Question

How many statements are false about chondrichthyes?

I) gills are separate without operculum

II) presence of heterocercal caudal fin

III) teeth are modified cycloid / ctenoid scales

IV) due to the absence of air bladder, they have to swim constantly to avoid sinking

V) males have a pair of claspers on the pectoral fin

Answer 1

After evaluating each statement provided about Chondrichthyes, two statements are found to be false: the teeth are not modified scales, and males have claspers on the pelvic fins, not the pectoral fins. The incorrect options are 4,5.

Step-by-step explanation:

The Chondrichthyes, or cartilaginous fishes, include well-known creatures such as sharks, rays, and skates. To answer the student's question, we will evaluate each statement provided about Chondrichthyes:

1. Gills are separate without operculum: This is true for Elasmobranchii (sharks, rays, and skates) but not for Holocephali (chimaeras), which have gill covers.
2. Presence of heterocercal caudal fin: This is predominantly true for sharks, which is a significant group within the Chondrichthyes.
3. Teeth are modified cycloid / ctenoid scales: This statement is false because the teeth of Chondrichthyes are not modified scales; rather, they are unique structures.
4. Due to the absence of air bladder, they have to swim constantly to avoid sinking: While many sharks do need to swim to maintain buoyancy, this is not true for all Chondrichthyes, as some rays and chimaeras can rest on the seafloor.
5. Males have a pair of claspers on the pectoral fin: This is false; the claspers are found on the pelvic fins, not the pectoral fins.

Considering the information provided, the statements III and V are false. Therefore, the correct option is that two statements are false about Chondrichthyes.