1.1. preamble - shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/4505/9/09_chapter 1.pdfexternal...
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1.1. PREAMBLE:
Pharmacognosy is defined as the study of drugs and drug
substances as well as potential drugs and drug substances from
natural sources and also search for drugs and drug substances from
natural sources (American Society of Pharmacognosy). From the wide
range of natural sources, marine is the source of choice for the region
of Goa. Being located almost on every side by the water body, a search
for newer drugs from this is but apt. The word marine is
representative of all those that are related to seas and oceans both
inside as well as around them.
Before going into the details of the literature a brief introduction
about the topic is being presented. In this, the topic is mainly divided
into three aspects, Proteins, GFP-like proteins and Zoanthids. To
begin with proteins and their importance is discussed in brief followed
by the discussion on GFP-like proteins and their speciality and
concluding with the description of marine zoanthids.
1.2. PROTEINS AND THEIR IMPORTANCE:
Proteins are the most abundant biological macromolecules,
occurring in all cells and in all parts of the cells. These are polymers
containing combinations of 20 different amino acid residues joined to
its neighbour by a specific type of covalent bond. They occur in great
variety and ranging in size from relatively small peptides to huge
polymers with molecular weights in millions, together may be found in
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a single cell. Moreover, proteins exhibit enormous diversity of
biological function (Fig.1.1. & Fig.1.2.) and are the most important
final products of the information pathways. They also play the role of
molecular instruments through which genetic information is
expressed[1].
Every protein has a specific order of arrangement of amino acids
and can be described at four levels of structural hierarchy (Fig.1.3.). A
description of all covalent bonds (mainly peptide bonds and disulphide
bonds) linking amino acid residues in a polypeptide chain is its
primary structure which clarifies the sequence of amino acid residues.
Secondary structure refers to residues giving rise to recurring
structural patterns. Tertiary structure describes all aspects of the
three-dimensional folding of a polypeptide. When a protein has two or
more polypeptide subunits, their arrangement in space is referred to
as quaternary structure[1].
Fig.1.1. The light produced by fireflies is
the result of a reaction involving the
protein luciferin and ATP, catalyzed by
the enzyme luciferase
Figure.1.2.The protein keratin, formed by
all vertebrates, is the chief structural
component of hair, scales, horn, wool,
nails, and feathers
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At the higher levels of structure (quaternary), they are also
classified as fibrous proteins, having polypeptide chains arranged in
long strands or sheets and globular proteins, having polypeptide
chains folded into a spherical or globular shape. Fibrous proteins,
usually consists of largely of a single type of secondary structure;
globular proteins often contain several types of secondary structures.
The former, play the role of structures, provide support, shape and
external protection to vertebrates, whereas the latter are mostly
enzymes and regulatory proteins[1].
Super secondary structures, also called motifs or simply folds,
are particularly stable arrangements of several elements of secondary
structure and the connections between them. Many examples of
recurring domains or motif structures are available (Fig.1.4.), and
these reveal that protein tertiary structure is more reliably conserved
than primary sequence. Proteins with significant primary sequence
Fig.1.3. Levels of structure in proteins. The primary structure consists of a sequence of
amino acids linked together by peptide bonds and includes any disulfide bonds. The
resulting polypeptide can be coiled into units of secondary structure, such as an _ helix.
The helix is a part of the tertiary structure of the folded polypeptide, which is itself one of
the subunits that make up the quaternary structure of the multisubunit protein, in this
case hemoglobin1.
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similarity, and/or with demonstrably similar structure and functions
are said to be in the same protein family. A strong evolutionary
relationship is usually evident within a protein family[1].
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Fig.1.4. Organisation of proteins based on motifs. Shown above are just a small number of the
hundreds of known stable motifs. They are divided into four classes: all α, all β, α/β, and α+β.
Structural classification data from the SCOP (Structural Classification of Proteins) database
(http://scop.mrc-lmb.cam.ac.uk/scop) are also provided. The PDB identifier is the unique number
given to each structure archived in the Protein Data Bank (www.rcsb.org/pdb).
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Two or more families with little primary sequence similarities
sometimes make use of the same major structural motif and have
functional similarities; these families are grouped as superfamilies[1].
The simple string of letters denoting the amino acid sequences of a
given protein belies the wealth of information this sequence holds.
The study of molecular evolution generally focuses on families of
closely related proteins. Usually, the families chosen for analysis have
essential functions in cellular metabolism that must have been
present in the earliest viable cells, thus greatly reducing the chance
that they were introduced relatively recently by lateral gene transfer.
