Question

Hard calcium carbonate structures are used as skeletons by

• A. Echinodermata
• B. Protochordata
• C. Arthropoda
• D. Nematoda

Answer 1

The correct option is A

Echinodermata

The correct option is A.
Explanation for the correct option:
Option A:

1. Phylum Echinodermata includes Marine invertebrate animals which generally have a spiny skin.
2. These are triploblastic, radially symmetrical organisms with an unsegmented body.
3. They possess an exoskeleton made of calcium carbonate. Calcareous spines are present all over the body.
4. They reproduce sexually and have a high power of regeneration.
5. Some examples are starfish, sea urchin, sea cucumber.
6. A water driven tube system is present in phylum Echinodermata.
7. This is a hydraulic system which is used for the purpose of locomotion, food, waste transportation and respiration.
8. The system consists of canals that connect numerals tube feet.

Explanations for the incorrect options:
Option B:

1. Protochordata bodies acquire a lengthy, rod-like structure for support called the notochord at a specific point in their existence.
2. Organ system level organization can be seen in them.

Option C:

1. Arthropods are also extremely important to humans since they are employed in a wide range of manufactured goods.
2. Examples include Bees generating honey, and their honeycombs are filled with beeswax, which is commonly used to make candles, and furniture polish.

Option D:

1. Nematoda is a broad phylum of worms that includes roundworms, threadworms, and eelworms.
2. Nematode species can live "freely" in soil, freshwater, and the ocean.
3. These are particularly important in the cycling of nutrients and the release of nutrients for plant growth.
4. They feed on bacteria, fungi, protozoans, and even other nematodes.

Final answer: Hard calcium carbonate structures are used as skeletons by Echinodermata.