Phylum Annelida

If you have an avid interest in gardening, you must have surely come

across earthworms. Did you know one can find one million

earthworms in just one acre of land? These earthworms belong to the

Phylum Annelida. They create healthy soil and plants grow extremely

well in these types of soils.

Phylum Annelida

Having over 17,000 species, Phylum Annelida is a large phylum.

Annelids are also known as ringworms or segmented worms. They

exist in various environments including marine waters, fresh waters

and also in moist terrestrial areas. The size of the annelids can range

from a few millimetres to an amazing three metres in length. The

Australian earthworm measures around 3 metres. Furthermore some

species from this phylum exhibit some unique shapes and brilliant

colours.

Annelids exhibit bilateral symmetry and are invertebrate organisms.

They are coelomate and triploblastic. The body is segmented which is

the most distinguishing feature of annelids.

Learn more Phylum Coelenterata here.

Characteristics of Phylum Annelida

● They have a long and segmented body.

● Annelids are bilaterally symmetrical.

● They are triploblastic.

● Also, they exhibit organ system grade of organisation, showing

organ differentiation.

● The body is covered with a thin cuticle.

● They are coelomate. A body cavity or coelom is present.

● Annelids live in moist environments, moist soil, freshwater and

marine water.

● They have parapodia and chitinous setae, used for locomotion.

● Their body appears red due to the presence of haemoglobin.

● Excretory and nervous systems are present.

● The digestive system is complete and developed.

● Respiration happens through the general body surface.

● These invertebrates have a true closed circulatory system.

● Sexes may be separate or united, wherein they are called

hermaphrodites.

● Fertilization can be internal or external.

Learn more about Phylum Aschelminthes here.

Videos om Animal Kingdom

Examples of Annelids

● Earthworm

● Leeches

● Lugworms

● Polychaetes

(Source: Wikipedia)

Learn more about Phylum Echinodermata here.

Solved Question for You

Q: How are earthworms helpful to farmers?

Ans: To a farmer, earthworms are the most helpful and friendly

creatures. They are burrowing creatures and play an important role in

improving the soil texture and enriching the soil. Earthworms plough

the soil by eating their way through the soil. They digest the soil along

with the dead leaves and any other organic material. By doing this,

they constantly loosen the upper layer of soil. This results in good

water percolation and air penetration. The droppings of the earthworm

also enrich the soil, making it good for plants to grow.

Q: Where do annelids live?

Ans: Annelids can live in marine or freshwater habitats or even in

moist terrestrial environments.

Q: Where can you find leeches?

Ans: Freshwater leeches can be found in freshwaters. Marine leeches

can be found in oceans. Leeches crawl well and are good swimmers.

Q: On a rainy day, you notice a long, brown, bilaterally symmetric

organism in your garden. This organism has a body that is divided into

segments, from the head to the tail. Under which phylum will you

classify the organism, looking at its features? What do you think is the

organism?

Ans: Since the organism is long, brown and bilaterally symmetrical,

with a segmented body, it can be classified under phylum Annelida.

The distinguishing characteristic is the segmented body. And Annelids

also live in moist terrestrial areas. This annelid is an earthworm,

which can be found in moist soils.

Phylum Arthropoda

On a pleasant evening, you decide to go to a park. However, you end

up having painful itchy eruptions on the skin. Clearly, you were bitten

by an insect. After all, insects are everywhere. They belong to a group

of animals called the Phylum Arthropoda, which form the largest

percentage of the world’s organisms. They make up about 80 percent

of the known species of animals! It is quite hard to escape them.

Phylum Arthropoda

Arthropods are joint-legged animals and you must have come across a

few of these animals. Some prominent ones include insects, spiders,

ants, bees, crabs, shrimps, millipedes, centipedes etc. Scientifically

speaking, they all come under the Animal Kingdom under phylum

Arthropoda.

The success of the arthropods can mainly be attributed to the presence

of exoskeleton, which makes them versatile, is protective in nature

and also allows flexibility and mobility. You can see arthropods living

on land and in water. They are also a source of food for many animals

and human beings too!

(Source: Pinterest)

Learn more about Phylum Coelenterata here.

