Starfish with 10 or 11 arms have been spotted in deep waters off the Maltese coast, marine biologists have announced. 

It is the first time the unusual-looking starfish species, Coronaster briareus, has been reported in the Mediterranean, with the species usually making its home in the western Atlantic ocean. 

Traditionally, Mediterranean starfish are of the five-armed Echinaster sepositus variety. 

“This is a quite a discovery," said Oceana senior director Ricardo Aguilar. "What we don’t know for sure is how or why these starfish are in the Mediterranean. Either they travelled a long way from the Atlantic into Mediterranean waters, or they simply had not been spotted earlier because the animals were observed in deep waters."

University of Malta biologist and researcher Patrick J. Schembri said the discovery "goes to show just how little we know about the sea which surrounds the Maltese Islands.”

The starfish most people are used to only have five arms.

Researchers from Oceana and the University of Malta spotted 26 starfish at depths ranging from 240 to 562 metres using an underwater robot. Some of the animals reached up to 25 cm in diameter and had a fiery-red colour and characteristic pom-pom-like white wreaths, known as pedicellariae, along the arms, giving them a fuzzy appearance.

The discovery was made in the course of the EU-funded LIFE BaĦAR for N2K project which seeks to identify new marine areas to add to Malta's Natura 2000 sites. The Natura 2000 is a network of protected areas throughout the EU considered to be the largest of its kind across the globe. 

News of the starfish discovery has been published in peer-reviewed journal Marine Biodiversity.