The slender rhabditiform larvae of which of the following helminths move about in water and are ingested by species of cyclops-
**Core Concept**
The question is testing the student's knowledge of the life cycle of a specific helminth, specifically the migration of larvae in water and their ingestion by a particular invertebrate host, cyclops. This concept is crucial in understanding the epidemiology and transmission of certain parasitic infections.
**Why the Correct Answer is Right**
The correct answer is Dracunculus medinensis, the Guinea worm. The slender rhabditiform larvae of D. medinensis are indeed ingested by species of cyclops, a type of small crustacean that serves as the first intermediate host in the parasite's life cycle. The larvae then undergo development and eventually infect the cyclops, which are then ingested by a human host, typically through drinking contaminated water. This is a critical step in the transmission of the parasite to humans.
**Why Each Wrong Option is Incorrect**
* **Option A:** Ascaris lumbricoides - The larvae of A. lumbricoides are ingested through contaminated food and water, but they do not migrate through water and are not ingested by cyclops.
* **Option B:** Toxocara cati - The larvae of T. cati are primarily ingested through contaminated soil and are not associated with cyclops.
* **Option C:** Anisakis simplex - A. simplex is a marine nematode that infects fish and is ingested by humans through raw or undercooked seafood, but it is not associated with cyclops.
**Clinical Pearl / High-Yield Fact**
The Guinea worm infection, caused by D. medinensis, is a classic example of a "waterborne" disease, highlighting the importance of safe drinking water in preventing parasitic infections.
**Correct Answer:** D. Dracunculus medinensis.