Nudibranchs

Main Photo by paulhypnos

Meet the deeply fabulous Blue Glaucus, or Glaucus atlanticus... aka Blue Dragon, Sea Swallow, Blue Angel, Blue Sea Slug, Blue Ocean Slug and Lizard Nudibranch!

Photo by Atli Arnarson

They free float (upside down) and drift in currents by swallowing air bubbles and storing them in a gas-filled sac to maintain buoyancy!

As they drift in the ocean currents they are vulnerable to being washed up on beaches after storms...

Photo by M Hooper

Photo by csm2mk RTW

They are found in temperate and tropical ocean waters worldwide, specifically the Atlantic, Pacific, and Indian oceans! Although they have been found east and south coasts of South Africa, in European waters, near Mozambique, and off Australia’s east coast.

It's beautiful colouring help them to camouflage with the ocean and sky!

Their body has a form of coloration known as countershading. The dorsal side (facing downward) is silvery grey, camouflaging it against the seas bright surface. While the ventral area (facing upwards) is dark and pale blue, and its head is covered with dark blue stripes, camouflaging against the seas blue colour!

Photo found here

This combination of colours and the countershading on its body gives it protection from predators above and below!

They grow to around 3cm when mature, and live between 1 month to up to a year!

Always a good idea to handle a poisonous creature!

Photo by Zekoo1

Their bodies are flattened, and tapered and sport six appendages that branch out into 84 finger-like cerata.

Photo by Sylke Rohrlach

They are voracious predators, their favoured prey is the Portuguese man o’ war. This looks like a jellyfish, but is actually a cnidarian and has numerous stinging cells (nematocysts) in its tentacles

Portuguese man o' war (Physalia physalis Photo by Helene Hoffman

They transfer undigested nematocysts (stinging cells) from their prey to the cerata to use them to sting when hunting, or if it feels threatened!

Sexual reproduction could be problematic for a creature with a deadly sting....Fortunately, they have long, curved S-shape bends in their penises to avoid injury!

Blue Glaucus Party!!

Photo found here

They lay strings of 12-20 eggs, which they deposit on the carcasses of their prey, or left on any other floating mass they encounter!

Photo by Todd Aki

As well as the Portuguese man o' war, they will also eat by-the-wind-sailor velella, the Blue Button, and the violet snail.... as well as each other!

Porpita porpita- Blue Button Photo by paulhypnos

Stalking a Blue Button....

Photo by paulhypnos

Apart from cannibalism, the Loggerhead Sea Turtle is one of the main predators of the Blue Glaucus.

Dinner......

Photo by J_turner6

Info via American Ocean and Treehugger

Main photo, Four-colour Nudibranch - Godiva quadricolor, by Rafi Amar

Godiva quadricolor is found on the South African coast from the Cape Peninsula to East London, and is an aeolid nudibranch!

Above, by Gary Cobb and David Mullin

It grows between 35-58mm in length and lives at depths up to 20 m!

Above, by Gary Cobb and David Mullin

It feeds on anemones and transfers its stinging cells to the cerata on its back giving it protection from predators....

Above, via Science Photo Library

......It will also eat other nudibranchs!

Above photo, by Guido Villani

It has also been reported from the Mediterranean, off western Australia and West Africa (although the ones found in Australia differ in colour, and may be another species)

....Here it is laying eggs!

Above, photo by Guido Villani

Info via wikipedia, here, and here!

edit- I forgot to do the image pop out thing yet again

Main image, Pikachu Nudibranch - Thecacera pacifica, by Rafi Amar

Thecacera pacifica is a species of Dorid nudibranch, It is also known as the Pikachu nudibranch!

Above, Photo by Connie Chen

It is found on the African coast of the Indian Ocean (Mozambique), Indonesia and Vanuatu. It has also been found on the Gulf of Mexico!

Above, Photo by Brian Mayes

They grow to around 2-3cm in length, and live underneath loose rock and sand!

A video of one wobbling around in the sea!

They also seem to have some variety in colour and patterning....!

Above, Photo by Francis Lau

Above, Photo by Ludovic

Info via wikipedia, and seaslugforum

edit- Once again I forgot to do the pop out image thing

adj_DSC7484 sparkly nudi, by Erwin Poliakoff

Facelina rhodopos, by Rafi Amar

Antiopella cristata, by Jose Salmerón

It is a gift from the sea to find it, for me the most beautiful nudibranch in the Mediterranean.

