write the salient features about the annelida phylum
Answers
Salient features of Annelids:-
They are mostly aquatic and few are terrestrial forms.
Most of them are free living and some are ectoparasites.
The body is elongated, cylindrical or flattened. ...
True metameric segmentation is present. ...
Body is triploblastic and bilaterally symmetrical.
They have tube within a tube body plan.
Explanation:
Salient features of Annelids
They are mostly aquatic and few are terrestrial forms.
Most of them are free living and some are ectoparasites.
The body is elongated, cylindrical or flattened. It is divided into segments by ring-like grooves called annuli.
True metameric segmentation is present. The number of segments is fixed with no gain or loss of segments in their life.
Body is triploblastic and bilaterally symmetrical.
They have tube within a tube body plan.
The body cavity is a true coelom (schizocoelomate or eucoelomate), as it is lined by mesodermal epithelium.
Alimentary canal is complete and segmentally arranged. It is divided by vertical septa into compartments.
Circulatory system is of closed type, and appears for the first time in animal kingdom.
Blood is red in color due to haemoglobin (Hb) which dissolves in plasma.
The heart is neurogenic.
Respiratory organs are absent, so gaseous exchange occurs by general body surface.
Excretory system consists of coiled tubes, the nephridia which are ectodermal in origin.
They may be ammonotelic or ureotelic.
They are hermaphrodite and sexual reproduction occurs with the formation of gametes.
Fertilization may be internal or external.
Development may be direct (with no larval stage) or indirect (with a larval stage).
Classification:
Phylum Annelida is divided into following four classes.
Class: Polychaeta
They are marine forms.
Body bears a distinct head that consists of two pairs of eyes and tentacles.
Body is segmented with unjointed locomotory appendages called parapodia.
Parapodia bears setae which are long and numerous. Setae help in fixation.
Clitellum is absent.
Sexes are separate and fertilization is internal in water.
Development includes a larval stage called Trochophore
e.g. Nereis (the sandworm), Aphrodite (the sea mouse), Chaetopterus (the paddle worm) etc.
Class: Oligochaeta