Cyclostome refers to a group of primitive jawless vertebrates known as the Cyclostomata, which includes two living species, lampreys and hagfish. The term "cyclostome" originates from the Greek words "cyclo," meaning circle, and "stoma," meaning mouth, signifying the circular shape of their mouths.
Cyclostomes are characterized by their lack of jaws and paired fins, distinguishing them from more advanced vertebrates. They possess a round, suckering mouth surrounded by teeth made of keratin, which they use to attach to other fish for feeding. Typically, they have elongated, eel-like bodies with a cartilaginous skeleton.
Living cyclostomes also share other shared features, including a single nasal opening located on top of their head and multiple gill openings on their sides. They lack typical scales, bare no true stomach, and possess a primitive kidney system. Cyclostomes possess a relatively simple nervous system and lack true vertebrae, although they have a notochord, a flexible rod that provides support during movement.
Historically, cyclostomes have been incredibly important organisms for understanding the evolution of vertebrates. Their ancient lineage and anatomical simplicity have made them subject to extensive studies, which have shed light on several fundamental aspects of early vertebrate evolution, including embryology, neurobiology, and immunology.
In conclusion, cyclostome refers to a group of snake-like jawless vertebrates, including lampreys and hagfish, which possess a round, suckering mouth, lack jaws and paired fins, and exhibit several key primitive anatomical features.