I like to investigate the origin of the names of the species and I especially liked the one of this nudi price:

"Antiopella" the fact that it is a marine animal and in particular a nudibranch suggests that it is Antiope, the daughter of the guardian of the winds Aeolus and Enarete, lover of Poseidon, there it is😊😉

cristata: from Latin [cristatus, a, um] = crested, crested, related to the caruncle among the rhinophores.

Janolus by Sergi Garcia

Nudibranchs in particular are especially popular with divers and underwater photographers because of their often vibrant and beautiful color patterns. The coloration is useful for more than just a pretty photo, however. Bright colors warn predators that these nudibranchs would make a bad meal because they are armed with toxins and other defenses Smithsonian

edit- had to re-upload the photo

Blue Dragon by Bill Kuiper

Blue Dragon nudibranchs are very common to the southeast coast of Australia and have a few color variations. Juveniles are white with blue rhinophores, and adults vary from dark purple to lavender to golden brown. I have seen these grow to a length of approximately 4 inches...

Text from here

Here are some images of the sargassum-looking nudibranch in case you don't want to load the PDF file!

Main image, Glossodoris Sedna by Cajo Producciones

Above Glossodoris stellatus by digidiverdeb

Above Glossodoris angasi by Brian Mayes

Above Glossodoris acosti by Rafi Amar

Above Glossodoris hikuerensis by @halimeda

Above Glossodoris atromarginata by Wisnu Purwanto

Above Glossodoris sedna by Guillem Mas

Above Colemans Glossodoris by Steve Gillespie

Above Glossodoris cincta by Luc L. Legrand (thanks for 7 M views)

Above Glossodoris rufomarginata by divemecressi

Above Gossodoris cincta by jack pokoj

Above Glossodoris atromarginata by divemecressi

Above Glossodoris rufomarginata mating by Ludovic

Above Glossodoris cruenta by Tavistock

Above Averns Glossodoris with a Colemans Glossodoris by Steve Gillespie

Above Glossodoris sp. 16

Above Glossodoris sibogae by Thomas Vignaud

Above Glossodoris sp. 10

Above Glossodoris electra

Above Glossodoris rubroannulata

Above Glossodoris buko by Bernard Picton

Main photo by ilan Lubitz

Elysia marginata are Sacoglassons (a type of sea slug) and are found in the Indo-Pacific ocean at depths of 0-10 metres

Above photo by budak

They eat algae and store the chloroplasts in its body. The chloroplasts continue to photosynthesize and provide its host with a source of food!

Above 'Pair of leaf slugs on algae. They feed on green algae and can grow from 3 to 8cm long. Photo by Wesley Oosthuizen.' source

They have the ability to regenerate a completely new body (including a new heart) from their head, after it detaches itself from its old body! (A process called autotomy- self amputation)

Above photo by Sonja Ooms

Their ability was discovered by Sayaka Mitoh, a doctoral student at Nara Women's University in Japan, who spotted the decapitated head of E. marginata circling its separated body in one of the tanks in the lab

Above 'This image shows the head and the body of Elysia cf. marginata, a day after autotomy.' (Image credit: Sayaka Mitoh) source

Quite naturally she thought the slug would soon die, however..

"After a few days, the head started regenerating the body and I could see [the] beating of the heart. It was unbelievable," Mitoh told Live Science. "I was really happy and relieved when I found it could regenerate the body." source

• A, Head and body of Elysia cf. marginata, just after autotomy (day 0), with the pericardium (heart) remaining in body section (arrow)
• B, day 7
• C, day 14
• D, day 22, showing whole-body regeneration.
• E, Head and body of Elysia atroviridis (individual no. 1) just after autotomy (day 0).

Above text and photo source

The head continued to grow its new body over the next 3 weeks, including all vital organs, reaching about 80% of its original size!

Above gif source

"The [original] body continues to move and live for days to months," Mitoh said. "You can see the heart beating" inside them, she added. However, the decapitated bodies did not appear to be capable of growing new heads themselves. source

The old bodies remained active for several days to months, until they started to shrink, turn pale due to the chloroplast loss, and eventually died. The beating heart remained visible until the body had fully decomposed!

So, why such an extreme behaviour?

In other animals self amputation usually occurs when escaping a predator, however this may not be the case here....

