Difference between Cell Biology and Cytology

Cytology is the branch of science which deals the Study of cell structure only but cell biology  include study of cell structure, function & Reproduction also so we can define both the terms like-

Cytology:- Study of cell structure.

Cell biology :-Study of cell structure,function & Reproduction.

Father of modern cytology   – C.P. Swanson

Father of Indian cytology   –  A.K. Sharma

Institutes of Cell & Molecular Biology

  • National centre for cell science, Pune.
  • Institute of life sciences, Bhubaneshwar.
  • National Institute of oceanography, Panjeem.(Goa)
  • Advance center for cell & chromosome Research (Kolkata).
  • National Institute of Immunology, New Delhi.
  • National Brain Research center, Manesar, Gurgaon.
  • Centre for cellular and molecular Biology, Hyderabad.
  • Center for DNA finger printing and diagnostics Hyderabad (CDFD).
  • Institute of genomics and integrative biology, New Delhi.
  • International Centre for Genetic Engineering & Biotechnology (ICGEB) – New Delhi

    History

    • Robert Hook (1665) in his book Micrographia coined the term “Cell”. He first observed cell in a piece of cork (dead cells) (Greek word cella = Small hollow space or Chamber)
    • Malpighi (1671) & Grew (1682) first observed living cells in plants and called them “Bladders” and “Utricles” respectively.
    • Leeuwenhoek (1674) first observed animal cells (Free animal cells) and called them “Animalcule”.

      CELL  THEORY 

      M.J. Schleiden (1838)  –  German Botanist

      T.Schwann (1839)        –  German Zoologist

      (1) Living organisms are made up of cells and substances produced by cells (Cell is structural units)

      (2) All cells arises from the preexisting cells only (confirmed by Rudolph virchow (1855) by stating “Omnis cellulae cellula“. Virchow proposed “Cell Lineage theory”. [Karl Nageli showed that plant cells arise from the division of pre existing cells].

      (3) All cells are basically similar in structure and metabolic function.

      (4) Vital activities of an organism are due to the activities of its cells (Cell is functional units).

      (5) Each cell has a unit of heredity.

      Exception of cell theory : –

      According to this theory all the living organism are made up of cells. Viruses are exception of this theory because virus lacks cell organization.

      According to modern scientists all the acellular organismmonera and protista, Xanthophytes,(Vaucharia) Phycomycetes (Rhizopus) are exception of cell theory.

    • Cell Principle
    • First of all cell hypothesis was proposed by Schwann (1839).
    • It was raised to the status of cell theory by Schleiden and Schwann.
    • It was modified, when R.Virchow (1855), Put forward the theory of cell lineage or development of cells from preexisting cells. (“Omnis cellulae cellula”).
    • As a result of these additions the cell theory has been as “cell principle or cell doctrine” the cell principle is better than cell theory as it applies almost to all the living things, plants, animals and microbes and it also incorporates nearly all the modern findings about a cell.Modern cell theory or cell principle states that :
    • 1) The body of all living beings is made up of cells and their products.2) Cell is the unit of structure of body of all organisms.3) A cell is made up of a small mass of protoplasm having a nucleus, a number of organelles and covering membrane.

      4) Each cell is capable of independent existence but a cell organelle can not survive independently.

      5) All cells have fundamental similarity in structure, chemical composition and basic metabolic reactions.

      6) Life exists only in cells because all activities of life are performed by cells.

      7) New cells arise from pre-existing cells through division.

      8) Each cell contains the whole complement of genetic information not for itself but for the whole organism (Totipotency)

      9) Genetic information are stored and expressed within the cells.

      10) Life transferred from one generation to the next only in the form of cells.

      11) All cells of present day organisms have evolved from primitive cells of the remote past.

      12) They have a common ancestry.

      13) The cells of an individual get transformed structurally and functionally to perform specific function, loss of centriole in nerve cells. Lost of nucleus in mammalian RBCs & form of sperms.

      14) Cells maintain homoeostasis and their internal environment.

      15) No organism, organ, or tissue can have any activity that is absent in its cell.

