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Phylum Mollusca > Class Gastropoda > sea slugs > Subclass Opisthobranchia > Order Nudibranchia
Nudibranchs
Order Nudibranchia
updated Sep 12
if you learn only 3 things about them ...
Pronounced 'noo-dee-brank', which means 'naked gills'.
In some, the gaudy colours warn of their toxic nature or unpleasant taste.
These slugs eat other animals. Not all slugs are nudibranchs.

Where seen? Nudibranchs may be encountered on many of our shores. They are especially more likely to be seen near reefs. Also on coral rubble and rocky shores with sponges and other encrusting animals. Some are well camouflaged. The colourful ones may also be hard to spot as they blend in with their equally colourful prey. Many are quite small.

What are nudibranchs? Nudibranchs belong to Phylum Mollusca.They are snails of the Class Gastropoda that lack shells as adults.

Features: Nudibranchs have lost their shells as adults; 'Nudibranch' (pronounced 'noo-dee-brank' to rhyme with 'bank') means 'naked gills'. To protect themselves, some produce distasteful substances, toxins and even acids. They advertise this with bright warning colours. Others are camouflaged to match their surroundings. Those that eat colourful creatures such as sponges or corals, may themselves be colourful to match their prey.
Being small and flat, they can easily hide in narrow places.

Some nudibranchs breathe with a flower-like feathery external gill on their backs. Others lack this feathery gill and their gills are hidden between the body mantle and the foot. Many nudibranchs have two pairs of tentacles. One pair is near the mouth called oral tentacles, usually used to sense things by touch. The second pair is on top of the head and called rhinophores. Rhinophores are believed to 'smell' or detect chemicals in the hunt for prey and mates.

Sometimes confused with flatworms, as well as other sea slugs that appear similar but belong to different orders. Here's more on how to tell nudibranchs from flatworms, and nudibranchs from other sea slugs.

Stored stolen stingers: Aeolid nudibranchs have long, slender bodies with clusters or rows of elongated portions called cerata. These contain extensions of the digestive system and may also help the nudibranch breathe. Some nudibranchs, like Cerberilla nudibranch (Cerberilla sp.) protect themselves with the stingers of the sea anemones or corals that they eat. These stingers are passed, undischarged, to the cerata. The cerata of these nudibranchs have special sacs at their tips that contain the stinging cells of their prey. These stingers are undischarged and now protect the nudibranch.Here, the stingers remain 'live', ready to fire off and protect the nudibranch.

What do they eat? Most nudibranchs are carnivores, each species usually specialises in a particular victim. Being small and slow, they feed on immobile creatures like barnacles, sponges, ascidians, hard corals, soft corals, sea anemones, zoanthids, peacock anemones, sea pens and eggs of other creatures including other nudibranch eggs.

Fierce slugs: Like other molluscs, many nudibranch have a rough tongue (called a radula). Each species has specially adapted 'teeth' on the radula to deal with its prey. Those that eat sponges have many scythe-like teeth to scrape at the sponges. Some nudibranchs lack a radula and simply secrete digestive juices on their prey and suck up the soften soupy result.
Others that feed on corals have well-developed jaws to hold onto the coral polyp while they gouge out the flesh with hooked teeth. Those that feed on bryozoans or ascidians have a pair of large teeth to cut open their prey.

Nudibranch babies: Nudibranchs are simultaneous hermaphrodites, that is, each animal has both male and female reproductive organs at the same time. They practice internal fertilisation. So each nudibranch has a complex system of tubes to avoid self fertilisation, to introduce sperm while at the same time receiving sperm from a partner, and for laying eggs.

They mate in pairs, lining up side-by-side, facing opposite directions in order to exchange sperm. Then they go their separate ways and each lays its egg mass, usually on the prey that they eat or on a hard surface nearby. Eggs are often ribbon-like, laid in a rosette. Here's some photos of nudibranch egg ribbons. In most, the eggs hatch into free-swimming larvae which have shells. Often, the larvae only undergoes metamorphosis and settles down when it is near its particular prey! The juveniles lose their shells and eventually turn into adult nudibranchs.