Above photo by budak

The head can take several hours to detach from the body, so not exactly a quick get away from a predator

Instead it is suspected that it is a means of ridding itself of parasites. There is a slight groove towards the end of the head which acts as a breakage plane, and the similar head severing species Elysia atroviridis all had internal parasites when they detached from their bodies....

However, no parasites were detected in Elysia marginata that did the same.....

Above photo by Javier Diaz Frogmen

The ingested chloroplasts are thought to help in the regeneration of the new body and keep the head alive in the absence of the digestive system organs (which remain with the body).

One individual that was studied underwent autonomy and regeneration twice, which researches think is the limit...(which probably means it didn't survive the third time scientists went to work with a scalpel)

Interestingly this behaviour was only exhibited by young Elysia marginata. When older animals were decapitated their heads survived up to 10 days, and didn't regenerate before dying

Above photo by Antonio Venturelli

All information from wikipedia, here, here, here, here, here and here

As always I'm not an expert, any errors let me know in the comments and I'll edit

And I shall leave you all with a reprise of my current favourite gif....

Main photo 'A giant dendronotid nudibranch swimming in mid-water'

Above, 'The opalescent nudibranch is a predatory mollusk with no shell'

Above, 'Hooded Nudibranchs on Kelp'

Above, 'Hooded Nudibranchs'

Above, 'Hooded Nudibranch, Melibe leonina - British Columbia, Canada'

Above, 'Opalescent nudibranchs and ascidians'

Above, 'Sea Lemon Nudibranch, Anisodoris nobilis - British Columbia, Canada'

Above, 'Nudibranchs (Nembrotha kubaryana) feeding on stalked ascidians. All nudibranchs are carnivorous, mostly preying upon sessile invertebrates such as ascidians, sponges, bryozoans and cnidarians (hydroids, corals, anemones). (Komodo, Indonesia) (photo: Gayle Jamison)'

Above, 'Nudibranch, Miamira magnifica - Izu, Japan'

Above, 'Hypselodoris infucata; Lembeh Strait, Indonesia'

Selected underwater photography here, more nudibranchs, and his books

Title photo by Doug Anderson

More photos of Emperor shrimp (Periclimenes imperator) riding on various nudibranch hosts...

Solo riding....

Above photo of Ceratosoma trilobatum, by Jack

.....or with a pal....

Above photo of Ceratosoma trilobatum, by Jack

...Tandem....

Above photo by Stefano Scortegagna

Above photo of Ceratosoma gracillimum with eggs by Pauline Walsh Jacobson

Above photo of Ceratosoma tenue by Eric Cheng

Above photo of Nembrotha lineolata, by Colin Salmon

Above photo by Doug Anderson

Above photo by Michel Duchayne

Above photo of Dendrodoris tuberculosa, by Brian Mayes

Above photo of ceratosoma nudibranch, by KIYOSHI OKADA

Above photo of Ceratosoma tenue, by Gomen S

Above photo by Colin Robson

.... Hail The Emperor!

Above photo of Hypselodoris infucata, by Anilao~Critters

Title photo by Todd Aki

• Nudibranchs are hermaphrodites (having both male and female sex organs), but they still require a mate in order to reproduce as they cannot self fertilize

Above nudibranch reproductive system by Carissa Shipman, found here

• The reproductive organs are usually next to each other inside the nudibranchs body, and the exterior reproductive opening being on its right lateral side

Above, 'External anatomy of a Tambja verconis nudibranch (by wadeangeliart) found here

• Being simultaneous hermaphrodites increases their opportunities to find a mate, as both partners will transfer sperm, and lay eggs, via reciprocal reproduction.....although there are some exceptions as we will discover!

Above photo Bennett's nudibranchs Mating' by John Turnbull

• Nudibranchs will follow the scent trail left by potential partner. When they catch up with them they start courtship which involves the gentle touching of each other

Above photo by ilan Lubitz

• Depending on the species, the nudibranchs will then orientate their bodies so that their reproductive openings are facing, allowing their swollen gonopores to connect

Above photo of Nembrotha chamberlaini mating, by Jim Greenfield

Above photo of Nembrotha purpureolineata, by Brian Mayes

• Nudibranchs will take every opportunity they can to mate when finding a partner. One quirk of their anatomical development whilst maturing into adults is that the male reproductive organs will grow, and be functional before their female organs. This is called protandry....