      16) All cells have a full genetic information coded in their DNA, but each cell type uses only a part of information, require for its special function or structure.

      17) A cell has definite life span.

      Objections :

      (a) Nucleus is absent in prokaryotes, mature RBCs.

      (b) Prokaryotes lack a number of cell organelles present in eukaryotes.

      (c)  Virus do not obey theory of cell lineage.

      (d) A number of nuclei present in coenocyte or syncytial

 

Zoologylearningpoint channel

Zoologylearningpoint channel link

https://www.youtube.com/channel/UC48ShFOo6BcplE7_9DiytHQ

Zoologylearningpoint channel’s Trailer=

https://www.youtube.com/watch?v=u2GrGG53tsQ

Links of zoologylearningpoint channel’s lectures=

Origin of Life – Ancient Theories for Origin of Life=

https://youtu.be/lOe1PfVcZ8w

AFM(Atomic Force Microscopy)=

https://youtu.be/G9om5FEOb9o

Confocal Microscopy =

https://youtu.be/W5qIZdJi64Q

ORIGIN OF LIFE

ORIGIN OF LIFE

Big-Bang Theory :
                             Proposed by Abbe Lemaitre. According to this theory, the universe originated about 15 billion years ago due to a thermonuclear explosion of a dense entity. This thermonuclear explosion is called Big-bang. About 4.6 billion years ago, the origin of our solar system took place by the gaseous clouds formed due to this explosion. These gaseous clouds collapsed and converted into flat disc-like structure made up of atoms and small particles due to their own gravitational pull. These flat-disc like structure is called SOLAR-NEBULA. The very hot central part of this solar Nebula became still hotter & converted into the sun. Now, due to condensation of atoms and dust particles moving around the sun formation of the other planets took place [Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune]. The solid part of our planet earth was called Lithosphere and the gaseous part was known as atmosphere. When the earth’s surface cooled down and its temperature decreased to 1000 C, water formed on it.


Ancient Theories for origin of life :
1. Theory of special creation –Mythology based theory
Supporter of this theory was father Suarez. According to Bible
life and everything was created by god in 6 days.

1st day: Earth and heaven
2nd day : Sky and water
3rd day : Land and plants
4th day : Sun, moon and stars
5th day : Fishes and birds
6th day : Land animals and first man Adam and from his 12th Rib first woman Eve.

According to hindu mythology the world was created by God Brahma. (The first man was Manu and the first woman was Shraddha). According to it life has not changed ever since its origin. Special creation theory lacks scientific evidences so it is not accepted.

2. Theory of Spontaneous Generation (Abiogenesis or Auto genesis) –
This hypothesis was supported by ancient Greek philosophers like Thales, Anaximander, Xenophanes, Plato, Empedocles, Aristotle. According to this theory life was originated from nonliving things or decaying and rotting matter like straw, mud etc. spontaneously. They believed that the mud of theNile river could give rise to frogs, snakes, crocodiles. Abiogenesis was strongly supported by Von Helmont. He claimed that formation of mice occurs in 21 days, if a sweat soaked dirty shirt is kept in wheat barn.

3. Cosmozoic Theory –
Proposed by Richter.
Protoplasm reached on earth in the form of spores or other simple particles from some unknown part of the universe with cosmic dust and they gave rise to various forms of life.

4. Cosmic panspermia theory –
Proposed by Arrhenius. According to this theory organisms existed throughout the universe and their spores could freely travel through space from one star to the other.


5. Theory of Eternity of Life –
Helmhotz believed that life is immortal.


6. Theory of Biogenesis –
Harvey (1651) and Huxley (1870)
Omnis vivum ex ovo or vivo. New organisms can be originated on earth only by pre-existing life. This theory reject the theory of Spontaneous generation but cannot explain
origin of life. To prove Biogenesis and to disprove abiogenesis experiments were performed by – Francesco Redi’s Experiment (Italian 1668) –
He took cooked meat in three jars one was uncovered, the second was covered with
parchment and the third was air tight. He observed that maggots developed only in the uncovered jar while maggots could not developed in the meat in closed jars. This proved that larvae were formed from eggs laid by the flies in open jars. Since the meat in closed jars could not be visited by flies so no larvae could develop. Therefore life originated from preexisting life.
Lazzaro Spallanzani (Italian 1767) –
He boiled vegetables and meat to prepare a sterlized nutritive soup and he kept some of it in air sealed flasks and some in loosely corked flasks. He observed that the soup in sealed flask remained sterile while microorganisms appeared in the soup in loosely corked flasks. Thus even microorganisms were formed from pre-existing ones in the air rather then spontaneously.

