Intriguing “living fossil” shrimps discovered at Arapiles

A “living fossil” whose lineage dates back more than 300 million years has been found at Mount Arapiles-Tooan State Park in western Victoria. Tadpole Shrimps (Lepidurus apus viridis) have an intriguing life cycle that can include blowing around in dust for years until they can colonise in temporary puddles.

Parks Victoria Area Chief Ranger Zoe Wilkinson said this discovery in Biodiversity Month is a timely reminder of the many strange and more secretive creatures that exist across Victoria.

Ms Wilkinson said she and The Friends of Arapiles community group were surprised when they climbed to the top of rock outcrops at the park after heavy rains to find the shrimp swimming in a puddle.

“I knew they were something special. They seemed like living fossils and really ancient looking, like the little extinct marine trilobites,” said Ms Wilkinson.

“These animals have an unusual lifecycle. They start life as an extremely hardy egg that can dry out completely and then blow around in the dust and rest in the soil for years.

“When the timing of spring rains is just right, the eggs hatch and the shrimp start swimming around in shallow puddles. They look like a miniature horseshoe crab with a big shield on their back, but only grow to about 40 mm long. Tadpole Shrimp are never found in deeper creeks, streams or ponds where fish and larger predatory insects live. Any that do hatch probably get snapped up pretty quickly.

“Our parks are special places and with the good winter rains, nature is very busy this spring. Although it is easy to overlook the smaller things, I encourage everyone to take the lead from children. Stop, crouch down and take a moment to look around. You’ll be amazed to discover the activity going on in the miniature world within our parks,” said Ms Wilkinson.

Last week Senior Curator in Entomology at Museum Victoria, Dr Richard Marchant, drove to Hamilton to study these animals in roadside puddles.

“These are a very ancient group of shrimps, dating back more than 300 million years. A sign of how primitive they are is their large numbers of legs (up to 70 pairs) which is very different from the more recent crabs and lobsters that just have ten legs,” said Dr Marchant.

“We still know so little of their life cycle. Every animal we looked at was a female carrying eggs and virtually nothing is known about the males. Maybe the males aren’t around for long. We’ll have to sit and wait next time heavy spring rains are just starting to try and decipher the puzzling life cycle of these wonderful animals.”

For more examples of Victoria’s natural riches, see Parks Victoria’s Biodiversity Month social media posts at: https://www.facebook.com/ParksVictoria/posts using #biodiversitymonth