A true coelom is __________.

• A. a body cavity lined with tissues derived from the endoderm
• B. a body cavity lined with endoderm and mesoderm
• C. a thoracic body cavity
• D. an abdominal body cavity
• E. a body cavity lined with mesoderm

Answer: (E)

Verified step by step guidance

1. Understand the definition of a coelom: A coelom is a fluid-filled body cavity that is completely lined by tissue derived from mesoderm.
2. Differentiate between the terms: The endoderm, mesoderm, and ectoderm are the three primary germ layers in the early embryo. The mesoderm is the middle layer, which gives rise to muscles, bones, and the circulatory system.
3. Identify the characteristics of a true coelom: A true coelom is specifically lined by mesodermal tissue on both sides, which distinguishes it from other types of body cavities.
4. Evaluate the options given: Analyze each option to determine which one correctly describes a true coelom. The key characteristic is the mesodermal lining.
5. Conclude with the correct choice: Based on the definition and characteristics, the correct answer is 'a body cavity lined with mesoderm.'