Louis Pasteur (French 1862) –
Pasteur is popular for Germ Theory of Diseases or Germ theory and he disproved abiogenesis. He prepared sterlized syrup of sugar and killed yeast yeast by boiling them in flasks. He took two flasks one of broken neck and another of curved neck (swan neck flask). No life appeared in swan neck flask because germ laden dust particles in the air were trapped by the curved neck which serves as filter while in broken neck flask colonies of microorganism were developed. By the experiment he proved that life comes only from pre-existing life.


Modern theory of origin of life
(Oparin-Haldane theory of origin of life)
Naturalistic theory OR Theory of Chemical Evolution–
This theory was proposed by Russian Scientist A.I. Oparin and J.B.S.Haldane (England born Indian scientist) Oparin’s theory was published in his book ‘ORIGIN OF LIFE’.
Important Points
>According to this theory life originated by the composition of chemicals.
>Oparin’s theory is based on Artificial Synthesis. So also called as artificial synthetic theory.
>At the time of origin of life free O2 was absent, so first life was anaerobic.
>In the primitive atmosphere free oxygen was present but complete oxygen consumed in composition so primitive atmosphere of earth was reducing.
>Oxygen was reproduce by photosynthesis and atmosphere converted in oxydizing.
Chemical Evolution
1. The atomic stage –
The earth was originated about 4.6 billion years ago. Early earth had free atoms of all those elements which are essential for the formation of protoplasm. The lightest atoms like carbon, hydrogen, nitrogen and oxygen formed the primitive atmosphere. Most abundant of all of them was hydrogen.


2. Molecular stage (Origin of molecules and simple Inorganic compounds) –
Free atoms combined to form molecules and simple inorganic compounds. Due to presence of high temperature, active hydrogen atoms combined with all oxygen atoms to form water and leaving no free oxygen. Thus the primitive atmosphere was reducing (without free oxygen) unlike present oxidizing atmosphere (with free oxygen). Hydrogen atoms also combined with nitrogen to from NH3. (The first molecular compounds formed were probably water and Ammonia). These Lighter elements also formed CO2, CO, N2, H2 etc.


3. Origin of early organic compounds –
The nitrogen and carbon of the atmosphere combined with metallic atoms forming nitrides and carbides. Water vapour and metallic carbides reacted to form the first organic compound Methane(CH4). Later on hydrogen cyanide(HCN) was formed. Water which formed on earth due to high temperature evapourated so clouds were formed. Water vapour changed into rain drops and by the collection of water on earth primitive oceans were formed.


4. Origin of simple organic compounds –
Water of primitive oceans contained large amount of methane, ammonia, hydrogen,
cyanides, carbides, nitrides. These early compounds interacted and formed simple organic compounds like, aldehyde, Ketones, Alcoholes, Pentose and hexose sugar, Amino Acids, Glycerol, Fatty Acids, Purines, Pyrimidines etc. Energy was obtained from U.V. Rays of sunlight, cosmic rays and heat of volcanic eruptions.


