Beguiling beauties: nudibranchs

By Jeremy Wolff | September 8, 2017

While Port Stephens is said to be a hotspot with an estimated 250 different species scattered across the seabed, we’ve narrowed down a list of our favourites.

BRILLIANTLY COLOURED, nudibranchs can be easily spotted clinging to rocks and coral. Although these molluscs may seem vulnerable without a hard shell, the bright, patterned skin of some species protects them by warning predators of their toxicity and foul taste, while other species are highly camouflaged.

“Nudibranchs have always fascinated people, especially scientists who appreciate their varied survival strategies,” says Clay Bryce, a zoologist and mollusc expert at the Western Australian Museum in Perth. There are more than 3000 species worldwide, with 700 in Australian waters.

`Nudibranch’ comes from the Latin word for ‘naked gill’, and refers to their frilly exposed gills. Some have finger-like `cerata’ on their backs, rather than a plume of gills, and they are nearly blind, relying on scent and touch via a pair of horn-like rhinophores on their heads. Like their land-living slug cousins, they are hermaphrodites, with the reproduc-tive organs of both sexes. They can lay up to 1 million eggs, which hatch into larvae. Very few survive, but some will grow to surprise divers with their wonderful colours. 

Photography by Clay Bryce.

Phyllidia Ocellata

(2.5-6CM*)

Common throughout tropical waters of the West Pacific and Indian oceans, this species has brightly coloured wart-like tubercles along its body. As with many nudibranchs, it can secrete toxic chemicals from its glands when harassed.

Phyllidia Ocellata

Flabellina Rubrolineata

(2-4CM)

This species can transfer stinging cells from the hydroids (feathery invertebrates with stinging cells attached to rock) it eats to the tip of its cerata, which can be deadly for predators. It is found from the Indo-Pacific region to the Red Sea and even the Mediterranean.

Flabellina Rubrolineata

Bornella anguilla

(3-7CM*)

Divers and predators are often confused by this creature, because this nudibranch can swim like an eel and is surprisingly fast. Other swim-ming nudibranchs include the enormous ‘Spanish dancer’, which has been recorded at more than 40cm in length.

Bornella Anguilla

Nembrotha purpureilineata

(2-5CM)

Common throughout the West Pacific and Indian oceans, this nudibranch can retract its rhino-phores and gills when attacked. N. purpureolineata is of average size for a nudibranch, but falls prey to much larger species, which can reach lengths of 30cm.

Nembrotha Purpureilineata

Godiva Sp.

(2-4CM)

Species in the Godiva genus are rare, with small populations, and are therefore difficult to describe. They generally have unusual clumps of cerata and large tapering rhinophores. When they are disturbed, their cerata stand erect, up to 1.2cm high. Godiva species also feed on hydroids.

Godiva Sp

Chromodoris westraliensis

(3-5CM)

With its orange pair of tentacles and a tuft of feathery gills, this species is easily recognisable and is endemic to Western Australia. Chromo-dorid nudibranchs feed on sponges, storing the sponge toxins in their own bodies to later release into the mouths of hapless predators.

Chromodoris Westrliensis

Goniobranchus albopunctatus

(4-7 CM)

This rare nudibranch belongs to the Chromodorididae family and is Indian oceans as far north as found in the Indo-West Pacific. Like most nudibranchs, it moves terised by its translucent purple on a broad muscle called a foot,which leaves a slimy trail and makes them easily tracable by predators. it’s particularly conscpicuous with a very wide, yellow foot.

Goniobranchus albopunctatus

Thorunna florens

Identified in the West Pacific and Indian Oceans as far north as Japan, this Chromodorid is characterised by its translucent purple body. However, like other nudibranches, colour variations can be found within the same species. Some have a reddish mantle and two yellow stripes, whole others, such as this, have spots. 

Thorunna Florens