Above photo of Hypselodoris bullocki mating, by Coppertane....a possible protandry mating, due to size difference

• They can still take the opportunity to mate though as a 'male'..... It has been suggested that any sperm passed to the 'male' partner, can be stored within their bodies until their female organs have matured. It will then use the stored sperm to fertilize its eggs!

Above photo of pelagic nudibranchs mating by Rajiv Bhambri

• Mating duration depends on species, and can vary from brief encounters to several hours!

Above photo by Tony Wu

• There are 3 basic mating positions depending on species- right side to right side..... (see photo below)

Above, Nembrotha chamberlaini, by Andrew Wu

• .....Head to head.....(see photo below)......

Above, Lobiger viridis, from here

• ......And head to tail, which is either a reciprocal, or a unilateral process depending upon flexibility of the species, or even partner aggression......(see photo below)...

Above, Mariaglaja inornata, from here. The genitals are separate in this species- the penis is in the head, and the vagina in the tail

[Above] The gastropterid sea slug Sagaminopteron ornatum will sometimes form a circle of two to achieve reciprocal mating, or at other times as illustrated here, act unilaterally as a male by approaching from behind to copulate with another acting as a female. source

• Hypodermic Insemination is the preferred method used by some species. The penis has a sharp point which is used to stab the partner in order to deliver a packet of sperm. This can be done either as a mutual act, or happening unilaterally with one nudibranch taking advantage to inseminate another....This can occur amongst some of the sacoglassans

Above photo of Costasiella usagi, by eunice khoo....not as cute as I originally thought....

• Goniobranchus reticulatus is an unusual nudibranch as after it has mated the external part of its penis detaches! And within 24 hours it grows back.....!

Scientists think this mating strategy has evolved so the sperm of rival nudibranchs stored in the vagina of their mate will not accidentally get passed on to future mates source

Above photo of Goniobranchus reticulatus by Bernard Picton...with or without penis...(Schrodinger's penis?)

...And finally a shrimp jockey on a pair of mating nudis....

Above photo by Ludovic

Information from-

here

here

and the fantastic Nudibranch Domain

As always, I'm not an expert...any errors let me know in the comments, and I'll edit my post!

Main photo..........Spanish Dancer Nudibranch. Photograph by David Doubilet

There are more than 3,000 known nudibranch species, and scientists estimate there are another 3,000 yet to be discovered. So-called Spanish dancers, like this one off the coast of New South Wales, Australia, boast some distinctions over other nudibranchs: First, they can be enormous, reaching a foot and a half (46 centimeters) long. Most nudibranchs are finger-size. Second, it can swim, a skill most of its cousins lack.

Above, Tritonia Nudibranch. Photograph by Jeffrey de Guzman

Members of the mollusk family, nudibranchs abandoned their shells millions of years ago. Their scientific name, Nudibranchia, means "naked gills," and describes the feathery gills and horns that most, like this Tritonia species, wear on their backs.

Above, Nudibranch, Philippines. Photograph by Libor Spacek

Nudibranchs, nicknamed "nudis," are best known for the impossible array of colors and designs they sport. They derive coloring, as well as toxicity, from the food they eat. Their wild hues tell potential predators, "You'd best look elsewhere for a meal."

Above, Nudibranch, Palau. Photograph by Ernie Collier

Though partial to tropical climes, nudibranchs thrive throughout the oceans, in warm water and cold, from sandy shallows and reefs to the murky seabed a mile down. Chromodoris nudibranchs, like this one photographed near Palau, are generally a warm-water species.

Above, Egg-Laying Nudibranch. Photograph by Jeffrey de Guzman

Nudibranchs are hermaphroditic, carrying both male and female reproductive organs. Mating pairs fertilize one another and lay up to two million eggs in coils, ribbons, or tangled clumps, as this purple-painted Hypselodoris is doing.

Above, Green-and-Orange Nudibranch. Photograph by Jeffrey de Guzman

Nudibranchs are blind to their own beauty, their tiny eyes discerning little more than light and dark. Instead the animals smell, taste, and feel their world using head-mounted sensory appendages called rhinophores and oral tentacles.