Characteristic features of Phylum Arthropoda

● The body structure shows bilateral symmetry.

● They are triploblastic.

● They can be found in all types of habitats – land, water and

soil.

● They have jointed limbs.

● The body is segmented into three regions – Head, Thorax and

Abdomen.

● The body cavity is filled with blood and is called the

haemocoel. The blood is white in colour.

● The exoskeleton is hardened and is made of chitin.

● They have a well-developed central nervous system.

● The head is well developed and bears the sensory organs and

brain.

● They have compound eyes and mosaic vision.

● The digestive tract is complete with the mouth and anus at

opposite ends of the body.

● They have an open circulatory system with dorsal heart and

arteries.

● Respiration is through the general body surface or by gills in

aquatic forms and through trachea or book lungs in terrestrial

forms.

● Sexes are separate and sexual dimorphism is exhibited.

(Source: Pinterest)

Learn more about Phylum Aschelminthes here.

Examples

● Limulus polyphemus (King Crab)

● Scorpions

● Spiders

● Ants

● Prawns

● Crabs

● Cockroach

● Butterfly

● Mosquito

Learn more about Phylum Echinodermata here.

Solved Questions for You

Q: Write a few lines on the exoskeleton in Arthropods.

Ans: The exoskeleton in Arthropods is hardened and is made of chitin.

It can be further stiffened in a few species by calcium carbonate. In

arthropods, the exoskeleton is non-expandable and hence as the

organism grows, it has to shed its exoskeleton so that it can be

replaced by a new exoskeleton. This process is called moulting.

Q: Name a few arthropod insects that are carriers of diseases.

Ans.

Insects Disease

Housefly Typhoid, cholera, Diarrhoea

Sandfly Kala-azar

Mosquito Filariasis, Dengue Fever, Malaria

Rat Flea Bubonic plague

Tsetse fly African Sleeping sickness

Q: Book lung is a characteristic of which Phylum?

Ans: Phylum Arthropoda

Q: What is the process of conversion of small cockroach into an adult

cockroach?

Ans: Metamorphosis

Q: The coelomic cavity in Phylum Arthropoda is filled with?

Ans: Haemocoel

Q: Which is the largest Phylum and state a few distinguishing

features?

Ans: The largest phylum is Phylum Arthropoda. The distinguishing

features are:

● Presence of jointed legs

● Body is divided into head, thorax and abdomen

● Body is bilaterally symmetrical and triploblastic.

Phylum Aschelminthes

Did you know there are some parasites that live in the intestines of

human beings? Yes, sometimes humans and animals suffer from such

infestation of worms, called ringworms. These ringworms are a

prominent species of Phylum Aschelminthes, also known as

pseudocoelomates. Let us learn more about them.

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Phylum Aschelminthes

Aschelminths can be free-living or parasitic. The free-living

organisms are extremely abundant in soils and sediments and they

feed on bacteria. While some others are plant parasites and can cause

disease in crops that are economically important. The others are

parasites that can be found in animals and human beings. Some of the

parasitic worms include hookworms, pinworms, Guinea worms, and

intestinal roundworms.

Ascaris lumbricoides is the Giant Intestinal Roundworm that is an

endoparasite living in the human intestine. They are very common in

children. These worms cause a disease called ascariasis. Many adult

roundworms live inside the intestine, causing obstruction to the

intestinal passage. This causes abdominal discomfort, colic-like pain,

impaired digestion, diarrhea, and vomiting. Generally, deworming

medicines are given to get rid of these roundworms from the body.

Characteristic features of Phylum Aschelminthes

● The body of these organisms is unsegmented and triploblastic.

● They have a pseudocoeloem, where the body cavity is not lined

by the mesodermal layer.

● They are bilaterally symmetric.

● The body is cylindrical or thread like with elongated, slender

worm-like appearance and tapering at both ends.

● Body wall has epidermis, muscle layer and is covered by

cuticle.

● The body size of these organisms varies from microscopic to

several centimetres in length.

● These organisms are mostly parasitic, with a few free-living

● They exhibit an organ system level of organization.

● Externally, there is little differentiation between the anterior

and posterior regions. But internal cephalization is present.

