Nudibranchs and Sea Slugs of Guam (Part II)

We continue with another random selection of nudibranch and sea slug diversity from Guam. 

"Cincta" is Latin for "surrounded" or "encircled"; Glossodoris cincta is surrounded by an attractive margin of yellow and blue along the mantle.   Dollabella auricularia is the largest of the sea slugs known as "sea hares", and can grow as large as a big man's shoe.  Phaneropthalmus smaragdinus is one of the primitive sea slugs that still retains a partial shell inherited from its snail-like ancestors, though it is greatly reduced and hidden by the mass of the body.  Noumea angustolutea is sometimes found under coral rubble on shallow patch reefs.  Phyllidia guamensis is known only from Guam and the Northern Mariana Islands, and is one of the area's more commonly seen nudibranchs as it is often exposed on the reef during the daytime.  Hypselodoris maculosa has striking coloration and markings.  Notobryon and other members of this family can swim by laterally flattening and flexing the body, and some live on floating algae drifting with the ocean's currents.  Some primitive sea slugs, like Bullina vitrea, still retain an obvious external shells.  Like many nudibranchs, little is known about the natural history of Noumea norba.  The group of nudibranchs know as Aeolids, like this Aeolidiella sp., are characterized by numerous body projections called cerata.  This lace-like unidentified discodorid may be a form of Halgerda sp.  The magnificent Phyllodesmium magnum feeds on soft corals and is a very rare sighting on Guam.

Harlequin Shrimp: Hymenocera picta

Few animals match the harlequin shrimp (Hymenocera picta) for charismatic coloration and behavior.  Like many shrimp, they often live in pairs.  There is debate as to whether there is a second species, Hymenocera elegans; painted ("picta") or elegant ("elegans"), the Latin names seem appropriate.  "Harlequin" is an archaic term for a type of clown, in reference to their festive coloring and ornamentation.  

Despite this comical name, if you are a sea star, they are no joking matter.  Harlequin shrimp are unrelenting predators.  Their wide, flat claws are modified to act as spatulae and are use to pinch and pry off the tube feet of starfish, so they can abscond with their prey to a protected location.  One of their preferred prey, the blue starfish Linckia laevigata, are too large to abduct whole, so they will feed on a small portion of the whole starfish or simply amputate a "leg" and make away with the separated limb.  Even the formidable coral-consuming crown of thorns starfish (Acanthaster planci) has been know to fall prey to these killer clowns.  

As I am striving to provide a science-minded resource, I should emphatically point out that their ecology and behavior should not be interpreted through a human sense of morality or propriety...harlequin shrimp, like all living creatures, are their own embodiments of a pinnacle of evolutionary success.  Millenia of struggle for adaptive and reproductive success have produced an evolutionary solution in the harlequin shrimp that -- whether we admire it for its beauty or condemn it for it's predatory tactics -- has earned it a lasting role on the stage of reef ecology.

Nudibranchs and Sea Slugs of the Philippines (Part I)

The Philippine Islands are an epicenter of marine biodiversity in the Pacific, including an incredibly diverse community of nudibranchs and sea slugs.  However, like most other members of marine ecological communities, particularly in developing nations suffering poverty and political unrest, nudibranch diversity is threatened and suspected to be in decline in the Philippines.  While we strive to protect these communities, let's also learn a little more about what it is we stand to lose.  