All text and photos from National Geographic

Title photo Emperor shrimp on glossodoris nudibranch, by Ludovic

Above photo by Eric Cheng

-The Emperor Shrimp (Periclimenes imperator) is a species of shrimp with a wide distribution across the Indo-Pacific

Above, Nudibranch (Dermatobranchus ornatus), with Emperor Shrimp by Brian Mayes

-It lives commensally on a number of hosts (this is a long term symbiosis where one species gains benefits, while the other doesn't benefit, but is otherwise unharmed)

Above photo by EcoDivers1

-It will hitchhike on slow moving invertebrates including sea cucumbers, starfish (rare), molluscs...and also nudibranchs!

Above, Emperor shrimp on Nembrotha nudibranch by Roberta Cipressi

-The shrimp is only 19mm, and from it's vantage point it gains access to a stream of nutrients while perched on it's host

Photo by Jessie Weng

-The shrimps vibrant colours advertise the fact that it is unpalatable and help it camouflage on its host

Above, 'Ceratosoma tenue & Emperor Shrimp' by Allen Lee

Spot the shrimp.....Above, '(Jorunna funebris), actually two of them copulating. And an Emperor Shrimp...is attached!' photo by Ülar Tikk

-They also help by removing parasites and dead tissue from their host

Above, '(Periclimenes imperator) on a Glossodoris cincta Nudibranch' by Scott Rettig

Above, Tambja morosa with Periclimenes imperator by Benjamin Naden

-They live approx 2-3 years, and will often change hosts. Having a host is essential for the shrimps survival

Above photo by Brian Mayes 'I was surprised to see the shrimp change hosts and leave his small companion behind

-The shrimps are protandrous hermaphrodites. They are born with male reproductive organs and can change their sex to become female as they age and mature

Above photo by Georgette Douwma

-Finding a partner for reproduction can be complex as their dependence on their hosts can impact mating opportunities

Above, '(Periclimenes imperator) takes a ride on a Bumpy Mexichromis (Mexichromis multituberculata)' by David Guillemet

-After finding a suitable mate the female shrimp releases her eggs into the oceans current....

Above, 'Emperor shrimp on ceratosoma nudibranch' by KIYOSHI OKADA

-When the eggs hatch the small larvae will go through several life stages and molts, until eventually finding a companion to ride on....

Above photo by Brian Mayes

....reminds me of being sat on the sofa with my dog.....

Above photo by REINHARD DIRSCHERL

All info from wikipedia and also here and here

Above, 'Zenopontonia rex with Nembrotha milleri' by élanarchist

Above, '(Periclimenes imperator) with a Ceratosoma Tenue nudibranch as its commensal host' by Jun V Lao

I'm not an expert, if there are any mistakes let me know in the comments and I'll edit my post!

Title photo sp. 7 by Ludovic

Costasiella is a genus of sacoglossan sea slugs

Sacoglossons are 'solar powered sea slugs' aka 'sap sucking sea slugs' which live by ingesting the cellular content of algae. Some will just digest this fluid, others will store the living chloroplasts in their own tissues, which continue to photosynthesize benefiting the sea slug!

Above photo C. kuroshimae by Michaels Bubbles

There are currently 17 different species in the genus, and they are tiny some are only 2mm! The largest can be up to 13mm!

Above photo sp. 2 by Jean-Marie GRADOT

Costasiella kuroshimae was discovered off the coast of the Japanese Island of Kuroshima, and later also found in the sea off Japan, The Philippines and Indonesia. They have 2 dark coloured eyes, and 2 rhinophores (club shaped structures) that look like sheep ears, these have given them the name of 'leaf sheep'

Above, C. kuroshimae by Anilao~Critters

From the limited information that I could find, C. kuroshimae itself has 7 different types (numbered as sp 1-7) and within each sp there are subtle variations

Above, C. kuroshimae by Todd Aki

Above photo sp. 5 by Anilao~Critters

Above, C. kuroshimae by Vania Kam

Above photo of C. kuroshimae with spiral shaped egg mass, by Kelly McCaffrey

Above 'family tree' of Costasiella, with the different types of C. kuroshimae sp 1-7 source

Other species of Costasiella include C. Usagi....

Above, photo by Allen Lee

Above, photo by Allen Lee

Others within the genus...

Above, photo by Ludovic

Above, photo by Patrick Ess

And finally, some more photos of the Leaf Sheep (C. kuroshimae)....

Above, Costasiella sp. #1 photo by Jenna Szerlag

.......weeeeeeeeeeeeeee!!

