Question

The echinoderm in which mouth is used for both ingestion and egestion is
A. Echinarachnius
B. Ophiothrix
C. Echinus
D. Antedon

Answer 1

Ingestion is the process of taking up food inside the body for digestion and nutrition. On the other hand, egestion means expelling waste products from the body. Usually, both of these processes happen through separate organs. The mouth is generally for the ingestion of food. The organism that uses the mouth for both ingestion and egestion is called the brittle star.

Complete answer: Ingestion and egestion are two main processes included in the digestion system of all the organisms. The ingested food should be digested and broken down during which waste products are formed. These waste products if stay in the body for longer periods turn toxic that can harm the organism. Thus, it needs to be expelled through the process of egestion. Ingestion occurs through oral structures usually through a defined mouth. Egestion occurs through anal structures.
Echinarachnius is an inhabitant of sandy bottoms found below the low tide level areas. They can live up to a depth of 5,000 feet. They have round, flat, and disc-shaped shells. They have spines all over their shells that are maroon in color. They have a mouth for ingestion and anus for egestion. It is commonly known as the sand dollar.
Ophiothrix is a species found around the coasts of Western Europe. It is commonly known as the brittle star. It has extremely variable coloration. They can be red, violet, yellowish, or pale grey. They have around five arms that are white with pink bands. These arms are attached to a central disk which is covered in spines. It is a scavenger animal that eats and excretes from its mouth.
Echinus is a sea urchin species. It has a swollen dome-shaped body covered in longitudinal spines radiating directly from the surface. It has a separate mouth and anus for ingestion and egestion respectively.
Antedon or feather star is a free-swimming crinoid. It has five pairs of feathery arms that are attached to a concave central disc. The mouth is present on the upper surface for ingestion and the anus is present for egestion on the lower side.

Thus, we can conclude from the above discussion that the right answer is option B.

Note: The Ophiothrix is a common meal of many shallow level predators. The spiky structure and camouflage ability give them the advantage to hide and stay safe. A brittle star can live up to 10 years and usually spawns between May and January. It bears planktonic larvae.