Anatomy of a Sea Cucumber's Internal Organs

Sea cucumbers are inhabitants of most marine environments. They reside in shallow and warm waters but are also frequently found on the ocean floor. They resemble different types of worms and are classified in the echinoderm phylum (taxonomic rank below Kingdom and above Class). Echinoderms are characterized by the presence of tiny bones, sometimes referred to as ossicles, a water-vascular system, which pumps through an internal opening (maldreporite), suction-tube feet, and by their regenerative abilities.

Holothuroidea

The sea cucumber falls into the holothuroidea class, and while there are many different types of sea cucumbers, they are all distinguished by several common traits. They have oral tentacles, which may arise as finger-like projections, feather-like projections, or flattened, plate-like projections. These tentacles surround the oral opening and are used to retrieve food. As they extend into the oral cavity, they connect to the calcareous ring. On the internal side, this ring is contiguous to the muscles controlling the oral tentacles and the internal muscles that contract the sea cucumber's worm-like body. The ring, decorated with symmetrical spokes on the inside, circumnavigates the throat of the holothuroidea.

Respiration

Also extending from the ring are longitudinal canals, which comprise the water-vascular system. Running along the dorsal (back) and ventral (front) of the sea cucumber are the respiratory trees, which are used for gas exchange. Some species release the respiratory trees through the anus when faced with some sort of danger. The trees become sticky and can entangle or confuse a predator. These organs can regenerate within a just few days.

Digestion

Sea cucumbers posess an esophagus, stomach, and intestine which break down food and then eject it through the cloacal opening and then the anus. Their diet consists of plankton, dead matter, organic materials and algae. In addition, holothuroidea have structures called Polian vesicles, which exist in pairs and pinch off from the calcareous ring on the dorsal side. The job of the Polian vesicles is to maintain body pressure and hold reserve amounts of fluid.

Reproduction

Sea cucumbers have the option of breeding both sexually and asexually. They release sperm and eggs into the water. They also range between one sex or the other, and some are hermaphrodites. They release eggs or sperm from the gonad, which is attached to the oral cavity by the gonad duct, and hovers in the body cavity above the stomach. In order to expel their reproductive materials, they latch on to a hard surface, extend upright, and rock back and forth. The chances of sea cucumber eggs and sperm meeting depend on the concentration of sea cucumbers in that area. This type of fertilization is precarious, as many obstacles arise.

Significance

These sausage-shaped sea creatures live between five and 10 years. They can grow to be about 5 meters. In tropical parts of the world, they are a gourmet delicacy or used by fisherman to lure bigger and tastier sea life to their nets and hooks. In addition, their healing properties are being studied by scientists. Holothuroidea may have anti-inflammatory medicinal advantages.

References

• Tree of Life: Holothuroidea
• National Geographic: Sea Cucumber
• Starfish: Echinoderms