● There is no distinct head. However, the mouth is present in the

anterior

● The digestive system is complete, with a mouth and anus.

● The mouth in these organisms is terminal and is surrounded by

lips bearing sense organ.

● Amphids and papillae are the main sensory organs.

● The nervous system consists of a nerve-ring that encircles the

oesophagus. From it, nerves extend out anteriorly and

posteriorly.

● Respiratory organs are absent. Respiration occurs through the

general body surface. It is aerobic in free-living forms and

anaerobic in parasitic organisms.

● The excretory system has canals and gland-like

● Sexes are separate and are unisexual, exhibiting sexual

dimorphism.

● Fertilization is internal.

● They are ovo-viviparous, oviparous or viviparous.

● The life cycle of these organisms is complicated. It may be

with or without an intermediate host.

Examples

● Ascaris lumbricoides – Round Worm

● Enterobius vermicularis – Pinworm

● Ancylostoma duodenale – Hookworm

● Wuchereria bancrofti – Filarial worm

● Loa loa – Eye Worm

Solved Questions for You

Q: How is the body cavity of an Aschelminth different?

Ans: The body cavity of phylum Aschelminthes is called

pseudocoelom. It is filled with pseudocoelomic fluid. The body cavity

is not lined by the mesodermal layer.

Q: What causes Ascariasis in humans?

Ans: Ascariasis in humans is caused by roundworms and is

scientifically known as Ascaris lumbricoides. It is an endoparasite,

living in the intestines of humans, causing intestinal obstruction,

abdominal pain, and diarrhoea.

Q: What is the scientific name of pinworm?

Ans: Enterobius vermicularis

Phylum Chordata

Do you know which is the fastest animals on earth? No, it is not the

Chetah. In fact, it is the Peregrine Falcon. The biggest animal is the

blue whale. The three-toed sloths are said to be the slowest. All these

animals fall under the same phylum, the Phylum Chordata. Let us

learn more about Chordates. 

Phylum Chordata

This phylum is probably the most notable phylum, as all human

beings and other animals and birds that are known to you, fall under

this phylum. The most distinguishing character that all animals

belonging to this phylum have is the presence of notochord.

Chordates show four features, at different stages in their life. They are:

● Notochord– It is a longitudinal rod that is made of cartilage and

runs between the nerve cord and the digestive tract. Its main

function is to support the nerve cord. In Vertebrate animals, the

vertebral column replaces the notochord.

● Dorsal Nerve Cord – This is a bundle of nerve fibres which

connects the brain to the muscles and other organs.

● Post-anal tail – This is an extension of the body beyond the

anus. In some chordates, the tail has skeletal muscles, which

help in locomotion.

● Pharyngeal slits–They are the openings which connect the

mouth and the throat. These openings allow the entry of water

through the mouth, without entering the digestive system.

(Source – Lumen Learning)

It will surprise you but this phylum is a very diverse phylum, with

about 43,000 species. Most of these organisms can be found in the

subphylum Vertebrata. In the animal kingdom, this is considered as

the third largest phylum.

Phylum Chordata is again divided into three subphyla. They are:

● Urochordata

● Cephalaochordata

● Vertebrata

The first two phyla have very few species in between them. The major

subphylum is Vertebrata, where you come across a variety of fishes,

reptiles, birds and animals. Vertebrates have a distinguishing

backbone that is made up of bone or cartilage. The brain is enclosed in

a skull. There is a proper circulatory system, nervous system and a

skeletal system that gives proper shape and support.

Learn more about Phylum Hemichordata here.

Subphylum Vertebrata is further divided into five classes. They are:

● Pisces

● Amphibia

● Reptilia

● Aves

● Mammalia

Browse more Topics under Animal Kingdom

● Phylum Annelida

● Phylum Arthropoda

● Phylum Aschelminthes

● Phylum Coelenterata

● Phylum Echinodermata

● Phylum Hemichordata

● Phylum Mollusca

● Phylum Platyhelminthes

● Phylum Porifera

Explore more about the Animal Kingdom

Animal Kingdom

● Phylum Hemichordata

● Phylum Platyhelminthes

● Phylum Coelenterata

● Phylum Mollusca

● Phylum Porifera

● Phylum Echinodermata

● Phylum Annelida

● Phylum Aschelminthes

● Phylum Arthropoda

Characteristic Features of Phylum Chordata

● They are bilaterally symmetrical and triploblastic.

