Simply green

A few days ago I told my friend Brenna that I’d hunt around in the marine lab for a bit of a green alga that she wants to press. I had a pretty good idea of where to look, only the animals I’d seen it on had been removed from the exhibit hall. I asked for and got permission to examine the animals behind the scenes. And fortunately I had remembered correctly, and I was able to pick off some nice clumps of dark green stuff.

Bryopsis corticulans is a filamentous green alga. It grows to about 10 cm in length and is a dark olive color. When emersed it sometimes looks almost black. I’ve seen it in the intertidal in a few places, where at low tide it resembles nothing so much as a shapeless slime. It’s very difficult to see the beauty of organisms when they’re out of their natural element, which in this case is water.

B. corticulans emersed during low tide at Mitchell’s Cove.
8 June 2016
© Allison J. Gong

But see how pretty it is when submerged?

Bryopsis corticulans
23 January 2017
© Allison J. Gong

One of the reasons I love the algae is their very inscrutability. I enjoy discovering the beauty of organisms that, at first glance, don’t look like much. Many of the filamentous algae, both the greens and the reds, have a delicate structure that requires close examination to be appreciated. Fortunately, I have access to microscopes, so close examination is very easy.

The thallus of B. corticulans is relatively simple, consisting of a bipectinate arrangement of filaments.

Apical tip of Bryopsis corticulans.
23 January 2017
© Allison J. Gong

Here’s a closer view:

Thallus of Bryopsis corticulans.
23 January 2017
© Allison J. Gong

This is a shot of the main axis and side filaments. The small green blobs are chloroplasts. One thing to notice is that there are no crosswalls separating any of the filaments. That’s because the thallus is coenocytic, essentially one large cell with a continuous cytoplasm. Coenocytic cells are common in fungi, the red and green filamentous algae, and a few animals. In animals, coenocytic cells are often referred to as syncytial. They can arise in one of two ways: (1) adjacent cells fuse together; or (2) nuclear replication occurs as usual during normal mitosis but cytokinesis (division of the cytoplasm) does not. However the syncytium arises, it can result in very large cells. Even though B. corticulans itself is a small organism, some algae in the Bryopsidales consist of single cells that can be over 1 meter long!

Sometimes things that appear simple at first glance conceal a deeper complexity when you look more closely.

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  1. Pingback: Beginnings and leavings | Notes from a California naturalist

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