Tunicate – Part 2

By Jon Zahourek


Vertebrate Anatomy is a System of Subsystems


The key to vertebrate movement is the axial subsystem. If you own a “backbone,” you’re a vertebrate. Vertebrates represent the vast majority of the phylum Chordata. There are 69,963 species including our ancestral jawless fishes, tetrapods (amphibians, reptiles, birds, and mammals).



The same axial subsystem can be seen in all these species, and for that matter, that consistency has been the key to vertebrates for over 530 million years, considered the “age of fishes” even now. That subsystem makes us all family—even though some of us can fly and some of us do nothing but swim.


The functional capabilities, of course, vary. In some species, the functional capabilities were enriched—through the process of evolution—by the addition of subsequent subsystems.


These subsystems allowed for new skills and talents.


Around 400 million years ago, the branchial (gill-arch) anatomy evolved into jaws and more. At roughly the same time, the machinery of a paired set of pectoral fins evolved. Those were followed by a second set, the pelvic fins.


Each subsystem evolved because it added adaptive functionality to the machinery of the whole system. Around 150 million years ago, primate mammals evolved, fully vertebrate and fully patterned in system and subsystem—axial, branchial, and appendicular.


The Anatomy in Clay® Learning System offers a revolution in anatomy study because it allows us to see how these subsystems come together to form the whole. In the human body, the axial anatomy is all we require to live. The appendages, of course, are not necessary.

The axial system is the “heart” of our skeletal system—it houses our heart-lung system and our digestive organs. This axial system gives us the connection to tunicates, the marine chordate animals (such as ascidians) that are filter-feeders.


Tunicates have a thick tunic-like covering—sometimes wryly referred to as “gut and gonads in a bag.” Though possessing only a simple nervous system, its internal cavities are reminiscent of the thoracic and abdominal cavities that maintain the necessary separation of our internal organs. Tunicate anatomy includes a pharynx in one sac and its visceral, digestive organs in another. Many are mobile as juveniles but immobile as adults—and rely on the food they can gather as water passes through them—their anatomy is the template of our own.


As you build muscles using the Anatomy in Clay® Learning System, always remember that you can see far back into our anatomical, evolutionary past.

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