Answer:
Roundworms:
The size of roundworms ranges from microscopic to as long as a meter long. Most roundworms have a hard, sharp lance on their head, and some have bristles on the head. Most of the roundworms are protected by an adaptable yet solid, furrowed body covering.
Roundworms are very primitive living beings, having no respiratory or circulatory system of a host. They have an empty body with two openings at the closures. Be that as it may, the head isn't particular or recognizable to the unaided eye.
Roundworms reproduce sexually and can finish their life cycle in immature puppies, however as the little pupps immunity system develops (for the most part by a half-year-old enough), the larval phases of the roundworm will become captured and will encyst (become encased in a sore) in the puppy's muscles. They can stay encysted in the pooch's tissues for a considerable length of time or years.