| |
Nudibranchs
Order Nudibranchia |
|
|
Kanga
nudibranch
Hypselodoris kanga
|
|
|
| Nudibranchs
are tiny but among the most beautiful and spectacular mollucs.
They are sometimes seen on the coral rubble area. |
|
'Nudbranch'
means 'naked gills'.
|
|
Snails with no shells: Nudibranchs
are gastropods like the more familiar snails. Nudibranchs, however,
have lost their shells as adults. 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 also easily hide in narrow places.
Stored stolen stingers: Some nudibranchs
have projections on their backs called cerata. These contain extensions
of the digestive system and may also help the nudibranch breathe.
Some nudibranchs (like the Cerberilla
nudibranch) can protect themselves with the stingers of the sea
anemones or corals that they eat. These stingers are passed, undischarged,
to the cerata. These cerata have special sacs at the tips that store
the stinging cells. Here, the stingers remain 'live', ready to fire
off and protect the nudibranch.
Nudibranch features: Some nudibranchs
breathe with a flower-like feathery external gill on their backs.
Many nudibranchs have two pairs of tentacles. One pair is near the
mouth. The second pair is further back and called rhinophores. Rhinophores
are believed to detect chemicals in the hunt for prey and mates.
Nudibranch food: 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. Each species
has specially adapted teeth to deal with its prey. Those that eat
sponges have many scythe-like teeth to scrape at the sponges. Some,
like the Blue-spotted nudibranch,
lack these special teeth and instead, releases digestive juices that
dissolve the sponge into a soup which is then sucked up. 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.
Baby: 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. 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. However, they are part of the attraction for divers
and other visitors to natural habitats. |
|
Kanga nudibranch
Hypselodoris kanga
Villosa nudibranch
Thordisa villosa
Blue-spotted nudibranch
Dendrodoris denisoni
Polka-dot nudibranch
Jorunna funebris
(About 5cm)
Cerberilla nudibranch
Cerberilla sp.
|
|
quick
facts
Small ones about 1-5cm, large ones can reach 8-12cm. They
are sometimes seen in the coral rubble area, seagrass lagoon and sand bar.
Classification:
Subclass Opisthobranchia
Class Gastropoda
Phylum Mollusca |