5. Origin of complex organic compounds –
The small simple organic molecules combined to form large complex organic molecules. e.g.–
– Amino acids Joined to form polypeptides and proteins, which were non-enzymatic.
– Simple sugar units combined to form polysaccharides.
– Fatty acids and glyceroles united to form fats and lipids.
– Sugar, nitrogenous bases, phosphates combined into nucleotides which polymerized into nucleic acid, which unable to replicate. These macromolecules forms main component of protoplasm hence the possibility of origin of life in primitive oceans could be established. After long time the water of primitive oceans became rich mixture of organic compounds as a result of chemical evolution. Haldane called this saturated water of oceans as prebiotic soup or hot dilute soup. The major requirement for promoting polymerisation is the availability of continuous source of energy and removal of water from the surface of reactants so that they can concentrate and prevent depolymerisation. Experimental evidence for formation of simple organic compounds –
By Stanley Miller. Who was a student of Harold Urey. In this experiment Miller took the mixture of methane, ammonia and hydrogen (ratio 2 : 1 : 2) in a large flask and passed steam over it by boiling water and connecting it with a glass tube. Electric spark was discharged at 800 °C in the mixture by using two tungston electrodes as source of energy.
After 18 days this fluid was collected and analysed. This dark red fluid was found to contain.
– Simple amino acids – glycine, alanine, aspartic acid.
– Simple organic acids – farmic, acetic, oxalic, lactic, succinic acids. etc.
– Pentose, hexose, aldehyde, ketone etc.
From these compounds how various forms of life was originated we will studied it in Biological evolution.

CONSERVATION BIOLOGY

The planet is populated with a vast richness of living organism—so vast that we have only cataloged a minority of the species that exist. Unfortunately, we are altering ecosystems and ecosystem process to an extent that we are accelerating the extinction of species, creating a biodiversity crisis. Conservation biology, a recently conceived subdiscipline of biology, is dedicated to countering the biodiversity crisis.

 The Biodiversity Crisis: An Overview

Extinction is a natural phenomenon, but it is the current rate of extinction that underlies the biodiversity crisis. The high rate of ecosystem degradation is being causes by one species—Homo sapiens.
A. Numerous examples indicate that estimates of extinction rates are on track
Extinction rates are usually expressed as the number or percentage of species expected to become extinct in an area in a unit of time. Estimates are difficult at best. Since birds are among the most studied animals, the extinction rates for less well-known, nonavian taxa are sometimes based on the rate of loss of bird species. Most often, extinction rates are estimated from the concept of species-area relations in which the number of species in an area is directly related to the size of the area.

This rule predicts that, on average, about 50% of the total number of species will be lost in an area where 90% of the habitat is lost. The absence of clear documentation of the rate of extinction has led some to argue that there is no reason to worry at this time. Population  ensus data, however, indicate that extinction of known organisms is occurring at an alarming rate..
• 11% of the 9040 known species of bird are endangered
• 680 of the ca. 20,000 known plant species are in danger of becoming extinct by the year 2000
• Approximately 20% of the known species of freshwater fish have become extinct or
have become threatened during recorded history.
In order to know for certain that a given species is extinct, we must know its exact distribution and habits. However, we do not have a complete catalogue of biodiversity and knowledge of the geographic distribution and ecological roles of Earth’s species, thus, our understanding remains incomplete.

B. The major threats to biodiversity are habitat destruction, over-exploitation, and
competition by exotic species The most significant threat to biodiversity is human alteration of habitat. Human activities which disrupt entire systems include development, logging, war, and oil spills
• 73% of the IUCN’s designations of extinct, endangered, vulnerable, and rare species are
related to destruction of natural habitats.
• Marine biodiversity also is threatened by human activity. About 93 % of the coral reefs
(reefs are estimated to support about 1/3 of the known species of fish) have been
damaged, if the current rate of destruction continues, 40% to 50 % of the reefs could be
lost within 30 to 40 years.
Overexploitation of wildlife by humans is another source of threat.
• Species threatened by excessive commercial harvest or sport hunting include whales,
American bison, Galapagos tortoises, and numerous fishes.
• The often illegal trade of rare animals and animal products also jeopardizes many
species. The introduction of exotic species can cause a variety of problems. Although most transplanted species fail to survive, there are notable exceptions.
• The introduction of Nile perch into Lake Victoria in east Africa has resulted in the loss
of 200 of 300 species of chichlids
• Fire ants, which were accidentally introduced into the southern United States from
Brazil in 1918, have continued to spread northward
• Displacement by introduced species is considered at least partially responsible for 68%
of the IUCN’s listings of extinct, endangered, vulnerable, and rare species.

