Due to its global position, Australia has a fantastically diverse nudibranch and sea slug fauna that ranges from the intertidal areas down to and beyond 300 metres.
Nudibranchs and sea slugs occur in every marine habitat, including mudflats, sandy rubble bottom, rocky reefs and coral reefs in temperate and tropical regions right around the coast. Many species discovered are endemic and only found in Australia, while others are widely distributed across the entire Asia/Indo Pacific.
Neville Coleman runs Underwater Naturalist Nudibranch/Sea Slug ID courses using his highly acclaimed NUDIBRANCHS ENCYCLOPEDIA as a text ID guide book.
The courses are designed to ease scuba divers, snorkelers and reef walkers over the traditional hurdles associated with scientific nomenclature ( names) and give everybody a better understanding of what Nudibranchs and Sea Slugs are all about.
The Red – backed Doto Doto sp. lives on Gymnangium sp. hydroids that grow along shady gutters and in caves around 20 metres.. It grows to 15 mm and lays a white egg ribbon.
(Lord Howe Island South Pacific)
The number of Australian nudibranchs thought to live in Australian seas is around 2000 or more, species. However, this number increases every few weeks, as more and more new records are discovered and new species found.
In the past, the recording and discovering new records and species was a primary function of the scientific community, complimented by a few enthusiastic amateur specialists.
Scientific specimens are held by various Australian Museums and these were mostly accumulated by Museum expeditions to various areas around Australia. Although Australia has a major natural history museum in each state it does not necessarily mean that there is a curator, or scientist working in each specific marine field.
Nudibranchs belong to the Phylum Mollusca and as such would be under the responsibly of a Curator of Molluscs if the museum employed one.
Originally discovered by the author at 18 metres at Rottnest Island, Western Australia in 9/1971. the Haloed Chromodoris Chromodoris sp. feeds on the sponge Darwinella rosea and grows to 50 mm.
( Rottnest Island, Western Australia)
Although there are hundreds of undescribed species in Australian Museums there are only a few specialists actually describing new species in Australia. So, it is a very slow process waiting for reference names to catch up with the material housed in state museums.
However, we do have some very good nudibranch/sea slug World of Water ID websites where various species of nudibranchs and sea slugs can be compared and identified.
Known from Lord Howe Island and New Caledonia, Coleman's Janolus Janolus sp. is one of the hundreds of Australian nudibranchs and sea slugs awaiting description. It grows to 22 mm and is found beneath ledges on an undetermined bryozoan. The first specimens were recorded in 10/1986.
( Lord Howe Island, South pacific )
Todays new age explorers are underwater photographers and marine naturalists who capture the soft bodied sea slugs and nudibranchs in underwater imagery and share these wonderful sea creatures from nature's richest underwater realms with the world.
In an effort to familiarise the reader with the finite differences between the different ORDERS of nudibranchs and sea slugs that are formally included in the scientific taxonomy ( the scheme of classification of animals and plants) I have included the distinctive characteristic descriptions from NUDIBRANCHS ENCYCLOPEDIA.
Within each ORDER there will be a number of images and captions illustrating some Australian species within that ORDER.
Subclass: Opisthobranchia (O-PIS-THO-BRANK-EE-A)
With such a long, difficult to remember name (Opisthobranchia) and their soft featureless bodies
(out of the water) in comparison to shells, it is no wonder it has taken many years for opisthobranchs to become popular. Yet this subclass of gastropod molluscs has members with remarkable lifestyles and features, colours and shapes which rival the science fiction beings of outer space.
These molluscs may have reduced external shells, or no shells at all in their adult form.
They may have exposed gills, hidden gills, or no gills at all, depending on the respiratory functions of the skin, or other parts of the body (such as pustules or cerata).
Most have a well-defined head, one pair of rhinophores and at least one pair of oral tentacles.
The eyes are reduced, or non-existent in the majority of species, with most only acting as light receptors. Scientists have separated this subclass into eight different orders, four of the most well known are shown here.
