Question

Aurelia has
A. Two smooth oral arms
B. Two nematoblast rich oral arms
C. Four tentacles
D. Four cnidoblast rich oral arms

Answer 1

Hint: Cnidoblasts are one of the distinguishing features of the Cnidarians. Aurelia is also a Cnidarian. Its manubrium has four oral arms.

Complete answer: Aurelia sp., also commonly known as jellyfish has an umbrella-like framework i.e. the structure is inverted. Aurelia's the concave or sub-summit structure has a mouth called manubrium.
It carries four lobes which are called oral arms. The oral arms are abundantly furnished with stinging capsules or nematocysts found in cnidoblasts or cnidocytes.
Now what are cnidoblasts – these are cells that contain one giant secretory organelle called a cnidocyst. It can give other species a sting.
The phylum Cnidaria is characterized by the presence of this cell called cnidocyte.

So, the correct option is D. Four cnidoblast rich oral arms

Note: The jellyfishes are the common names of some animal species of the phylum Cnidaria or Coelenterata. Aurelia is a scyphozoan jellyfish species.
These animals are usually referred to as moon jellies.