Above, Costasiella sp. #1 photo by unknown

Information via wikipedia- Costasiella and C. kuroshimae, also from here and here

Apologies folks, if this post is a bit patchy and garbled, there really isn't a lot of information about these nudibranchs...but I thought the photos were really nice!

cross-posted from: https://lemmy.ml/post/14071485

Title photo by Michaels Bubbles

Cyerce nigra is well-known for its cerata that resemble overlapping leaves or a ruffled ball gown.

It is found in the Central Pacific, Palau, Papua New Guinea, Philippines, and grows to 15mm to 30mm in size

Above photo by The Three P Beach Resort Romblon

Above photo by elebe.foto

The dorsal surface features alternating black and white/yellow stripes.....

Above photo by Ludovic

.......while the ventral surface has orange or yellow spots on a black background.

Above photo by rob jeff

Both sides have an orange or yellow edge with two faint black and white lines.

Above photo by Rickard Zerpe

Above photo by touchement

On its head are forked receptors that are hollow halfway through and have the same striking colors, but with a different pattern.

Above photo by Ludovic

Above photo by Patrick Ess

[It]....lives on [the] sandy bottom, on algae fields in shallow water or seldom on coral fields...

Above photo by AGNIESZKA ADAMCZYK

...[It] feeds on algae genus Udotea, especially on Udotea geppiorum

Above photo by joycelynchang

Info from here and here

edit, forgot to add location and size!

edit 2, this isn't showing up in mander for some reason, hence the cross post

Title photo by Michaels Bubbles

Cyerce nigra is well-known for its cerata that resemble overlapping leaves or a ruffled ball gown.

It is found in the Central Pacific, Palau, Papua New Guinea, Philippines, and grows to 15mm to 30mm in size

Above photo by The Three P Beach Resort Romblon

Above photo by elebe.foto

The dorsal surface features alternating black and white/yellow stripes.....

Above photo by Ludovic

.......while the ventral surface has orange or yellow spots on a black background.

Above photo by rob jeff

Both sides have an orange or yellow edge with two faint black and white lines.

Above photo by Rickard Zerpe

Above photo by touchement

On its head are forked receptors that are hollow halfway through and have the same striking colors, but with a different pattern.

Above photo by Ludovic

Above photo by Patrick Ess

[It]....lives on [the] sandy bottom, on algae fields in shallow water or seldom on coral fields...

Above photo by AGNIESZKA ADAMCZYK

...[It] feeds on algae genus Udotea, especially on Udotea geppiorum

Above photo by joycelynchang

Info from here and here

edit, forgot to add location and size!

2nd edit- forgot to add a link!

Title photo by Johnny Chiou

This nudibranch, photographed at the top of a reef, looks like it's about to take off in flight.

Location: Kenting,Taiwan

Above photo by Marchione Giacomo

An emperor shrimp shows off his symbiotic swagger by taking a ride on the back of this regal-looking nudibranch.

Location: Lembeh Strait, Indonesia

Above photo by Francis Perez

This is a Glaucus atlanticus nudibranch who moves with the current and eat false jellyfish, Physalia physalis

Location: Tenerife, Canary Islands

Above photo by Maurizio Pasi

Photograph of a vibrant nudibranch caring over its ribbon of eggs.

Location: Capo Noli, Italy

Above photo by Lynn Wu

This tiny little nudibranch (Costasiella sp.) looks so cute. White head and black rhinophores; cerata green with reddish tips. It looks like a sheep stopped eating grass.

Location: Bali, Indonesia

Above photo by Martin Klein

A beautiful nudibranch posing for the camera.

Location: Lembeh, Indonesia

Above photo by Irwin Ang

Location: Anilao, Philippines

Above photo by Filip Staes

This Nembrotha nudibranch was searching for food inside a tunicate vase.

Location: Lembeh/Sulawesi, Indonesia

Above photo by Jett Britnell

An Opalescent Nudibranch, sometimes called a Flame Tip nudibranch, laying a ribbon of eggs.

Location: Browning Passage, British Columbia, Canada

Above photo by Lynn Wu

This Chamberlain's Nembrotha nudibranch looks like a bull getting ready to charge at the photographer.

