Question

annelids and echinoderms are triploblastic but we know that notochord is formed from mesoderm. so why does they do not possess notochord?

Answer 1

Dear Student,

Notochord is the feature of chordates and is absent in the less developed forms.

The organisms having dorsal supportive notochord and nerve chord is known as chordates. All animals of phylum Chordata like mammals, fishes, birds, reptiles and amphibians are chordates.

The organisms that do not have notochord, nerve chord or gill slits are non chordates. Phylum Protozoa (amoeba), Phylum Porifera (sponges), Phylum Coelenterata (jellyfish), Phylum Platyhelminthes (planaria), Phylum Nematoda (Ascaris), Phylum Annelida (earthworm), Phylum Arthropoda (insects), Phylum Mollusca (snails), Phylum Echinodermata (starfish) and Phylum Hemichordata (Balanoglossus) belong to the group of non chordates.

Regards,