Marine Tank Gallery II
Marine Tank Gallery II
Written by Monday, 30 September 2002 00:00
A member of the Echinodermata phylum, class Asteroidea (sea stars) first described by Retzius in 1805. A medium-sized, bright orange-red starfish with five slender tapering arms and a small disc. The surface of the body is soapy in texture, with regular indentations, from which groups of dark red papullae (gill structures) can be extended. The papullae are shown dark pink under actinic lighting. The maximum diameter of Echinaster sepositus reaches 20cm. Commonly found on rocky substrata in both sheltered and moderately exposed conditions. Also found on muddy, sandy or mixed substrates and amongst eel grass beds. Not found at depths below 200m. The specimen in my tank was collected in May 2002 at a depth of approximately 4 meters. Similar in overall shape to Henricia oculata, but the soft, soapy surface and bright orange colouration are very distinctive. Adult Henricia oculata is also smaller in diameter. This is a very common Mediterranean species which is also present in the West French coast and the Channel islands. Many children use to collect those sea stars and let them dry under the sun – an unnecessary act of cruelty. As with all species in my tank, every effort has been made for their correct identification – however, information is very limited and photos even more so.
When we went for our regular bi-weekly collection in the nearby beach there was a high wind and rain. Definitely the wrong day to go for anything - especially collecting marine species. However, when returning back from a fruitless effort (we had been searching for some sea stars), we came across a large crab which was definitely brought there by the waves. Measuring a generous 7 cm (body only) it was collected and added in the right tank (no fish in there). It immediately run for shelter (too many caves and overhangs in there) but after an hour or so its curiosity won. It came out and started a tour of the tank, examining every stone in it. Whenever we approached the tank it run to its preferred shelter and became almost invisible, so a photo was definitely out of the question. However after many visits we found it resting with its back against the front glass (see photo at the top). Surprisingly, the animal can't see what is going on behind it, it seems its vision is built to observe things that take place in front of it - only. Makes some sense, since it is usually sitting against a rock to protect its back but still it was a perfect opportunity for some pictures. The crab didn't move at all, despite the use of flash and the close range of the camera (about 5 cm from it). I have tried many books to find the scientific name of this species but it seems I will have to buy a book focused on crabs exclusively. This crab was collected at a depth of less than 50 cm under a huge rock with very small crevices for its size. Finally, after so many months, Andreas Iliopoulos concluded that most probably this crab is a Carcinoides (Carcinus) maenas (North Atlantic shore crab) or C. aestuarii (Mediterranean shore crab). Both species live in the intertidal zone and are quite common.
What a lovely creature! In the second row of photos the same crab is in the tank with the fish. I didn't quite move it myself, it went there on its own. I had heard about the ability of the octopus to escape from its tank but no book mentioned that this is also possible for a crab. Well, it is. After spending a couple of days in the tank it was originally placed it decided to take a walk and ended in the tank next to it. Bear in mind that all tanks are covered with black paper so the crab could not see that there was another tank next to its own. I estimate that it went out of its tank for a walk and when it sensed water just entered the other tank. Happy fellow! I observed that from the moment it entered the new tank with the fish, it stopped rushing for shelter when someone approaches the tank. Not to mention the amount of macroalgae consumed in day 1! So the good news is that its a herbivore crab therefore there was no reason to keep it separately. Of course, I do prefer to be the one that makes those decisions!! The crab is a herbivore, though it will accept a mussel, if offered. I hope that somebody can identify this animal with certainty.
Checking my marine tanks every 2-3 hours when I am at home has become second nature. Usually a quick glance confirms that everything is ok and that all inhabitants enjoy their lives in the tanks. However sometimes I am surprised (nicely or nastily). One of those nasty surprises was when I saw a big crab claw on my sponge. When you see those claws in your tank the first thing that crosses your mind is "Oh, God, its dead". The second thought that crossed my mind is that I had to collect all the pieces otherwise my water would be fouled very quickly. While looking at the tank, searching for more pieces, I started examining the inhabitants to identify the responsible for the crab's early demise. It soon became evident that nobody could be responsible for that. The poor crab must have died by itself. After spending some more time to see where the main body was lying I decided to check one of those pieces closer. I took one of the claws out and examined the opening to see how much flesh was still in it. To my surprise (see below) the claw was empty, surgically clean. It was only then that the word "ekdysis" (moulting) crossed my mind. If it is the first crab you have ever had it is obvious that - despite the homework which was already done - you have to see the phenomenon in order to believe it. After searching the tank more carefully, I found the crab hidden below a rock, trying its new pair of claws. I know that crabs do not moult unless the conditions are favourable (a credit to George here) and that this is a procedure which is really very copious for the crab - this is the reason it will only do it for a definite number of times throughout its life. So my herbivore beauty should be bigger now still waiting for its chitin skeleton to harden enough before attempting one more of its beloved tours of the tank. Needless to say, the old pair of claws was collected and kept as a souvenir from the first ekdysis that took place in my tanks.
Read article on Starting a marine (Mediterranean) tank.
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