Crustaceans: The Swiss Army knife of life

Crustaceans are like the Swiss Army knife of life, revealing an appendage for any occasion. Multifunctionality is the crustacean M.O., with their limbs cleverly turning to just about any task.

Over many millennia these limbs have modified themselves, becoming sensory organs, mouth parts for feeding, weapons for defence and attack, specialised swimmers, tools for cleaning, grasping, digging, mating, and holding young.

These assorted appendages reflect the huge diversity of crustacean species, and even more the diversity of the environments in which they thrive – from the depths of ocean trenches to rocky shores, mud flats, damp underbrush, and even underground.

Some crustaceans have mastered multifunctionality, while others specialise in a particular function. The skills illuminated below are but a glimpse at a single feature among a multitude we can find in these complex creatures.

Alert antennae

Southern kōura, (Paranephrops zealandicus), Dunedin, 2016. Photo by Danilo Hegg

The amazing antennae are like an extension of the kōura’s brain, receiving and reporting on complex intel of its surroundings. This can be handy in the variable visibility of the open ocean. Before the kōura ventures from the comfort of its sheltered nook to brave the open water, it employs these adroit appendages. Flick, swish, the antennae are activated.

Sensitive to environmental stimuli, the first sign of danger is a stirring in the water. But these are more than mechancical feelers that can detect food or dangerous movement. The antennae’s chemosensory receptors prickle as a foreign smell wafts toward the kōura. A potential predator. Trusting its feelers, the cautious kōura retreats back into its rocky home.

Legging it for food

Cluster of gooseneck barnacles (Lepas anatifera) with cirri extended to catch planktonic food. Photo by Crispin Middleton / Seacologynz

Feather-like legs, or cirri, unfurl gracefully from the mouth of the goose barnacle, extending out into the water column to lie in wait for plankton and food particles to become caught up in their feathery filter.

Once its waving legs are tickling with food, the cirri are pulled back into the shell. Safely inside the barnacle’s hard shell, food is cleaned off the cirri and passed along to the stomach for digestion.

World-class weapon

Mantis shrimp (Anchisquilloides mcneilli) with its front limbs folded in. Photo by Peter Marriott. NIWA

Spying its prey, the mighty mantis shrimp takes its mark. Its raptorial limbs are poised, hinging like a velociraptor’s. Ready, set, attack.

In a flash, the spear-tipped limbs shoot forward, at the speed of a bullet from a gun. The idle fish does not see it coming. The jagged spear pierces through the fishes’ belly. The gratified mantis retracts its spear, along with its freshly caught dinner.

Deft diggers

The paddle crab (Ovalipes catharus) of New Zealand. Photo by Rick Webber

The aptly named paddle crab is a keen swimmer, using its oar-shaped back legs to sweep smoothly through the water. A snapper fish looms before the crab, disrupting its high tide swim.

The snapper eyes our crab – it’s hungry. Three times the size, the snapper is the clear champion to back, but this crab has another trick up its proverbial sleeve. Quickly, the crab uses its paddles to dig itself backwards into the sandy seabed. Beady eyes and antennae are all that peer out of their seabed burrow.

Look too quickly and you’ll miss this shy crustacean – just like the startled snapper.

This page was developed in association with NIWA Taihoro Nukurangi.