● Chordates are coelomate and show an organ system level of

organisation.

● They have the characteristic notochord, dorsal nerve cord,

pharyngeal slits.

● Also, they have a post-anal

● In this phylum, the nervous system is dorsal, hollow and single.

● The heart is ventral, with a closed circulatory system.

● The habitat of these animals is widespread. So we can find

them in the marine environment, fresh waters as well as

terrestrial environments.

Learn more about Phylum Arthropoda here.

Examples

● Ascidia, Salpa, Doliolum – Urochordata

● Branchiostoma – Cephalochordata

● Lizards, fish, frogs, turtles, humans, parrots, elephants, gorillas

– Vertebrata

(Source: Wikipedia)

Learn more about Phylum Annelida here.

Solved Examples For You

Q: Can chordates be found in a specific kind of habitat?

Ans: We find Chordates in diverse habitats, including marine,

freshwater and terrestrial habitats.

Q: Which subphylum does Branchiostoma belong to?

Ans: Cephalochordata

Q: “All vertebrates are chordates but not all chordates are

vertebrates.” Justify

Ans: Vertebrata is a subphylum of Chordata. The vertebrates have a

vertebral column, something like the notochord. Vertebrates show all

the characteristic features of the phylum Chordata, such as the

notochord, dorsal nerve cord, pharyngeal slits and post-anal tail.

But the phylum Chordata also has other two subphyla, called the

Urochordata and Cephalaochordata. These are invertebrate animals

but show some distinguishing attributes of Chordates, like the

presence of notochord. And hence, we can say that all vertebrates are

chordates, but not all chordates are vertebrates.

Phylum Coelenterata

As you read this, you probably must be wondering if this is another

group of animals that you know nothing much about. But, if you have

seen the movie, Finding Nemo, you most certainly have seen a sea

anemone on screen! A sea anemone is a member of Phylum

Coelenterata. It has a symbiotic relationship with the clownfish. Some

of the other animals that belong to this phylum include coral animals,

true jellies, sea pens, comb jellies, hydra, etc. Let us learn about these

fascinating creatures.

Phylum Coelenterata

These are typically invertebrate animals, which show a very simple

level tissue organisation. They are aquatic animals and are mostly

found in marine environments, attached to the rocks at the bottom of

the ocean. A few species are also found in freshwater habitats.

Coelenterates can be found solitarily or in colonies. You can find them

sedentary or free swimming.

Coelenterates can be called as the simplest animal group that has true

tissues and have the characteristic coelenteron or the gastrovascular

cavity.

(Source: Wikipedia)

Characteristic Features of Phylum Coelenterata

● They are multicellular organisms, exhibiting tissue grade of the

organisation.

● They are diploblastic, with two layers of cells, an outer layer

called the ectoderm and the inner layer called the endoderm.

There is a non-cellular layer that is the mesoglea in between the

ectoderm and the endoderm.

● They show radial symmetry.

● They have a single opening in the body through which food is

taken in and also waste is expelled out.

● The opening in the body is surrounded by tentacles.

● Digestion takes place in the body cavity which is the

coelenteron.

● They can live in marine or freshwater habitats.

● They can be solitary or live in colonies. Each individual is a

zooid.

● These organisms show two morphological forms – Polyps and

Medusa.

● Polyps contain exoskeleton and endoskeleton.

● The skeletons are composed of calcium carbonate.

● Most if the coelenterates are carnivorous in nature with a few

exceptions such as the s corals. They get their food from other

animals that live symbiotically within them.

● Digestion is both intracellular and extracellular.

● Tentacles have special structures known as the nematocysts

which help in capturing and paralyzing prey. Coelenterates

simply wave their tentacles and when a prey comes in contact,

the nematocysts inject the toxin that paralyses or kills the prey.

Nematocysts are the most distinguishing feature of this

phylum.

● Coelenterates do not have sensory organs.

● Respiration and excretion occur through simple diffusion.

● The circulatory system is absent.

