The Spanish dancer (Hexabranchus sanguineus) is an unusually large nudibranch — this one was perhaps about 20 cm long — and one of the most strikingly-colored of the incredible spectrum of nudibranchs. I saw this specimen as I re-entered, through a hole that leads to the open sea, a semi-protected 'rock pool' on the very last fumes of air in my SCUBA tank. It was the first of its species that I'd seen and is still the only big one that I've yet encountered. It's hard to forget how majestic it seemed as it moved across the rock pool's boulders. 'Sea slugs' may not sound like something that many would find particularly attractive, but take a look at some of the species shown at The Slug Site and I think you might agree that these animals are amazing for their aesthetic qualities alone. (Hole in the Wall, Northeast PNG coast)
A very large nudibranch on the sand just above the wall at a spectacular inshore drop-off site. This nudibranch seems like it must be a Spanish dancer because of its massive size and general appearance — everything's certainly in the right place and proportion — but the relatively drab color scheme is something that I've not yet seen on any photographs of the Spanish dancer. A quick look at some of the resources linked at the bottom of this Web page confirmed that this species has many different color schemes in its repertoire, so I'm fairly confident that this is a Spanish dancer. The lack of red (there is some red in the color, but not the brilliant shades of the Spanish dancer) is not the result of the strobe being too far away, though I did have a wide-angle lens on when I took this photo, hence the non-frame-filling grandeur of the shot, and there appear quite definite patterns of black lines that I have also yet to see in photos of the Spanish dancer. (Hole in the Wall, Northeast coast)
This Risbecia tryoni nudibranch had me thinking it was the Kunie's chromodoris (Chromodoris kuniei) pictured in my rather sketchy marine-invertebrate ID book until I visited the Sea Slug Forum and found the two and other similar-lookng species. Either way, it's another nudibranch that looks as if it is aglow from the inside. This specimen was tooling about the reef of a lagoonal island. (Wongat Island, Madang)
An appropriately-named magnificent chromodoris (C. magnifica) at night on the fringing reef around the peninsula that was my home for two months. (Jais Aben, Madang)
A pustulose phyllidiid (P. pustulosa) crosses a colorful part of the reef on the side of a deep, current-swept pass in the barrier reef. (Rasch Passage, Madang)
The charmingly-named pustulose phyllidia is a lot cuter if you can get past its name. Comparing these shots with the others on this page gives some idea of how variable this species' coloration is.(Restorf Island, Kimbe Bay)
Another of the same species on a deep seamount. Nudibranchs are basically molluscan snails that have lost their shells, and they are extremely abundant in some coral reef areas, as well as in temperate waters. Papua New Guinea is probably host to more species than anywhere else — 600 or 700 (depending upon who you believe) species have been described from Madang Lagoon, alone, and there may be as many as 1000 species in that one body of water. (Joelle, Kimbe Bay)
A phyllidiid nudibranch (probably Phyllidiella rudmani) crawls across a bright orange microcionid sponge (Thalysias vulpina). (Restorf Island, Kimbe Bay)
Like a Volkswagen parked beside a Cadillac, two phyllidiid nudibranchs sit side-by-side in the shelter of a barrier-reef island. I am fairly sure that both are varicose phyllidias (Phyllidia varicosa) but one or both could be a celestial phyllidia (P. coelestris), a very similar-looking species. Generally, nudibranchs show a lot of variation in color and pattern and these two similar species, in particular, are quite confusing. (Pig Island, Madang)
Probably P. varicosa — the varicose phyllidiid — this colorful nudibranch was hanging on against the current in a barrier-reef pass. (Milinat Pass, Madang)
The same species in a calmer setting, in the lee of a lagoonal island. (Pig Island, Madang)
Close-up of a phyllidiid nudibranch (P. varicosa) on a rubble slope on the east side of a nearshore island. These nudibranchs feed on sponges and concentrate the sponges' chemical defenses in their own tissues. (Restorf Island, Kimbe Bay)
An elegant phyllidiid (P. elegans) on rubble off the shore of a picture-perfect nearshore island. (Restorf Island, Kimbe Bay)
An unknown nudibranch (probably of family Phyllidiidae) on the rubble of a steep-sided nearshore reef. (The Crater, Kimbe Bay)
A colorful nudibranch (Caloria indica) photographed against equally-brilliant reef substrate on a night dive on an open-ocean reef looks like nothing so much as a molluscan harlequin. Many nudibranchs are characterized by vivid coloration that can be almost beyond belief — many are toxic, and it's possible that their bright coloration advertises their unpalatability (such warning coloration is known as 'aposematic' coloration). This specimen was tiny, but some nudibranchs grow to quite a good size. Tubercular nudibranchs — those with the finger-like projections that this species has — feed on hydroids and other stinging organisms and are somehow able to transport their prey's nematocysts (stinging cells) to the tips of their dorsal projections, arming themselves with their own (borrowed) potent stinging defense. (May Reef, Kimbe Bay)
A Forskal's side-gilled slug (Pleurobranchus forskalii) moves determinedly across the sand near a beautiful lagoonal island like nothing so much as a minature Sherman tank. This pleurobranch mollusk was one of several fascinating animals that I encountered while attempting an underwater circumnavigation of the island and was one of the reasons why I never made it out of the island beach's sand slope during that particular dive — the sand can be an interesting place and is definitely worth a closer look! (Wongat Island, Madang)
FeBrina divemaster Andrew, who was my dive buddy on the night dive from which thos and the above picture came, turned up this unusual beastie. I'm not even sure that it's a nudibranch and am still searching for clues as to exactly what it is. A few millimeters long, its back is also covered with finger-like projections, but these ones appeared to be hollow. I recently discovered a photo of a similar-looking animal that's not a mollusk at all, but a marine polychaete worm of genus (Lepidonotus) — a scale worm — so perhaps that's what this mystery 'slug' is. I'll update when I find out for sure. (May Reef, Kimbe Bay)