Tag Archives: animals

Nature

The Sedentary Lives of Moss Animals

I knew from my friend’s lively cry that something big was afoot: “There is some kind of colonial animal living over here!”

She was knowledgeable about outdoor creatures, so I had little reason to doubt her unlikely comment.  I came running over to where she was pointing.

“There, there, at the lip of the spillway—can you see it?”  She was pointing at something twelve feet from where I stood on the concrete abutment above the dam that released water from Lake Dubonet to the Platt River system below.  “No, I can’t see—it’s too dark!

“Just look.  It’s perched on the edge of the spillway.”

My eyes were getting used to the shade cast by the abutment.  “I see it!” I proclaimed, “and I think I know what it is,” I replied with a bit of hesitation in my voice.  “It’s a freshwater sponge!  I haven’t seen one in years.  Let me get a picture of it.”

I worked myself down, as close as I could to where the thing was growing.  It looked like a mass of gelatin, as large as a loaf of bread, without any recognizable appendages, without a head or a tail.  Colonial animals, indeed!  What else could it be?

Image courtesy of the author.

I took a couple of photographs with my camera held down as close as I could get it to the creature.  The flash went off, so dark it was down there.  I include the view in this article along with one taken by someone else, someone with an easier animal to photograph.

When I got home, I immediately began to have doubts about my identification.  Freshwater sponges are not gelatinous, for one thing.  They are rough to the touch, and generally green.  I thought about my Invertebrate Biology course I had taken so many years ago—and I remembered.  I emailed my friend: “It’s not a freshwater sponge.  It’s a bryozoan, a moss animal!” Not having seen the species for nearly forty years, it was easy to see how I could have misidentified it.

Bryozoans are sedentary creatures made up of individuals with scores of tentacles, all of them connected to a horseshoe-shaped structure called a lopophore.  They are not related to corals—which do not have a lopophore—but extract food from the water the same way they do: filtering out living organisms.  This they do by movements of their tentacles and the cilia (moving hairs) upon them.

Fluted Bryozoan in Monterey, California. Image courtesy of Ed Bierman, through Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Fluted_Bryozoan_(Hippodiplosia_insculpta).jpg

Like sponges and corals, they encrust various substrates—wood, rock, old tires, even water intakes–scarcely moving during their lives.  The species my friend had found, Pectinatella magnifica, is known to move as a young colony, at the rate of two centimeters per day.  Its possibilities for adventure are clearly limited by its sluggishness.

“Bryozoan” translates from the Greek as “moss animal.”  In both freshwater and salt water, some species form mats somewhat reminiscent of a bank of moss, though they are rarely colored green.  The species I photographed, genus Pectinatella, secretes a gelatinous outer body that looks like an unappetizing jam one might put on bread.  No one would be tempted to do so, however, given its unprepossessing appearance.

However they might offend our mammalian standards for beauty, bryozoans choose attractive ponds and streams to live in: they prefer unpolluted water, water uncontaminated by mud, debris, or pollutants brought in by humans.  Just as lichens point to unpolluted air, bryozoans indicate clean water. 

The life cycle of Bryozoans lacks the drama of sperm from one colony actively seeking out eggs in another.  Generally, sperm cells from one colony fertilize eggs from the same: a larva grows from the fertilized egg, and is eventually released into the water, often as the colony dies at the end of the summer season.

No one brags about the bryozoan he has captured.  No one raves about how good they taste.  No one tells of the sport they had in catching their first bryozoan.  They live uninteresting lives unaffected by the major currents of a world dominated by other organisms.  Does that make them less interesting to those of us who know them?  Not at all.   

Nature

Godzilla vs. Spongilla: A Contrast in Life Styles

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A sponge is the antithesis of a super hero.  It stays in place, sifting out plankton (microscopic algae and animals) from the water that passes through its body.  Its body is not of great interest, lacking appendages altogether, not even possessing tentacles that might enwrap evildoers and others that would do it harm.  Its personality is not engaging, either, since it does not have a brain. 

To get its food, it has many small openings that take in its tiny prey, and a few larger ones that expel the water it has cleansed.  The pumping system that carries on the circulation is primitive: cells with tiny whip-like appendages (flagella) line passageways, setting up the current.  There are no robust hearts in sponges.

A simple animal reproduces simply.  In some species of sponge, balls of cells (gemmules) form in mid- to late summer that can break off from the parent animal and grow into a new sponge somewhere else.  This asexual form of reproduction is perhaps the most common means of making new sponges.   However, sperms and eggs can be made inside its body, those fertilizing each other in a display that has nothing to do with affection.  You wonder, without courtship, without males showing off what they’ve got, what is the point of reproduction like that?