The premise is simple; if two organisms are closely related, the
sequence of their genes and proteins should be similar or the
sequences increasingly diverge as the evolutionary distance between
two organisms’ increases. The members of protein families are called
homologous proteins or homologs (Fig.1.5.). Homologs present in the
same species are called as paralogs and from different species called
as orthologs. The process of tracing evolution involves first identifying
suitable families of homologous proteins and then using them to
reconstruct evolutionary paths[1].
Fig.1.5. A signature sequence in the EF-1_/EF-Tu protein family. The signature sequence (boxed)
is a 12-amino-acid insertion near the amino terminus of the sequence. Residues that align in all
species are shaded yellow. Both archaebacteria and eukaryotes have the signature, although the
sequences of the insertions are quite distinct for the two groups. The variation in the signature
sequence reflects the significant evolutionary divergence that has occurred at this site since it
first appeared in a common ancestor of both groups
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For most efforts to find homologies and explore evolutionary
relationships, protein sequences (derived either directly from protein
sequences or from the sequencing of the DNA encoding the protein)
are superior to non-genic nucleic acid sequences (those that do not
encode a protein or functional RNA). Knowledge of the sequence of
amino acids in a protein can offer insights into its three-dimensional
structure and its function, cellular location and evolution. Most of
these insights are derived by searching for homologies. Thousands of
sequences are known and available in data bases accessible through
the internet. A comparision of a newly obtained sequence with this
large bank of stored sequences often reveals relationships (Fig.1.6.)
both surprising and enlightening[1].
Fig.1.6. Evolutionary tree derived from amino acid sequence comparisons. A bacterial
evolutionary tree, based on the sequence divergence observed in the GroEL family of proteins.
Also included in this tree (lower right) are the chloroplasts (chl.) of some nonbacterial species.
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1.3. GREEN FLUORESCENT PROTEIN-LIKE PROTEINS AND THEIR
SPECIALITY:
Bioluminescence (biofluorescence) is the capacity of living
organisms to emit visible light[2]. In doing so they utilized a variety of
chemiluminescent reaction systems. Many a times the word
phosphorescence has been erroneously used to describe marine
bioluminescence. Some terrestrial species (eg., fireflies) have the same
ability, but this adaptation has been most extensively developed in the
oceans. Bioluminescent species occur in only five terrestrial phyla,
and only in one of these (Arthropoda, which includes the insects) are
there many examples. In contrast, bioluminescence occurs in 14
marine phyla, many of which include numerous luminescent species.
All oceanic habitats, shallow and deep, pelagic and benthic, include
bioluminescent species, but the phenomenon is commonest in the
upper 1000m of the pelagic environment[3].
Bioluminescence involves the oxidation of a substrate (luciferin) in
the presence of an enzyme (luciferase). The distinctive feature of the
reaction is that most of the energy generated is emitted as light rather
than as heat. There are many different and unrelated kinds of
luciferin, and biochemical and taxonomic criteria indicate that
bioluminescence has been independently evolved many times. Marine
animals, are unusual, however, in that many species in at least seven
phyla use the same luciferin. This compound is known as
coelenterazine because it was first identified in jellyfish (coelenterates)
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and its molecular structure is derived from a ring of three amino acids
(two tyrosines, and a phenylalanine). Nevertheless, many other
marine organisms use different luciferins. In some animals (eg.,
jellyfish) the luciferin/luciferase system can be extracted in the form of
a stable ‘photoprotein’ that will emit light when treated with
calcium[4,5].
1.3.1. History:
The first report was made by Davenport and Nicol, which
described the green fluorescence of the light organs of Aequorea
victoria (Fig.1.7. & Fig.1.8.) in 1955. The photoprotein responsible for
this bioluminescence was identified as Aequorin along with the
discovery of a companion protein Green Fluorescent Protein (GFP)
(Fig.1.9.) by Shimomura et.al., in 1961[6]. Though the
chemiluminescence (in vitro) of aequorin is blue, the bioluminescence
(in vivo) of Aequorea victoria is found to be green and the reason is
identified, as the radiation-less energy transfer between aequorin and
GFP, in vivo, by Morin and Hastings in 1969[7]. In 1979, Shimomura
et. al., proteolyzed denatured GFP, analysed the peptide that retained
visible absorbance and correctly proposed that the chromophore
(Fig.1.10) is a 4-(p-hydroxybenzylidene) imadazolidin-5-one attached
to the peptide backbone through the 1-and 2- positions of the ring[8].
