Which of the following best describes a key difference between the first cnidarians and sponges (phylum Porifera)?

• A. Sponges have radial symmetry, while cnidarians have no symmetry.
• B. Sponges have a nervous system, whereas cnidarians do not.
• C. Cnidarians possess true tissues and specialized stinging cells (cnidocytes), while sponges lack true tissues and specialized cells for prey capture.
• D. Cnidarians are exclusively sessile, while sponges are motile as adults.

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by understanding the key characteristics of sponges (phylum Porifera). Sponges are simple organisms that lack true tissues and organs. They rely on specialized cells, such as choanocytes, for feeding and water circulation, but they do not possess specialized stinging cells.
2. Step 2: Next, examine the characteristics of cnidarians. Cnidarians are more complex than sponges and possess true tissues, including an organized nervous system and muscle tissues. They also have specialized stinging cells called cnidocytes, which are used for prey capture and defense.
3. Step 3: Compare the symmetry of sponges and cnidarians. Sponges generally lack symmetry or may exhibit asymmetry, while cnidarians typically have radial symmetry, which allows them to interact with their environment from all sides.
4. Step 4: Analyze the mobility of sponges and cnidarians. Sponges are sessile as adults, meaning they are fixed in one place, while cnidarians can exhibit both sessile and motile forms depending on their life stage (e.g., polyp and medusa forms).
5. Step 5: Based on the provided options, identify the correct answer by focusing on the presence of true tissues and specialized stinging cells (cnidocytes) in cnidarians, which distinguishes them from sponges that lack these features.