What is a bryozoan?
Bryozoans belong to Phylum Bryozoa and are colonies of tiny individual animals (often only clearly seen with a microscope). Each tiny animal, called a zooid, builds a hard casing around itself. The box-like house has an opening with a tiny door, through which its tentacles emerges to filter feed. The colony forms as the zooids reproduce by budding. Each new casing remaining attached to the colonial members around it, forming a beautiful regular pattern of box-like houses. Some colonies take the shape of encrusting layers, others develop into delicate ruffles or branching forms. Here's more about some bryozoans seen in Singapore.
|Dr Dennis P. Gordon showing us the glorious variety of bryozoans.|
What is a sea pencil?
Sea pens are so named because they resemble feathery quills used to write with in olden days. The sea pencil is a sea pen but isn't feathery, so I called it a sea pencil! (It also looks like the Vicks Vapor Inhaler thingies that you stick into your nose when you have a cold!). They are quite common at Changi, but only at night. During the day, they retract into the ground at low tide.
In a fossil, it does seem quite possible to mistake the 'bone' of a sea pencil for the tiny 'houses' of a colonial bryozoan. But Dr. Björn Berning points out, there are a number of morphological differences between the axis of a sea pen and a bryozoan colony by which one can separate the two.
And this is indeed what Dr. Björn Berning kindly explained to me when he emailed and shared the press release below about how a fossil called Pywackia is not a bryozoan but may represent the earliest known octocoral with a sea pen-like morphology and organization!
Wow! I'm so glad I did a webpage of the sea pen even though I didn't know its identity (sadly, the situation for many of Singapore's common marine creatures). The moral of the story: share your sightings, share your photos (even of dead and decaying animals), post up pages of your observations even if you don't know what it is you are looking at. You never know how it might help a scientist somewhere in the world wide web!
The big bonus for me, is that finally, I learn the ID of the sea pencil. It is Lituaria sp.! Thank you Dr. Björn Berning and Dr Dennis P. Gordon!
Meanwhile, the good doctors have their work cut out correcting the error that has crept into textbooks about the fossil record of bryozoans. Hopefully, this blog post will help a little towards this effort.
Here's the press release (pdf) about how Pywackia is not a bryozoan.