Animal Kingdom Part 2

(Phylum Porifera, Coelenterata and Ctenophora)

Phylum Porifera / Parazoa / Sponges:

The porifera are the lowest multicellular animals (metazoans) without definite true tissues. In other words, they have “cellular level” of body organization. The word “Porifera”means pore bearers (Gr., porus = pore; ferre = to bear); They have                                                           numerous minute pores, called ostia, in their body wall through which a continuous current of outside water is taken into the body. 5,000 species are

known.

General characters:

1. All porifera are aquatic, sedentary/sessile, asymmetrical or radially symmetrical animals. They are the first multicellular organisms.
2. The sponge are diploblastic. Ectoderm is composed of pinachocyte and endoderm is composed of choanocyte. Both these layers are called pinachoderm and choandoderm respectively.
3. The body is perforated by numerous minute pores called ostia.
4. The ostia open into a large central cavity called spongocoel.
5. The spongocoel opens to the outside by a large opening called

osculum.

6. The most characteristic feature of this phylum is the presence of a an inter-communicating system of cavities known as canal system.

6. They have an endoskeleton of calcareous spicules or silicious spicules or spongin fibres or sometimes none.

7. Excretion and respiration takes place by diffusion through general body surface.
8. They have a great power of regeneration.
9. Reproduction takes place both by asexual and sexual methods. The asexual reproductive bodies are called gemmules
10. Development is indirect or direct. The common larval are

parenchymula, amphiblastula, etc.

Diagram of a partially sectioned generalized spong

Source: http://www.thinkquest.org

Types of Canal System in sponges:

1. Ascon type- eg. in Leucosolenia

Ascon type canal system

Source: http://www.thinkquest.org

2. Sycon type- eg. in Sycon(=Scypha). It is formed by folding of body wall. Choanocytes are limited only to flagellated canals

Sycon type canal system

Source: http://www.thinkquest.org

3. Leucon type- eg. in class Demospongiae. It is formed by further folding of flagellated canals of the sycon type. Choanocytes are limited to flagellated chambers only.

Leucon type canal system

Source: http://www.thinkquest.org

Classification

Class1. Calcarea

1. Skeleton of Calcareous spicules.
2. Choanocyte cells are largeand conspicuous Examples : Clathrina,Leucosolenia, Sycon, etc., Smallest sponge is Leucosolenia.

Class 2. Hexactinellida

1. Skeleton of six rayed triaxon, silicious spicules,

2. These are also knownas glass sponges. Examples : Euplectela, Hyalonema, etc. Euplectela is given as a precious Gift in Japan. Hyalonema is also known as Glass rope sponge.

Class 3. Demospongia

1. Skeleton is either composed of spongin fibres or silicious spicules or a  combination of both.
2. The silicious spicules never six rayed
3. The canal system complicated- Rhagon type

Examples : Spongilla, Chalina, Euspongia, Hippospongia, Oscarella, etc.,

Spongillais a fresh water sponge. Euspongia is bath sponge

Phylum Cnidaria /Coelenterata

The phylum “Cnidaria” derives its name from the presence of stinging cells called Cnidoblasts / Nematoblasts. The coelenterates have tissue level of body organisation. They are the first true metazoans (eumetazoans) with a radial symmetry. The word“Coelenterata” refers to the presence of an internal cavity called coelenteron, or gastro- vascular cavity, which functions both as digestive and body cavities.

About 9,000species are known.

General Characters :-

1. The coelenterates are aquatic and solitary or colonial
2. Two basic types of individuals occur in the life cycle. They are

polyps and medusa

Polyp                                         Medusa

Source: http://www.thinkquest.org

3. They diploblastic. The wall body wall is made up of two layers of cells, namely the ectoderm and the endoderm with a non–cellular layer in between called mesogloea.
4. They have characteristics cells called Nematocysts or stinging cells.
5. The coelenterates are acoelomate animals
6. A gastrovascular cavity or coelenteron comparable to the gut of higher animals is present.
7. Mouth is present; but anus is absent
8. Digestion is both extracellular as well as intracellular
9. Respiratory, excretory and circulatory system are absent
10. Nervous system is diffuse-type, composed of a loose network of nerve cells
11. Reproduction is both by asexual and sexual methods
12. Development is indirect as there are one or two forms of larva
13. Life history of some forms includes alternation of generations or

metagenesis. i.e. the asexual sessile Polypoid stage alternates with sexual free swimming Medusoid stage. In plants, the asexual satge is diploid and sexual stage is haploid, But in coelenterates both poly and medusa are diploid so this type of alternation of generation is called Metagenesis.

Body wall of a Coelenterate

Source: http://www.thinkquest.org

Cnidoblast           Cnidoblast discharged

Source: http://www.thinkquest.org

Classification:

Class 1. Hydrozoa.

1. They are both marine and fresh water. Gastro-vascular cavity without stomodaeum, septa or nematocysts bearing gastric filament
2. Skeleton is horny perisarc in some forms, while coenosarc secretes a skeleton of calcium carbonate forming massive stony structure or coral reefs in other forms.
3. They are notable to exhibit polymorphism. Medusa is provided with true muscular velum.
4. Many hydrozoa exhibit alternation of generation
5. Gonads ectodermal in origin and discharged externally.
6. Cleavage is holoblastic, ciliated planula larva.

Examples : Hydra, Tubularia, Bougainvillea, Obelia, Sertularia, Plumularia Companularia, Millepora, Physalia, Porpita, Velella, Aurelia, Cynaea, Rhizostoma etc.

Physalia is also known as Portuguese man of war. Aurelia is also known as Jellyfish.

