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Presented by Charles & Linda Raabe
Mactan Island, The Philippines
© 2010 All Rights Reserved


    If there is one creature that strikes fear into most hobbyist, its this one. Of course I feel very differently and am a strong advocate of thier usefullness in our tanks. Yes, there are risks involved, but I feel those risks are given far to much publicity.

Safe for a live deep sand bed



Photo by Charles Raabe   Photo by Charles Raabe   Photo by Charles Raabe
Picking up sand to injest and strip of organic matter


With a little knowledge and care taken, a sea cucumber can and will be very helpfull in keeping your sandbed looking clean and fresh. Most everyone has heard of the horror storys of a cucumber "nuking" their tanks, I have never had this happen and know of no one that has. Now Sea Apples are a different story, I would never have one in my tank since they are the most likely to nuke a tank and when they do, its right up there with small nuclear devices.

  Photo by Charles Raabe

   With roughly 6000 known species of Echinoderms alive today, and approximately 900 of those described species are sea cucumbers, it would of course be impossible to describe each one as for its suitability within our aquariums. Within the Echinoderm family, The Sea Cucumbers belong to the Class Holothuroidea, which is further divided into three main groups, although only the first two are commonly sold in the pet trade: the Dendrochirotacea (or filter-feeding sea cucumbers), the Aspidochirotiacea (or deposit feeding sea cucumbers), and the apodacea (or medusa worms). It is the Aspidochirotiacea (deposit feeders) that we would be interested in as the filter feeding sea cucumbers are not suitable for our aquariums. The above photographs show a good example of what the business end (feeding) of a deposit feeding sea cucumber looks like.
    When purchasing a cucumber, as with everything, you should research that specific species, if possible,  I say if possible, because there is very little known as this group of animals is very little studied. Thankfully most deposit feeding sea cucumbers that I am familiar with are very similiar and only differ in their adult size. When choosing from the few varieties of sea cucumber species normaly available to the hobby, I would first ensure that the sea cucumber will not become a very large specimen as it will most likely not find enough to eat within our aquariums.

   The majority of the species of deposit-feeding sea cucumbers that are offered for sale are usualy members of the genus Holothuria.  The most commonly offered is the  tiger-tai, H. hilla from the Red Sea and Indo-Pacific, and H. impatiens or H. thomasi from the Caribbean.  Other species include H. floridana (a mottled and highly variable-colored Caribbean cucumber that is common along the Gulf shores southward along the coast of Central America as far as Colombia), H. atra (a black cucumber from the Read Sea and Indo-Pacific), and H. edulis (the edible sea cucumber which is black along the upper surface, and bright pink along the belly, also from the Red Sea and Indo-Pacific).  Each of these species consume organic detritus and ingest fine-grained sands to digest off the bacteria, microalgae and diatoms that cover the surface of each sand particle, thus cleaning the surface layer of our sandbeds.
   If purchasing from a local store, I would ensure the fish store has had the cuke in their care for at least a month (if possible), I say this because during shipment they can be stressed and may have expelled their "guts", which they do as a defensive measure and it may not survive. Although this is becoming less of a concern as shipping methods have improved greatly.
  Since the most common cause for the demise of a sea cucumber within our aquariums is from starvation, I would not get more than one at first and give it a few months to determine if the single sea cucumber is able to fully process the surface layer of your sandbed. Again, I would not purchase a large species as not only will they most likely slowly starve to death, but due to their size, they very frequently only extend half of their length out of the rock work onto the sandbed, which over due time, means that as they gather sand grains, it all gets expelled back behind your landscape causing those areas to eventualy get a very deep sandbed while the depth of your sandbed at the front of your tank gets shallower by the day.

Photo by Charles Raabe   Photo by Charles Raabe
A species that came into my aquarium as a one inch long hitch hiker and has grown to adulthood since

 
   While not a complicted animal to care for, there are a few concerns to take into consideration when adding a sea cucumber to your aquarium. Not being the quickest or brightest of creatures, any pump inlet that is not covered or protected will pose a very real danger to your sea cucumber. Keeping the inlet guards that should have come with your pump when you purchased it, in place, will prevent any such accidents from happening.
   You will also want to ensure that you do not have any species of fish that are known to be predators of sea cucumbers. Most Trigger fish, some Wrasses and Butterfly fish will nip at the tube feet of sea cucumbers. Although sea cucumbers are nocturnal, our rock landscaping usualy does not provide enough protection to hide in and be completely safe from predatory fish.
   Other than those few simple precautions, a sea cucumber's only real danger within our aquariums is from starving to death. If you notice that your sea cucumber is slowly shriking (getting smaller), then it would be a good idea to try and find it another home that can provide the amount of detritus and organics it needs to thrive.

