates present only in marine or saltwater.
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Finding relationships with factors affecting shell morphology will also garner ones
comparative skill via statistical procedures, as it is intended for scientific
exploration. Growth, as not limited to shells, can be also used to other aspects even
outside of the study. This can be applied to other fields of knowledge as well.
Scope and limitations
This study was conducted within three assessments: morpho-anatomical
assessment which allows comparison of collected specimens to available credible
database in the internet and identification of basic parts of the shell which
demarcates the shell morphology between gastropods and bivalves, taxonomic
assessment with the construction of a dichotomous key, and mathematical
assessment which includes weighing of the sample and measuring the maximum
estimated surface area of each shells both in estimated and exact quantities. The
estimated surface area will be measured through forming segments along points
and establishing a polygon excluding the curvatures present in shells whereas the
exact surface area allows the inclusion of curvatures.
The assessments aforementioned were the only factors conducted within the
study. In terms of the statistical aspect of the study, parametric measures were
observed due to the ratio or scale data of mass and surface area, the sample which
exceeds or equals 30 (n=30 or n>30), and the use of Pearson product-moment
correlation coefficient. Due to the variables set forth and the random sampling, the
study will not investigate factors related to biodiversity such as population index or
density within the vicinity.
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REVIEW OF RELATED LITERATURE
Phenotypic Plasticity
Phenotypic plasticity is rather a predominant feature in animals than plants,
as most animals adjust within the scope of environmental conditions than plants
(Doughty & Reznick, 2004). Moreover, phenotypic variations allows evolutionary
mechanisms to modulate differences acquired by individuals of different wide
range of organisms (West-Ebhard, 1989). This feature modifies animals within
certain aspects of variations in environment, allowing morphological features to
change in comparison to their descendants. An anecdote of which includes
migration of animals which support the optimal reaction norm for morphological
variations to procure (De Jong & Behera, 2002). A feature of this is considered to
be an advantage. Nonetheless, one of the disadvantages includes difficulty in
classifying species of type especially in cladograms which takes account ancestral
traits. The phenotypes, controlled by genotypic combinations from ancestral traits,
will be limited due to non-genetic regulation of traits such as variations of instincts
among individuals of the same kind (DeWitt, Sih, & Wilson, 1998).
Although most scientists regard phenotypic plasticity as an adaptation due
to natural selection, it must not be assumed due to the existence of delocalized
adaptation (Hollander, Collyer, Adams, & Johannesson, 2006) in which changes in
morphological trait is seen only within a specific part of an organism. Moreover,
the coping mechanism of phenotypic plasticity as means of environmental
heterogeneity allows a vague sense of certain factors that are not subjected to
phenotypic variation but also depending upon the situation (Hollander, Collyer,
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Adams, & Johannesson, 2006). Hence, natural selection is just one of the factors
which affects morphological variation, as it acts not only within a single domain of
trait solely, either correlated within another factor affecting an organism, but also
within the trade-offs between competing factors in the overall system of an
organism which allows reduction of particular parts present in their ancestors in
terms of evolution (Reznick & Travis, 1996).
In the scope of marine invertebrates, evolution of phenotypic plasticity is probably
due to factors of architectural constraints such as shell form of the body mass and
growth (Trussell, 1999). Within this particular study of his, the shell form, body
size, and strength was taken into account (Trussell, 1999).
Growth Factors
Growth of an animals is highly associated with factors affecting upon it.
These can be in the forms of either quantitative or qualitative attributes.
Quantitative factors such as height and mass are highly studied due to their
empirical results.
