For the most part, a person who knows a hydroid, knows a whole bunch of hydroids. While it is true that many hydroids will be found in one environment together, the main reason it’s hard to get to know just a single individual hydroid is because these animals tend to form colonies. Numerous individuals will be joined together into what appears to be one unit.
Take for example the Ostrich-plume Hydroid (Aglaophenia latirostris). The graceful beauty of this species is popular with divers and underwater photographers, but what looks like a feather is actually a composite of many tiny animals working together, similarly with Obelia spp. and many other calm water hydroids. They are extremely unpopular among boat owners as they are persnickety fowling organisms. Again, what may look like a single animal is actually a “joint venture” of numerous little critters. Furthermore, when a whole bunch of these colonies of various species crowd together on the bottom of a boat, it is hard to distinguish one species from another, much less one colony from the next.
There is, however, one California hydroid that is very different. While it does follow the general rule of “hydroids-of-a-tentacle, flock together,” and is found in abundance with others of its kind, it stands alone in being completely solitary in its habits.
This particular hydroid, the fairy palm hydroid (Corymorpha palma) can grow up to five inches tall , quite big for a hydroid. And, sure enough, it does look like a miniature palm tree. It has a single stalk, which is topped by a double circle of tentacles. These will gently sway in the currents in much the same way as real palm trees can sway in a tropical breeze.
Well, that is as long as the tide is in and the current remains. The fairy palm hydroid inhabits shallow muddy areas of Southern California, areas which are not particularly famous for their great visibility. Of course, they still have their own interesting ecology, which makes them worth “looking into,” even if such needs to be done through the murk.
The visibility does greatly improve when these areas are exposed at low tide. Then, however, a pretty fairy palm hydroid looks no more charming than a deflated balloon.
So it is better to check out this species when the tide is in. When there is sufficient current, the fairy palm hydroid will filter feed for its food, catching what it can on its lanky tentacles. Mud flats, though, often have very still water and during these times, the fairy palm hydroid has become more active in foraging for food. Its stalk is solidly anchored in the soft mud, so it forages by bobbing its tentacled crown into the nutrient rich mud, sifting through the mud a bit, then after straightening itself up again, transfers its catch into its mouth. They will repeat this maneuver again and again, as often as every three minutes.
Most hydroids go through two major stages in their lives—the attached stage which most people are more familiar with, and then a jellyfish-like stage where they can swim around a bit. The fairy palm hydroid likewise has both sages. But the jellyfish-like offspring of this species that otherwise always stands alone will not venture out on their own. They are, in fact, real homebodies and go through their whole jellyfish-like cycle as buds attached between the tentacles of their parent.
Eventually, though, they will have to leave. The larval babies of the next generation will crawl down the stalk of their protective parent and take their chances against the ravages that may await them. If they can survive the normal dangers of growing up, the extra stresses that sometimes come living on the mud flat environment, plus the nudibranchs that love to dine on members of this species, they too will become uniquely beautiful members of California’s underwater world, hydroids that truly stand alone.