Simplify the following text for a Grade 10 native English-speaking person.
Original: Osteichthyes are the most various group of vertebrates , consisting of over 29,000 species , making them the largest class of vertebrates in existence today .
Simplified: The vast majority of fish are osteichthyes , which is an extremely diverse and abundant group consisting of over 29,000 species . It is the largest class of vertebrates in existence today .