Meet the wonderful Sea Cucumber. This is actually an animal, it is alive and it responds to your touch. This is known as an echinoderm. It is in the same phylum as the sea stars and urchins. These animals seem to be vastly different, but they have one characteristic that puts them all in the same phylum. When a cross-section is observed each of these animals, barring an injury are visibly divided into 5 fairly identical sections, the sea cucumber being on one side tends to change the “bottom” section a bit.. This characteristic is the reason they fall into the Enchinoderm Phylum. They also have an endoskeleton just below the surface of the skin. This is composed of microscopic, calcified ossicles that are interconnected by connective tissue.
Sea Cucumbers are most often found in sea grass beds or in sandy areas around the reefs. The importance of this animal is to clean the sands. It acts as a vacuum taking in sand and processing it in the stomach area and releasing it out removing most everything but the sand. There are several varieties here in our reef, the two most commonly found here are the Donkey Dung (Holothuroidea Mexicana) and the Furry (Astichopus multifidus).
Like most other echinoderms when threatened Sea Cucumbers lose parts of their body and have the ability to regenerate the lost parts. In the case of the Sea Cucumber they basically eject their stomachs from the inside and push it out the anus. Another form of defense that some Sea Cucumbers employ is to release a series of sticky string-like substances that entangle and confuse predators.
Mobility and Communication:
Sea Cucumbers are actually very mobile as most have hundreds of tiny tube-like feet to propel them along the ocean floors. Communication is complex and typically done through a series of hormonal releases into the seawater. When a female release her eggs, she releases a hormone to inform the males that there are unfertilized eggs and they need to release sperm nearby. They can be found in large groups or alone.
The Sea Cucumber uses a water vascular system in place of a circulatory system. This system forms a sort of hydraulic system that enables the “legs” to move about. It also employs a secondary circulatory system known as a haemal system. This is composed of a series of rings with the central haemal ring attached to the pharynx and runs along the water vascular system, but have a series of vessels running along the radial canals and opening or sinuses. In larger species these vessels are connected to many muscle ampules that operate as a series of “hearts” pumping the fluids throughout the body.
The mouth area of all Sea Cucumbers have modified feet that are larger and more specialized. These “mouthfeet” are more like retractile tentacles and work in that fashion helping to draw things into the mouth to be digested. Sea Cucumber have the penta-radial symmetry, but because they have developed into a more bi-lateral symmetry on the outside it is not immediately evident just by site. The fact that all the feet are located on one side and they are moving along on the “bottom” the radial symmetry might be slightly off in size and shape on that side.
The Sea Cucumber can reproduce both sexually and asexually. Most commonly reproduction is done sexually by a mass release of sperm and egg cells by a large number of Sea Cucumbers within proximity of each other. During the developmental stages most zygotes are free-floating and are often consumed by plankton feeders due to their small size in the early stages. There are about 30 species which pick up the zygotes and internally develop them inside a small pouch. These zygotes will then be released as small juveniles.