C. Biodiversity is vital to human welfare

We care about the loss of biodiversity?
Answers to this question-
• Biophilia, the human sense of connection to nature and other forms of life, is centered around aesthetics and ethics.
• Biodiversity is a crucial natural resource and threatened species could provide crops, fibers, and medicines.
• 25% of the prescriptions dispensed from pharmacies in the United States contain substances derived from plants.

In the 1970s, alkaloids isolated from the rose periwinkle of Madagascar were found to inhibit cancer cell growth and result in remission of childhood leukemia and Hodgkin’s disease.
• The loss of species results in the loss of genes and all the genetic potential.
• Humans are dependent on ecosystems and other species. By allowing the extinction of species and degradation of habitats to continue, we are taking a risk with our own species survival. In an effort to influence policy-making, ecologists and economists have estimated the cost of replacing ecosystem “services” as a measure of the services’ value at US$33 trillion.

D. Change in ecological and evolutionary time is the focus of conservation biology Globally, an area half the size of the U.S. has been protected as natural areas .

Three concepts form the roots of conservation biology
1. Preservation is the practice of setting aside select areas to remain natural and undeveloped.
2. Resource conservation is a management scheme aimed at balancing “multiple uses” of natural resources (e.g., agricultural, industrial, preservation, recreation)
3. Evolutionary/ecological view recognizes that natural systems are the result of millions of years of evolution and that ecosystems processes are critical for the maintenance and proper function of the biosphere.
The goal of conservation biology is preserve individuals species and to sustain ecosystems, where natural selection can continue to function and to maintain the genetic variability upon which it acts.
• Conservation biology follows the ecological tenets of nonequilibrium discussed in
• Consideration of human presence is vital in conservation biology because no ecosystems are unaffected by humans. Conservation biology seeks to foster human activities that sustain ecosystems and reduce the current rate of environmental degradation.

The Geographic Distribution of Biodiversity
Biodiversity is not evenly distributed and there are recognizable patterns of distribution, including clines (gradual variation), hot spots, concentrations of diversity, and ranges of migratory species.
A. A gradual variation in biodiversity correlates with geographical gradients
Biogeographers have long recognized the existence of clines in species diversity in the form of major geographical gradients.
• The number of terrestrial bird species in North and Central America increases steadily
from the Arctic to the tropics.
• The number of marine benthic species increases with depth.Four hypotheses have been developed to explain clines, and more generally, the factors that influence patterns of diversity in all communities.
1. Energy availability. Holds that because solar radiation is greatest in the tropics, theresource base is greatest there.
2. Habitat heterogeneity. Holds that tropical regions experience more local disturbances that contribute to greater environmental patchiness; the greater patchiness allows a greater diversity of plants species to form a resource base for diverse communities of animals.

3. Niche specialization. Holds that the stability and predictability of tropical climate may
allow organisms to specialize on a narrower range of resources; smaller niches would
reduce competition and contribute to greater species diversity.
4. Population interactions. Holds that diversity is self-propagating because population
interactions coevolve, and the resulting predator-prey and symbiotic interactions in a
diverse community prevent any populations from becoming dominant.
Many ecologist believe that a complex combination of factors is responsible for clines.
B. Biodiversity hot spots have high concentrations of endemic species
Biodiversity hot spot = Relatively small areas with exceptional concentrations of species
Endemic species = A species found nowhere else
Biogeographers have identified 18 vascular plant hot spots
• These hot spots contain about 20% of the known vascular plant species and 7% of all
land vertebrate species.
• Six of the 18 hot spots have lost close to 90% of their original habitats to human
development; as a result, the biodiversity hot spots also are hot spots of extinction.
Islands are hot spots of bird extinction.
• 30% of all bird species are endemic.
• Approximately 90% of the 104 species of birds lost in the last 400 years were endemic
on islands
• Today, all of the areas where over 10% of the bird species are threatened with
extinction are islands (e.g., Hawaii, Philippines, New Zealand).
• It seems likely that most of the non-avian threatened species also are endemic on islands. In the U.S., most of the endangered species are found in the areas with the most endemic species: Hawaii, southern California, southern Appalachians, southeastern coastal states. Most of these species are threatened because of loss of habitat due to human population growth and agriculture. Studies of biodiversity and recent extinctions show that many threatened, endangered, and potentially endangered species are concentrated in biodiversity hot spots.
• This pattern suggests that with appropriate measures, many species could be saved in relatively small areas.
• The biodiversity crisis is a global problem and focus on hot spots should not detract form efforts to preserve biodiversity in other areas.
C. Migratory species present special problems in conservation
The preservation of migratory species is complicated by a life history that involves residence in multiple jurisdictions.
• Monarch butterflies, for example, migrate from Canada to Mexico. Human intrusion is making the migration an “endangered phenomenon.”
• Similar situations exist for migratory songbirds, sea turtles, and marine mammals. Successful conservation efforts for such species require international cooperation and the careful preservation of habitat in both parts of the species’ range.