The curcial break-through came with the cloning of the gene by
Prasher et.al., and the demonstrations by Chalfie et.al., and Inouye
and Tsuji, that expression of the gene in other organisms creates
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fluorescence[9,10,11]. Therefore, the gene contains all the information
necessary for the post-translational synthesis of the chromophore, and
no-jellyfish-specific enzymes are needed.
Fig.1.7. Jellyfish Aequorea victoria
Fig.1.8. The light-emitting organs are located along the edge of the umbrella
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Fig.1.10. Reactions in Chemiluminescence of Aequorin
Fig.1.9. Green Fluorescent Protein
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1.3.2. Chemistry:
The structure of GFP has been reported to have been solved
using seleniomethionyl-substituted protein and multi-wavelength
anomalous dispersion (MAD) phasing methods. The electron density
maps produced by the MAD phasing are clear, revealing a dimer
comprised of two quite regular barrels with 11strands on the outside
of cylinders (Fig.1.11). These cylinders have a diameter of about 30 Å
and a length of about 40 Å. Inspection of the density within the
cylinders revealed modified tyrosine side chains as part of an irregular
helical segment. Small sections of α-helix also form caps on the end of
the cylinders (Fig.1.12). This motif or folding arrangement, with a
single α-helix inside a very uniform cylinder of β-sheet structure,
represents a new protein class (α+β), as it is not similar to any known
protein structure. Two protomers pack closely together to form a
dimer in the crystal. The protein is comprised of 238 amino acids and
has a molecular weight of 26.9 KDa. Its wild type
absorbance/excitation peak is at 395 nm with a minor peak at 475
nm with extinction coefficients of roughly 30,000 and 7,000 M-1 cm-1
respectively. The emission peak is at 508 nm[11].
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Fig.1.11. The overall shape of the protein and its association into dimers. Eleven strands of β-sheet
(green) form the walls of a cylinder. Short segments of α-helices (blue) cap the top and bottom of the
'β-can' and also provide a scaffold for the fluorophore which is near geometric center of the can.
This folding motif, with β-sheet outside and helix inside, represents a new class of proteins. Two
monomers are associated into a dimer in the crystal and in solution at low ionic strengths. This
view is directly down the two-fold axis of the non-crystallographic symmetry.
Fig..No.1.12. A topology diagram of the folding pattern in GFP. The -sheet strands are shown in
light green, α-helices in blue, and connecting loops in yellow. The positions in the sequence that
begin and end each major secondary structure element are also given. The anti-parallel strands
(except for the interactions between stands 1 and 6) make a tightly formed barrel.11
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1.3.3. Chromophore Biosynthesis:
The production of visual colour is related to the formation and
maturation of a chromophore system. The part of the biomolecule
responsible for the production of any sort of colour or luminescence is
called chromophore. It is a covalently unsaturated group (eg:- C=C,
C=O, NO2 etc), responsible for absorption of energy from a radiant
source and brings about electronic transitions within the molecule.
When these transitions are of -* or n-* type, the chromophore
system that is formed, produces colour in the visible region of the
electromagnetic spectrum. However, when these transitions are not
stable and electrons drop back to the ground state from the excited
state emitting energy in the form of radiation, then it is called
fluorescence and the chromophore is then called the fluorophore[12].
In GFPs the chromophore is generated only under conditions
permissive of protein folding; that is, the polypeptide must be able to
obtain its native three-dimensional structure to become visible
fluorescent. It is generated in the presence of molecular oxygen. This
autocatalytic mechanism (Fig.1.13) is initiated by an intrachain ring
closure that leads to the formation of a cyclopentyl group from the
backbone of the original peptide (Ser65, Tyr66 and Gly67)(Fig.1.14).
The fluorophore originates from an internal Ser-Tyr-Gly sequence
which is post-translationally modified to a 4-(p-hydroxybenzylidiene)-
imidazolidin-5one structure. Studies on recombinant GFP expression
in Escherichia Coli led to a proposed sequential mechanism initiated
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by a rapid cyclization between Ser65 and Gly67 to form a imidazolin-
5-one intermediate, followed by a much slower (hours) rate-limiting
oxygenation of the Tyr66 side chain by O2[13].
