The human liver fluke (Fasciola hepatica) exhibits a complex digenetic life cycle with distinct larval stages, where the free-swimming ciliated larva enables dispersal from the snail intermediate host. For Q.26—”Free swimming ciliated larva of human liver fluke is”—the correct answer is option 3: cercaria.

Option Analysis

Option 1: Miracidium
Miracidium is the first larval stage, ciliated and free-swimming, but it hatches from eggs in freshwater to penetrate snails specifically, not associated with liver fluke dispersal post-snail. Short-lived (few hours), it lacks a tail.
Incorrect; precedes snail infection, not the post-snail free-swimming phase.​

Option 2: Sporocyst
Sporocyst is a sac-like, non-ciliated generation inside the snail’s tissues, undergoing asexual reproduction (polyembryony) to produce rediae. Stationary and internal, no free-swimming phase.
Wrong; not ciliated or free-living.​

Option 3: Cercaria
Cercaria is the final snail-derived larva: tail-bearing, ciliated, free-swimming in water for hours/days, exiting snails en masse under favorable conditions (warm, moist). It encysts as metacercaria on vegetation.
Correct; matches “free swimming ciliated larva” precisely in liver fluke cycle.​

Option 4: Metacercaria
Metacercaria is the encysted, infective stage on plants/herbage, dormant and non-motile (no cilia or swimming). Excysted by definitive host digestion.
Incorrect; sedentary cyst, not free-swimming.​

Life Cycle Stages Overview

Cycle: Eggs → miracidium → snail (sporocyst/rediae → cercariae) → metacercaria → adult in bile duct. Requires snail (Lymnaea) intermediate host.

Exam Relevance

Essential for CSIR NET/GATE Parasitology: Distinguish trematode larvae—miracidium (egg hatch), cercaria (snail exit). Human infection via contaminated watercress; fascioliasis causes liver damage.