A portion of the animal phylum Chordata comprised of the subphyla CEPHALOCHORDATA; UROCHORDATA, and HYPEROTRETI, but not including the Vertebrata (VERTEBRATES). It includes nonvertebrate animals having a NOTOCHORD during some developmental stage.

Small fish-like marine creatures often used in phylogenetic comparative studies of CHORDATES.

Common name for a family of eel-shaped jawless fishes (Myxinidae), the only family in the order MYXINIFORMES. They are not true vertebrates.

Phylum in the domain Eukarya, comprised of animals either with fully developed backbones (VERTEBRATES), or those with notochords only during some developmental stage (CHORDATA, NONVERTEBRATE).

Sharks of the family Squalidae, also called dogfish sharks. They comprise at least eight genera and 44 species. Their LIVER is valued for its oil and its flesh is often made into fertilizer.

The process of cumulative change at the level of DNA; RNA; and PROTEINS, over successive generations.

The relationships of groups of organisms as reflected by their genetic makeup.

The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.

Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.