Modern sharks, rays and skates are united under the Chondrichthyes class. All Chondrichthians have cartilaginous skeletons. The males have intromittent organs called claspers, which are derived from the pelvic fins of the fish. All fertilization occurs internally and females my be either oviparous or viviparous. All Chondrichthians have no swim bladder. Sharks in particular rely on their large pectoral fins and oily livers to maintain bouncy. This also comes with the benefit of being able to traverse a variety of depths without expanding or compressing as much as a fish with a swim bladder would. Another interesting characteristic of Chondrichthians is the presence of placoid scales, teeth like structures which produce a sand-paper like skin.
A subclass of Chondrichthyes is the Elasmobranchs, which means plated gills. This class may be further seperated into Selachians, the sharks, or Batoids, the rays and skates. Seleachians have their plated gills on the side of their head while the gills of Batoids are located ventrally. A Batoids pectoral fins will be fused to the side of the head, in place of the gills location. Rays and skates differ by their means of reproduction. A ray is viviparous, giving live birth, while a skate is oviparous and will lay eggs.
Comments
Organization
The paragraph gives an adequate amount of information, but the organization of the sentences makes this amount of information seem kind of overwhelming... I think organizing the sentences in a more logical way would greatly improve the paragraph.
There is a lot of information
There is a lot of information in these sentences but they don't seem to be well organized, making reading semi difficult. I would also try and explain some terms more in depth, such as "oviparous" or "viviparous", or at least breifly provide the difference.