● Asexual reproduction is seen in polyps, through budding and

sexual reproduction is seen in medusa form, through gametic

Classification of Phylum Coelenterata

This phylum is further divides into three classes:

● Hydrozoa

● Scyphozoa

● Anthozoa

Examples

(Source: Wikipedia)

● Hydra

● Aurelia ( Jelly Fish)

● Physalia

● Meandrina

● Adamsia (Sea Anemone)

Learn more about Phylum Echinodermata here in detail.

Solved Questions For You

Q: In which phylum, do organisms have nematocysts. Explain their

significance.

Ans: Nematocysts are found in the organisms belonging to Phylum

Coelenterata. They are, microscopic stinging structures that are

present in the tentacles. Their primary use is to capture and paralyze

prey such as fishes and marine animals.

Q: Are coelenterates diploblastic or triploblastic?

Ans: Coelenterates have two layers of cells, ectoderm and endoderm.

Hence they are diploblastic.

Phylum Echinodermata

Echinoderms are animals that you must be knowing. If you know a

starfish, then you are well aware of what an echinoderm is.

Echinoderms are animals that are invertebrates. The name actually

means spiny skin! All the animals in this phylum exhibit spiny skin

and hence are grouped together. Let us find out more about them.

Phylum Echinodermata

(Source: Wikipedia)

Echinodermata may look morphologically (structure and form)

dissimilar at a glance, but they all share the same characteristic

features. These animals have some really unique shapes and have

beautiful colours. They are important ecologically and geologically, as

they provide valuable clues about the geological environment.

Did you know that they can regenerate limbs? When a starfish, with

five arms, losses one arm, it has the capacity to regenerate the lost

arm. This regeneration can take any time between several months to

years, as the wound has to heal and then only are the new cells

regenerated.

Echinoderms are marine animals and can be found in the depths of the

ocean as well as in the intertidal zone. An interesting feature of this

phylum is that all animals belonging to Echinodermata are marine.

There are no freshwater or terrestrial organisms in this phylum. Water

vascular system present in the echinoderms is a unique circulatory

system. This accounts for the gaseous exchange, circulation of

nutrients, waste elimination as well as locomotion. This system has a

central ring canal and radial canals that extend along each arm.

Through these structures, water circulates. The madreporite is a

structure present on top of the body. This is responsible for regulation

of the water in the water vascular system.

Characteristic Features of Phylum Echinodermata

● These are exclusively marine animals.

● The larval forms show bilateral symmetry and adult forms

show radial symmetry.

● They are triploblastic.

● It exhibits organ system grade of organisation.

● They have a true coelom.

● The body is uniquely shaped. It can star like, elongated or

spherical.

● The body is unsegmented without a head.

● The body surface is covered with calcareous spicules.

● Body cavity has the distinguishing water vascular system.

● Tube feet help in locomotion.

● The brain is absent but a nervous system is present with a nerve

ring and radial nerve cords.

● Respiration occurs through tube feet and gills.

● Sense organs are poorly developed and include tactile organs,

chemoreceptors, terminal tentacles etc.

● Sexes are separate.

● Fertilisation is external.

● Lost parts can be regenerated.

Classification of Phylum Echinodermata

Phylum Echinodermata is classified into the following classes:

● Asteroidea

● Ophiuroidea

● Echinoidea

● Holothuroidea

● Crinoidea

Examples

(Source: Wikipedia)

● Asterias (Starfish)

● Echinus (Sea urchin)

● Antedon (Sea lily)

● Cucumaria (Sea cucumber)

● Ophiura (Brittle star)

Learn more about Phylum Aschelminthes here in detail.

Solved Questions For You

1. Water vascular system is a peculiar feature of which phylum?

Ans. Phylum Echinodermata.

2. Give an example of an Echinoderm that is found in freshwater

habitat.

Ans. Echinoderms are exclusively marine animals. There is no

freshwater echinoderm.

3. The organs of locomotion in Echinodermata are called?

Ans. Tube feet.

4. Aristotle’s Lantern is a characteristic feature of which

echinoderm?

Ans. Sea Urchin

Phylum Hemichordata

This is a phylum that contains marine deuterostome animals. They are

sometimes considered as the sister group of phylum Echinodermata.

