by Dr J Floor Anthoni (2009)
Seaslugs are like the butterflies amongst the flowers, highly specialised
and colourful, often with fantastic shapes. They belong to the molluscs,
the snails, clams and inkfish, yet they look so different. They slide around
on their feet like snails do, but they do not have a hard shell for protection.
They are highly visible and colourful, yet are not eaten. They are highly
specialised in what they feed on, which makes them impossible to keep in
marine aquariums. Their scientific name is nudibranch, meaning naked
gill, because they do not hide their gills inside a shell or sack.
But some can withdraw their gills into their bodies. See also our page
about sea hares.
For corrections and suggestions, e-mail
-- Seafriends home -- images
-- stock photo index -- underwater
photography -- Rev 20090629,
New Zealand's underwater scene is that of kelp forests, usually exposed
to the open ocean. Sessile animals like sponges, bryozoa, hydrozoa and
anemones are not numerous, and where they are found, there is often too
much wave action for nudibranchs. Nudibranchs are delicate feeders specialised
in eating sponges or the polyps of tiny coral-like animals called bryozoa
(moss animals). Because these tiny polyps live inside secure boxes, nudibranchs
have mouths specialised to reach the polyps inside. Even so, one can find
sea slugs specialised in sucking plant sap, crunching hard sponges, and
even ones predating on other sea slugs.
For a very interesting article about seaslugs, visit http://slugsite.us/bow/nudi_han.htm
f050511: sea slugs may have originated from sea hares like
this black-tail sea hare (Aplysia dactylomela), which still has
a thin shell hidden under its skin. Although its gills are on its back,
they are not exposed but hidden under two layers of skin folds.
f050525: the spotted side-gill slug (Pleurobranchia maculata)
is not considered a nudibranch, because it is hiding its gills on the right
hand side under its mantle. Here the gills can be seen poking out from
the rear end of its mantle.
f039237: ornate berthella side-gill slug (Berthella ornata?),
which comes out in the night.
f019307: ornate berthella side-gill slug (Berthella ornata),
photographed at night.
f040422: this green sap-sucking blue-spotted elysia (Elysia
sp.) has no gills at all but its elaborate wings act like gills. It
is a very small sea slug (15mm).
f018701: the archidoris (Archidoris wellingtoniensis)
is a large sea slug, weighing up to half kilogram. It feeds on certain
kinds of sponges and here it has just flattened a yellow nipple sponge
f039911: the archidoris has various colours. Here we encountered
one during a night dive while it was feasting on a salmon coloured sponge.
The scatter in the photo is live zoo plankton.
f040530: the variable aphelodoris (Aphelodoris luctuosa)
is a true nudibranch which is highly variable in colour. All sea slugs
are both male and female at the same time (hermaphrodites) and they can
f039834: two mating aphelodoris nudibranchs. Nudibranchs
mate top to toe as their mating organ is on the righthand side. Because
their shapes are flexible, they can grow or shrink their sexual organs
f003621: although this aphelodoris looks quite different,
it is possibly just another Aphelodoris luctuosa.
f005125: a white nudibranch (Atagema carinata) with
a sandpapery skin, found eating a sponge in a degraded harbour.
f037835: the gem nudibranch (Dendrodoris dennisoni, Dendrodoris
gemmacea) has blue spots on a brown background and a beautiful skirt
all around. Its gills are also spectacular.
f039736: a reddish-brown variant of the gem nudibranch.
f050207: a young gem nudibranch is still mainly white but
already showing its characteristic blue spots.
f050534: the black doris (Dendrodoris nigra) is always
jet black with a thin red margin. Its horns and gills can hardly be distinguished.
f038822: the goldribbon doris (Chromodoris aureomarginata)
is a small but elegant sea slug, always completely white with a gold margin.
f017214: an unidentified doris (Doris granulosa?).
f051020: the clown doris (Ceratosoma amoena) has orange
polka dots on a purple-white skin, with purple horns and purple gills.
