This is a Short-tailed nudibranch, a very colourful relative of snails and slugs. This amazing animal is one of Victoria’s largest and most common nudibranchs!
This species lives on the seafloor moving along using its muscular foot, feeding on sponges. Being a soft-bodied animal without a shell, it needs a way to protect itself from its predators. Given that it is so brightly coloured, camouflage is not its chosen survival strategy. Instead, it moves about in plain sight advertising its presence, knowing that predators will leave it alone. Why? The sponges that it eats provide the answer.
This nudibranch concentrates noxious chemicals from the sponges it eats, storing them in a red patch or “horn” behind its gills. The chemicals, which have an unpleasant taste, act as a chemical deterrent to would-be predators. It is suggested that the bright colour of the “horn” acts as a lure, attracting the predator, who will have a nasty taste in its mouth after taking a bite.
The name nudibranch means naked gills and on this nudibranch, the gills rise as a feathery plume at the tail end of the animal. These nudibranchs can withdraw their gills into their body to prevent a predator nibbling on them.
To make sense of its environment the nudibranch does have eyes, but they are small and buried beneath the skin. These eyes can only detect light and dark. As the nudibranch is effectively blind, it needs to use other senses to navigate its environment. Its main sensory organs are the two rhinophores sticking up at the front of the body. Each rhinophore has an elaborate array of taste and scent receptors which detects various chemicals in the water. These chemicals may be from their food, other nudibranchs, potential mates or predators. To protect the rhinophores from damage, a nudibranch can withdraw into a pocket beneath the skin.
Nudibranchs are hermaphrodites, which means they have both male and female reproductive organs, but they do not fertilise themselves. After mating, eggs are laid on a solid surface in a ribbon of jelly. The short-tailed nudibranch lays the eggs in a counterclockwise spiral. The eggs hatch and the larvae join the plankton community for a short period of time. At this stage of their lives, they have a shell which is lost when they change from the larval stage into a juvenile nudibranch.
So next time you are looking around the rocks at low tide keep a lookout for this nudibranch. There are so many different species of nudibranchs. Watch this video to see some amazing nudibranchs.
If you would like to learn more about the fascinating world of nudibranchs and the huge diversity of life that can be found in the shallows along our shorelines please contact Education Director Mandy Robertson on education@dolphinresearch.org.au
