**Core Concept**
The cyclodevelopmental life cycle is a type of life cycle exhibited by certain parasites, particularly those belonging to the phylum Platyhelminthes, which includes tapeworms. This life cycle involves two hosts: an intermediate host where the parasite undergoes asexual reproduction and a definitive host where the parasite reaches maturity and reproduces sexually.

**Why the Correct Answer is Right**
The cyclodevelopmental life cycle is characteristic of tapeworms, such as Taenia saginata and Taenia solium, which have a complex life cycle involving two hosts. In this life cycle, the parasite undergoes a series of developmental stages in the intermediate host, which is usually a vertebrate, before reaching maturity in the definitive host, usually a carnivore. The parasite undergoes asexual reproduction in the intermediate host, producing cysticerci, which then develop into the adult tapeworm in the definitive host.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the cyclodevelopmental life cycle is not characteristic of protozoan parasites, which typically have a different type of life cycle.
**Option B:** This option is incorrect because the cyclodevelopmental life cycle is not seen in nematode parasites, which have a different type of life cycle involving a third-stage larva.
**Option C:** This option is incorrect because the cyclodevelopmental life cycle is not seen in ectoparasites, which typically have a different type of life cycle.

**Clinical Pearl / High-Yield Fact**
Tapeworms with a cyclodevelopmental life cycle, such as Taenia saginata and Taenia solium, can cause significant morbidity in humans, particularly if the cysticerci are ingested. It is essential to diagnose and treat these infections promptly to prevent complications.

**Correct Answer: D. Tapeworms.**