Name two phyla which have open circulation.
Mollusca and echinodermata
What is polymorphism? Give an example.
The presence of more than two types of individuals in a colony which differ in their structure as well as function is called polymorphism. E.g., honey bees.
What are cnidoblasts?
The stinging cells present on the tentacles of coelenterates like Hydra, which inject hypnotoxin into the prey to hypnotise it.
What are the excretory organs in flatworm?
Protonephridia or flame cells.
What are the skeletal elements in sponges?
Needles called spicules and spongin fibres are the skeletal elements in sponges.
Give the names of two groups of animals that are haemocoelomate.
Molluscs and arthropods
What is haemocoel?
When a well-defined cavity is absent and the spaces present contain colourless blood, i.e., haemolymph, it is called haemocoel.
Name the cavity present in the coelenterates.
Coelenteron