Phylum Hemichordata is a small phylum with only a 100 known

species, with animals having a worm-like appearance. Some species

may be solitary or some occur in colonies. Let us study them further.

Phylum Hemichordata

(Source: Britannica)

These animals are also called as Acorn Worms. They were initially

grouped under Phylum Chordata. But, research has proven that none

of these organisms does not have a post-anal tail or even the

notochord, which is a distinguishing feature of chordates. Hence, these

animals have been given a separate phylum, called the Hemichordata.

They are typically found in oceans, living on the seafloor. They vary

greatly in size, ranging from a few millimetres to almost one and a

half meters. Balanoglossus gigas, a hemichordate species can be of

1.5 meters in length. These species feed on small organic particles.

They can be either filter feeders or substrate eaters.

Most of the organisms belonging to this phylum have a modified

proboscis, due to which they have got the name Acorn worms. These

animals show a few chordate characteristics but are not completely

chordates. Hence they have been given the name Hemichordata (Half

chordates). Another notable feature of these organisms is the threefold

division of the body, with the preoral lobe, collar, and a trunk. The

collar bears the tentacles in a few species. The trunk has the digestive

and reproductive organs.

Learn more about Phylum Arthropoda here.

Characteristic Features of Phylum Hemichordata

● Hemichordata is bilaterally symmetrical and triploblastic

animal.

● They are exclusively marine animals.

● They can be solitary or in colonies.

● Hemichordata have a true body cavity or coelom.

● The digestive tract is complete with an anus and can be in the

form of a U shaped tube or straight.

● A buccal diverticulum is present in the proboscis.

● Body is divided into three regions – Proboscis, Collar and

Trunk.

● Circulatory system in open type.

● Respiration occurs through gills.

● The proboscis has a glomerulus, which is the excretory organ.

● A primitive nervous system is present.

● Sexes are separate or united.

● Reproduction is mostly sexual reproduction.

● Fertilization is external.

● Development is mostly indirect. But a few species exhibit

direct development.

Learn more about Phylum Annelida here.

Classification of Phylum Hemichordata

Phylum Hemichordata is again divided into two classes:

● Enteropneusta: This class includes acorn worms. They have a

vermiform body and are found on sandy beaches near seas in

warm climates.

● Pterobranchia: They have a tube-dwelling and live in deep sea

waters. They are bottom dwellers who attache to other

organisms for their survival.

Examples

(Source: Wikipedia)

● Balanoglossus

● Saccoglossus

Learn more about Phylum Porifera here.

Solved Questions For you

Q: Balanoglossus belongs to which phylum?

Ans: It belongs to Phylum Hemichordata.

Q: In hemichordates, the body is divided into three regions. Name

them.

Ans: The three regions of the body are Proboscis, Collar and Trunk.

Phylum Mollusca

Molluscans are very diverse animals and form an important part of the

ecosystem in the world. Some animals that you are familiar with like

snails, octopuses, squids, oysters, clams etc. all belong to Phylum

Mollusca. Did you know that Molluscs with shells can produce pearls?

Some of these are also eaten by humans in different regions of the

world. Let us educate ourselves about this phylum of the Animal

Kingdom.

 

Phylum Mollusca

Many organisms belonging to this phylum have a calciferous shell.

The bodies are generally very soft and are covered by the hard

exoskeleton. They can be found in terrestrial regions as well as in the

depths of the seas. You will be amazed to know that the size of the

molluscans can range from 20 metres to one millimetre, with a few

microscopic animals too. These animals continue to have an important

role in the lives of humans.

They are a source of food as well as jewellery. The hard shells are

used to make beautiful jewellery pieces. In some regions of the world,

these are also raised as pets, even though it sounds bizarre. Pearls that

are obtained from bivalves and gastropods are valuable as these pearls

are lined with nacre. Natural pearls are formed when a small foreign

object gets stuck in between the mantle and shell of the mollusc.

The bivalve molluscs are used as bioindicators of the freshwater and

marine environments. But not all molluscans are good for humans.

Some are pests like the snails and slugs.

Learn more about Phylum Arthropoda here.

Characteristic Features of Phylum Mollusca

● They are bilaterally symmetrical.

