selkäjänteisihin

Selkäjänteiset is the Finnish term for chordates, a phylum of animals that includes vertebrates and several related invertebrate groups. The defining characteristic of chordates is the presence of a notochord, a flexible rod that supports the body, at some stage of their life cycle. In many chordates, the notochord is replaced by a vertebral column during development, forming the backbone of vertebrates.

Other key features shared by all chordates include a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. The dorsal hollow nerve cord develops into the central nervous system, while the pharyngeal slits are involved in feeding and respiration in some species and are modified for other functions in others. The post-anal tail extends beyond the anus and is used for locomotion in many species.

The phylum Chordata is divided into several subphyla. Cephalochordata, such as lancelets, retain the notochord throughout their lives. Urochordata, or tunicates, have a notochord only in their larval stage. Vertebrata, the most diverse subphylum, includes fish, amphibians, reptiles, birds, and mammals. These animals possess a vertebral column that protects the spinal cord and provides structural support.