04 September 2008

So many phyla so little time

Which animal phylum consists of one and only one species? The Placozoa. And the only species in that phylum is the simplest animal of them all, Trichoplax adhaerens.

I have never seen a Trichoplax, which is a rather small (1-2 mm) creature. But I have seen members of smaller phyla, such as rotifers. So size is not a reason why I have not seen a Trichoplax. In fact, some other phyla that have members much larger than Trichoplax are among those phyla that I have so far not had the pleasure of getting acquainted with. What are those phyla?

But, first, I need to figure out how many animal phyla there are. However, that is not an as easy task as it seems. Wikipedia lists 36, the Animal Diversity Web lists 32 and the University of California Museum of Paleontology gives 25 extant animal phyla.

There are some significant differences between these disparate lists. For example, the ADW list includes the Myxozoa, whereas the other 2 lists don't; the UCMP list unites the rotifers and the acanthocephalans, while the Wikipedia list keeps them separate. It is really pointless to attempt to consolidate them or to argue that one is better than the other.

Instead, I will list a compilation of some of the phyla of which I have yet to see a live member: Acanthocephala, Chaetognatha, Gnathostomulida, Hemichordata, Nematomorpha, Nemertea, Onychophora, Priapulida, Sipuncula, Echiura, Phoronida, Loricifera, Pogonophora, Brachiopoda, Placozoa and so on.

I may have seen a kinorhynch once while looking at a marine sediment sample under a microscope, but I lost the animal—whatever it was—after a brief glance at it. Also, I am not sure if I have seen bryozoans.

I would like to see at least one live member of all animal phyla before I die.

Follow-up post: How many phyla have you eaten?


Christopher Taylor said...

Bryozoans are pretty easy to find on any stretch of rocky coast. If you've ever seen a lace-like pattern of carbonate encrusting a rock or shell, you're looking at the remains of a bryozoan colony.

I've seen chaetognaths once. They are really cute.

Frank Anderson said...

Of the phyla you haven't seen alive, I have seen: Chaetognatha, Nematomorpha, Nemertea, Sipuncula, Echiura (which is really a subgroup of Annelida), Phoronida and Brachiopoda.

With several of these, it helps immensely to have gotten a graduate degree in invertebrate zoology right on the California coast!

Like Tim, I am also a vegetarian, and thus I will not knowingly eat other metazoans (though I'm sure I ingest nematodes and insect parts on a daily basis, and I had a chordate's egg for breakfast).