BUBBLE SHELLS ID
Order: Cephalaspidea (KEF-AL-ASPID-EE-A)
The name bubble shell gives the general impression that all the species have shells, though this is not always the case. Some epifaunal species have very strong shells, which they can retract into while others may be infaunal and have very thin shells, or none at all.
Typical well known Bubble Shell, the Rose – petal Bubble Shell Hydatina physis occurs in at least 5 Australian States and although it is not endemic to Australia it certainly serves the purpose as a good ID reference to Bubble Shells. It grows to 50 mm, feeds on polychaete worms and lays a white egg mass.
( Rottnest Island, Western Australia)
There are no rhinophores on the head which has an expanded head shield used for burrowing beneath the substrate in search of prey. Most are carnivores feeding on a range of smaller invertebrates including polychaete worms, molluscs and forams. Some are thought to nibble sponges and others eat filamentous algae.
They all emit copious amounts of slime, a few can swim and a number are nocturnal.
Although the Lined Bubble Shell Bullina lineata appears to more associated with algal turf than pure sandy areas this beautiful little bubble shell grows to 20 mm and feeds on polychaete worms. It occurs from Japan to Indonesia, Hawaii, Western Australia, Queensland, New South Wales, Lord Howe Island, and south to New Zealand. ( Cook Island, New South Wales)
SEA HARES ID
Order: Anaspidea (AN-ASPID-EE-A)
Due to large numbers being washed up on the beaches after storms, the habit of forming mating chains in the shallows and squirting out purple ink when harassed, the sea hares are more well known than many other groups.
They have an oral tentacle on each side of the mouth and smaller cylindrical rhinophores on the head. Eyes as such are non-existent, only minute, black-pigmented, photo-receptors are present.
One of the most colourful sea hares found in Australia, the Juliana Sea Hare has a wide distribution, from the Red Sea to Renunion in the Indian Ocean across to the South Pacific. It grows to 190 mm and unlike many sea hares it is not able to swim, due to having fused posterior lobes. Specimens have been observed feeding on brown algae and it has no defensive ink gland.
( Lord Howe Island, South Pacific)
The 'Eyed' Sea hare Aplysia oculifera is an excellent swimmer and 'takes off' at the slightest hint of disturbance. It grows to 100 mm and is found from Japan to north Western Australia.
The body develops posteriorly to a globular shape and a short or long tail may be present. Well developed parapodial flaps enfold the body, which has a thin fragile open-mouthed shell beneath the mantle and purple "ink" glands.
Most species eat green, brown or red algae and seagrass and lay large masses of spaghetti-like egg strings.
Order: Sarcoglossa (SACO-GLOSS-A)
Mostly small in size and diverse in body shape, these intricate complex critters are often difficult to find and even harder to photograph. Some have flamboyant colours, others are all green (similar to their seaweed hosts) and many show extraordinary body filamentation for such small creatures.
This species of Pink – edged Cyerce Cyerce sp. was first discovered by the "Albatross Expedition" of the Indo – Pacific in 1908 and was painted from a living animal so wel that it still stands as an ID guide for today. The species ranges from Japan to the South Pacific and grows to 20 mm.
( Lord Howe Island, South Pacific )
Ranging across the Indo – Pacific Souverbie's Lobiger lobiger souverbii is a shelled sapsucker with enormous lobal ornamentation. During the day it hides deep down in bunches of its host algae Caulerpa cupressoides, coming forth to feed at night. It grows to 15 mm and is generally found in shallow water.
( Lord Howe Island, South Pacific)
They have two rhinophores on the head and the more primitive species (bivalve gastropods etc) may have a thin external shell which they can retract into by various degrees.
Many sapsuckers (especially the green ones) retain microscopic algae components from their food. This process is called chloroplast symbiosis.
Various different kinds of sapsuckers may only be found on one species of algae and are thought to be species specific. Others eat several species of green algae, red algae and diatoms as well as fish and opisthobranch eggs.