Fig.1.14. Model of the fluorophore and its environment superposed on the MAD-phased electron
density map at 2.2 Å resolution. The clear definition throughout the map allowed the chain to be
traced and side chains to be well placed. The density for Ser65, Tyr66 and Gly67 is quite consistent
with the dehydrotyrosine - imidazolidone structure proposed for the fluorophore. Many of the side
chains adjacent to the fluorophore are labeled.
Fig.1.13. Fluorophore formation in GFP. Folding of proteins promotes cyclization which
is followed by debydration of the ring and oxidation of the tyrosine
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Combinatorial mutagenesis suggests that the Gly67 is required for
formation of the fluorophore. While no known co-factors or enzymatic
components are required for this apparently autocatalytic process, it is
rather thermosensitive with the yield of fluorescently active to total
GFP protein decreasing at temperatures greater than 30ºC. However,
once produced, GFP is quite thermostable[11].
1.3.4. Physical & Chemical Characteristics:
GFP is very resistant to denaturation requiring treatment with
6M guanidine hydrochloride at 90C or pH of <4.0 or >12.0. Partial to
near-total renaturation occurs within minutes following reversal of
denaturing conditions by dialysis or neutralization. Circular
dichroism predicts significant amounts of -sheet structure that is
subsequently lost on denaturation. Over a non-denaturing range of
pH, increasing pH leads to a reduction in fluorescence by 395nm
excitation and an increased sensitivity to 475nm excitation.
Reduction of purified GFP by sodium dithionite results in a rapid loss
of fluorescence that slowly recovers in the presence of room air. While
insensitive to sulfhydryl reagents such as 2-mercaptoethanol,
treatment with the sulfhydral reagent dithiobisnitrobenzoic acid
(DTNB) irreversibly eliminates fluorescence[11].
The remarkable cylindrical fold of the protein seems ideally
suited for its function. The strands of -sheet are tightly fitted to each
other like staves in a barrel and form a regular pattern of hydrogen
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bonds. Together with the short helices and loops on the ends, the
‘can’ structure forms a single compact domain and does not have
obvious clefts for easy access of diffusable ligands to the fluorophore.
Photochemical damage by the formation of singlet oxygen through
intersystem crossing is reduced by the structure. The tightly
constructed -can would appear to serve this role well and also
provide overall stability and resistance to unfolding by heat and
denaturants[11].
1.3.5. Physiological Functions:
The pigments containing these proteins display slow decay
rates, characterized by half-lives of 20days. The slow turnover of
GFP-like proteins implies that the associated energetic costs for being
colourful are comparatively low. Moreover, high in vivo stability makes
GFP-like proteins suitable for functions requiring high pigment
concentration such as photoprotection. The underlying mechanism,
however, remains controversial, as some FPs have spectral properties
that appear to be inappropriate for photoprotecting tissue by
modulating the intracellular light climate, other FPs are spectrally well
suited to fluorescence energy transfer and dissipation of light energy
via radiative and nonradiative pathways. An antioxidant function has
recently been suggested[14].
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1.3.6. GFP Homologs Comprise a Superfamily:
The group of structural homologs of Green Fluorescent Protein
(GFP) that all share the GFP-like “beta-can” fold are regarded as a
superfamily following the criteria proposed by the Protein Information
Resource(http://pir.georgetown.edu/pir,http://www.otherinfo/sfdef.h
tml.) The reason for such a classification is that this group unites at
least two clearly definable protein families. The first one consists of
G2FP domains, which are incapable of autocatalytic chromophore
synthesis and are found within multi-domain proteins of the
extracellular matrix. The second one includes fluorescent and/or
coloured proteins capable of synthesizing the chromophore auto-
catalytically and which are not found in a multi-domain context[1].
1.4. ZOANTHID TAXONOMY:
Zoanthids are hexacorallians belonging to the order Zoantharia, of
the class Anthozoa, under the phylum Coelenterata/Cnidaria.
1.4.1. Phyllum Coelenterata/Cnidaria:
Coelenterata have a pronounced radial symmertry, the body being
star-like, with the organs arranged symmetrically on lines radiating
from a common centre. The word “polyp” is fregquently applied to the
individual coelenterate animal or zooid, was originally introduced on a
fancied resemblance of hydra to a small cuttle fish (Fr – Poulpe,
Lat – Polypus)[15].
