Question

Почему ланцетника называют бесчерепным?

Answer 1

Нет ни черепа, ни позвоночника.

Answer 2

Латцетники (лат. Branchiostoma, или Amphioxus) — род примитивных морских животных из семейства латцетников (Branchiostomidae), подтип бесчерепные (Acrania), класс голохордовых (Cephalochordata). Взрослые особи ведут придонный образ жизни — населяют песчаное дно чистых морских вод; личинки являются планктоном в прибрежных зонах и открытом море. Типичный представитель рода — европейский ланцетник (Branchiostoma lanceolatum илиAmphioxus lanceolatus). Рассматривались как промежуточное звено между позвоночными и безпзвоночные животными

Answer 3

Why is the Lancelet Called "Boneless"?

The lancelet, also known as amphioxus, is often referred to as "boneless" due to its lack of a true vertebral column or backbone. This characteristic sets it apart from vertebrates, which have a distinct vertebral column. The lancelet's body is supported by a notochord, which is a flexible rod-like structure that provides support and allows for movement. This absence of a true backbone is the reason behind the nickname "boneless" for the lancelet.

Evolutionary Significance

The lancelet's lack of a true backbone is of particular interest in the study of vertebrate evolution. It is considered to be a key feature in understanding the transition from invertebrates to vertebrates. The notochord, which supports the lancelet's body, is believed to have played a crucial role in the evolution of the vertebral column in early vertebrates.

Conclusion

The nickname "boneless" for the lancelet stems from its unique anatomical feature of lacking a true vertebral column, which is a defining characteristic of vertebrates. This distinction has significant implications for the study of vertebrate evolution and the understanding of the transition from invertebrates to vertebrates.