Location: Anilao, Philippines

Above photo by Tom Radio

Nudibranch species: Hermissenda crassicornis

Location: Puget Sound, WA, United States

All images and info from here

Main photo by David Borg

The pilgrim hervia is an aeolid sea slug, its average size is between 3 and 5 cm. The body is thin and slender, with a long sharply pointed tail

Above, photo by Antonio Martin

The orange horns are called rhinophores, and act as their nose—nudibranchs in general have poor eyesight, and instead use their rhinophores to "smell" their food. Their rhinophores are smooth, begin in white, changing to orange with white tips. The tusks are called oral tentacles, and are used to shovel food into their mouths. The tentacles are white, smooth, and usually a fair bit longer than the rhinophores. The mouth opening sits between and slightly below these tenacles.

The orange patch between marks where the eyes are, but I'm yet to read that the colour has anything to do with its vision. source

Above, photo by jordi benitez

Its body coloration is milky white with 8 to 10 clusters of dorsal cerata which can be bright red, purple, brown or blue, with the tips coloured in luminescent blue. [Cerata- are dorsal and lateral horn-like growths on it's upper body]

Those cerata act like gills, and each one contains a terminal outgrowth of the digestive gland, a diverticulum. (An outgrowth of the digestive gland or hepatopancreas of the animal)

Above, photo by Mario Pesce

This species occurs in the Mediterranean Sea and in the eastern Atlantic Ocean from the Channel south to Senegal. This sea slug prefers to live on rocky bottoms and slopes in clear and well-oxygenated water, between 5 and 50m in depth

The pilgrim hervia feeds on hydroids (small predators related to jellyfish)...

These look a bit like spindly underwater branches source

Above, photo by Bart

In recent years, C. peregrina has been the subject of study in "kleptopredation". This is eating food not for just its own nutrients, but for the nutrients of what the food itself consumes! In short, it was found that C. peregrina prefer consuming hydroids that have recently fed themselves (hydroids are predators too) source

Above, Cratena peregrina nudis laying eggs, Greek Aegean. Photo by Ivan Bakardjiev

Info from wikipedia, unless stated otherwise

Title photo by Carlos Fernandez-Cid

While I was reading up on information for a nudibranch post, I was surprised to learn that they are also found in UK waters. And also on occasion, we sometimes have exotic visitors like Babakina anadoni if we're lucky....

Usually, they are to be found in

....warm Atlantic waters including off the west coast of Spain, the Canary Islands and the coastlines of Portugal and rarely southern France. It is also known from the eastern Atlantic in The Bahamas, as well as the French Caribbean and the coast of Brazil

In 2022 (possibly a result of global warming) one was found much further North than it's usual range, off the Isles of Scilly, UK. It was found by Allen Murray, a volunteer diver taking part in the Wildlife Trusts Seasearch initiative where people are asked to record wildlife found during their scuba dives Source

The following year another was found even further North in a rock pool at Falmouth, Cornwall, Mainland UK!

Photo by Carlos Fernandez-Cid of B. anadoni eating Candelabrum cocksii. Cabo Udra. Ría de Pontevedra

It grows to be around 20mm long, and the ground colour of it's body is purple

[The] chemosensory organs (rhinophores) and other structures covering the surface of the body (cerata) are contrasting shades of purple as well as different colours including blue, white, yellow and pink

Photo by Carlos Fernandez-Cid

It was only described in 1979, and it was named in honour of Emilio Anadón Frutos (1917-1997)

....who was a professor of zoology and marine biology at the University of Oviedo, Spain

Photo by Carlos Fernandez-Cid

Personally, I think they look like one of those large foamy, pink shrimp sweets, with candy corn growing out of it....

Info from wikipedia unless stated otherwise

Title photo- 'A Goniobranchus kuniei nudibranch in the waters of Komodo National Park, Indonesia. Image credit: Òscar Montferrer'

I came across this article while looking for some info to answer a comment, and thought the photos were too good not to share. The article is interesting too!

Above 'A Goniobranchus geminus nudibranch in the waters of Tulamben, Bali, Indonesia. Image credit: Òscar Montferrer'

Above 'A Doto greenyamieri nudibranch in the waters of Amed, Bali, Indonesia. Image credit: Òscar Montferrer'

Above 'A Phyllodesmium iriomotense nudibranch in the waters of Amed, Bali, Indonesia. Image credit: Òscar Montferrer'

Above 'A Cyerce kikutarobabai nudibranch in the waters of Amed, Bali, Indonesia. Image credit: Òscar Montferrer'

Any errors will be mine, I couldn't do my usual copy/paste and had to type all the names and locations myself