Photo by Charles Raabe  Photo by Charles Raabe

A note on Sea Apples :  Please do not purchase them. While being very colorfull and a temptation to add one to our aquariums, these animals are not suitable for keeping within our aquariums. Being filter feeders and not deposit feeders as the other sea cucumbers are, they are almost guaranteed to slowly starve to death.  Once stressed or having died, a Sea Apple is one of the most toxic of their family and will kill a great many of your other aquarium pets quickly. The risk is far too great to take a chance on trying to keep an animal that is all but impossible for us to feed properly.


Not suitable for Reef Aquariums


   The most important feature distinguishing the sea cucumbers is a calcareous ring that encircles the pharynx or throat. This ring serves as an attachment point for muscles operating the oral tentacles and for the anterior ends of other muscles that contract the body longitudinally. Sea cucumbers are also distinct as echinoderms in having a circlet of oral tentacles. These may be simple, digitate (with finger-like projections), pinnate (feather-like), or peltate (flattened and shield-like). A third key feature, found in 90% of living species, is the reduction of the skeleton to microscopic ossicles. In some species, the ossicles may be enlarged and plate-like.
   The holothurian water vascular system consists of an anterior ring canal from which arise long canals running posteriorly. Despite their similarity to the radial canals of other echinoderms, these latter structures arise embryologically in a quite different manner. For this reason these canals in holothurians have been recently renamed longitudinal canals. In holothurians, the larval structures that would form the radial canals in other echinoderms instead become the five primary tentacles. Also, holothurians with the exception of members in Elasipodida have a madrepore that opens into the coelom (body cavity). In contrast, elasipodans and nearly all other echinoderms have a madrepore that opens externally.



   Some sea cucumbers possess organs not found in other invertebrates. In some Aspidochirotida, the respiratory trees display Cuvierian tubules. In most species, these are apparently defensive structures. They can be expelled through the anus, whereupon they dramatically expand in length and become sticky, entangling or deterring would-be predators, such as crabs and gastropods. Many forms, with the exception of members of Elasipodida and Apodida, possess respiratory trees used in gas exchange. These are paired, heavily branched tubes attached to the intestine near the anus. This type of breathing ("cloacal breathing") is also present in an unrelated group, the echiuran worms.

    The Orders of Holothuroidea (sea cucumbers)
Apodida
Contains about 269 species in 32 genera and three families. Tentacles are digitate, pinnate or, in some small species, simple. Respiratory trees are absent. Tube feet are completely absent. The calcareous ring is without posterior projections. The body wall is very thin and often transparent. Found in both shallow and deep water.
Elasipodida
Contains about 141 species in 24 genera and five families. Tentacles are shield-shaped and used in shovelling sediment. Respiratory trees are present. The calcareous ring is without posterior projections. With the exception of Deimatidae, the body wall is soft to gelatinous. All forms live in deep water.
Aspidochirotida
There are about 340 species in 35 genera and three families. Tentacles are shield-shaped. Respiratory trees are present. The calcareous ring is without posterior projections. The body wall is generally soft and pliant. Most forms live in shallow water, though one family is restricted to the deep sea.
Molpadiida
There are about 95 species in 11 genera and four families. Tentacles are simple. Respiratory trees are present. The calcareous ring is without posterior projections. The body wall is generally soft and pliant. Most forms live in shallow water, though one family is restricted to the deep sea.
Dendrochirotida
Contains about 550 species in 90 genera and seven families. Tentacles are highly branched and extended to filter material from the water column. Respiratory trees are present. Some members with a calcareous ring composed of numerous small pieces or having long posterior extensions. Possess muscles for retracting the oral introvert. The body wall may be hardened from enlarged plate-like ossicles. Live either attached to hard bottoms or burrow in soft sediment. Most species live in shallow water.
Dactylochirotida
Contains about 35 species in seven genera and three families. Tentacles are simple or with a few small digits. Respiratory trees are present. The calcareous ring is without posterior projections. Possess muscles for retracting the oral introvert. All members have a rigid body encased in enlarged flattened ossicles. The body is usually "U" shaped. All members live burrowed in soft sediment. Most live in deep water.
A SAND DWELLING SEA CUCMBER
   While searching for the sand synaptids, as shown below, I often come across a sea cucumber species sharing exactly the same habitat as the synaptids, always found at least six inches deep in the sandbed areas located at the edges of sea grass beds. At first, I thought that much like other sea cucumbers that they were just using the sand as a day time hiding place, but noting that they are only ever found by me seeming to share the same habits as the synaptids, I took one home and placed it within my aquariums deep sand bed. For a period of three months, I never once saw it come up out of the sandbed yet often saw it up against the glass of the aquarium always at least three inches down. Noting a few extra sand "volcanoes" than normal each morning was another clue as to what this sea cucumber was doing. I fully believe that this species of sea cucumber never comes up out of the sand and spends its life injesting sand grains for organic material much like a surface dwelling sea cucumber does.
  Considering the hobbyists who do not have the luxory of collecting tropical live sand for their DSB and can only hope that the live sand they purchase contains the needed sand infauna to make a deep live sand bed functional, I believe that both this and the synaptid species, if ever introduced or exported to the hobby, would negate a great many concerns with live deep sand beds and at the same time, eliminate the constant need to replenish the tiny sand infauna that we rely upon now, which can be almost impossible to replenish without having to purchase even more live sand to exchange within the aquarium.

