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SC-4317
BIO-INORGANIC CHEMISTRY
ASSIGNMENT

CALCIUM-BASED BIOMINERALS
IN ASCIDIANS AND MOLLUSCS

NAME

:

NUR ALIMATUL HAKIMAH BINTI NARUDIN

REGISTRATION NO
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:

4

SUBMISSION DATE

:

25TH MARCH 2019

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They both are classified under the
same major clade but is then divided into two different subphyla: ascidians from deuterostomia,
whereas molluscs belong to protostomia
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One of the differences between these two subphyla is that blastopore forms future
anus first in deuterostomia, whereas in protostomia, future mouth is formed first
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Phylogenetic tree among Nephorozoa

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5%
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Among these three classes, ascidian is
the most diverse class of subphylum urochordata
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Phylogenetic tree of Ascidians

Ascidians are marine invertebrate animals that are permanently attached to hard surfaces
on the ocean floor
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They are commonly known as sea squirts
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Characteristics of the tunicate tadpole larva

Ascidians generally come in three different forms: compound (one big sack), solitary (one
single ascidian), and social (a bunch of solitary ascidians gathered together)
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These two openings are called siphons: an incurrent oral branchial and an
outcurrent atrial siphon (Figure 4, 5 & 6)
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Ascidian showing the top siphon

Figure 5
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Internal anatomy of an ascidian in detail

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Molluscs live in marine and freshwater habitats as well as on land
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Molluscs belong to the phylum mollusca which is the second largest phylum of
invertebrate animals
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Lophotrochozoan is one of the clades of protostomia
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Platyhelminthes
Echinodermata
Deuterostomia

Rotifera
Nemertea

Nephorozoa

Chordata
Bryozoa

Ecdysozoa
Protostomia

Brachiopoda
Phoronida

Lophotrochozoa
Annelida
Mollusca
(Molluscs)
Figure 7
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Freshwater snails are important recyclers of
plant and animal waste
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Because of this,
molluscs are considered excellent ecological indicators of the freshwater and marine
environment as their indicator provides a window into the health of entire ecosystem
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Biominerals

Biominerals can be defined as inorganic materials that can be produced by living organism
via processes known as biomineralization
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Over half of the elements essential
for life are incorporated in biomineral deposits
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Living organism, such as ascidians and molluscs, are able to form biominerals
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Molluscs produce calcite and other carbonate minerals to form their shells, while ascidians
formed calcitic spicule
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CALCIUM-BASED BIOMINERALS IN ASCIDIANS AND MOLLUSCS
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Calcium-based Biominerals
Calcium carbonate is a calcium-based biomineral that is used to make the spicules of
ascidians and the shells of molluscs
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Calcium carbonate, in its three non-hydrated crystalline polymorphs (calcite, aragonite
and vaterite), represents one of the most important inorganic materials with respect to the
biomineralization processes in organisms
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However, only the two most thermodynamically stable structures, which are
calcite and aragonite, are deposited extensively as biominerals (Table 1)
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In general, the precipitation
of calcium salts provides an effective means to control the Ca2+ ion concentration in biological
fluids
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Table 1
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Calcium-based biominerals can be found precipitated in the
shaped spicules which act as a structural support or as a deterrent against predators
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They are formed in close association with cells
called sclerocytes, which secrete a very tough organic layer as well as in forming the mineralized
spicule
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Figure 8
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pachydermatina
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Copyright 2005, with permission from Elsevier)
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However, since vaterite is highly unstable and its crystal system is hexagonal, it can recrystallize
to calcite easily when exposed to water
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, 2009)
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Calcium-based biomineral in Molluscs
Due to their soft bodies, many have used their rigid shells to maintain their soft tissues,
protect themselves against predator and prevent desiccation
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The shells are composed of 95 – 99% calcium carbonate and less than 5% organic matrix
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The organic matrix holds and binds to the
crystal of aragonite, which causes the shells to be stiff
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Chitin (a polysaccharide) is also used with the calcium carbonate to give structural support to
shells
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This composite material is much harder and stiffer than pure chitin, and is
tougher and less brittle than pure calcium carbonate
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The shell structure
can be seen in figure 9 below
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Shell structure of the freshwater mussel

The shell layers of molluscs are formed from calcium carbonate as aragonite or calcite
corresponding to different mineral textures
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The shell of an adult mollusc may contain either aragonite alone, or a mixture of layers of
aragonite and calcite
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The inner nacre layer of aragonite
is then deposited
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Diagram of a section through the edge of the shell and attached mantle of a bivalve mollusc
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CONCLUSION
Ascidians and molluscs are invertebrate animals that are classified under the same clade
called nephorozoa, but is then separated into two different subphyla
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Ascidians used calcium carbonate to make spicules, while molluscs used calcium
carbonate to produce their shells
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The shell of mollusc consists of three layers
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When
organic matrix, such as chitin and conchiolin, is combined with the calcium carbonate, it will make
the shell stiff and rigid
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Meanwhile, the spicule of ascidian acts as a structural support, and also as protection
from predators
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4
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A
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(1989)
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Oxford University Press,
New York
Mann, S
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Inorganic materials, 2nd edn
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(2001)
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Oxford University Press, New York
Mann, S
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R
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& Birchall, J
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(1988)
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Nature 334:692–695
Mann, S
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& Williams, R
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P
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Napolitanio, L
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Ascidian showing the top syphon
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raja-ampat-tour
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htm
Plummer, L
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& Busenberg, E
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The solubilities of calcite, aragonite and
vaterite in CO2-H2O solutions between 0 and 90°C, and an evaluation of the aqueous model
for the system CaCO3-CO2-H2O
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, Gittenberger, A
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, Rius, M
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, Swalla, B
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&
Turon,
X
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Ascidiacea
World
Database
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marinespecies
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, Mahamid, J
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, Ma, Y
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(2009)
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Front Mater Sci 3(2):104–108
Wilt, F
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(2005)
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Biol
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