All of the following statement are correct except.

Options

A. In Balanoglossus,excretion takes place through proboscis gland
B. All vertebrates are chordates but all chordates are not vertebrates
C. Placoid scales are found in Osteichthyes
D. Mammary glands are defining character of all mammals

Answer

To solve the question, we need to evaluate each statement provided and identify the one that is incorrect. Let's analyze each statement step by step.

### Step 1: Analyze the first statement
- **Statement**: In Balanoglossus, excretion takes place through the proboscis gland.
- **Analysis**: This statement is correct. Balanoglossus, which is a hemichordate, does excrete waste through its proboscis gland.

### Step 2: Analyze the second statement
- **Statement**: All vertebrates are caudates, but all caudates are not vertebrates.
- **Analysis**: This statement is also correct. All vertebrates belong to the subphylum Vertebrata, which is part of the phylum Chordata (caudates). However, not all members of Chordata are vertebrates, as there are other groups like tunicates and cephalochordates.

### Step 3: Analyze the third statement
- **Statement**: Placoid scales are found in Ostrich fish.
- **Analysis**: This statement is incorrect. Placoid scales are characteristic of cartilaginous fish (like sharks), not bony fish (which are referred to as "Ostrich fish" in this context). Bony fish typically have cycloid or ctenoid scales.

### Step 4: Analyze the fourth statement
- **Statement**: Mammary glands are defining characters of all mammals.
- **Analysis**: This statement is correct. Mammary glands are indeed a defining characteristic of mammals, as they produce milk for nursing their young.

### Conclusion
The incorrect statement among the options provided is the third one: "Placoid scales are found in Ostrich fish."

### Final Answer
The statement that is incorrect is: "Placoid scales are found in Ostrich fish."

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