General Characters of All Phylum of The Invertebrates.

Table of Contents

Invertebrates are a group of animals that lack a backbone or vertebral column. There are over 30 phyla of invertebrates, but some of the most common and important phyla include:

Protozoa

They are microscopic.
They are acellular or unicellular animalcules.
Simplest and most primitive of all animals.
The body is naked or bounded by a pellicle.
Reproduction is asexual by binary fission.
Example: Amoeba proteus, Trypanosoma gambiense, Leishmania donovani, Euglena viridis, Eimeria tenella, Paramecium caudatum, Elphidium crispum, etc.

Porifera

The members of this phylum are commonly known as ‘Sponge’.
They are found all over the world.
They are exclusively marine. Only a few live in freshwater.
They are colonial.
They are multicellular animals.
Their body wall contains numerous pores.
Food and oxygen enter the body through the pores of the body wall.
Their body has no compact tissue, organ, or organ system.
Example: Spongilla etc.

Cnidaria

This phylum was previously known as Coelenterata.
They are present almost all over the world.
They are mostly marine. But many species live in freshwater too.
They are diverse in shape, size, and color.
Some of them are solitary and some are colonial.
The body consists of two embryonic layers: epidermis or ectoderm and gastrodermis or endoderm.
Between the two layers; a gelly-like layer is present called Mesoglea which is not a true layer.
The body cavity is known as the coelenteron.
The coelenteron helps in digestion and circulation.
Epidermis bears cnidoblast which is a special type of cell.
Example: Obelia, Hydra, etc.

Platyhelminthes

They are mostly parasitic.
Some of them are ecto-parasite and some of them are endo-parasite.
Some free-living species live in fresh and saline water. And some of them also live in wet and damp soil.
Their body is flat.
They are bisexual.
The body is covered with a thick cuticle.
The body contains a sucker and hooks.
The flame cell is the excretory organ.
The digestive system is incomplete.
Example: Taenia solium, Liver fluke, Ascaris lumbricoides etc.

Nematoda

This phylum is also called the Nemathelminthes.
Their body is tubular and cylindrical.
The body is covered with thick skin.
Their digestive system is complete as the digestive system starts from the mouth and ends at the anus.
Respiratory and circulatory systems are lacking.
They are unisexual.
The true coelom is absent.
Example: Roundworm.

Annelida

They are mostly found in the temperate and tropical regions of the world.
Their body is tubular.
The body is segmented.
Each segment bears setae that help the annelids in locomotion.
Nephridia is their excretory organ.
Example: Hirudinaria granulosa (Leech), Earthworm, etc.

Arthropoda

It is the largest phylum of the animal kingdom because it contains the largest number of species.
They can live everywhere in the world.
Some of them are parasitic and some of them are free-living.
Many species of this phylum contain wings that help them fly.
Their body is segmented.
Their body bears joint appendages.
A pair of compound eyes and antennae are present on the head.
The body is covered with a hard chitinous exoskeleton.
The body cavity is filled with blood. Their blood is known as haemocoel.
Example: Prawn, Cockroach, Hermit crab, etc.

Mollusca

They live in almost all environments of the world.
They are soft-bodied.
Their body is covered with a hard shell.
They use their muscular foot for locomotion.
They respire with their lungs or gills.
Example: Pila globosa (Snail), Mussel, etc.

Echinodermata

They are exclusively marine. No freshwater species are present.
They live in all seas and oceans of the world.
Their dermal skin bears spines.
The body is divided into five equal parts.
A unique water vascular system is present.
They move with the help of their water vascular system.
No distinct head is present.
No dorsal and ventral surface is present. They have oral and aboral surfaces.
Example: Asterias (Sea Star), Sea cucumber, etc.