A study of factors affecting growth with their specific correlation takes
place within marine invertebrates. In the study of length and mass relationship for
adult aquatic and terrestrial invertebrates in California, development of animals
with their complexity associated due to phenotype changes is also associated due
to length-mass relationship (Sabo, Bastow, & Power, 2002). Moreover, the method
of their research involves the determination of r-value to correlate length and mass
in both aquatic (marine) and terrestrial animals. Another study involves
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determination of biomass via regression of dry mass in body length (Rogers,
Bushcbom, & Watson, 1977). Other factors that are quantifiable involves empirical
relationship of mass and linear body relationships in terms of aquatic insects which
is said to be useful in ecological researches since they provide a rough estimation
of body length given its complementary factor such as mass (Johnston & Cunjak,
1999).
MATERIALS AND METHODS
In November 21, 2015, there were collected at least 30 specimens in no particular
order. The specimens hence are randomized. The parameters of the collection
within the intertidal zone of Magellan Bay, Lapu-Lapu City, Cebu was observed.
The sampling collection occurred in two specific regions of the intertidal zone. The
first was the collection of samples with predominance of the gastropod shells (10
18' 43.3656'' N, 124 0' 51.5700'' E), and the second with the predominance of
bivalves shells (10 18' 46.2528'' N, 124 0' 52.1100'' E). The given coordinates
were in approximation.
The specific parameters such as the length or area at which the specimens were
taken is unimportant with the study, as this entails only the correlation of variables
set forth and not with the biodiversity or population size of bivalves and univalves
present. It is important to take heed of the notion that the samples were taken at
once in a particular region of the intertidal zone as this study is in lieu of random
sampling.
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In the experimental protocol, two quantitative measurements were taken: the shell
dry mass, and the surface area. These two protocols were done to all the 30 samples
collected.
The shells were dried and left exposed to air to evaporate the moisture present on
each shells. It is important to take notice that prior to the weighing of the samples,
the shells must not contain any moisture as it affects the accuracy of the dry weight
data. After taking the moisture out of the shells, they were weighed with an
analytical balance to obtain accurate data. In gravimetric or any weighing
procedures done, the prior notice must set forth to the bubble within the balance as
it must be centered within the apparatus. Adjusting the knobs on each corners of
the balance will make the bubble within the center indicating that the apparatus is
significantly correct, as the obtained weight were crucial in the scope of the study.
After the weighing process, each specimens then were placed with labels along the
shell integuments using a marker. The labelling must be done after the weighing.
Moreover, the use of surgical gloves or tissue paper while holding the shell was
done as fingerprints or any particulates other than the shell will also affect the data.
In obtaining the maximum estimated surface area, each shells once dried were
traced within a graphing paper. In graphing the two shelled molluscs such as the
bivalves, the dorsal and ventral valves were separated along their hinge. Both of the
valves were traced. Nonetheless, the maximum between the two valves will be
regarded as data in the surface area. Meanwhile, the one shelled molluscs such as
the monoplacophorans and gastropods were traced in accordance to the maximum
outline of the shells surface. Hence, the curvatures of each shells were included in
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tracing. With respect to the accuracy, the pencil used for tracing must be pointed
and dark enough for clarity.
The traced surface areas were now set with relevant points of relative extrema
(relative maximum and relative minimum). The calibration used was based on
centimeters. With this, the standard graphing paper which has a scale of 0.5 cm X
0.5 cm was used. The traced shells were assumed to be within a Cartesian plane,
with the x and y-coordinates serving as point of reference.
The traced shells in graphing paper would be transferred according to the points
lying within the curvatures and segments formed. This will allow surface area
measurements via graphing calculators and software. A software used for obtaining
the surface area is through the aid of GeoGebra , a free of charge computer
application retrieved from https://www.geogebra.org/. Significant points from the
shell trace were obtained. Such points referred were the x-intercepts, y-intercepts,
points within the intervals of 0.5 cm, and critical points of increasing and decreasing
functions indicating relative extrema.
As the points previously obtained were part of the inputs, the formed shell within
must be that of approximately similar to the previously traced. The graphing
software would provide an estimated surface area, as the quantity obtained excludes
the area of the curves but only obtaining the area formed as segments. Manual
computation for the areas on each curve using integration, with the summation of
these area between the curves and segments, would provide the exact surface area
of each shells.
