Question

Invertebrates: Mollusc, Annelid, Echinoderm

For each invertebrate, answer the following:

a. Identify the body symmetry and body cavity.

b. Briefly describe its circulatory system.

c. What are two specialized characteristics and features?

Answer 1

	Mollusca	Annelid	Echinoderm
Body Symmetry	Bilateral symmetry. Few species do show torsion and hence loose symmetry.	Bilateral Symmetry	Bilateral symmetry in Larva but radial in adult.
Body Cavity	Haemocoel	True Coelomate	True coelomate
Circulatory System	Open circulatory system where blood flows through the empty blood spaces and not in the blood vessels. Caity is called haemocoel as it is filled with blood.Single heart pumps blood to aorta and passes it to visceral mass through blood vessels.	Annelids have closed circulatory system in which the blood flows in network of blood vessels. There are five hearts to pump blood towards dorsal blood vessels. Blood is collected through various vessels like supraoesophageal etc.	Water canal system present for circulation. All substances are transported with the water only. It enters through the madreporite and passes through ambulacral gooves in the arms that further stretches to the tube feet.
Two special features	Body divided into Head , visceral mass and ventral foot. Has blue blood due to pigment haemocyanin	Show metameric segmentation i.e body divided externally as well as internally into segments. Presence of clitellum in most species for ootheca formation.	Presence of water ambulacral system for circulatory system. Bilateral symmetry in Larva but radial in adult. Presence of spiny skin