The Comparison of Mass and Surface Area of Molluscs from the Intertidal Zone of Magellan Bay,...

7/25/2019 The Comparison of Mass and Surface Area of Molluscs from the Intertidal Zone of Magellan Bay, Lapu-Lapu City

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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)


4 Bivalvia Heterdonta

Laevichlamys squamosa

(Gmelin, 1791)

5 Bivalvia Heterodonta

Mirapecten moluccensis

(Dijkstra, 1988)


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)


11 Gastropoda Prosobranchia Canarium sp. (Roding, 1798)



Theliostyla albicilla fasciata

(Krauss, 1848)

14 Gastropoda Prosobranchia Maculotriton sp. (Deshayes, 1834)



(Krauss, 1848)


17 Gastropoda Caenogastropoda Cypraea sp.(Linnaeus,1758)


Perotrochus sp.

(Fischer & Bernardi, 1856)


20 Gastropoda CaenogastropodaCypraea sp.

(Linnaeus, 1758)






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(Krauss, 1848)


27 Gastropoda Caenogastropoda

Chelycypraea testudinaria

(Linnaeus, 1758)


Aloconatica kushime

(Shikama, 1971)



(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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The Comparison of Mass and Surface Area of Molluscs from the Intertidal Zone of Magellan Bay,...

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