Question

1. Since sponges have a sessile lifestyle, how are they able to protect themselves from predators? What type of spicules do the sponges you use for cleaning posses?

2. IN cnidarians that possess both polyp and medusa forms, why is it advantageous for the reproductive stage to be the medusa form?

3. Explain how the lifestyle of the box jellyfish differs from that of the true jellyfish.

Answer 1

Answer 1. Sponges are aquatic invertebrates belonging to phylum Porifera. The word porifera means 'pore bearing.' Thus, sponges have porous body .

• Sponges are sedentary i.e., they can't move and remain attached to substratum.
• Sponges have internal skeleton called Endoskeleton which provides them support and protection.
• Endoskeleton consists of sharp rod shaped structures referred to as Spicules. Spicules are made of silica, calcium carbonate and spongin, a tough protein.

Protection methods in sponges-

• Spicules besides providing support, also provide protection to sponges. They make it difficult for predators to eat and swallow sponges with spicules.
• Sponges also protect themselves by producing harmful chemicals for predators. For example, The Micronesian sponge Oceanapia sp. is an example as the sponge allocates
  the highest concentrations of the pyridoacridine alkaloids
  kuanoniamine C and D in tissue parts that are most apparent
  to predators.

Sponge used for cleaning-

• Commonly used sponge for cleaning is Euspongia which is also called 'common bath sponge.' Euspongia is a marine sponge of commercial importance and found in Mediterranean sea, West Indies and along American coasts.​​​​​​​
• Euspongia skeleton is made of spongin fibres which form a network, the thickest fibres run radially and each ends in a conulus.The silicious spicules are absent in Euspongia. The cleaned and dried spongin skeleton of Euspongia is used as commercial bath sponge.