Feeding ecology and diet

Trematodes are obligate parasites, which means that they require nourishment from a host organism. Adult digenetic trematodes die soon after removal from the host, while members of Aspidogastrea may survive independently for a month or more.

Digenetic trematode first-stage larvae, or miracidia, do not feed. For this reason, they must find a first intermediate host very quickly, usually within one or two days of hatching. The eggs of some species don't even hatch until they are eaten by the first intermediate host. Miracidia develop into sporocysts, which also do not feed. The redia stage that often develops from the mother sporocyst in some taxa use their mouths to rip away and eat bits of host tissue. In fact, rediae will eat just about anything, including sporocysts of other species.

Adult trematodes attach to the host organism using suckers. They will eat blood cells, mucus, and loose cells; in some cases, they secrete enzymes that begin to digest tissue before consumption. Some genera, such as Schistosoma and Faciola species, adhere to the host in the blood vessels, liver, and other sensitive areas, inflicting damage to the host by releasing toxic materials through their excretory pores. In some cases, high numbers of trematodes can even plug small body passages or openings, like the host's ureter or bile duct; or interfere with digestion or respiration. Occasionally, mollusk hosts are so irritated by these tiny invaders that they begin coating them with layers of nacreous material, turning the trematodes into pearls.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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