Which of the following statements is correct for the phylum whose organisms are characterized by the presence of a dorsal hollow nerve cord and paired pharyngeal gill slits ?

Options

A. In all protochordates , notochord extends from head to tail region and is persistent throughout the life.
B. The members of the class to which Myxine belongs show the presence of a sucking and circular mouth without jaws.
C. Members of the class Osteichthyes show the presence of an air bladder , a streamlined body and four gills covered by operculum.
D. Thee members of the class to which the frog belongs are cold blooded , show external fertilization and a three chambered heart i.e one auricle and two ventricles.

Answer

To solve the question regarding the phylum characterized by the presence of a dorsal hollow nerve cord and paired pharyngeal gill slits, we will analyze the options step by step.

### Step 1: Identify the Phylum
The organisms characterized by a dorsal hollow nerve cord and paired pharyngeal gill slits belong to the phylum **Chordata**. This phylum includes organisms such as vertebrates, tunicates, and lancelets.

**Hint:** Remember that the key features of Chordata include the dorsal hollow nerve cord, notochord, pharyngeal slits, and post-anal tail.

### Step 2: Analyze the Options
Now, let’s analyze the provided options one by one to determine which statement is correct.

1. **Option 1:** "In all protocordates, the notochord extends from head to tail region and persists throughout life."
- This statement is incorrect. While the notochord is present in some protocordates, it does not persist throughout life in all members.

**Hint:** Protocordates include groups like hemichordates, urochordates, and cephalochordates, and the notochord's persistence varies among these groups.

2. **Option 2:** "The members of the class to which Myxine belongs show the presence of a sucking and circular mouth without jaws."
- This statement is correct. Myxine (hagfish) belongs to the class Cyclostomata, which are jawless fish with a circular mouth.

**Hint:** Cyclostomata is known for its jawless condition and unique feeding adaptations.

3. **Option 3:** "Members of class Osteichthyes show the presence of an air bladder, a streamlined body, and four gills covered by operculum."
- This statement is partially correct but does not pertain to the dorsal hollow nerve cord and paired pharyngeal gill slits characteristic of Chordata.

**Hint:** Osteichthyes refers to bony fishes, which do have these features, but they are not the focus of the question.

4. **Option 4:** "The members of the class to which frog belongs are cold-blooded, show external fertilization, and have a three-chambered heart."
- This statement is also incorrect as it does not directly relate to the defining characteristics of the phylum Chordata.

**Hint:** Frogs are amphibians and have specific reproductive and physiological traits that differ from the primary characteristics of Chordata.

### Step 3: Conclusion
Based on the analysis, the correct answer is **Option 2**, which accurately describes the characteristics of the class Cyclostomata, including Myxine.

**Final Answer:** Option 2 is correct.