Choroideans

Choroideans are a group of animals that belong to the phylum Chordata, which also includes vertebrates. They are characterized by the presence of a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a muscular postanal tail at some point in their development. Choroideans are further divided into two subphyla: Urochordata (tunicates) and Cephalochordata (lancelets).

Urochordates, commonly known as tunicates or sea squirts, are sessile filter feeders that live in marine environments. They have a tunic, a protective outer layer, and a siphon, a structure used for feeding and respiration. Tunicates are further divided into two classes: Ascidiacea (sea squirts) and Thaliacea (salamander tunicates).

Cephalochordates, or lancelets, are small, free-swimming marine animals. They have a notochord that extends the entire length of their body and a dorsal nerve cord that runs along the top of the notochord. Lancelets are the closest living relatives of vertebrates and are often used in scientific research to study the evolution of vertebrates.

Choroideans are important in the study of evolutionary biology, as they provide insights into the early evolution of vertebrates. They are also of interest to marine biologists due to their unique adaptations and ecological roles in marine ecosystems.