III. Conservation at the Population and Species Level
Much of the attention of the biodiversity crisis has focused on species.
Endangered species are species that are in danger of extinction in all or a significant portion of its range
Threatened species are species that are likely to become endangered in the foreseeable future throughout all or a significant portion of its range.
A. Sustaining genetic diversity and the environmental arena for evolution is an ultimate goal
Species are only one component of earth’s biodiversity. Other components include:
• Genetic variability within populations of species
• Myriad biotic and abiotic factors that provide the arena for evolution
Modern conservation science attempts to concentrate more on sustaining ecosystem processes and the evolutionary lineages that species represent than on conserving individual species. Alteration of ecosystems by human activities already makes it impractical to conserve all the genetic diversity within most species.
Conservation biology has focused on understanding the dynamics of small populations, diagnosing declines, assessing the factors responsible for a population’s decline, and determining how to revise declines and sustain small, often fragmented populations.
• Currently, conservation efforts lag far behind the rate of decline and loss of species.
• Many species are at critically low numbers and the strategy has mainly been to reverse the trend.
• Conservation biologists also use some features of crisis management and apply some
untested hypotheses and concepts.
B. The dynamics of subdivided populations apply to problems caused by habitat fragmentation
Degradation of habitats often leads reduction in the area of suitable habitat as well as to fragmentation of the remaining area.
• Some ecologists have likened fragmentation to islands surrounded by areas of human
activity.
• The island model may be overly simplistic, and concepts developed by studying subdivided populations may prove to be more useful to conservation efforts.
Metapopulation = A subdivided population or a network of subpopulations of a species
• Vary greatly, depending on size, quality, spatial arrangement, and persistence of habitat patches
The subpopulations of a metpopulation are separated into habitat patches that vary in quality.
• Patches with abundant, high-quality resources tend to have persistent subpopulations that produce more offspring.
• Low-quality patches may be populated only when new individuals reared in high-quality patches disperse to them.
• Dispersal is essential to maintaining genetic variability within subpopulations; a subpopulation that is cut off from others may eventually become genetically extinct.
Human activity may impact population structure.
• Fragmentation may result in the conversion a population to a metapopulation with
reduced genetic variability.

• Human encroachment on a metapopulation (e.g., loss or reduction of habitat patches;
restriction of dispersal) may decrease the number, size, and or genetic variability of subpopulations.

Molecular Taxonomy

Molecular Taxonomy is the classification of organisms on the basis of the distribution and composition of chemical substances in them. Molecular techniques in the field of biology have helped to establish genetic relationship between the members of different taxonomic categories . DNA and protein sequencing, immunological methods, DNA-DNA or DNA-RNA hybridization methods are more informative in the study of different species. The data obtained from such studies are used to construct phylogenetic trees. Fitch and Margoliash ,(1967) made first phylogenetic tree based on molecular data .This tree was so close to the already established phylogenetic trees of the vertebrates that the taxonomists realized significance of molecular data and this made them understand that other traditional methods are although important but molecular evidences could be final or confirmatory evidences.

