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June 2020

Prickly youngsters

While casting for bait I unfortunately caught these little crustaceans. They felt like touching broken glass. I could see three large barbs, one protruding from the head the other two from the rear or tail. I have fished the region and this river for years and I have never seen them before.

Answer

Mantis shrimp larvae, unknown species. Photo: David Falchetti.

Illustration of a larval Alima neptuni by Ernst Haeckel. Note the sharp front spine (rostrum) and pair of rear spines on the carapace. The feathery rear appendages are used for swimming.

Adult Peacock Mantis Shrimp (Odontodactylus scyllarus). Photo: QM, Gary Cranitch.

Our curator of crustaceans said that they look like “stomatopod (mantis shrimp) larvae. The long single spine is the rostrum, and the typical stomatopod tail must be tucked under the shell to form the bulbous lump that looks a bit like a head sticking out.”

Mantis shrimps are famous for their bright colours, keen eyesight, and lightning-fast strikes. Some species pair for life. After mating the female broods a mass of eggs (in some cases tens of thousands of them!) under her abdomen, before the tiny larvae hatch and swim away to begin life on their own. Larval crustaceans commonly look little like adults, and in many cases were initially named as separate species by scientists. Larvae undergo several moults (shedding of their exoskeletons) as they age, increasing in size and changing shape with each moult. With each moult, they start to look a little more like an adult. Free-swimming crustacean larvae form part of the marine zooplankton, and are a major food source for many other marine animals. Thus, relatively few of the numerous larvae that hatched from a single egg mass will survive to adulthood. However, the sharp spines of these mantis shrimp larvae may deter some would-be predators!

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