Sponges do have a skeleton of sorts, however.  In the ocean, some of them have a soft one made up of spongin, a substance that becomes flexible and absorbent upon being rehydrated.  Those sponges have been used for hundreds of years in the Mediterranean Sea and elsewhere for scrubbing everything from floors to human bodies.  Mostly replaced by plastic substitutes, they are occasionally used today.

Many years ago I took a course in invertebrates at the University of Michigan’s Biological Station at Pellston, Michigan, and was surprised to learn that we have a freshwater sponge that inhabits our lakes: Spongilla lacustris (a few other species can be found here, too).  As I observed it, its body most often was in the form of a greenish blob attached to sticks or pondweed–the green color, I found out, came from algae inhabiting the animal.  It was not at all gooey or gelatinous, but felt rough to the touch and a bit like glassy bits stuck together when dried.  Unlike its ocean brethren with its spongin, it had a skeleton made of crystal-like tiny elements made of silica, the same stuff that comprises most of our sand in Northern Michigan.

At least one animal appreciates Spongilla–but not for its appearance or life habits.  Spongilla fly larvae feed on it with zest, later pupating to become small flies we are certain to ignore among the multitude of other flies that hatch in lakes and ponds.  No life form–not even the sponge–is too humble to escape predators.

Spongilla is very particular about where it lives: it must have the cleanest, purest water around.  For that reason, it is considered to be an indicator of pristine, unpolluted lakes.  Far from being a pestilence, freshwater sponges are a gift.  We should not condemn them for what they are not—gifted superheroes of the animal world.  They are not delicious, not cute, not pretty, but they do constitute a component of our most treasured biological communities, the clear lakes that grace our landscape in Northern Michigan.  Let us rejoice in their presence here.

Nature

A Handsome Animal That Does Not Milk Cows: the Milk Snake

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Milk snakes do not milk cows, contrary to legend.  They do hang around barns and other structures–sometimes houses.  Someone I know shares her dwelling with occasional milk snake intruders which apparently enjoy living in the crevices of the foundation.  It does little good to let her know that they are only looking for rodents and other small varmints—she does not like them.  To her credit, they have become only an occasional nuisance, and are only evicted from the premises rather than summarily decapitated, a common response of humans.

Image courtesy of the Virginia Herpetological Society.

I saw one quite recently, three feet of torpid elegance stretched across a bike path near where I live.  Fearing for its life–since it nearly blocked the right-of-way of bicycles–I stamped on the ground to get its attention.  With apparent nonchalance, it moved to one side and then into the tall grasses beside the river, its tongue flicking out every few seconds as snakes do.

Indeed, why do they do that?  Reference books tell me that this is their sense of smell, but that statement is not quite accurate, since the actual organ of smell is inside their mouths.  The tongue only samples the air outside.  Since they don’t bring air directly past their olfactory membranes, then they can only smell whatever comes to them on the wind, a strange mechanism at least from our point of view, since we can sniff.  What smells would they be sensitive to?  Rodents, one might guess, and other milk snakes, females especially–if a male snake is the prime actor.

Milk snakes are harmless, but that does not mean they will not attempt to discourage those who would cause it irritation.  Like many of its relatives, it will coil, hiss, and strike to incite fear in the hearts of its perceived enemies.  It should be forgiven for that behavior, not beheaded.

These creatures are most commonly seen in spring and fall.  They go after their prey after nightfall, seeking out mice with their flicking tongues, ready to wrap themselves around them in an instant, squeezing them so they cannot breathe.  That is what constrictors do.

The triangle on the head of this eastern milk snake is very distinct. Image courtesy of the Virginia Herpetological Society.

Milk snakes are given the name Lampropeltis triangulum triangulum, the “triangulum” element referring to a triangle or Y-shaped marking at the top of its head.  In larger snakes dull red bands decorate its body, but smaller ones will have brighter red stripes bordered with black, all set upon a creamy white background.

After your initial surprise at seeing one, you will have to admire this animal for its stunning appearance.  As so many snakes and reptiles are disappearing because of habitat disruption, they are to be treasured all the more.  Let us live in peace with them.

Want more on snakes? Check out these TADL books about snakes

  • Holman, J. Alan, Harding, James H., Hensley, Marvin M., and Dudderar, Glenn R., Michigan Snakes, Lansing: Michigan State University Press, 1993, 2006.
  • Holman, J. Alan, The Amphibians and Reptiles of Michigan: A Quaternary and Recent Faunal Adventure, Detroit: Wayne State University Press, 2012.

Richard Fidler is co-editor of Grand Traverse Journal.