● They are triploblastic, which three layers.

● They show organ system grade of organisation.

● The body is soft and unsegmented.

● Body is divisible into three regions – head, a visceral mass, and

ventral foot.

● Body is covered by a mantle and shell.

● They can be found in different habitats, both aquatic and

terrestrial.

● The body cavity is a haemocoel, through which blood

circulates.

● The digestive system is well developed and complex. It has a

radula, which is a rasping structure that has chitinous teeth. It is

used in feeding.

● The nervous system is made up of paired ganglia, connectives,

and nerves.

● The circulatory system is open, with heart and aorta.

● Respiration occurs through gills called ctenidia.

● The ventral muscular foot helps in locomotion.

● They have a pair of kidneys (metanephridia)

● Sexes are separate and reproduction is through sexual

reproduction.

● Fertilisation can be internal or external.

Learn more about Phylum Annelida here.

Classification of Phylum Mollusca

The different classes under phylum Mollusca include:

● Bivalvia

● Gastropoda

● Cephalopoda

● Monoplacophora

● Amphineura

● Scaphopoda

Examples

● Clams

● Mussels

● Octopus

● Pila ( Snail)

● Oyster

● Cuttlefish

● Squid

Learn more about Phylum Porifera here.

Solved Questions For You

Q: Write a few sentences about Octopus.

Ans: An Octopus is sometimes known as the Devilfish. It belongs to

the class Cephalopoda. It is a soft-bodied mollusc with eight arms.

Octopuses can camouflage very well in their surroundings. They have

ink glands that they use to defend themselves or escape from

predators. They show all the characteristic features of Phylum

Mollusca and are triploblastic, bilaterally symmetrical, and found in

various regions of the ocean.

Q: Which is the second largest phylum after Arthropoda?

Ans: Phylum Mollusca.

Q: Mantle, foot and restricted coelom are the characteristic features of

which phylum?

Ans: Phylum Mollusca.

Phylum Platyhelminthes

Did you know, potentially life-endangering parasites can live in the

human body for up to several decades? These parasites, known as

blood flukes, have the ability to regenerate themselves and so can

survive in hostile environments. These worms belong to Phylum

Platyhelminthes. Let us explore this phylum.

Phylum Platyhelminthes

(Source: Wikipedia)

Platyhelminthes very commonly known as flatworms or tapeworms,

these animals are soft-bodied invertebrate animals. There are around

20,000 species of these animals. A few of these live as parasites on

humans and other animals. It is because of this parasitic nature that

they do cause some amount of trouble for the host animal. A few

species belonging to this phylum can be a major cause of certain

diseases. Schistosomiasis, or bilharzia or bilharziasis, is a disease

caused by these parasitic flatworms belonging to the family

Schistosomatidae.

The most distinguishing feature of these invertebrates is their flat

body. As the body does not have any cavity, they are flat. The body is

also not segmented and they do not have specialized systems. Around

eighty percent of the flatworms are parasitic in nature, while a few

free-form flatworms are also present. The free-living species are

scavengers or predators. The parasitic species feed on the tissues of

the host organism in which they live.

The animals in this phylum have a diverse range in size. Some are

microscopic, while a few go up to two feet long. They are also

hermaphrodites, which mean that both the sexes are present in the

same organism.

Learn more about Phylum Chordata here.

Characteristic features of Phylum Platyhelminthes

(Source: Britannica)

● Their body is dorsoventrally flattened.

● They exhibit bilateral symmetry.

● Also, they are triploblastic, with three germ layers.

● They do not have a body cavity and are acoelomate.

● Body is soft and unsegmented.

● They are mostly parasitic with a few free-living

● They exhibit an organ system grade of organization.

● The digestive system is incomplete or absent. There is a single

opening which leads to a well-developed gastro-vascular

cavity. The anus is absent. There is no true stomach structure.

In a few species, the digestive system is completely absent.

● Respiratory and circulatory systems are absent. Respiration

generally occurs through diffusion through the general body

surface.

● The excretory system has protonephridia with the flame

● There is primitive nervous system present.

● These animals are hermaphrodites.

● Sexual reproduction happens through gametic fusion.

