Tunicates, commonly called sea squirts, are a group of marine animals that spend most of their lives attached to docks, rocks or the undersides of boats. To most people they look like small, colored blobs. It often comes as a surprise to learn that they are actually more closely related to vertebrates like ourselves than to most other invertebrate animals.
Tunicates are part of the phylum Urochordata, closely related to the phylum Chordata that includes all vertebrates. Because of these close ties, many scientists are working hard to learn about their biochemistry, their developmental biology, and their genetic relationship to other invertebrate and vertebrate animals.
A tunicate is built like a barrel. The name, “tunicate” comes from the firm, but flexible body covering, called a tunic. Most tunicates live with the posterior, or lower end of the barrel attached firmly to a fixed object, and have two openings, or siphons, projecting from the other. Tunicates are plankton feeders. They live by drawing seawater through their bodies. Water enters the oral siphon, passes through a sieve-like structure, the branchial basket that traps food particles and oxygen, and is expelled through the atrial siphon.
One clue that tunicates are related to vertebrates is found in the tunicate larva, or tadpole. It even looks like a tiny tadpole, and has a nerve cord down its back, similar to the nerve cord found inside the vertebrae of all vertebrates. The Cerebral Vesicle is equivalent to a vertebrate’s brain. Sensory organs include an eyespot, to detect light, and an otolith, which helps the animal orient to the pull of gravity.
Tunicate tadpoles mature extremely quickly, in a matter of just a few hours. Since the tadpoles do not feed at this stage of their lives, they have no mouths. Their sole job is to find a suitable place to live out their lives as adults. When ready to settle, a sticky secretion helps them attach head first to the spot they have chosen. They then reabsorb all the structures within their tail and recycle them to build new structures needed for their adult way of life.
https://depts.washington.edu/fhlk12/links/StudentProjects/Tun.biology.html
God had a reason for creating these beautiful creatures just as He had a reason for each one of us. As the sole work of the Sea Squirts is to find a suitable place to live out their lives as adults, so our work, or contribution, is to “walk in the light of the Lord” (Isaiah 2:5) and to “Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven” (Matthew 5:16).