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

What kingdom are you from?

We’ve seen how Carl Linnaeus’s system classifies Lucy. How is the classification that refers to her different from the one that refers to us?

Applied to humans, a Linnaean chart could be filled out in the following way. (Notice the prevalence of Greek and Latin terminology.)

Domain: Eukaryota – containing all organisms which have cells with a nucleus.

Kingdom: Animalia – including organisms with eukaryotic cells that have a cell membrane but lack a cell wall, are multicellular, and heterotrophic (meaning that they cannot synthesize their own food, as plants do.)

Phylum: Chordata – including animals with a notochord, dorsal nerve cord, and pharyngeal gill slits.

Subphylum: Vertebrata – animals possessing a backbone, which may be made of cartilage, to protect the dorsal nerve cord.

Class: Mammaliaendothermic vertebrates with hair and mammary glands which, in females, secrete milk to nourish the young.

Subclass: Placentalia – including animals that give birth to live young after a full, internal gestation period.

Order: Primates – including animals with a collar bone, eyes that face forward, grasping hands with fingers, and two types of teeth: incisors and molars. 

Family: Hominidae – including primates with upright posture, a large brain, stereoscopic vision, a flat face, and hands and feet with different specializations (such as grasping and walking).

Genus: Homo – having an s-curved spine, “man.”

Species: Homo sapiens – characterized by a high forehead, well-developed chin, and thin skull bones.

While Latin and Greek are no longer used when scientists write or e-mail each other, these languages continue to survive in the names given to plants and animals. For those few among us who did study Latin and Greek, here is one practical application of hours and hours of learning vocabulary and conjugating verbs: it allows one to more easily see the origins of the terms used and thus facilitates our understanding of what is meant.

For all those others who did not study these ancient languages, consider the old saying “The more it changes…”