ARTICLE 138    February 2016

SUMMER'S BLUE INVASION - Sea Lizards

by Jenny Edwards

 

Bluebottles, By-the-wind Sailors and Violet Snails (Janthina) ) that float on rafts of bubbles have all been washing ashore lately.  Among them are peculiar little creatures called sea lizards or ocean sea slugs that have prompted quite a few people to contact Nature Coast Marine Group to ask what they are.

 

Sea lizards (Glaucus spp) are only about 35mm long at most but after being tumbled by the waves they are usually folded up to blue or silver blobs half that size.  We found some floating in rockpools at Broulee and were able to see them undamaged.

 

Sea lizards are a type of nudibranch (naked-gilled sea slugs).  Two species occur around Australia.  They drift upside down under the surface film of the ocean. On each side of its body a sea lizard has three outgrowths.  They are each shaped a little like a hand with many fingers called cerata.  These are used to “row” the animal and to somersault it back to its preferred position if it is turned over by the waves.  A sea lizard also has floaties in the form of a gas bubble in its stomach to help keep it near the surface.

 

The cerata have other uses.  They help with respiration and the digestive system extends into them.

 

Both species eat Bluebottles and By-the-wind sailors (Vellella vellella).  The sea lizards are able to digest their prey without discharging the stinging cells.  They select the most venomous of these cells and pass them to the tips of the cerata where they are concentrated.  When the cells mature they can be used by the sea lizard for defence and have been known to give a particularly nasty sting.

 

When seen from above a sea lizard has bands of light and dark blue on it uppermost or foot side (as pictured).  From below the animal looks silver.  This counter-shading helps camouflage it.  To a sea bird, the sea lizard’s blue colouring blends with the ocean.  To a fish, the silver side looks like the shiny under surface of the water.

 

When it comes to sex, sea lizards find their cerata tend to keep them apart so they have very long penises compared to the length of the animal. Sea lizards lay a short single strand of eggs in a tube of invisible mucus.  Imagine a microscopic pearl necklace.  The strings drift in the water until the larvae hatch.

 

The Margined or Little Sea lizard (Glaucilla marginata) is the most common in our area.  It looks much the same as its larger cousin (Glaucus atlanticus) but has a shorter tail and has multiple rows of cerata instead of a single row.

 

The Nature Coast Marine Group has an extensive program of activities where members can have fun learning about our marine environment.  New members are always welcome.  To find out more about the Group and to see other stories in this series, visit the website www.ncmg.org.au or search for Nature Coast Marine Group on Facebook to see our videos and follow us there.

 

Photo by Jane Elek           The larger Sea lizard at Broulee