Sea Slugs
were @SpeciesofUK from 20th to 26th January, 2014.
Sea slug
is a common name given to thousands of marine gastropod molluscs that lack
external shells.[1]
They are related to our familiar land-dwelling slugs and snails.
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| Polycera quadrilineata [Flickr Creative Commons © Frank Gloystein] |
The main
grouping of sea slugs is the so-called ‘nudibranchs’.[2]
It is these that form the subject of this post.
Nudibranchia is a clade (subgrouping) of gastropods.
Nudibranchs
are found right across the world, from Antarctica to the UK. However they are
most abundant in tropical waters. Most (but not all) spend their lives crawling
on the sea floor.[3]
There are
more than 3,000 known species of nudibranch. And new ones are being identified
all the time.[4]
They are
usually oblong-shaped, sometimes quite thick, other times rather flattened.
They vary from 0.5-31 cm long.[5]
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| Ancula gibbosa [Flickr Creative Commons © Ken-ichi] |
Some
nudibranchs live for only a couple of weeks. But others can live to the ripe
old age of one year.[6]
The word
‘nudibranch’ comes from the Latin for naked and the Greek for gills.[7]
There are two main types of nudibranch – dorids and
eolids.
Dorid
nudibranchs have gills shaped into branchial plumes in a rosette on their
posterior end.[8]
By
contrast, eolid nudibranchs have obvious cerata (finger-like appendages) on
their back which functions as gills by enabling gaseous exchange directly into
the body.[9]
All
nudibranchs are molluscs so they have a shell, but it's shed in the larval
stage, leaving them with just a fleshy covering, or 'mantle'.[10]
 |
| The White Fleshy Mantle of Polycera quadrilineata [Flickr Creative Commons © Eric Burgers] |
The
mantle can extend out in the form of growths, for example the elegant cerata of
eolid nudibranchs or as ‘tubercules’ (spotty growths).[11]
 |
| Coloured Cerata on Cuthona caerulea [Flickr Creative Commons © Christophe Quintin] |
.JPG)
On a nudibranch’s
head there are two ‘rhinopores’. There are sensory tentacles, rhino being
Ancient Greek for nose.[12]
 |
| Nudibranch Rhinopores [Wikimedia Commons © Scott F Cummins et al] |
The rhinophores work by detecting chemicals dissolved in the water and sometimes currents. Most species can withdraw them into a protective pocket.[13] They are similar in principle to the sensory tentacles of terrestrial snails.[14]
In many
nudibranchs, the gills form feather-like structures around the anus.
 |
| Gills of a Nudibranch (rear of this image) [Flickr Creative Commons © Asbjørn Hansen] |
The eyes
of a nudibranch are simple and able to detect little more than light or dark.[15]
Sea slugs can be extremely colourful!
There is
a huge amount of variation in the colours and patterns of sea slugs. Many are
downright drab, but others have become renowned for their spectacular, bright
colours.[16]
 |
| Janolus cristatus [Flickr Creative Commons © Antoni] |
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| Flabellina pedata [Flickr Creative Commons © Manuel Sánchez-Mateos Paniagua] |
Sea slugs derive their colour from the food they eat. This explains some of the brightness but also why many are actually very well camouflaged.[17]
They are carnivores.
Nudibranchs
eat sponges, anemones, corals, barnacles and even other nudibranchs.[18]
They feed
by scraping off bits of their prey using their radula (a chitinous ‘tongue’).[19]
Some eat
poisonous species and cleverly retain the poisons themselves and secrete these
as a defence against their own predators.[20]
Nudibranchs have both male and female reproductive
organs.
This is
extremely beneficial to these solitary, slow-moving animals. When a nudibranch
meets another nudibranch, it knows it’s definitely a potential mate, as it has
all the right parts![21]
Nudibranchs
mate by lining up side by side with their right sides together. They both pass
a sperm packet to each other, and they both lay eggs.[22]
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| Mating Nudibranchs [Flickr Creative Commons © Lenny Cliffbanger] |
 |
| Mating Nudibranchs [Flickr Creative Commons © Dan Hershman] |
After about a week nudibranch eggs develop into free-swimming larvae, and later settle on the ocean bottom to grow into an adult.[23]
Strange but true...
Some sea
slugs are solar-powered. They store algae in their outer tissues and live off
sugars produced by the photosynthesis.[24]
Sea slug species.
Here’s a quick run
through of some of the sea slug species you could find around the UK.
