Hint: Megascolex is a family of large-sized earthworms that are found in Australia, New Zealand, and North America. They have multiple nephridia per segment which are kidney like units in invertebrates. They have either lumbricus setae or perichaetine setae.
Complete answer: Megascolex earthworms belong to a class of Oligochaeta. They belong to the family Megascolecidae. These are large-sized earthworms. The Oligochaeta represents a subclass of animals in the phylum Annelida. This subclass includes many aquatic and terrestrial worms which include all of the earthworms. It includes around 10,000 known species of worms. These worms are characterized by setae which are hair-like structures on the surface of the body. The Megascolex may have eight or more than eight setae. These worms lack lateral fleshy protrusions called parapodia.
The worms included in Oligochaeta have a well-segmented body. They have the most spacious coelom or body cavity which they use as a hydroskeleton. Megascolides australis and Amynthas mekongianus are the largest known worms in this subclass. They proliferate in moist and humus-rich soils. They create burrows that are of various sizes. A few of the earthworms are found in trees and among damp moss. They are also found in aquatic environments having a small and slender body. The aquatic worms usually have transparent body walls. The Oligochaeta has four main families called Glossoscolecidae, Moniligastridae, Megascolecidae to which Megascolex belongs, and Lumbricidae.
So, from the above discussion, we can conclude that option B is the correct answer.
Note: The Oligochaetes have their first segment called prostomium as a smooth lobe or cone which lacks sensory organs. The remaining segments of the body have bristles or chaetae. The aquatic worms have larger chaetae as compared to terrestrial worms.