Trichinella spiralis
Trichinella spiralis is a parasitic nematode (roundworm) which is found in many warm-blooded carnivores and omnivores, including pigs. Males of T. spiralis measure between 1.4 mm and 1.6 mm long and are more flat anteriorly than posteriorly, while females of T. spiralis are about twice the size of the males and have an anus found terminally.
Characteristics of a Nervous System in T. spiralis
Trichinella spiralis larvae within the diaphragm muscle of a pig
Trichinella spiralis is a parasitic nematode (roundworm) which is found in many warm-blooded carnivores and omnivores, including pigs. Trichinella has a direct life cycle, which means it completes all stages of development in one host. Transmission from one host to another host can only occur by ingestion of muscle tissue which is infected with the encysted larval stage of the parasite. When ingested, muscle larvae excyst and enter tissues of the small intestine, where they undergo development to the adult stage. Male and female adult parasites mate and produce newborn larvae which leave the intestine and migrate, through the circulatory system, to striated muscle tissue. There, they penetrate a muscle cell, modify it to become a unique cyst, and mature to become infective for another host. The total time required for this development is from 17 to 21 days. Adult worms continue to produce larvae in pigs for several weeks before they are expelled. Once adult worms are expelled and larvae reach and encyst in musculature, no further contamination can occur.
Although these parasitic nematodes do not have nervous systems, the actions that they perform are similar to those of organisms with nervous systems, and the information above stands as proof. Trichinella spiralis is sensitive to changes in its environment and then is able to act on these changes. For example, when male and female adult parasites mate, their larvae is able to migrate from the intestine to striated muscle tissue. This is action in itself is very similar to the actions performed by a nervous system, as the larvae is able to perform and coordinate its movements. Furthermore, the parasitic nematode can recognize, penetrate a muscle cell, and then modify it to become a unique cyst. All of these actions are performed in a way that would require a nervous system, yet T. spiralis does not have one.
Although these parasitic nematodes do not have nervous systems, the actions that they perform are similar to those of organisms with nervous systems, and the information above stands as proof. Trichinella spiralis is sensitive to changes in its environment and then is able to act on these changes. For example, when male and female adult parasites mate, their larvae is able to migrate from the intestine to striated muscle tissue. This is action in itself is very similar to the actions performed by a nervous system, as the larvae is able to perform and coordinate its movements. Furthermore, the parasitic nematode can recognize, penetrate a muscle cell, and then modify it to become a unique cyst. All of these actions are performed in a way that would require a nervous system, yet T. spiralis does not have one.