Chordates are characterized by organisms that have at least a dorsal nerve cord, a notochord, pharyngeal pouches, and a tail.

The hollow nerve cord goes along the back part of the body. The notochord, which is present during the embryonic stage of chordates, goes below the nerve cord and supports it. The pharyngeal pouches are used for gas exchange. The tail, which is made up of bones and muscles, are used for swimming by the aquatic chordates.

There are two distinct groups of chordates that do not have vertebrae or backbones and they are the tunicates and lancelets. Both organisms are described as soft-bodied animals living in marine environments. They have a hollow notochord, pharyngeal pouches, and tails at some stage of their developmental cycle.

**Tunicates** are also referred to as “sea-squirts”. These animals are filter-feeders and sessile– usually found attached to docks, rocks, or boats. They are under Phylum Chordata as their larval stage exhibits the presence of the notochord, hollow nerve chord, and tail. However, adult tunicates neither have a notochord nor a tail.

**Lancelets** are small, fishlike organisms that ate usually found on the sandy ocean bottom. Unlike the tunicates, Lancelet has a body structure that exhibits a definitive head region that houses the mouth which is used for feeding and digestion, and they are not sessile.

Under the phylum Chordata, some species are placed in a subphylum called Vertebrata. Members of this subphylum are vertebrates, wherein they have a vertebral column. In vertebrates, they have a spinal cord instead of a dorsal, hollow nerve cord in chordates. Also, when the embryo of a vertebrate starts to mature, the notochord is replaced by vertebrae. This backbone acts as an endoskeleton that supports and protects the spinal cord of vertebrates.

A vertebrate’s endoskeleton protects and supports the animal’s body and gives the muscles a place to attach. The difference is that a vertebrate’s skeleton grows as the animal grows and does not need to be shed periodically like an anthropod.

**Lancelets** are small, fishlike organisms that ate usually found on the sandy ocean bottom. Unlike the tunicates, Lancelet has a body structure that exhibits a definitive head region that houses the mouth which is used for feeding and digestion, and they are not sessile. Moreover, these organisms use their **pharynx and thin body surface for gas exchange**.

Tunicates are also referred to as “sea-squirts”. These animals are filter-feeders and sessile– usually found attached to docks, rocks, or boats. They are under Phylum Chordata as their larval stage exhibits the presence of the notochord, hollow nerve chord, and tail. However, adult tunicates neither have a notochord nor a tail

The life cycle of a tunicate contains a larval stage and adult form. The larval stage contains all the chordate characteristics and it can also move from one place to another. This is a great advantage for this organism as they can travel and search for food and an appropriate place for them to mature. On the other hand, adult organisms are sessile and thus, rely on filter-feeding for nutrition.