The little shrimp that lives under rocks in clean streams is small, translucent, barely visible, darting for cover when you lift a stone. It is called Paratya, the common freshwater shrimp, and it is everywhere in New Zealand's healthier waterways. It is also tiny. A full-grown adult is the length of your fingernail. But it used to be bigger. Much bigger. There was a giant among shrimps, and it hopped through our rivers for thousands of years before we accidentally erased it. Size and ecological role made it special. A 6-to-8-centimetre shrimp is a substantial creature – thick-bodied, long-legged, with antennae that wave like whips. It would have been visible from the bank, schooling in the shallows, grazing on algae-covered stones. It was a grazer and a shredder – scraping biofilms from rocks, tearing up dead leaves, turning coarse organic matter into fine particles that smaller creatures could eat. It was the river's recycling crew, and it worked tirelessly. It lived in schools, often hundreds of individuals in a single pool. It was nocturnal – hiding under stones by day, emerging at night to feed. It moulted regularly, shedding its exoskeleton to grow larger. It bred in fresh water – unlike many shrimps that need brackish or marine conditions – laying eggs that hatched into tiny, fully formed shrimplets. It was a complete, self-contained, freshwater creature. And it was food. Eels ate it. Bullies ate it. Native galaxiids ate it. Kingfishers ate it. The giant shrimp was a protein pipeline, turning algae and leaves into fish food. Trout and sediment destroyed it. Brown trout were introduced from Europe in the 1860s and 1870s. They are voracious predators of invertebrates – including shrimps. A school of giant shrimps, visible from the surface, slow-moving, would have been an all-you-can-eat buffet. Trout wiped them out in stream after stream. At the same time, deforestation sent silt into the rivers. Shrimps cannot breathe in silt. Their gills clog. Their feeding grounds disappear. They starve, suffocate, vanish. The smaller form of Paratya survived. It is faster, more cryptic, harder to see. It hides deeper under stones. It breeds faster. But the giant form is extinct. A few specimens in old museum jars – alcohol-faded, legs curled, antennae broken – are all that remain. The river hopper is a name for something you will never see. A summer night, a gravelly riffle, and the water surface dimpled by hundreds of shrimps hopping backwards in unison – a shimmer of life, a dance of the detritivores. It used to happen here. It does not happen now. We introduced the trout. We cleared the forest. We silted the stream. Then we wondered where the hoppers went.