Which of the following statement is incorrect?

Options

A. Notochord is mesodermally derived structure formed on the dorsal side during development of all invertebrates
B. In annelids closed type of blood vascular system is present
C. Animals in which anus is formed earlier than mouth are called deuterostomiate
D. Ctenophores are diploblastic animals

Answer

To determine which statement is incorrect, we will analyze each statement provided in the question step by step.

### Step 1: Analyze the First Statement
**Statement:** "Notochord is a mesodermally derived structure from the dorsal side during the development of all invertebrates."

- The notochord is indeed a structure that is derived from the mesoderm.
- It is present in all chordates, which include both vertebrates and some invertebrates (like cephalochordates).
- Therefore, this statement is **correct**.

### Step 2: Analyze the Second Statement
**Statement:** "In annelids, the closed type of blood vascular system is present."

- Annelids, such as earthworms, do possess a closed circulatory system, where blood is contained within vessels.
- This is similar to the circulatory system of humans.
- Thus, this statement is also **correct**.

### Step 3: Analyze the Third Statement
**Statement:** "Animals in which the anus is formed earlier than the mouth are called deuterostomes."

- This definition is accurate. Deuterostomes are characterized by the development of the anus from the blastopore, while the mouth develops later.
- Therefore, this statement is **correct**.

### Step 4: Analyze the Fourth Statement
**Statement:** "Ctenophores are diploblastic animals."

- Ctenophores (comb jellies) were traditionally classified as diploblastic, meaning they have two germ layers (ectoderm and endoderm).
- However, recent research indicates that some ctenophores may have a third germ layer, making them triploblastic.
- Thus, this statement is **incorrect**.

### Conclusion
The incorrect statement is: **"Ctenophores are diploblastic animals."**

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