Photo by Linda Raabe  Photo by Linda Raabe



  Sea Cucumbers  -  A great article about selecting one, providing their needs and many other concerns dealing with their care.

  More Sea Cucumbers  -  Another great article detailing their needs as well as providing some identifcations.

 




Family - Synaptidae   Order - Apodida
Common name = Medussa Worm
  The Medussa Worms  -  Closely related cousins of the sea cucumbers.

   While not actualy a worm, this family group of sea cucumbers get their nick name simply due to their long, skinny appearance and their lack of any obvious legs, that, and having a crown of feeding appendages that stand out. I see a great many Synaptids out on the sea grass beds crawling along ever so slowly while they mop up the abundant organic debris. With no visible means of propulsion (legs), I had often wondered at how they move themselves across the substrates. It was my wife Linda who quite by accident discovered how they do so. Having microscopic "hooks" covering their skin, enables them to be very "sticky", which Linda found out when her bare leg brushed against one while snorkeling and had it stick to her. Needless to say, She did a fairly good imitation of Jesus as she walked on water back to shore while screaming like a girl.  Being that "sticky" allows the synaptids to anchor any one section of themselves and move across the substrates in an inch worm fashion.

   THE APODIDA :  Contains about 269 species in 32 genera and three families. Tentacles are digitate, pinnate or, in some small species, simple. Respiratory trees are absent. Tube feet are completely absent. The calcareous ring is without posterior projections. The body wall is very thin and often transparent. Found in both shallow and deep water.

   Sand Dwelling Species :  While searching through the near shore sand beds for various worm species, I came across the species shown in the below photos. I remembered how the surface dwelling species are very efficient at collecting organic particles and thought that might the sand dwelling types be as equally efficient.
   Being that our aquarium's deep sand beds are the only truly organic loaded environment we have, and strive to maintain the sand infauna that keeps our deep sand beds functional, I thought with these synaptids, I might be able to avoid the possible problems that an organic laden sand bed might cause to my aquarium system and collected three of them for my deep sand bed. Having had them for quite a length of time now, I can say that they are indeed a great benefit to my deep sand bed. They spend their entire time moving slowly through entire depth of the sand bed injesting the sand and cleaning it of any organics. Their movement through the sand bed also ensures that there are no pockets of stagnant water and sand while at the same time, slowly shifting the sand between the upper and lower levels, preventing any formations of clumps.
   I believe this single species will eventually become popular with reef keeping hobbyists as a means to maintain deep sand beds with little to no effort while enjoying not having to repopulate the normal microscopic sand infauna, it appears that these synaptids easily take over such roles. In due time, it is my hope to introduce these synaptids to the hobby and make our keeping of marine systems a bit easier and much more natural. Might then the deep sand bed critics be forced to find a different dead horse to beat upon.


A 2mb Movie of a Sandbed Synaptid in action


         Photo by Charles Raabe   Photo by Charles Raabe
A sand burrowing Synaptid ( Chiridota sp. ),  Excellent for keeping a DSB functional.

   Normaly I would not recommend the surface dwelling synaptids as a member of a reef aquarium simply because they require a great deal of organic debris to survive. Not something our aquarium systems are set up to provide. That and most species are fairly large, the most commonly seen species here in the Philippines averages two to six feet long. However, on occassion, I do get a small species that hitch hikes in with live rock and appears to do well. Keep in mind that this is an animal that is at the most, two inches long (as shown below) and is the only one in the entire aquarium system. Being that small most likely allows it to just get by on what my system can provide for in the way of organic debris. The smaller species also tend to be nocturnal and rarely seen.

Photo by Charles Raabe   Photo by Charles Raabe   Photo by Charles Raabe
A Typical surface dwelling Synaptid,  which mops up detritus / organics.


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