Which animal does not possess a larval stage in its life cycle?
A) Ascaris
B) Frog
C) Taenia
D) Pheretima

Hint: Larvae, plural larvae, or larvas, are developmental stages in many animals that occur after birth or hatching but before the adult form is reached. These immature, active forms are structurally distinct from adults and have evolved to adapt to a different environment.

Complete Answer:
In some species, the larva is free-living, while the adult is attached or immobile; in others, the larva is aquatic, while the adult lives on land. The mobile larva expands the geographic distribution of the species in forms with nonmobile adults. The locomotor structures of such larvae are well developed.
A larva has a well-developed alimentary system and can function as a food gatherer in some species (the larval stage occurs when food is abundant). It stores food in order for the transition to the adult stage to take place. Some larvae are involved in both dispersal and nutrition.
Ascaris is monogenetic because it only has one host, a man, through which infection occurs directly. The cleavage pattern is spiral, determinate, and holoblastic. The first larva is formed 10 to 14 days after cleavage and is known as rhabditiform larva or first larva, as it is not an infective stage. In another week, it moults into the second larva, which can infect the host.
Tadpole, also known as a polliwog, is the aquatic larval stage of frogs and toads. Tadpoles have short, oval bodies, broad tails, small mouths, and no external gills when compared to salamander larvae.The majority of tadpoles are vegetarians, though a few species are carnivorous or even cannibalistic.
Taenia solium, a human tapeworm, has a larval stage called Cysticercus cellulosae. The cysticerci are found in pig skeletal and cardiac muscle, as well as human muscles and the central nervous system. Taenia solium infects humans after they consume raw pork.
Earthworms are members of the Annelida family, which reproduces sexually. The cocoon contains many fertilised eggs, but only one embryo develops fully, while the other ova serve as nurse cells. Without a free larval stage, development is direct. The young worm crawls out of the cocoon after 2-3 weeks of development.
Pheretima posthuma is the scientific name for an earthworm in the phylum Annelida. These are worms that have grown in length. They develop from the egg to form the larvae, which then develops into the adult. During the larval stage of the life cycle, there are no changes in the body of earthworms, nor do they form any structures.

The correct Answer is option (D) Pheretima.

Note:
The amount of time spent in the larval stage varies between species. Some have long larval periods, either hatching early, maturing late, or both. Some organisms have a brief larval phase or none at all.