Surprising meetings within the feather stars

For divers in tropical waters feather stars are a common sight. Almost all around the world feather stars bring colour to the under water environment. Despite its nice colours divers normaly do not pay too much attention to these animals. We are more likely to pay attention to all the fish around us; search for the bog animals and leave the feather stars on its own. We think of it as less interesting animals. But this means that we will miss a number of surprising meetings.

Feather stars realy give colour to the under water environment. In tropical water you will encounter them in all kinds of colours. From dull black or brown coloured to beautiful yellow or warm red coloured. And all variations inbetween are possible. And as soon as you think you have seen all the colours you will find an example who combines colours for example black combined with yellow or white. Please take a moment to examine the colour patterns of this bicoloured feather stars; you will be surprised by the different patterns.

Despite all the different colours feather stars all have the same construction. The central body is formed like a cup. At the bottom of the central body the feather star has a number of very thin legs, named the cirri. With these cirri or legs the feather stars can get a hold on the reef. Their favorite spots are on top of rocks or large spunges.

On top of the body the featherstar has a number of long arms. Some feather stars look rather poor with only five arms; whereas there are also featherstars with more than 200 arms. But for all featherstars it counts that they each have a base of five arms. From there the arms divide further into more arms. If you should accidentally touch the arms of the featherstar you will feel that these arms are extremely sticky. This sticky substance helps the featherstar with catching its food. Featherstars will undertake nearly no activities to find himself some food. The only thing they do is position themselves at a good spot on the reef, preferably in a bit of current. Thanks to the current nutricious water flows by. And thanks to the sticky substance on its arms the food will become stuck in the arms quite easily. Afterwards the only thing to do is bring the food to its mouth.

Scientist are not really agreeing about the number different featherstars. But it seems that there are more than 600 different types of featherstars. The identification of different featherstars is very difficult because they have to catch the animal and have to take the arms apart in order to analyse them.

Featherstars can move around on the reef. Using its curri they move themselves slowly to a spot with a good chance of food or a place with more current. If you swim along the featherstar you will hardly notice any movement. But if you swim by the same spot a couple of minutes or hours later you will see that the featherstar has moved to a different spot.

Featherstars have a slgiht prefference for the dark nocturnal hours. At day time you will find them frequently between stones or sponsen. Or they are standing with their armes curled to their body. The curling and closing of the arms is also the featherstars response to danger. If you come too close he will fold his arms in order to protect himself. At night the feather star moves on top of the reef and he streches his arms to collect food.

The featherstar really is an animal to take a longer look to. Not only because of its splendid colours or its combination of colours. No, the featherstars have some more surprises for us. There are different small animals living closely together with the featherstar.

The first animals we found in several featherstars were the commensal shrimps. You will find commensal shrimps in many symbiotic life forms. They live in anemones, corals, on sea cucumbers and so on. This commensal shrimp living on the featherstar is clearly smaller than the ones we found earlier on sea cucumbers. If you learn to look well you will notice that there are a lot of shrimps living in different feather stars. Unfortunately still little is known about the reason for this symbiotic lifestyle. From the point of view of the shrimp we can imagine a number of reasons why he would like to live between the arms of the featherstar. The arms give him a good protection and moreover the shrimp can benefit from the leftovers of the plankton which the featherstar collects with its sticky arms.
But the advantage for the featherstar still remains a bit unclear. A possibly might be that the shrimp acts as a housekepper for the featherstar. Unfortunately little is known about this.

Because featherstars have a lot of different colours also the shimps have different colours. By taking over the colours of the featherstar they not only profit from the protection of the arms but they also get some security by their camouflage.

As mentioned before commensal shrimps have several different colours. In a yellow black coloured featherstar we encountered a almost identical coloured shrimp. It is very impressive to see how this shrimp is able to adapt to the colours of its host. Also the colour combination black, red and white was seen several times, The lines of the featherstar almost seamless go over in the ones of the shrimp. In a black and white featherstar the shrimp has adapted its colours again.

Just a minute later we encounterd another featherstar. Switched on by enthusiasm of our dive guide with every time he discoveres a shrimp in the featherstar we now start looking at them ourselves. And we have success; the only thing is we do not find a shrimp but a very small fish that sticks its head out of the arms of the featherstar.
The Criniod clingfish (gobiescodiae) have a specific preference for living in featherstars. This fish has a dark-coloured body with white lines over the full length of its body. Just as minute later we would be able to the crionoid clingfish even better. Between the arms of the featherstar he layed deliciously quiet in the central part of its host.

At one of our following dives we again found a shrimp in a featherstar. We immediately assumed that this was another commensal shrimp. But this anmimal was a bit larger than the shrimps which we had found so far. Again we became curious. First of all was the blue color of the shrimp intreged us. This time he did not entirely have the same colour as its host. After having asked our guide it appeared that it was a snapping shrimp (synalpheus stimpsoni) to be. Also for this shrimp the numer of colours is amazing. He frequently has a dark colour with bright yellow dots. But the one we found is dark coloured with lines on his body. A major feature of this shrimp is that he hase one slightly enlarged claw. These clawes have given the shrimp its name. With the claws he can make a snapping sound under water.

Also small galathea’s appear to have found a shelter in the arms of a featherstar. And why not, it is a fairly easy live. The featherstar catches the food for your and the only thing you have to do is wait for the leftovers. There is no need to feer for attackers. At first because they can hardly see you and moreover the frequently violent colours of the featherstar are an indication of possible toxic material. Just like the earlier found fishes also the galathea has white lines over their body. Although they belong just like the shrimps to the group crustacea they nevertheless look completely different. At first there is the form of their body. Shrimps have elongated; rather slim bodies whereas the galathea has a slightly rounder body with a pointed nose. The long claws are also characterising for the galathea. The colouring of the galathea depends on the host they live in.

There is a possibility for a great number of variations. But the pattern on their body nearly always is the same. Nearly all galatheas in featherstars have white lines over their body. The only exception which we have found is a red galathea. This red one proved to be equally coloured. The white lines on the galathea appears to be an extreem good camouflage in the featherstar. In general you will find only one small animal in a featherstar. Therefore we were very surprised to see a large number of small galatheas in one featherstar.

A group animals which have something in common with the featherstars are the brittle stars.These animals also have a central body disk with a lot of smooth snakelike arms. Generally these arms do not branch off. Except for the Medusahead we encountered. At the Medusa the head arms are branched off in uncountable number of arms. At day time these animals mostly are hiding in small openings in the rocks. At night he climbs actively on top of the reef to spread out its arms broadly in the water. Sometimes its arms can get an amplitude of around 2.5 meter. Very surprised we were when we found a small guest between all these arms. This small commensal shrimp (Periclimenes lanipes) had adapted its coulour perfectly to the colour of the Medusahead. For us with our untrained eyes the shrimp was very difficult to find. We wondered why our guide spend this much time with the medusa. But after a while the little shrimp came; fortunately he stayed vissible long enough for a photograph. Afterwards he disapeared rapidly between the arms of its host; and we were not able to find him again.