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The body of the Coelenterata, then consists of body-wall enclosing
a single cavity called “Coelenteron”. The body wall consists of an inner
and an inner and an outer layer of the cells, the “endoderm” and
“ectoderm” respectively. Between the two layers there is a substance
chemically allied to mucin and usually of jelly-like consistency, called
the “mesoglea”. The mesoglea may be very thin and inconspicuous, as
it is in Hydra and many other sedentary forms, or it may become very
thick as in the jelly-fishes and some of the sedentary Alcyonaria[15].
Another character, of great importance, possessed by all
coelenterate is the “Cnidae”. These are organelle-like capsules with
eversible tubules. There are three types of cnidae – nematocysts,
ptychocysts and spirocysts. Three other features sometimes
considered to be diagnostic of cnidria are radial symmetry, planula
and polyp stages in developmonent, but all have exceptions. Although
many cnidarians exhibit radial symmetry, some are directionally
asymmetric, and many have a biradial or bilateral organisations. The
motile stage between embryo and settled juvenile in any given
cnidarians life cycle is typically termed a planula, and although this
stage is usually ciliated, sausage-shaped, and non-feeding, deviations
of this pattern have been well documented. Polyp forms are even more
variable than planulae being solitary or colonial; if colonial,, polyps
may be monomorphic or polymorphic; they may or may not have a
mineralized skeleton; they may be benthic or pelagic; and tentacles,
although commonly present, may be absent. The phylum Coelenterata
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is further divided into three classes Hydrozoa, Anthozoa and
Scyphozoa[15].
1.4.2. Class Anthozoa:
The class Anthozoa comprises of two reciprocally monophyletic
lineages, Octocorallia and Hexacorallia. All members of Anthozoa are
exclusively polypoid, and may be colonial, clonal or solitary skeleton-
less or with a mineralic and/or protinaceous skeleton. Anthozoa
currently contains 7,500 extant species[15].
Phylogenetic analysis of morphological data, has suggested atleast
three diagnostic apomorphies for Anthozoa: actinopharynx,
siphonoglyph and mesenteries (Fig.1.15). The actinopharynx
(=stomadeum, gullet) is an ectoderm-lined tube that projects into the
gastro vascular cavity (=coelenteron); this structure is found in all
Anthozoa, with one known exception, the black coral sibopathes. The
siphonoglyph (=sulcus) is a densely ciliated, often more highly
glandular region of the actinopharynx; it is single, paired or rarely
absent (e.g., in ptychodactarian sea anemones; the presence of a
siphonoglyph in antipatharians is disputed), and in asexually-derived
individuals, there may be more than two. The siphonoglyph reflects
the plane of bilateral symmetry for the polyp. Bilateral symmetry is
further defined by the mesentries (the term septa, which has been
used for these structures has been reserved for mesentreries of
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scleratinians), radially-arrayed sheets of tissue that extend all or part
of the way
from the body wall to the actinopharynx. Mesenteries are arranged in
cycles (members of each cycle form more or less simultaneously, and
bear the gametogenic tissue and epithelia-muscular cells that are
concentrated as retractor muscles. The free edge of a mesentry is
typically elaborated into a mesenterial filament with abundant gland
cells, nematocysts and cilia[15].
1.4.3. Sub-Class Hexacorallia:
The anthozoan subclass Hexacorallia comprises all scleractinian
and black corals, tube anemones, and sea anemones in the broadest
sence (i.e., orders Actinaria, Antipatharia, Ceriantharia,
Fig.1.15. Sketch showing the internal anatomy of Anthozoa.
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Corallimorpharia, Scleractinia and Zoanthidae). Hexacorallia
currently contains about 4,300 extant species. Most hexacorallians
have hexamerous symmetry, although eight or ten-part symmetry are
not uncommon. All members of Hexacorallia have spirocysts, a type of
cnida with a single-walled capsule and a tubule composed of tiny
entangling sub-threads[15].
1.4.4. Order Zoanthidea:
Members of order Zoanthidea (=Zoantharia, Zoanthinaria) are
clonal, soft bodied polyps with two rows of marginal tentacles. Their
internal anatomy and mesenterial arrangement is distinctive among
hexacorallians, and the group is presumed to monophyletic, although
no published studies have examined this question explicitly[15].
Zoanthideans have traditionally been grouped into two suborders:
Macrocnemina and Brachycnemina, which differ in the arrangement of
the mesenteries. The fifth pair of mesentry from the dorsal directive is
incomplete in the case of Brachycnemina and complete in the
macrocnemina. The families under the sub-order Brachycnemina –
Sphenopidae and Zoanthidae; the families under the sub-order
Macrocnemina – Epizoanthidae, Abyssoanthidae and
Neozoanthidae[15].
