A marine cartilaginous fish that can produce electric current is:
| 1. | Pristis | 2. | Torpedo |
| 3. | Trygon | 4. | Scoliodon |
| 1. | Gill slits are ventrally placed |
| 2. | Head and trunk are widened considerably |
| 3. | Distinct demarcation between body and tail |
| 4. | Their pectorals fins are distinctly marked off from cylindrical bodies |
| 1. | Male frog – a copulatory pad on the first digit of the hind limb |
| 2. | Female cockroach – anal cerci |
| 3. | Male shark – claspers borne on pelvic fins |
| 4. | Female Ascaris – sharply curved posterior end |
| 1. | Chordata – possess a mouth provided with an upper and a lower jaw |
| 2. | Chondrichthyes – possess cartilaginous endoskeleton |
| 3. | Mammalia – give birth to young ones |
| 4. | Reptilia – possesses 3-incomplete heart with one incompletely divided ventricle. |