International Code of Zoological Nomenclature

1. The International Code of Zoological Nomenclature (ICZN or ICZN Code) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. The rules principally regulate:
2. How names are correctly established in the frame of bionomial nomenclature
3. Which name must be used in case of name conflicts
4. How scientific literature must cite names

Zoological nomenclature is independent of other systems of nomenclature, for
example botanical nomenclature This implies that animals can have the same
generic names as plants.The rules and recommendations have one fundamental aim: to provide the maximum universality and continuity in the naming of all animals, except
where taxonomic judgment dictates otherwise. The Code is meant to guide
only the nomenclature of animals, while leaving zoologists freedom inclassifying new taxa. In other words, whether a species itself is or is not a recognized entity is as objective decision, but what name should be applied to it is not. The Code applies only to the latter, not to the former. A new animal name published  without adherence to the Code may be deemed simply “unavailable” if it fails to meet certain criteria, or fall entirely out of the province of science . The rules in the Code determine what names are valid for any taxon in the family group, genus group, and species group. It has additional (but more limited) provisions on names in higher ranks. The Code recognizes no case law. Any dispute is decided first by applying the Code directly, and not by reference to precedent. The Code is also retroactive or retrospective which means that previous editions of the Code, or previous other rules and conventions have no force any more today and the nomenclatural acts published ‘back in the old times’ must be evaluated only under the present edition of the Code. In cases of disputes concerning the interpretation, the usual procedure is to consult the French Code,lastly a case can be brought to the Commission who has the right to publish a
final decision.

 

 

 

Sycon (Scypha)

Classification

Phylum – Porifera – pore bearing animals,diploblastic with cavity spongocoel.

Class – Calcarea – Spicules calcareous, canal system asconoid/syconoid /leuconoid  type

Order – Heterocoela – Canal system syconoid type.

Genus- Sycon (Scypha)

Habitat- found in shallow water,Marine.

Habit- Clustered, more independent. Small buds may occasionally appear at the base of mature specimens.

Characters-

  • Body – vase like, more or less separate at the base.The base is attached to the substratum and the distal free end bears an opening called osculum.Osculum is surrounded by large monoaxon spicules, forming a collar around it.
  • The external surface reveal the presence of numerous pores called ostia,these are incurrent pores permitting entry of water.
  • Due to folding of the body covering numerous canals are formed called incurrent canals and radial canals.
  • Canal system of syconoid type stage I. Course of water current is Ostia > incurrent canals > prosopyles >radial canals >apoyles >spongocoel > osculum >outside body. Choanocytes are confined to radial canals.
  • Incurrent water through canal system facilitates respiration, nutrition and excretion.
  • Internal cavity is spongocoel.
  • Skeleton of calcareous spicules which are monoaxon, triaxon and tetraxon. Dense spicules almost hide the ostia.
  • Animal is bisexual.
  • Asexual reproduction (a) by budding under favourable conditions (b) by reduction bodies under unfavourable conditions.
  • In sexual reproduction fertilization is internal but cross due to
    protogynous condition.
  • Development is indirect through amphiblastula larva.
  • High power of regeneration is seen.Scypha_sp._sketch

Leucolosenia

Classification :
Phylum- Porifera -Pore bearing animals,diploblastic with cavity
spongocoel
Class- Calcarea -Spicules calcareous, canal system –
asconoid/syconoid/leuconoid types
Order- Homocoela- canal system of asconoid type
Genus- Leucolosenia
Habitat- Marine, inhabit shallow water
Habit- Colonial,sessile
Characters-
1. Colony has anastomosing vase shaped cylindrical tubes. Tubes are
attached horizontally at the base which in turn is attached to some rocks.
2. Osculum is present at the free distal end of each tube.
3. Simplest type of canal system-asconoid.Course of water current is
ostia—spongocoel—osculum.
4. Skeleton of monoaxon or triaxon calcareous spicules.
5. Choanocytes line the spongocoel.
6. Asexual reproduction is by budding and sexual reproduction is by
production of sperms and ova.
7. High power of regeneration is present.

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