● Asexual reproduction also happens in a few species through

regeneration and fission.

● Fertilization is internal.

● The life cycle of these organisms can be complex, especially if

they are parasitic, as this may involve one or more host

animals.

Learn more about Phylum Mollusca here.

Classification of Phylum Platyhelminthes

The different classes under this phylum are:

● Turbellaria

● Trematoda

● Cestoda

Examples

● Taenia (Tapeworm)

● Fasciola (Liver fluke)

● Taenia saginata (Beef tapeworm)

● Echinococcus granulosus – The dog tapeworm

● Planeria (freshwater flatworm)

● Opistorchis

Learn more about Phylum Hemichordata here.

Solved Questions for You

Q: Which is the phylum, where the body is dorsoventrally flat without

a body cavity?

Ans: Phylum Platyhelminthes.

Q: Give an example of a free-living

Ans: Planaria

Q: The digestive system is absent in which class of flatworms?

Ans: Class Cestoda.

Q: Phylum Platyhelminthes shows which grade of organization?

Ans: It is the first phylum to show organ system grade of organization

along with bilateral symmetry.

Phylum Porifera

Have you seen SpongeBob Square Pants? How weird would it sound

if it was called Porifera Bob Square Pants? The creator of this series

was a marine biologist who was fascinated with the ocean and used

many marine animals, including the Sponges in his animated cartoon

series. Read along to find more interesting bits of scientific

information about Porifera.

Phylum Porifera

(Source: Wikipedia)

This group of animals is probably considered as the oldest animal

group. They are also called as Sponges. These are by far the simplest

multicellular animals. Even though they are multicellular, they do not

have any tissues or organs. Sponges live in an aquatic habitat as they

have to have an intimate contact with water. Water plays a major role

in the feeding, exchange of gases and as well as excretion. The body

of the sponges has many holes or pores called ostia. The body

structure of sponges is designed in such a way that water moves

through the body, where it can filter out food and also absorb the

dissolved oxygen, along with eliminating waste material.

Organisms belonging to this phylum do not have specialised digestive,

nervous or circulatory system. Instead, they have a water transport or

canal system, which achieves the functions of digestion, excretion and

also an exchange of gases.

Their bodies do not show any symmetry and their shape is adapted so

as to allow maximum efficiency of water flow through the central

cavity that is present inside. They generally feed on bacteria and other

food particles that are present in the water. Their bodies have a large

central cavity called the spongocoel. Water enters through the ostia

into the spongocoel and goes out through the osculum. Cells called as

Choanocytes or collar cells line up the spongocoel and canals, with

their flagellum protruding out. It is the beating of this flagellum from

all choanocytes that moves the water all through the body of the

sponge.

Learn more about Phylum Coelenterata here.

Characteristic Features of Phylum Porifera

● They are generally marine aquatic organisms, with a few

freshwater species.

● Their bodies are asymmetrical.

● Body shape can be cylindrical, vase-like, rounded or sac-like.

● They are diploblastic animals with two layers, the outer dermal

layer and the inner gastral layer. There is a gelatinous,

non-cellular mesoglea, in between these two layers. This

contains many free amoeboid cells.

● The body has many pores called the ostia and a single large

opening called osculum at the top.

● Spongocoel is the body cavity that is present.

● They have the characteristic canal system for the flow of water

through the body.

● Sense organs are absent.

● There is an endoskeleton present with calcareous spicules

(calcium carbonate) or siliceous spicules (silica) or sponging

fibres (protein).

● Sexes are not separate.

● Asexual reproduction is seen through budding, fragmentation.

Sexual reproduction is seen in certain species, through gametic

fusion.

Learn more about Phylum Aschelminthes here.

Examples

(Source: Wikipedia)

● Sycon (Scypha)

● Spongilla (Freshwater sponge)

● Euspongia (Bath sponge)

Learn more about Phylum Echinodermata here.

Solved Questions For You

Q: Name a freshwater sponge.

Ans: Spongilla

Q: Where are the Choanocytes in Sponges present?

Ans: Cells called Choanocytes or collar cells are present lining the

spongocoel and canals. with their flagella protruding out.

Q: Are Sponges diploblastic or triploblastic?

Ans: Diploblastic.