Sharks and dogfishes differ from skates and rays by

Options

A. Their pectoral fins distinctly marked off from cyclindrical bodies
B. Gill slits are ventrally placed
C. Head and trunk are widened considerably
D. Distinct demarcation between body and tail

Answer

To answer the question about how sharks and dogfishes differ from skates and rays, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Characteristics of Sharks and Dogfishes**:
- Sharks and dogfishes have elongated bodies with pectoral fins located behind their heads on either side.
- Their pectoral fins are rigid and elongated, supported by cartilaginous structures called keratorrhicoids.
- These fins help them maintain buoyancy and maneuverability in the water.

2. **Understand the Characteristics of Skates and Rays**:
- Skates and rays have flattened, disc-like bodies.
- They possess five gill slits located on the underside of their bodies, and their mouths are also situated on the underside.
- Their large pectoral fins are shaped like wings, allowing them to glide through the water, and they have long, cylindrical tails.

3. **Analyze the Given Options**:
- **Option 1**: "Their pectoral fin distinctly marked off from cylindrical bodies."
- This option is correct as sharks and dogfishes have pectoral fins that are clearly separated from their cylindrical bodies.
- **Option 2**: "Gill slits are ventrally placed."
- This is incorrect for sharks and dogfishes, as their gill slits are not ventrally placed.
- **Option 3**: "Head and trunk are widened considerably."
- This is also incorrect; sharks and dogfishes do not have a considerably widened head and trunk compared to skates and rays.
- **Option 4**: "Distinct demarcation between body and tail."
- This is incorrect as well; while skates and rays have a more integrated body structure, sharks and dogfishes do not have a distinct demarcation.

4. **Select the Correct Option**:
- Based on the analysis, the correct answer is **Option 1**: "Their pectoral fin distinctly marked off from cylindrical bodies."

### Final Answer:
Sharks and dogfishes differ from skates and rays primarily in that their pectoral fins are distinctly marked off from their cylindrical bodies.

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