Human uses: Nudibranchs don't do well in captivity and are thus not extensively collected for the aquarium trade. Moreover, some nudibranchs such as the phyllids produce toxins that may kill its tank mates. However, they are part of the attraction for divers and other visitors to natural habitats.

Status and threats: None of our nudibranchs are listed among the endangered animals of Singapore. However, like other creatures of the intertidal zone, they are affected by human activities such as reclamation and pollution. Trampling by careless visitors and over-collection can also have an impact on local populations.

The Blue dragon nudibranch
can be numerous at times.
Beting Bronok , Jul 03


The Black-margined glossodoris is
among the most commonly
encountered nudibranch on our reefs.
St. John's Island, May 05


The Bohol nudibranch is
seasonally numerous.
Sentosa, Jan 06


The Lined chromodoris nudibranch is
another commonly seen nudibranch.
Pulau Semakau, Jun 05


The Polka-dot nudibranch is
very commonly seen.
Pulau Semakau, Jul 08



Purple foot nudibranch laying egg ribbon.
Chek Jawa, Jun 05

Order Nudibranchia recorded for Singapore
from Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist of The Molluscs of Singapore.
+from our observations.
^from WORMS

  Family Aeolidiidae
  Cerberilla asamusiensis (Cerberilla nudibranch)

  Family Actinocyclidae
  Actinocyclus sp. (Fugly nudibranch)
Actinocyclus japonica
Actinocyclus cf. papillatus
Actinocyclus verrucosus

  Family Arminidae
  Armina nudibranchs awaiting identification
Bumpy faced armina
  Armina babai (Big plain armina nudibranch)
Armina carneola
Armina semperi
(Semper's armina nudibranch)

Dermatobranchus sp. (Tiny striped nudibranch)
Dermatobranchus albus
Dermatobranchus ornatus
Dermatobranchus
sp.

  Family Bornellidae
  Bornella anguilla
Bornella stellifer (Starry mouthed nudibranch)
Bornella
sp.

  Family Chromodorididae
  Cadlinella ornatissima

Ceratosoma gracillimum
(Slender ceratosoma nudibranch)
Ceratosoma trilobatum

Chromodoris elisabethina
Chromodoris lineolata
(Lined chromodoris nudibranch)
Chromodoris orientalis
Chromodoris quadricolor
Chromodoris striatella

^Doriprismatica atromarginata=Glossodoris atromarginata
(Black-margined glossodoris nudibranch)
Glossodoris cincta
Glossodoris misakinosibogae
Glossodoris pallida
Glossodoris rufomarginata

^Goniobranchus coi=Chromodoris coi
^Goniobranchus fidelis=Chromodoris fidelis
(Reliable chromodoris nudibranch)
^Goniobranchus sinensis=Chromodoris sinensis
^Goniobranchus tumuliferus=Chromodoris tumulifera
(Cow chromodoris nudibranch)

Hypselodoris
sp. (Pink-gilled hypselodoris nudibranch)
Hypselodoris bullockii
Hypselodoris emma
Hypselodoris infucata
Hypselodoris kanga
(Kanga hypselodoris nudibranch)
+Hypselodoris maritima
(Maritima hypselodoris nudibranch)
Hypselodoris placida

Mexichromis multituberculata
^Mexichromis trilineata=Pectenodoris trilineata

^Miamira sinuata=Ceratosoma sinuatum
('Jolly Green Giant' nudibranch)

  Family Dendrodorididae
  ^Dendrodoris krusensternii=Dendrodoris denisoni (Blue-spot nudibranch)
Dendrodoris elongata
Dendrodoris fumata
(Rose nudibranch)
Dendrodoris kranjiensis
+Dendrodoris nigra
(Black dendrodoris nudibranch)
Dendrodoris singaporensis=^Dendrodoris atromaculata
Dendrodoris rubra=^Dendrodoris fumata
Dendrodoris tuberculosa
(Cauliflower nudibranch)

