Thursday, August 22, 2013

An unusual "moss"

It’s not so much that I feel compelled to point out that there’s a lot to see out in our vernal pools at this time of year; it just turns out that I’m finding some neat stuff lately. You should go out and look, too!

Mossy stick, or something else?
Here’s something you don’t see every day. About a month ago I was out with the Walden Pond State Reservation’s Junior Rangers leading a ponding activity in a vernal pool on the state reservation. I noticed a fuzzy section of a buttonbush shrub stem just below the waterline, which at first appeared to be covered in moss. I’m not sure what clicked to suggest it wasn't moss, but something did. I was pretty sure that it was a bryozoan, or moss animal, of some sort (one of the benefits of taking an aquatic macro invertebrates class with a professor who spent much of his career focused on esoteric animals is that you become aware of some unusual things). I went back a couple of days ago to collect some.

Doesn't look like much from here!
Back in the lab, I put the stick into a neat contraption for observing wee beasties, and was thrilled to see the fuzz turning into what I was expecting – a moss animal. It keys out to Plumatella recluse, for which there are only 6 other records in Massachusetts! Moss animals are colonial organisms in the Phylum Ectoprocta. The colony is made up of macroscopic zooids which can create a fairly large colony encrusting a substrate. Much like a coral or hydra, moss animals have tentacles that they extend, and wait for food items to become ensnared. In this species, the tentacles on the lophophore are arranged in a horseshoe shape.

Close-up of P. recluse zooids, lophophores, and sessoblasts.
Moss animals reproduce both asexually and sexually, the latter resulting in a planktonic larva that can establish a new colony. The third photograph shows small, brown “dots” throughout the mass. These are the result of one form of asexual reproduction they employ, and importantly, the way this species gets through dry periods in vernal pools. As environmental stresses increase (ie, the pool starts to dry out), individual zooids begin to produce statoblasts, which are little, round capsules containing the germ of the next colony. These either float (floatoblasts) and get carried away to other places, or stay attached to the parent substrate (sessoblasts) and await the cue to start the process all over again.

Sometimes sticks get fuzzy with moss and algae. Sometimes, though, they get fuzzy with really unusual animals masquerading as moss and algae. Keep an eye out! ~ MR Burne

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