Chondrichtyes are a class of cartilaginous fish which contains Holocephali and Elasmobronchii. There are about 40 extant species of Holocephali, one example being the ratfish. Female Holocephali are oviparous and will lay 1-2 eggs as a time. Males may be identified by the presence of claspers as well as a frontal tenaculum. The defining feature of the Holocephali is that they have a holostylic jaw suspension, meaning their upper jaw is fused with their braincase.
Elasmobrochii includes fish such as sharks, rays and skates. Although rays and skates are often placed into their own group known as the Batoids. This distinction is based on presence of gills on the sides of sharks, while rays and skates have gills located on their underside. All Elasmobrachi have placoid scales, that are similar to teeth in structure. Like teeth they have a pulp cavity, an enamel like substance that coats them and are even made of dentin. This has lead to the hypothesis that teeth are modified placoid scales, that migrated to the interior of the mouth. Of course, the opposite may also be true.
Comments
A lot of detail but
This was a detailed post with a lot of specific vocabulary, but I think it would have been easier to understand if you elaborated on some of the terms a little more. That being said, I thought the second part was really interesting, particularly the part about placoid scales; the way you related it to evolution was fascinating.
This paragraph was super
This paragraph was super detailed and had a lot of vocabulary. I think depending on the audience, it could use a bit more elaboration but if it was strictly for a scientific audience it's well suited.
Last sentence
This paragraph concentrated a lot of specific information, but the last phrase could be omitted because in the previous sentence it is stated that the fact is a hypothesis, implying that further investigation is necessary for proving its veracity.