1. | are marine animals and have cartilaginous endoskeleton |
2. | have a mouth located dorsally |
3. | have teeth that are modified cycloid or ctenoid scales directed backwardly |
4. | have the capacity to regulate their body temperature |
1. | In males, pelvic fins bear claspers |
2. | Some of them have electric organs [Torpedo] |
3. | None of them is viviparous |
4. | Some possess poison sting [Trygon] |
I: | They have four pairs of gills which are covered by an operculum on each side. |
II: | Due to the absence of air bladder, they have to swim constantly to avoid sinking. |
III: | Skin is covered with placoid scales. |
IV: | Mouth is mostly terminal. |
1. | Only II | 2. | Only II and III |
3. | Only I and IV | 4. | Only IV |