What does the presence of schistosomes indicate about their life cycle?

The presence of schistosomes indicates that they require a host to complete their life cycle. Schistosomes are a type of parasitic flatworm, belonging to the class Trematoda, and they undergo a complex life cycle that involves both a definitive host, usually a mammal, and an intermediate host, typically a freshwater snail.

In their life cycle, schistosomes are released as eggs in the host's blood, which then exit the host through feces or urine into the water. Upon entering the water, the eggs hatch into free-swimming larvae that must find and infect a suitable snail host to continue their development. Following their time in the snail, schistosomes transform into another larval stage, which eventually seeks out a definitive host, where they mature into adult worms. This parasitic mechanism highlights the importance of both the host and the aquatic environment for their survival and reproduction.

Given this life cycle, it's clear that a complete dependency on a host for development and maturity is essential for schistosomes, underscoring their parasitic nature.