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:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.