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The morpho-anatomical assessment was conducted by obtaining documentation of
specimens and comparison through online databases which offer taxonomic
hierarchy of the identity of the specimens. The database used particularly for this
specimen was retrieved from http://www.bagniliggia.it/WMSD/WMSDhome.htm.
RESULTS AND DISCUSSION
The results of this study both incorporates the taxonomic genus and species level
of each gathered specimens through phenotypic comparison such as the
morphological features which sets them distinct from one another and the
correlation of shell dry mass and estimated surface area represented via scatter plot
which includes the r-value in terms of PPMC.
Within the scope of the phenotypic comparison as part of morpho-anatomical
assessment, specimens are generally juvenile or not mature as compared with their
adult counterparts.
The following documentations include the shell with their frontal and abfrontal
features shown.
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Figure 1.1. The bivalve shells gathered during the field assessment. The left exhibits
the external morphology of the two-shelled molluscs as the right exhibits the
internal morphology. The first three specimens named according to their number,
Fimbria fimbriata (Linnaeus, 1758), were documented in varying sizes. The
perceptive sizes indicate their stages or age in general. Within the documentation,
an error was procured as both the third and fourth specimens were exchanged in
terms of their position within the documentation. The fourth specimen,
Laevichlamys squamosa(Gmelin, 1791) exhibits evident horizontal rings within its
frontal portion whereas the fifth specimen, Mirapecten moluccensis (Dijkstra,
1988) exhibits vertical rings.
Figure 1.2. The bivalves and gastropod shells gathered during the field assessment.
Similar instance applied from the previous figure. The last specimen gathered
which belongs to class Bivalvia was similar that of the first three. As a concluding
summary, there were seven bivalves gathered, four of which are F. fimbriata
(Linnaeus, 1758). All of the bivalves gathered are Lamellibranch. The rest of the
specimens (6-30) are of gastropods. Specimen number 7 and 8 are Aloconatica
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kushime (Shikama, 1971). Meanwhile, specimens 9 and 10 are Vexillum tusum
(Reeve, 1845).
Figure 1.3. The predominantly prosobranch and ophistobranch shells, the two of
the three subclasses of class gastropoda. The abfrontal region was presented at the
left while the frontal region was on the right. Specimens 11 and 12 are Canarium
sp. (Roding, 1798). Meanwhile, specimen 13 is Theliostyla albicilla fasciata
(Krauss, 1848) which is similar that of the specimen 15. Lastly, specimen 14
Maculotriton sp. (Deshayes, 1834). All of the specimens gathered so far based on
this figure are all prosobranchs.
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Figure 1.4. The gastropod shells gathered. The left portion was the abfrontal region
of the shell as the frontal region was on the right portion with the exposure of
aperture.
Figure 1.5. The gastropods shells gathered similar to the previous figure given.
Figure 1.6. The last gathered gastropod shells within the locale of the study.
The samples collected within the intertidal zone of the Magellan Bay, Lapu-Lapu,
Cebu City, Philippines ranges from 0.5143 g to 10.4441 g in terms of dry weight.
The shells are also similar to one another as it also distinguishes the stratification
of shell variances within the locale. The taxonomic classification of the specimens
was obtained via phenotypic comparison. The taxonomic classifications then might
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be subjected to visual biases. Hence, there will be a biased assumption of the
structure within its proximity or relativity and not with a guaranteed accuracy.
The collected specimens are predominantly gastropods, as the most collected are of
in the taxonomic classification of subclass Prosobranchia (Pechenik, 2014) of class
Gastropoda while the bivalves are predominantly of subclass Lamellibranchia
(Pechenik, 2014) of class Bivalvia. The tabulated taxonomic classification of the
specimens gathered will give a crude estimation of the predominance of gathered
species which attests the statement aforementioned.
