proglottid

A proglottid is a reproductive body segment of most tapeworms (class Cestoda). It forms part of the strobila, the chain of sequentially produced segments that make up the worm’s body. Each proglottid is a self-contained unit containing the organs necessary for sexual reproduction.

Structurally, a proglottid houses complete male and female reproductive systems, including testes, ovaries, oviducts, and a uterus. As proglottids mature, they fill with fertilized eggs. They are formed continuously near the neck region behind the scolex and move posteriorly along the strobila as new segments are produced. When gravid, a proglottid becomes laden with eggs.

Reproduction and transmission occur as proglottids detach from the worm and are excreted with the host’s feces. Fertilization typically happens within and between proglottids along the chain, producing eggs that are released into the environment. In many species, eggs hatch in intermediate hosts, enabling the tapeworm’s complex life cycle to continue.

Clinical and diagnostic notes indicate that proglottids, or their eggs, may be visible in feces or near the anal area of an infected host. The presence of gravid proglottids or characteristic eggs in stool samples is used to diagnose cestode infections. Proglottids can vary in number and size, and some tapeworms may produce thousands of segments, contributing to the worm’s overall length, which can reach several meters in some species.

Proglottids are a defining feature of cestodes; other flatworms do not form such a chain of reproductive segments.