  Family Discodorididae
  Asteronotus cespitosus

Atagema intecta (Black prickly nudibranch)
Atagema spongiosa (Purple foot nudibranch)

Discodoris boholensis
(Bohol nudibranch)
Discodoris fragilis=^Sebadoris fragilis
Discodoris cf. palma=^Tayuva lilacina

Hoplodoris nodulosa
(Beaded hoplodoris nudibranch)

Jorunna funebris
(Polka dot nudibranch)

Platydoris flammulata
Platydoris scabra
(Platydoris nudibranch)

Rostanga bifurcata
Rostanga
sp.

Sebadoris nubilosa

^Tayuva lilacina=Discodoris lilacina
(Spotted foot nudibranch)

Thordisa villosa
(Yellow foot nudibranch)

  Family Dorididae
  Doriopsis granulosa=^Doris granulosa

  Family Dotidae
  Doto sp. 1
Doto
sp. 2

  Family Facelinidae
  Cratena lineata
Cratena
sp.

Favorinus mirabilis

Phidiana militaris
(Phidiana nudibranch)

Phyllodesmium briareum
(Phyllodesmium nudibranch)
Phyllodesmium magnum

Pteraeolidia ianthina
(Blue dragon nudibranch)

Sakuraeolis nungunoides

  Family Flebellinidae
  Flabellina rubrolineata

  Family Galucidae
  Glaucus sp.

  Family Goniodorididae
  Goniodoridella savignyi

Murphydoris singaporensis

Okenia purpurata

  Family Gymnodorididae (previously in Polyceridae)
  Gymnodoris sp. (Yellow-spotted gymnodoris nudibranch)
Gymnodoris sp. (Tiny black gymnodoris nudibranch)
Gymnodoris alba
Gymnodoris ceylonica
Gymnodoris citrina
Gymnodoris inornata
Gymnodoris rubropapulosa
(Orange-spotted gymnodoris nudibranch)

  Family Lomanotidae
  Lomanotus vermiformis

  Family Phyllidiidae
  Phyllidia elegans
Phyllidia ocellata
(Eyed phyllid nudibranch)
Phyllidia varicosa
(Varicose phyllid nudibranch)

Phyllidiella nigra
(Black phyllid nudibranch)
Phyllidiella pustulosa (Pustulose phyllid nudibranch)
Phyllidiopsis loricata

  Family Polyceridae
  Kalinga ornata

Plocamopherus ceylonicus

Tambja
sp.

Thecacera
sp.

  Family Proctonotidae
  Janolus sp.

  Family Scyllaeidae
  Crosslandia daedali (Sargassum nudibranch)

Notobryon sp. (Notobryon nudibranch)

  Family Tergipedidae
  Cuthona sibogae (Cuthona nudibranch)

Phestilla melanobranchia


Subcuthona
sp.

  Family Tethydidae
  Melibe pilosa=Melibe vexillifera=^Melibe viridis
Melibe viridis
(Melibe nudibranch)

  Family Tritoniidae
  Tritonia bollandi
Tritonia
sp.

Links
  • The Sea Slug Forum by Dr Bill Rudman: everything you could possibly want to know about nudibranchs with fabulous photos and close-ups of nudibranch body parts, larvae and more. And lots of links. Go to the General Topics section and browse the many interesting articles. Dr Rudman helped identify our Chek Jawa nudibranchs and they are featured on his site.
  • The Slug Site has fact sheets with gorgeous photos of various slugs in the Branch of the Week collection.
  • A Guide to Singapore Nudibranchs by Uma Sachidhanandam: though without any description of the nudibranchs, there are lots of photos and locations where the species are found and a list of Singapore nudibranchs.
  • What can nudibranchs tell us about climate change? on the wild shores of singapore blog.
References
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