1. Is the fault in the components that perform any physical action?
Answer: Yes
2. Is the fault in components that move?
Answer: Yes
3. Is the fault in components that make the mechanism move?
Answer: No
4. Does the damaged component need to be replaced before deployment?
Answer: No
5. Can the replaced component be removed?
Answer: No
36) Sea cucumbers, Holothuroidea
Sea cucumbers live in all of the oceans, usually on the ocean floor. They can range from 0.75 inches to 6.5 feet and are omnivores (ÒSea CucumbersÓ). Their unique ability is being able to split in half and create two productive organisms by transverse fission (architomy) and fragmentation.
Transverse fission occurs at specific sites on the body of the sea cucumber. First the connective tissue of the dermis must become elastic enough to split. It is controlled by juxtaligamental cells, which secrete granule-derived substances in response to the nervous system. These molecules use stiparin and tensilin to alter the mutable collagenous tissue (MCT) (Dolmatov). Tensilin can be related to tissue inhibitors of metalloproteinases (TIMPs) (Dolmatov). TIMPs normally block matrix metalloproteinases (MMPs) and develop cross-linked complexes to
strengthen the MCT. When tensilin is present MMP destroys the cross-linked complexes allowing MCT to become pliable (Dolmatov). As the wall becomes more pliable it starts to constrict at the specific sites on the body, which increases as the body twists, stretches, and causes muscle contractions. Right before the sea cucumber breaks into two parts the walls fuse together not allowing any of its organs to escape. The anterior fragment has the aquapharyngeal complex (AC), gonads, and one or two segments of the gut. The posterior fragment has the cloaca, larger portion of the gut, and respiratory trees (Dolmatov). In the anterior fragment, the first descending portion of the intestine (1DP) undergoes partial atrophy while the posterior end is repaired. The 1DP grows back as the intestine from dedifferentiated cells and migration of enterocytes from the remaining 1DP (Dolmatov). The cloaca also develops from dedifferentiated cells and allows the intestine to grow into it to complete the digestive system. The longitudinal muscle bands are formed from coelomic epithelium which covers the muscles (Dolmatov). Respiratory trees also develop from transforming the dorsal wall of the anterior region of the cloaca caused by specializing cells in the luminal epithelium (Dolmatov). The body grows by an outgrowth that appears and dedifferentiates and re-differentiates the cells. In the posterior fragment of the sea cucumber the only major thing to form is the AC and strengthen the wall where it was separated from the other half. The AC is formed from connective tissue swelling and the intestine thinning and growing up the mesentery, while the wall is strengthened in the same way as the anterior end.
“Sea Cucumbers.” National Geographic. National Geographic Society, 2014. Web. 3 Dec. 2014.
http://animals.nationalgeographic.com/animals/invertebrates/sea-cucumber/
Igor Yu. Dolmatov, ÒAsexual Reproduction in Holothurians,Ó The Scientific World Journal, vol. 2014, Article ID 527234, 13 pages, 2014. Web. 3 Dec. 2014.
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