Question

Rhabdites occur in
A. Planaria/Dugesia
B. Fasciola
C. Taenia
D. Echinococcus

Answer 1

Hint: Rhabdites are rod-like structures, found in the cells of the epidermis in certain turbellarians, and in nemerteans. Rhabdites release with mucus and form a thick layer outside the body. They are a defensive mechanism, they are distasteful to most animals who would prey on rhabditid worms.

Complete answer:
Rhabdites is a greek word, which means rod-like. So, rhabdites is a minute, smooth, rod shaped structure, found in the cells of epidermis of some class of platyhelminthes. Rhabdites is a characteristic of Turbellaria but also found in nemerteans, gastrotricha and annelids. The actual function of Rhabdites is unknown but it helps in the defence mechanism of the worm. They release with mucus and form a thick layer over the body and provide adhesion, especially in strong currents. Rhabdites is distasteful to the animals who would prey on rhabditid worms. They also appear to be connected to ciliary motion.

We have four options:
> Planaria is a flatworm of the class Turbellaria. The scientific name of Planaria is Dugesia tigrina.

> Fasciola is commonly known as liver fluke, it is a genus of parasitic trematode.

> Taenia is a genus of tapeworm that includes some parasites of livestock which cause taeniasis and cysticercosis in humans.

> Echinococcus is a genus of cestoda which is a parasitic class of the platyhelminthes phylum.
As Planaria belongs to the class Turbellaria.

Hence, the correct answer is option (A).

Note: There are two terms rhabdites and rhabditis. Rhabdites is rod-like structures, found in the cells of the epidermis in certain turbellarians, and in nemerteans and rhabditis is a genus of a free-living, saprophytic, rhabditiform nematode which cause otitis externa in cattles. So, don't confuse between these two terms.