Question

13. How are sponges different from the rest of the animals? Explain. 14. For each of the structures below, define the term AND state the group of animals where you would find the structure. radula: spicule: nematocyst: scolex: complete digestive tract: HOX genes: proglottid: hermaphrodite: mantle: corona: 15. We have discussed several animals/groups of animals that are important from a medical standpoint. List and describe some of these medically-important invertebrates. (this includes animals from at least 3 phyla discussed so far).

Answer 1

Ans 13. Sponges belong to Phylum Porifera which is very primitive. Some features of sponges which stand them out from others are:

• They are multicellular and sessile ( cannot move) and are this fixed to the substratum. Belong to metazoa.
• They do not have any respiratory, digestive or circulatory system.
• They have special cells called as choanocytes which perform functions like driving water through the sponge body. These choanocytes have whip like flagella.
• There is a cavity in the center of body known as spongocoel, which ends in a small opening known as osculum.
• Body is made up of huge number of pores called as ostia.
• Skeleton is quite rigid made up of spicules or spongin fibres.
• They have no nervous system.
• All the activities of sponges is controlled by moving in and out of water through pores and osculum.

Ans 14. Radula : It is found in Phylum Mollusca. It is a mouth like structure used for feeding and contains tiny teeth. It is made up of protractor and retractor muscles.

Spicule: Spicules are found in sponges. They are a part of skeleton and can be silicious or calcarious. They provide strength and rigidity to the sponges.

Nematocyst : Elongated or spherical capsules present in Cnidarians. These are a machanism of self defence from preys. These are present in tentacles and are full of venom. Eg jellyfish.

Scolex : Found in Taenia solium and other flatworms. Present on the anterior end, contains hooks and suckers to attach to the host intestinal muscles.

Complete digestive tract : Found in Vertebrates.

HOX genes : These genes are a subset of homeobox genes. If present in insects such as Drosophila, they specify which appendages are to be formed on which body part. Appendages include antenna, legs or wings. In Drosophila, they are clustered on chromosome 3.

proglottid : Found in tapeworms. This is the name of each segment of the body consisting of complete reproductive cells and suckers n hooks. Mature proglottids are called as gravid proglottids.

Hermaphrodite : A body having both male and female sexual parts and produces both male n female gametes normally. Eg Flatworms.

Mantle : present in molluscs, it is dorsal body wall consisting of digestive, and reproductive systems. It secretes calcium carbonate and help in formation of outer shell.

Corona : Corona radiata is innermost membrane of ovum.

Ans 15. Important from medical point of view some of the invertebrates are ticks, lice, ants, spiders, cockroaches, wasps, spiders etc. Honeybees and their products, maggots involved in wound cleaning, medicinal leech and blister beetles. Few sponges show anti- inflammatory properties and can also fight tumors.