Question

Which one exhibits concentric tube-within-tube plan ?
A.Arthropoda
B.Oligochaeta/Earthworm
C.Mollusca
D.Echinodermata

Answer 1

Hint:Annelids are aquatic ( marine or freshwater ) or terrestrial , free living and sometimes parasitic.Characteristic features of annelida are segmentation like rings . Annelids exhibit organ system level of body organisation and bilateral symmetry .

Complete step by step answer:
- Oligochaeta/Earthworm are annelids which exhibit tubes within a tube body plan with multicellularity and bilateral symmetry .
-It refers to the development of a fluid filled cavity between the outer body wall and the digestive tube.
-This plan calls for the two openings one for food to enter the mouth or body and one for wastes to leave the body .
-As there are two openings so the digestive system is complete .

So option ( B ) is correct .

Some additional information:
-The body surface is distinctly marked out into segments or metameres and hence the phylum annelida.
-They are triploblastic animals And coelom is present .
-They possess longitudinal and circular muscles which help in locomotion.
-Aquatic annelids possess lateral appendages parapodia which helps in swimming.
-A closed circulatory system is present in annelida .
-Nephridia is the excretory organ which also helps in Osmoregulation.
-Neural system consists of paired ganglia connected by lateral nerves to the double ventral nerve cord.
-Nereis is an aquatic form . Earthworm and leeches are terrestrial forms .
-Animals are both unisexual and bisexual . Sexual reproduction is present.
Examples of annelida are Nereis , Earthworm and blood sucking leech.

Note:
Phylum annelida is the first phylum which presents a circulatory system .
Segmentation is only present in annelida , arthropoda and chordata.