Anatomy of Hydra showing body wall

Source: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBook%20Diversity_7.html

Life cycle of Obelia

Source: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBook%20Diversity_7.html

Obelia Medusa

Source: http://www.thinkquest.org

Class 2. Scyphozoa

1. Scyphhozoa cup shaped animals.
2. They are exclusively marine.
3. Medusae are large, bell or umbrella-shaped and without true velum (acraspedote). They are free swimming or sessile.
4. Marginal sense organs are tentaculocysts
5. Polypoid generation is either absent or represented by small polyp- scyphistoma which gives rise to medusae by strobilization or transverse fission.
6. Gastrovascular system is without stomodaeum, with gastric filaments and may or may not be divided by septa.
7. Mesogloea is usually cellular i.e. it contains some cells
8. Gonads are endodermal. Sex cells are discharged into the stomach. eg. Aurelia

Class 3. Anthozoa

1. They are also known as flower animals, are solitary or colonial and

exclusively marine.

2. They are exclusively polypoid. Medusoid stage is absent.
3. The oral end of the body bears hollow tentacles surrounding the mouth in the centre.
4. The stomodaeum is often provided with one or more ciliated grooves- the siphonoglyphs.
5. Gastrovascular cavity is divided into compartments by complete or incomplete septa or mesenteries.

6. Mesenteries bear nematocysts at their free edges
7. Mesogloea contains fibrous connective tissue and amoeboid cells.

Examples : Tubipora, Alcyonium, Heliopora, Gorgonia, Corallium, Metridium, Adamsia, Astraea, Fungia, Zoanthus.

Tubipora is commonly known as organ pipe

coral.

Adamsia is commonly known as sea anemone.

L.S. Sea Anemone( Metridium) showing its structure

Source: http://www.thinkquest.org

Phylum Ctenophora

Ctenophora is a small phylum containing only about 80 species. They are exclusively marine animals commonly called comb jellies or sea walnuts. They resemble Coelenterata as well as platyhelminthes.

Earlier, this phylum was placed under Coelenterata but later HATSCHEK (1889) placed it under a separate phylum calledCtenophora.

General Characters:

1. They are solitary, pelagic and transparent animals having tissue- grade of organization.
2. They have biradial symmetry.
3. Theyare acoelomate, unsegmented,diploblastic animals.
4. The mesogloea contains cells.
5. Nematocysts are absent.
6. Special adhesive cells called colloblasts are present in all ctenophores.
7. The gastrovascular system is well developed.
8. Skeletal system is absent.
9. Excretion and respiration by diffusion through general body surface
10. The nervous system is in the form of nerve net.(17) An aboral sense organ- statocys presentt.
11. Cilia areused for locomation. The cillia are arranged in the form of bands called comb plates.

12. They are hermaphrodites, development is indirect.It includes a

cydippid larva.

Example : Beroe, Cestrum Pleurobachia,Coeloplana, Ctenoplana, Velamen, hemiphora

Practice Test Paper

1. The most distinctive character of sponge is

(a) Presence of choanocytes (b) Unicellular (c) Marine (d) Asexual reproduction

2. Canal system is only found in the

(a) Coelenterata (b) Porifera (c) Platyhelminthes (d) Nemathelminthe

3. Which sponge is given as a gift in Japan

(a) Hyalonema (b) Euplectella (c) Tethya (d) Leucosolenia

4. Which one is not typical to all porifers

(a) Perforated body (b) Choanocytes (c) System of pores and canal (d) Presence of spongin fibres

5. Corals belong to the the phylum

(a) Protozoa (b) Porifera (c) Cnideria (d) Mollusca

6. Phylum coelenterata has remained at

(a) Cellular level of organisation (b) Organ level of organisation (c) Tissue level of organisation (d) Organ system level of organisation

7. Main cavity in the body of Hydra is called

(a) Gastrovascular cavity (b) Schizocoel (c) Haemocoel (d) Pseudocoelom

8. The larva of hydra is

(a) Planula (b) Rhabditoid (c) Trochophore (d) None of these

9. Mesogloea is present in the Phylum

(a) Porifera (b) Coelenterata (c) Annelida (d) Arthropoda

10. Hydra is

(a) Triploblastic, radial symmetry & acoelomate (b) Triploblastic, radial symmetry & coelomate (c) Diploblastic, radial symmetry & acoelomate

(d) Diploblastic, radial symmetry & coelomate

11. The level of body organization found in phylum porifera is ……… 12.The comb plates found in the phylum Ctenophora are used for……..

13. The body is perforated by numerous minute pores called…..
14. The ostia open into a large central cavity called 15.Name the larva found in coelenterates 16.Portuguese man of War is the name given to …….

17. What is metagenesis

18. The spongocoel opens to the outside by a large opening called…...
19. What is canal system
20. Briefly explain about skeleton in Porifera

Answers and Solutions

1. a
2. b
3. b
4. d
5. c

6. c
7. a
8. a
9. b
10. c
11. Cellular level of body organization
12. Locomotion
13. Ostia
14. Spongocoel
15. Planula
16. Physalia
17. Life history of some Coelenterates includes alternation of generation i.e. the asexual sessile Polypoid stage alternates with sexual free swimming Medusoid stage. In plants, the asexual satge is diploid and sexual stage is haploid, But in coelenterates both poly and medusa are diploid so this type of alternation of generation is called Metagenesis.
18. Osculum
19. The characteristic feature of the phylum porifera is the presence of a an inter-communicating system of cavities known as canal system. The canal system is vital for performing life activities of the sponge like respiration, circulation, excretion etc.