Order: Notaspidea (NOTE-ASPID-EE-A)
Medium or large oblong-shaped sea slugs, which have two well developed cylindrical rhinophores on the head and two oral tentacles attached to either side of an oral veil.
Although Forskal's Pleurobranch Pleurobranchus forskalii occurs across the Asia/Indo – Pcific area, my first encounter with this extroadrordinary side – gilled slug was in north Western Australia. It grows to 120 mm and comes in a number of colour variations. However, the pattern can still be identified, even when there are no markings.
Recorded from most Australian States, as well as New Caledionia and New Zealand, this species grows to 40 mm and lays pinkish/orange egg ribbons. It is thought to feed on sponges and corals and has defensive glands on its back which secrete white fluid.
( Port Hacking , New South Wales)
The gill is housed along the right side of the body between the well – developed foot and overlapping mantle.
Some species have flattened internal shells (Pleurobranchaceans), the Umbraculaceans having a flattened limpet-like external shell.
Order: Nudibranchia (NU-DI-BRANK-EE-A)
Nudibranchs are soft or firm bodied elongate slugs which, in their adult form, have no shells. The majority have externally retractable or contractible rear positioned gills arranged around the anus on the dorsal surface of the mantle.
Some have their gills along each side of the body beneath the mantle edge (Phyllidiidae), others respire by way of modified body ornamentation.
The head generally has two contractable or retractable rhinophores; oral tentacles and tentacular foot corners may also be present in many species.
( Houtman Abrolhos, Western Australia)
The Tasmanian Chromodoris Chromodoris tasmaniensis is endemic to southern Australia and can be found from the intertidal zone down to and beyond 50 metres. It feeds on the sponge Darwinella rosea, grows to 60 mm and lays large, direct – developing eggs which hatch out as small slugs.
( Currarong, New South Wales)
Shape and ornamentation is extremely diverse, ranging from smooth, firm, flat ovals (Platydoris) to long skinny serpent-like slugs covered in stinging cerata (Pteraeolidia). Size is variable, ranging from a few millimetres to around 300mm.
Some species may grow to different sizes at different locations depending on suitability and availability of food. Giant forms of the Spanish dancer exist in Indonesia, Fiji and Papua New Guinea but these are generally only observed at night.
Many species are so well camouflaged that detection is difficult, others appear to mimic their food source and may be discreet and inconspicuous. In contrast, the brightly-coloured flamboyant species blatantly advertise their presence to visual predators as a warning deterrent.
Another Australian endemic which breeds by direct – development, Bennett's Hypselodoris Hypselodoris bennetti occurs along the south east coast to just beyond the Queensland border. It grows to 40 mm and lays bright yellow egg ribbons.
(Coff's Harbour, New South Wales)
Feeding on gorgonian sea fans ( Menella sp.) the Ornate Dermatobranchus Dermatobranchus ornatus is widely distributed, from the Red Sea to Australia.
Although it may be seen in several colour variations it always maintains an orange mantle edging. The species grows to 60 mm.
( Port Hedland, Western Australia )
First found by the author at 20 metres off Rottnest Island, Western Australia in 3/1972, the Rottnest Halgerda Halgerda theobroma is endemic and yet to be found anywhere else. It grows to 50 mm.
Present in Australian waters from southern Queensland, south to south Western Australia the Sweet Ceratosoma Ceratosoma amoenum is also found in New Zealand. It has a range of colour variations and grows to 50 mm. The egg ribbons are pink and it has planktonic larval dispersal.
( Esperance, Western Australia)
Another nudibranch discovered by the author at Byron Bay New South Wales in 3/1975, Jackson's Hypselodoris Hypselodoris jacksoni is a common central east coast species which is also known from Lord Howe Island.
( Mooloolabah, Queensland, Australia )
Discovered at Busselton Jetty, Busselton in 4/1972 the orange – barred Mexichromis Mexichromis macropus was not described until 1983. It grows to 30 mm, feeds on Dysidea sp. sponges and is also found in South Australia.