Facelina annulicornis has a translucent body with scattered spots of
white pigment. It’s uncommon, and found
in the southern parts of the British Isles.[25]
Diaphorodoris luteocincta has a white mantle with a yellow rim and central
red blotch on the back. It’s found all around the UK.[26]
Onchidoris bilamellata has a brown pigment pattern and many club-shaped
papillae on the mantle. It has numerous retractable gills in a horseshoe.[27]
Acanthodoris pilosa has a unique ‘fluffy’ appearance. The colour is
variable from white to brown, purple and black.[28]
Polycera quadrilineata is translucent white with patches of yellow or
orange pigment forming
five longitudinal lines. Some individuals have fine black spots over the body.[29]
Tritonia hombergii
is the largest UK nudibranch, growing up to 20cm in length. The colour varies from white to
pinkish-brown. It has many irregular sized gills arising from the mantle edge.[30]
Tritonia nilsodhneri is pale pink or white. It is extremely well camouflaged on its
prey, the gorgonian coral Eunicella
verrucosa.[31]
Aeolidia papillosa is the largest eolid nudibranch in the UK. It is
known as the ‘shaggy mouse’.[32]
Cuthona caerulea
is transparent, with yellow yips to the oral tentacles and rhinopores. The
cerata have bright
blue pigment in the mid region, with an orange or red band above.[33]
Cumanotus beaumonti is translucent with speckles of gold pigment, and
numerous tapering long cerata. It’s scarce in the UK.[34]
Flabellina pedata
is pink-purple in colour. The cerata occur in bunches and are joined at their
bases.[35]
 |
| Flabellina pedata [Flickr Creative Commons © Géry Parent] |
Dendronotus frondosus is very variable in colour. It has large arborescent gills, oral processes and rhinophoral sheaths.[36]
Janolus cristatus
has numerous swollen cerata with iridescent bluish-white pigment in the tips.[37]
Cadlina laevis
has a flat oval body with small gills that retract into a pocket. It has characteristic
lemon-yellow glands towards the mantle margin.[38]
Greilada elegans
is orange in colour
with brilliant blue iridescent spots.[39]
Thecacera pennigera is translucent white with tiny orange, yellow and
black spots. It occurs in the south and west of the UK and feeds on the bryozoan Bugula plumosa.[40]
Archidoris pseudoargus is one of the most common nudibranchs on UK
shores. It is known as the sea lemon’. It has a mottled variable colour on the
mantle, which bears
many short blunt tubercles.[41]
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| Archidoris pseudoargus [Flickr Creative Commons © kqedquest] |
[1]
http://en.wikipedia.org/wiki/Sea_slug
[2]
http://en.wikipedia.org/wiki/Sea_slug
[3] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[4] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[5] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[6] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[7] http://i.word.com/idictionary/nudibranch
[9] http://marinelife.about.com/od/invertebrates/tp/Information-About-Nudibranchs.htm;
http://www.seaslug.org.uk/nudibranchs/anatomy.html
[11] http://www.seaslug.org.uk/nudibranchs/anatomy.html
[12] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/;
http://en.m.wikipedia.org/wiki/Rhinophore
[13] http://en.m.wikipedia.org/wiki/Rhinophore
[15]
http://en.wikipedia.org/wiki/Nudibranch
[16] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[17] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[18] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[19] http://marinelife.about.com/od/invertebrates/p/Nudibranchs-Profile.htm;
http://en.wikipedia.org/wiki/Radula
[20] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[21] http://marinelife.about.com/od/invertebrates/p/Nudibranchs-Profile.htm;
http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[24] http://animals.nationalgeographic.co.uk/animals/invertebrates/nudibranch/
[25] http://www.habitas.org.uk/marinelife/species.asp?item=W15250
[26] http://www.habitas.org.uk/marinelife/species.asp?item=W13420
[27] http://www.habitas.org.uk/marinelife/species.asp?item=W13320
[28] http://www.habitas.org.uk/marinelife/species.asp?item=W13190
[29] http://www.habitas.org.uk/marinelife/species.asp?item=W13630
[30] http://www.habitas.org.uk/marinelife/species.asp?item=W12420
[31] http://www.habitas.org.uk/marinelife/species.asp?item=W12450
[32] http://www.habitas.org.uk/marinelife/species.asp?item=W15510
[33] http://www.habitas.org.uk/marinelife/species.asp?item=W14670
[34] http://www.habitas.org.uk/marinelife/species.asp?item=W15200
[35] http://www.habitas.org.uk/marinelife/species.asp?item=W14600
[36] http://www.habitas.org.uk/marinelife/species.asp?item=W12670
[37] http://www.habitas.org.uk/marinelife/species.asp?item=W14310
[38] http://www.habitas.org.uk/marinelife/species.asp?item=W13820
[39] http://www.habitas.org.uk/marinelife/species.asp?item=W13670
[40] http://www.habitas.org.uk/marinelife/species.asp?item=W13760
[41] http://www.habitas.org.uk/marinelife/species.asp?item=W14030
Just found your blog when I was looking for information on Springtails, will be popping back to look through your older posts..thanks Amanda..
ReplyDeleteThanks for your comment. Hope you enjoyed the rest of the blog :)
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