Table 1. The taxonomic classification of the specimens gathered based on the class,
subclass, and genus and species taxa expressed in binomial nomenclature (scientific
name).
Specimen
Number
Class Subclass
Scientific name based on
morphological similarities
1 Bivalvia Heterodonta Fimbria fimbriata (Linnaeus, 1758)
2 Bivalvia Heterodonta Fimbria fimbriata(Linnaeus, 1758)
3 Bivalvia Heterodonta Fimbria fimbriata (Linnaeus, 1758)
4 Bivalvia Heterdonta
Laevichlamys squamosa
(Gmelin, 1791)
5 Bivalvia Heterodonta
Mirapecten moluccensis
(Dijkstra, 1988)
6 Bivalvia Heterodonta Fimbria fimbriata (Linnaeus, 1758)
7 Gastropoda Prosobranchia Aloconatica kushime
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(Shikama, 1971)
8 Gastropoda Prosobranchia
Aloconatica kushime
(Shikama, 1971)
9 Gastropoda Caenogastropoda Vexillum tusum (Reeve, 1845)
10 Gastropoda Caenogastropoda Vexillum tusum (Reeve, 1845)
11 Gastropoda Prosobranchia Canarium sp. (Roding, 1798)
12 Gastropoda Prosobranchia Canarium sp. (Roding, 1798)
13 Gastropoda Prosobranchia
Theliostyla albicilla fasciata
(Krauss, 1848)
14 Gastropoda Prosobranchia Maculotriton sp. (Deshayes, 1834)
15 Gastropoda Prosobranchia
Theliostyla albicilla fasciata
(Krauss, 1848)
16 Gastropoda Caenogastropoda Vexillum tusum (Reeve, 1845)
17 Gastropoda Caenogastropoda Cypraea sp.(Linnaeus,1758)
18 Gastropoda Prosobranchia
Perotrochus sp.
(Fischer & Bernardi, 1856)
19 Gastropoda Prosobranchia Maculotriton sp. (Deshayes, 1834)
20 Gastropoda CaenogastropodaCypraea sp.
(Linnaeus, 1758)
21 Gastropoda Prosobranchia Canarium sp. (Roding, 1798)
22 Gastropoda Prosobranchia Maculotriton sp. (Deshayes, 1834)
23 Gastropoda Caenogastropoda Vexillum tusum (Reeve, 1845)
24 Gastropoda Prosobranchia Canarium sp. (Roding, 1798)
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25 Gastropoda Prosobranchia
Theliostyla albicilla fasciata
(Krauss, 1848)
26 Gastropoda Prosobranchia Canarium sp. (Roding, 1798)
27 Gastropoda Caenogastropoda
Chelycypraea testudinaria
(Linnaeus, 1758)
28 Gastropoda Prosobranchia
Aloconatica kushime
(Shikama, 1971)
29 Gastropoda Prosobranchia
Theliostyla albicilla fasciata
(Krauss, 1848)
30 Gastropoda Orthogastropoda Mipus vicdani(Kosuge, 1980)
Fig. 2. The correlation of shell dry mass expressed in grams (g) and maximum
estimated surface area expressed in square centimeters (cm2).
y = 0.8072x + 1.4947
R = 0.5044
0.0000
2.0000
4.0000
6.0000
8.0000
10.0000
12.0000
14.0000
16.0000
0 2 4 6 8 10 12
Estimatedsurfacearea(in
sq.cm)
Shell dry mass (in g)
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The correlation of the two variables were obtained and investigated through
quantitative measurements. The test used in finding for the r value which denotes
relationship between the two variables was Pearson product-moment correlation
(PPMC). In obtaining the data, the shell dry mass was assumed as x values whereas
the estimated surface area as y. The r value represents a crude estimation of
interpreting the strength of correlation. The graph includes the r2 value.
Nonetheless, the r value is used for evaluating the strength of the correlation.