The Briareum Phyllodesmium Phyllodesmium briareum is named after the genus of the soft coral it lives and feeds on. The species is well distributed from the Philippines to Lord Howe Island in the South Pacific. Clusters of symbiotic zooxanthellae can be sen in the cerata. These zooxanthellae photosynthesise, supplying nutrients to the slug.
( Lord Howe Island, South Pacific
A southern Australian endemic originally discovered by the author off Fremantle, Western Australia in 7/1971, the Red Rostanga Rostanga calumnus was described in 1989. It lays it eggs and feeds on the sponge Clathria sp. and is also recorded in South Australia, Victoria and New South Wales.
When I discovered the Abstract Reticulidia Retulidia fungia at Lizard Island, Great Barrier Reef in 11/1975 I thought it was the best thing I had ever found. It was just so unlike any nudibranch, or sea slug I had ever seen before then, almost unbelievable that underwater nature could produce such an extraordinary design.
It was donated to the Australian Museum, but it took somebody else 20 years later to find another and the species was finally described in 1993. It is now known to range from Taiwan to the Philippines and Papua New Guinea and out into the South Pacific to Fiji.
A fabulous sea slug, this Three – lobed Ceratosoma Ceratosoma trilobatum was a new record when I found it at low tide off Darwin Northern Territory in 11/1972. It had been described in 1827 and is very distinctive having two lobes on each side of the body. it is a wide ranging species and occurs from the Gulf of Oman to eastern New South Wales and out to New Caledonia.
When I found this little beauty at Heron Island, Great Barrier Reef in 11/1974, I really thought I had another new species. I did in a way, but another naturalist had found it many years before at low tide in the Whisundays. Black's tambja Tambja blacki was eventually described in 2006 in honour of the intrepid American underwater photographer, Jim Black.
Red – girdled Glossodoris Glossodoris rubroannulata are never that common and generally found in caves or under ledges, feeding on sponge. The species grows to 60 mm and besides Queensland and the Great Barrier Reef it also occurs in New South Wales and New Caledonia. This Australian endemic has also been recorded from Lord Howe Island. When disturbed it gives off a noxious plume of white fluid.
( Mooloolabah, Queensland)
Atkinson's Okenia Okenia atkinsonorum was named for David and Leanne Atkinson who have done so much great work on recording the many species and behaviours of nudibranchs at Port Stephens, New South Wales. The species grows to 25 mm and feeds on the bryozoan Pleurotoichus clathratus.
( Heron Island, Great Barrier Reef)
Endemic to the east coast of Australia, the Splendid Chromodoris Chromodoris splendida has been recorded fro the Great Barrier Reef and southern Queensland down to southern New South Wales. It grows to 50 mm and is known to feed on the sponge Darwinella gardineri.
( Botany Bay, New South Wales)
First found and photographed by Carole Harris, the Rose – ringed Nembrotha Nembrotha roseannulata lives on the stalked, sand – dwelling compound ascidian Sigillina cyanea in areas of moderate current off Port Stephens New South Wales. It grows to 70 mm, lays orange egg ribbons and is a 'dinkum' Australian endemic.
Recorded from Japan to New Soth Wales and out to New Caledonia, the Acute Kaloplocamus Kaloplocamus acutus is a stunning sea slug. Its form, colour and general appearence are outstanding. It grows to 70 mm and has 6 well developed, branched frontal papillae.
( Lord Howe Island, South Pacific)
The Ambiguous Chromodoris Chromodoris ambigua is not uncommon by any means, but there are few images published. It lives from low tide level to 20 metres along the coasts of Tasmania, Victoria and South Australia where it feeds on the sponge Chelonaplysilla violacea.
( Port Phillip Bay, Victoria)
Wherever the the Blue Bryozoan Bugula dentata begins to grow in the summer season off the shores of the southern Australia there is a good chance to find Verco's Tambja Tambja verconis feeding on it. An easily identified species, it is only recorded from New South Wales, Victoria, Tasmania, Victoria, South Australia, south Western Australia and New Zealand.