Tunicates & Taxonomy

Next month, I will be teaching a class about animal groups, families, & taxonomy. Taxonomy shows us how animals (or other objects) are related to one another in a hierarchical structure. There are 7 major groups which we regularly classify animals into, but there are also a wide variety of sub- or super- categories. The major groups of biological classifications are listed below with two examples written out:


American Crow
American Crow
  American Crow North American Giant Octopus
Kingdom Animalia Animalia
Phylum Chordata Mollusca
Class Aves Cephalodpoda
Order Passeriformes Octopoda
Family Corvidae Octopodidae
Genus Corvus Enteroctopus
Species C. brachyrhynchos E. dofleini

Depending on whom you ask, you may find there are 30-38 phyla, the major categories of animals based on their general body plan and developmental or internal organizations. These phyla can vary from containing only one species (Placazoa) to well over a million (Arthropoda).

Coming from a Zoology background, I found that I really like taxonomy and seeing the order and relationships between animals helps me to make sense of how a rock hyrax and an elephant could possibly be close cousins. They are connected in a group called Afrotheria, a superorder of Eutheria (placental mammals) whose relationships have been shown through molecular & DNA anylases.

Here are their classifications:


Rock Hyrax
Rock Hyrax
  Asian Elephant Rock Hyrax
Kingdom Animalia Animalia
Phylum Chordata Chordata
Class Mammalia Mammalia
Infraclass Eutheria Eutheria
Superorder Afrotheria Afrotheria
Order Proboscidea Hyracoidea
Family Elephantidae Procaviidae
Genus Elephas Procavia
Species E. maximus P. capensis

An article came my way about very unusual sea animals found in Antarctica. When I saw the beautiful picture of the tunicates (also known as sea squirts), I wanted to remind myself what these interesting creatures were and who they were related to in the big tree of life.  Although they may look more like “glass tulips” than an animal, these creatures do eat & grow like other animals.  In fact, tunicates are in the same phylum as ourselves, Chordata.  Tunicates, ourselves, hagfish, fish, and other chordates all go through similiar developmental stages that include a notochord (provides support), pharyngeal gill slits (used in feeding), and a tail (helps with locomotion). 

When born, tunicate larvae are similar to small tadpoles, swimming about until they find a suitable rock to settle down on as an adult, cementing themselves to their new home.  Next, they go through many physical changes before fully becoming an adult.  Some tunicates will continue to stay afloat in the ocean their entire lifespan, going through similar metamorphosis as their sedentary cousins.  Tunicates are filter feeders, with in- and out-current siphons.  Food and water is filtered in through their these siphons, then expelled out along with any waste products. 

Here are a few unusual and interesting facts about tunicates:

  • Tunicates are the only animals capable of producing cellulose – produces cell walls in green plants.
  • Tunicate blood contains a high concentration of the metal, vanadium – a metal used to make Lacrosse shafts and simulated Alexandrite jewelry.
  • Tunicate fossils go back as far as the early Cambrian – about 540 million years ago.
  • Tunicates are said to “eat its own brain” during metamorphosis – the tunicate body digests the cerebrial ganglion – a mass of nerves that have a role similar to a brain.
  • Some Tunicates have recently been descovered as invasive species, sometimes hitching a ride on the hulls of ships from one ocean to another.
  • Tunicates are the vertebrates closest living relative.
  • Tunicates are currently being studied in science for certain chemical compounds useful in fighting cancer.


Royal Blue Tunicate
Royal Blue Tunicate
  Royal Blue Tunicate
Kingdom Animalia
Phylum Chordata
Subphylum Urochordata
Class Ascidiacea
Order Enterogona
Suborder Phlebobranchia
Family Diazonidae
Genus Rhopalaea

2 thoughts on “Tunicates & Taxonomy

  1. In the current issue of Sport Diver, in an article about the Phillipines, there is a very large stalked tunicate in one of the photos. It is about the same color blue as the Rhopalaea shown above. It appears to be about six feet long from the base of the stalk to the tops of the zooids. Can you help me identify it?

  2. Would you mind sending a photo to blogadmin at hmns dot org? We can then forward it to the right individual over here.

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