If you have spent much time looking at pond life with a magnifying glass, you have probably seen one of these. It’s an amazing structure, but what is it? Plant? Animal? Flying saucer with little anchors?

statoblast

One day while looking for rotifers, I found several of these structures attached by their anchor hooks to the aquatic vegetation in my pond water sample. And one of them appeared to be coming apart at the seams. Looking into the gap between the two halves showed a pallid blob of something inside - perhaps living tissue that would turn into some mysterious organism? I transferred the subject to a microscope slide with plenty of water, and put the slide in a Petri dish with some wet paper towel so that the drop of water containing the specimen would not evaporate.

Next day, the “alien” had started to emerge from its saucer-shaped home. It’s tentacles seemed to be filtering the water for bacteria and tiny algae cells.

Larva Emerges

Emerge

And the following morning, the hatchling had emerged completely from its case and was moving along a plant fiber at the blinding speed of half a millimeter per hour.

Zooid Walks

By afternoon a new individual was budding from the hatchling and soon a second set of tentacles was processing the water. What if these things kept on budding and enlarging? Would they take over the pond? Could they spread beyond the pond and infiltrate our society? Should I kill it while I have the chance? Not to worry. A close look at the organism’s structure identifies it not as an alien from outer space, but a fascinating species animal known as a bryozoan.

Ancestrula

These animals are often seen along the shores of lakes and ponds as they dry up in the summer, although they're seldom recognized for what they are. Instead they seem like blobs of jelly hanging from branches that were recently submerged. Close up, the blobs (at least the ones still submerged) are covered with individuals that look exactly like the hatchling, but with the posterior region of the body buried in protective jelly. If disturbed the tentacles jerk back in; then after a period of waiting, they gradually extend and re-establish a feeding current.

The colony members set up extensive feeding currents that bring in phytoplankton, food that is swallowed and passed along the individual’s digestive track. Processed material is eliminated though an anus located outside the half ring of tentacles, thus giving these animals their other name -- ectoprocts. Some of food goes to make the jelly the forms a substrate for the thousands of individuals making up the colony.

As some of the individuals extend from the protective jelly, a familiar structure appears—those little space ships with their rings of anchors.

Small Colony

In a bucket these capsules float to the surface, and its easy to imaging them catching on aquatic vegetation. A freezing winter will kill off the colonies, but with improving conditions the dormant embryos come to life, each the founding individual for a new colony of fresh water bryozoans. Since it is the “ancestor” to all of the other members in the colony, this founding member is called the ancestrula.

Bryozoan reproduction and dispersal also depends on sexually produced larvae, something I will be looking for in the future. There are a number of freshwater bryozoan species. Pectinatella magnifica  the bryozoan seen here, produces the largest colonies, some as big as footballs. Others consist of just a few individuals (zooids). However, if you are fortunate enough to live near an ocean, you can look for a much greater diversity of bryozoans. Look for furry growths on rocks and warf pilings, or sheets of tiny chambers on the blades of kelp. The seashore is a bryozoan empire, with about 4000 species of this little-known phylum to be found in almost every type of benthic habitat. Biologists estimate that there are hundreds or even thousands of bryozoan species yet to be identified and described.

Colony

Bryozoan terminology:

Bryozoan

A group of lophophorate animals classified as the Phylum Bryozoa. The word translates to “moss animals”.

Statoblast:

the floating reproductive structures containing the dormant, embryonic bryozoan. They are resistant to freezing, and thus form the over-wintering stage of some bryozoans.

Zooid:

the individuals that make up a bryozoan colony.

Lophophore (lophophorate):

the circular or horseshoe-shaped ring of feeding tentacles in bryozoans. The tentacles are covered with cilia, which move water and suspended food into the region of the animal's mouth. There are three different phyla of animals with various versions of the lophophore - bryozoans, phoronids, and brachiopods. Together, these anials are known as the lophophorates.

Ectoproct (= bryozoan):

Worm-like lophophorate animals in which the anus empties outside the ring of tentacles that forms the lophophore. The word translates to ‘outside’ ‘anus’. In another group of similar-lookng animal, the anus opening is inside the ring of tentacles - - these animals are known as Entoprocts. The relationship between the two groups is uncertain.