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1.4.5. Family - Zoanthidae:
Zoanthidae comprises of three genera Zoanthus, Isaurus and
Acrozoanthus which include variable number of species depending
upon the authors[15].
1.5. WHAT ARE ZOANTHIDS?
Zoanthids (Fig.1.16) belong to the same class Anthozoa as sea
anemones. Zoanthid taxonomy is undergoing some review so the
number of known zoanthid species range from 200 to 60 depending on
how the species are defined[16].
1.5.1. Where seen?
These tiny but tough flower-like animals often carpet rocky and
rubbly areas. Some are adapted be regularly exposed to the air at low
tide. These animals are often the first to settle on any vacated space
in a reef[16].
Fig.1.16. A picture of zoanthis polyps
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1.5.2. Features:
Zoanthids look like tiny anemones. But with sea anemones are
solitary polyps, most zoanthids live in colonies (Fig.1.17) like corals do.
They don’t produce a hard skeleton like the hard coral colonies.
Instead, their skin is leathery and composed partly of chitin (the same
substance that insect exoskeletons are made of)[16].
The typical polyp has a cylindrical body coloumn, topped by a
smooth, flat oral disc that is edged by short tentacles, usually in two
rows close to one another. The oral disc is often in a contrasting
bright colour from the usually brown or drab tentacles, usually in two
rows close to one another. When exposed to low tide, however, the
animals retracts its tentacles into its body column and then looks like
a strange blob of jelly[16].
Zoanthids may have three different living arrangements
(Fig.1.18). Each zoanthid polyp may be solitary but located near one
another. These polyps are large with thick, fleshy polyps on tall
Fig.1.17. A picture of mat of zoanthids
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coloumns. Or the zoanthid polyps are joined to one another by stolons
(tube-like structures that spread across the ground like a root or
runner) – the “liberae” form. Or the zoanthid polyp may be embedded
in a common mat of tissue – “coenenchyme”. The tissue may be
strengthened by incorporating sand. The colony may form mats on
the sand or encrust rocky areas – the “intermedea” and “immerse”
forms[16].
The shape of the same zoanthid species may vary depending on
where they are found. Those inhabiting arrears with strong waves
Fig.1.18.Diagram of colony and polyp structure forms of zoanthids. a) ”immersae” form,
with polyps deeply embedded in a well-developed coenenchyme; b) “intermediate” form,
intermediate in form, ususally with well-developed, thick polyps; c) “liberae” form, with
free-standing polyps extending well above a thin coenenchyme (stolons). Often with space between oral disks.
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tend to be short and hug the surface. Others found in deeper, calmer
waaters are taller, with longer tentacles[16].
1.5.3. Toxic Flowers:
Some zoanthids contain powerful toxins to protect themselves
against predators. The most toxic marine poison, palytoxin, was
discovered in a Zoanthid (Fig.1.19). Minute quantities of palytoxin can
paralyse and even kill. So zoanthids should not be handled with open
wounds on hand or mouth or eyes should be touched after handling
them. It is believed that the toxins are not produced by the animal
but by bacteria that live in symbiosis with the polyps. However, some
animals have adapted to the poison and even eat zoanthids. These
include the common hairy crab, filefishes and nudibranchs[16].
Fig.1.19. Colourful zoanthids which are toxic flowers
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1.5.4. What do they eat?
Most zoanthids feed on amphipods (Fig.1.20), plankton, some also
feed on finer particles. Many harbour zooxanthellae (symbiotic algae)
inside their bodies. These carry out photosynthesis and may
contribute nutrients to the host polyp[16].
1.5.5. Zoanthid Babies:
Zoanthids generally produce asexually – new polyps bud to enlarge
the colony. However, they also reproduce sexually. The polys may
produce sperm or eggs, but usually only one at a time[16].
Fig.1.20. Zoanthids eating amphipods
Fig.1.21. Zoanthid releasing eggs during spawing
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Eggs and sperms are released synchronously for external fertilization
(Fig.1.21.), in mass spawing similar to that practiced by hard
corals[16].
1.5.6. Status and Threats:
Zoanthids are not listed among the threatened animals. However,
like other creatures of the intertidal zone, they are affected by human
activities such as reclamation and pollution. Trampling by careless
visitors, and over collection also have an impact on local
population[16].