Hence, the r- value is 0.710309293. The r- value is obtained by the formula:
The inputs based on the formula were as follows: Summation of x and y values
(xy) = 541.696163, summation of x (x) = 95.8746, summation of y (y) =
122.2032, summation of the squared x values (x2) = 493.5824877, summation of
the squared y values (y2) = 739.7175888, and the number of samples (n) = 30.
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Fig. 3. The result of the maximum estimated surface area as sample for this research
study. The surface area documented above is for the first specimen which is a
bivalve. The points given in forming the surface area involves the intercepts, points
forming the curvature, and points within the lines. The measurement used was in
centimeters. The segments are formed by connecting the points. This will form the
surface area excluding the curves. The exact surface area will be obtained by
finding each area under the curve indicated by the white color whereas the
estimated surface area is indicated by the orange color.
The estimated surface area involves the product of all the distances formed from
points a and b as segment a. Meanwhile, the exact surface area is relatively difficult
compared that of the estimated surface area, as one involves integral calculus. The
formula for the area under the curve is in the form:
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The integration takes place by obtaining the f(x) which will be the equation of the
line segments formed by points a and b. These points represents the upper and
lower limits. This formula allows the area under the curve. The product of all the
areas under the curve added with the estimated surface area will give the exact
surface area, which was the data used for the correlation.
According to the intervals set forth as standard, the r- value denoted a very strong
positive relationship within the two variables. Hence, there was a strong positive
relationship between the mass and surface area in lieu of shell growth. Moreover,
the given crude estimation allows Nonetheless, the relationship of the two variables
were not connoted as independent and dependent variables as the inexistence of
cause-and-effect relationship within the parametric standards of this study was
observed.
The data highly suggests a strong positive relationship to shell mass and surface
area in general in which there is a direct proportionality between the two factors in
shell growth. Therefore, as the shell mass increases, so does the surface area vis-a-
viz within a linear association.
Table 2. Data obtained from the specimens in terms of dry weight and maximum
estimated surface area.
Specimen No. Shell weight (in g) Estimated Surface Area (sq. cm)
1 8.0838 8.6944
2 8.9413 11.4400
3 2.5737 4.4100
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4 2.1089 4.3800
5 4.1715 4.7800
6 5.5722 14.1200
7 2.2105 2.0000
8 10.4441 5.0800
9 4.7273 3.4500
10 4.3492 3.7700
11 1.4179 3.5800
12 3.3231 4.1600
13 2.0074 2.9700
14 2.0098 2.0000
15 3.4434 3.8100
16 4.225 4.1200
17 1.2522 1.9700
18 4.082 3.3300
19 0.6572 1.2000
20 1.2976 2.1300
21 0.8254 2.2500
22 0.6494 1.2000
23 6.4274 6.1600
24 2.3327 5.3000
25 2.0914 3.7088
26 1.8385 3.9600
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27 0.5143 1.4500
28 1.8195 2.6700
29 1.4688 2.9200
30 1.0091 1.2200
SUMARRY AND CONCLUSION
In general, the correlation of shell dry mass and maximum estimated surface area
was obtained using a Pearson product-moment correlation. The result was a strong
positive relationship among the two supported by the r-value of 0.710309293. The
variables treated equally within the experiment proper was observed to increase the
likelihood of potential phenotypic plasticity to molluscs due to efficiency of shell
growth. Although the shells were not investigated neither during their
developmental phase nor their aging indicators, the shells were identified with
factors indicating their growth coping mechanism. Moreover, phenotypic plasticity
present among the molluscs allow diversity yet being similar with the factors
contributing to their shell growth in general.
Therefore, the functional significance of the adaptation in one-shelled and two-
shelled molluscs represented by the gastropods and bivalves respectively was not
just due to adaptations to their environment but also due to their shell growth which
allows differentiation in appearance as part of phenotypic expressions yet with
similar factors of growth contributing schemes such as mass and surface area that
enables them to be varied as a phylum.
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