Which of the following statements about annelids, such as earthworms, correctly describes a characteristic of this phylum?

Introduction / Context:
This question focuses on the basic biology of annelids, a group that includes earthworms, leeches and many marine worms. Understanding their circulatory system, body cavity and methods of gas exchange is essential for questions in comparative animal physiology and classification. The goal is to identify the statement that correctly describes a key feature of annelids.

Given Data / Assumptions:
- Annelids are segmented worms with bodies divided into repeated units.- The options mention circulatory system type, nervous system pattern, gas exchange, body cavity and segmentation.- You are expected to recall general features of annelid anatomy and physiology.- The correct statement must match widely accepted textbook descriptions of annelids.

Concept / Approach:
To approach this question, review the hallmark features of annelids. They are triploblastic animals with a true coelom and a closed circulatory system. Their bodies are clearly segmented. Many annelids, especially earthworms, rely on gas exchange across a moist, highly vascularized body surface rather than having specialized lungs. Their nervous system consists of a ventral nerve cord and a more centralized brainlike structure, not a diffuse nerve net. By comparing these known features with each option, you can eliminate incorrect statements and select the one that aligns with the standard description of annelids.

Step-by-Step Solution:
Step 1: Recall that annelids have a closed circulatory system with blood confined to vessels, which eliminates any option that claims an open system.Step 2: Remember that they possess a ventral nerve cord with segmental ganglia, not a nerve net like jellyfish, so any claim about a nerve net is incorrect.Step 3: Note that annelids are coelomate animals, meaning they have a true coelom, so options describing pseudocoeloms are wrong.Step 4: Recognize that many annelids carry out gas exchange across their moist skin, which must remain damp for efficient diffusion of oxygen and carbon dioxide.Step 5: Compare each option and choose the one that matches the known reliance on cutaneous respiration, which is the statement about gas exchange across their moist body surface.

Verification / Alternative check:
You can verify the answer by thinking of the common biology example of an earthworm, which is often described as breathing through its skin.Textbooks also stress that earthworms die if their skin dries out because they depend on cutaneous respiration.Since this directly matches option C, and all other options contradict core features of annelids, the selection is confirmed.

Why Other Options Are Wrong:
Option A is wrong because annelids have a closed circulatory system, while an open circulatory system is typical of many arthropods and molluscs.Option B is wrong because a nerve net is found in cnidarians such as jellyfish, not in segmented worms, which have a ventral nerve cord.Option D is wrong because annelids are coelomate, not pseudocoelomate; pseudocoeloms are characteristic of nematodes.Option E is wrong because segmentation, also called metamerism, is a defining feature of annelids, so they clearly do not lack segmentation.

Common Pitfalls:
Students sometimes confuse annelids with nematodes and misremember which group has a pseudocoelom.Another common error is to misapply knowledge of arthropods and assume that many invertebrates share an open circulatory system.Finally, some learners mistakenly think only animals with lungs perform gas exchange, forgetting that simple diffusion across moist skin is effective in small organisms like earthworms.

Final Answer:
The correct statement is that annelids perform gas exchange mainly across their moist body surface.