Trilobites are

Options

A. Extinct arthropods
B. Connecting link between annelids and molluscs
C. Living fossils
D. Insects.

Answer

**Step-by-Step Text Solution:**

1. **Understanding Trilobites**: Trilobites are a group of extinct marine arthropods that existed during the Paleozoic era. They are characterized by their three-lobed body structure, which gives them their name "trilobite".

2. **Classification**: Trilobites belong to the phylum Arthropoda, which includes insects, arachnids, and crustaceans. They are not classified as amphipods, which are a specific group of crustaceans.

3. **Extinction**: Trilobites are indeed extinct, having disappeared from the fossil record approximately 250 million years ago at the end of the Permian period.

4. **Filter Feeding**: Trilobites were primarily filter feeders, meaning they fed by filtering small particles from the water, which is a characteristic of some marine organisms.

5. **Comparison with Annelids and Mollusks**: Trilobites do not serve as a connective link between annelids (segmented worms) and mollusks (snails, clams, etc.), as they lack the necessary characteristics to connect these two groups.

6. **Living Fossils**: The term "living fossil" typically refers to species that have remained relatively unchanged over long periods of geological time and still exist today. Since trilobites are extinct, they cannot be classified as living fossils.

7. **Conclusion**: Based on the analysis, the correct classification of trilobites is that they are extinct arthropods. Therefore, the correct answer to the question is that trilobites are extinct arthropods.

**Final Answer**: Trilobites are extinct arthropods.

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