It is relatively common. These two are mating and their sex organs are
f038829: a very large clown doris at over twice its normal
size, found in a degraded harbour where apparently their food was plentiful.
f050227: a lemon doris (Dendrodoris citrina) is a
small seaslug with a warty skin and coloured from pale yellow to pale orange.
f050601: an orange lemon doris (Dendrodoris citrina)
found in a rock pool.
f050228: an unidentified doris thought to be a lemon doris,
but this one has a smooth skin and carries its skirt in a different way.
f040034: an unidentified doris with very wide mantle flaps
and a smooth skin.
f040523: an unidentified doris (Rostanga rubicunda?)
feeling robust to touch.
f038806: two flat doris (Platydoris formosa), one
orange and one brown, partly overlapping (or mating?) while eating an orange
f040935: Willans cadlina (Cadlina willani) is only
2 cm long, here feeding on bryozoan firs.
f051418: unidentified seaslug, perhaps a lemon doris, but
well outside its habitat.
1011152: sandpaper doris (Alloiodoris lanuginata)
has a sandpapery hard back but is otherwise pliable as any seaslug. Found
near Leigh during a night dive.
Tambjas Tambjas have their gills on the middle of their backs, and most are
unable to withdraw them inside.
They are found in the cleanest of waters where fragile bryozoa and
hydroid firs abound.
f041308: fine lined tambja (Tambja mullineri). These
dark green sea slugs are always small.
f029405: long lined tambja (Tambja tenuilineata) on
left and on right a much smaller fine lined tambja, feeding on lace-like
f029804: two fine lined tambjas of two different species.
Note that the green crust is a sponge, not a seaweed.
f024329: a morose tambja (Tambja morosa) lost
on an orange crater sponge, must find its way up the cliff again towards
the bryozoan firs on which it feeds.
f037833: morose tambja (Tambja morosa) always has
bright blue marks on a dark black or greenish body.
f029424: the morose tambja prefers to eat bryozoa like these
orange stick bryozoa and the orange bryozoan firs below.
f040924: three Vercoes tambja (Tambja verconis) huddling
together. They prefer to feed on the blue-green bryozoan firs. These sea
slugs are very sociable.
f029425: two beautiful Vercoes tambja tail-gating on a patch
of green-blue bryozoan firs.
f037817: tambja gills are placed in the middle of their backs
and consist of five 'hands'. These are the gills of Vercoes tambja.
f024321: the sea tiger (Roboastra luteolineata) is
green with thin yellow/orange stripes and it hunts other sea slugs like
Sea slugs with gills all over
f018028: beautiful jason (Jason mirabilis) lives only
from the polyps of the hydroid tree (Solanderia ). It is a staunch
climber, its foot designed to hold on tight to the narrow branches.
f013137: two beautiful jasons finishing off the last polyps,
after which they lay ribbons of eggs in the same colour as their bodies.
f012406: this hydroid tree still has a large number of uneaten
polyps but the jason seaslugs make sure that this won't last.
f040927: a Mokohinau janolus (Janolus mokohinau) named
after the Mokohinau islands, is small and rare.
f028924: the fire janolus (Janolus ignis) comes out
only at night and prefers these whitish bryozoan firs.
f037905: a fire janolus (Janolus ignis) on hydroid
f041334: this warty janolus (Galeojanolus ionnae).
Its skin is made up of sticky tubercles that stick to any attacker.
f018320: a tritonia (Tritonia incerta) has two rows
of gills. It is a finger-long seaslug that feeds on the tough deadmans
finger soft corals (orange). Here the coral has withdrawn its polyps in
f032525: a beautiful tritonia (Tritonia incerta) in
search of soft coral, here passing edible colonial seasquirts.
f053613: an interesting observation illustrated by four images.
Here a small Tritonia incerta sniffing its way to its prey, about
20cm away. It knows precisely where to go.
f053616: The Tritonia now approaching its prey, a deadman's
finger Alcyonium cf aurantiacum. It appears an easy kill.
f053619: but before attacking, the Tritonium hesitates and
pauses for almost one minute.
f053620: the Tritonia suddenly lunges forward in 1/4 second,
but equally quickly the polyps withdraw and the seaslug is left without
a meal. But bigger Tritonia can chew through the tough crust of the deadman's
0904037: a young (3 cm) tritonia on a red seaweed, or is
it a different species?
f224634: tiny 5mm unidentified seaslug on a Callyspongia
ramosa thin finger sponge.
f052012: tawny speckled chelidonura (Chelidonura fulvipunctata),
about 3cm, comes out at night.
f036911: Gardiners philinopsis (Philinopsis gardeneri)
is a 2-3cm small slug, found in rock pools by day. It is sociable and often
found together or tailgating one another.These two are joined head to tail.