strobila

Strobila is a term used in zoology with two main senses in different animal groups.

In flatworms of the class Cestoda (tapeworms), the strobila is the chain of proglottids that makes up most of the worm’s body behind the scolex (head). The strobila forms by successive budding of proglottids at the neck region. Each proglottid progresses from immature to mature to gravid as it moves posteriorly. Gravid proglottids contain fertilized eggs and eventually detach from the posterior end of the strobila to exit with the host’s feces, enabling transmission to new hosts. The strobila’s length and the degree of local specialization for reproduction vary among species. Growth occurs through the continual addition of new proglottids near the neck.

In some hydrozoan cnidarians, the strobila refers to the polyp stage produced during strobilation. In this process, a sexually immature polyp undergoes transverse constrictions to form a stacked series of segments, each of which can bud off as a free-swimming medusa or ephyra. The strobila thus functions as an asexual reproductive stage that yields multiple offspring in rapid succession, contributing to the life cycle’s alternation of generations.

Etymology: the term derives from Greek strobilos, meaning a roll, whorl, or wheel.

Note: While both uses share a sense of segmentation and production of offspring, they occur in distinct phyla (Platyhelminthes vs. Cnidaria) and represent different developmental and reproductive strategies.