This Tritonia sp. and other members of the family Tritoniidae are specialized predators on soft corals, gorgonians and sea pens.   This Dermatobranchus sp., and others in the genus, belong to a group of nudibranchs called Arminids, which are also predators of soft corals.  Members of the Eubranchidae, like this Eubranchus sp.,  are small aeolid nudibranchs that feed on hydroids...also, note the eggs in this video clip.  Sakuraeolis nungunoides has distinct cerata, the body projections that assist in respiration, digestion and protection.  The volcanic appearance of the base of the gill cluster of Hypselodoris krakatoa inspired the species name of this attractive nudibranch.  Glossodoris averni and other close relatives are the only nudibranchs that vibrate their gills; this may increase their respiratory efficiency.  Some nudibranchs are very impressive mimics of their food sources; this sponge mimic may be a small individual of the very large species Atagema spongiosa ("cf" means "compare with")...or it may be something different, much remains to be learned about nudibranch diversity.  Another example of a sponge mimic is Halgerda dalanghita, seen here on an orange sponge which they prey on and blend into marvelously.  Glossodoris rufomarginata is named for the red margin around the mantle of the body.  "Cerato-" is Latin for "horn", and "soma" means "body"; the genus name of this Ceratosoma gracillimum describes the bodily outgrowths that surround, and may protect, the gills.  While we can't see it, one of the things that separates soft coral feeding Marionia sp. from other nudibranchs is the presence of stomach plates in the digestive tract.

With over 700 species of nudibranchs, >50% of which are not fully described by science, we've only just begun to explore the incredibly diverse nudibranch fauna of the Philippines.  Stay tuned for much more.

Sea Slugs: Euselenops luniceps

This strange sea slug combs sandy and silty sea bottoms for food with a large oral veil, which is fringed with tiny sensory "fingers" (papillae), though what it actually eats is not well known.  It rests within the sand when inactive, and quickly burrows when threatened.

Euselenops luniceps belongs to the Pleurobranchidae, a family of sea slugs known as "side-gilled slugs" with the gill hidden on the right side of the body under the mantle (the body edge).  Some pleurobranchs can be quite large, as long as 500mm!  This species grows to 70mm, though the animal in this video is only ~25mm, about the size of a U.S. quarter.

While some sea slugs move slowly, E. luniceps is quite fast!  The video is not sped up in any way -- this is the animal's natural speed.  This one was so fast that keeping the focus and camera stability was very difficult, so image quality suffered a little.  

The species is widespread throughout the Pacific, but it has net been recorded in Guam.  This video was shot in Anilao, Philippines.  

Nudibranchs and Sea Slugs of Guam (Part III)

More randomly selected video clips of the diversity of Guam's nudibranchs and sea slugs. 

This pair of Noumea varians lie near an egg ribbon.   Sagaminopteron bilealbum was described by our friends Clay Carlson and Patty Jo Hoff; it has only been found in Bile Bay and Agat, and its survival may depend upon protecting Guam's reef health.  The spots on Chromodoris aspersa may be a method of camouflage, making it appear like a colonial tunicate...I know I've almost overlooked them for that reason.  The lovely lilac color of the next nudibranch obviously influenced the name of Discodoris lilacina.  Haminoeids are herbivorous sea slugs that retain the ancestral shell; this Haminoea sp. appears to be undescribed.  Thurdilla gracilis belongs to a group called "sapsucking slugs" which feed primarily on algae.  Some nudibranchs, like Glossodoris hikuerensis, exude a milky toxin when harassed by predators.  The small aeolid nudibranch Flabellina bicolor has body projections that can autotomize, or break off without harming the animal, to help protect it from predator attacks.  The bizarre Kaloplocamus dokte was a very rare sighting; as far as we know it hasn't been seen on Guam before (or since).  The "precious" Chromodoris preciosa has a variable appearance throughout its broad range. 

Nudibranchs: Hypselodoris infucata

This is the first of some more web-friendly posts of just a single species.  More digestible clip lengths for you and smaller chunks of editing for me, allowing me to post more regularly.

This colorful nudibranch is widespread throughout the Pacific and has been accidentally introduced to the Mediterranean through the Suez Canal.  It feeds on marine sponges.  (Gosliner et al. 2008).  

Hypselodoris infucata was first described by Rüppell & Leuckart in 1828.

This individual was filmed in Apra Harbor on Guam.  We have previously seen this species only twice on Guam, but they were both very small (~10mm).  This is the largest one we've seen at ~25mm; they grow to 50 mm. 

Nudibranchs and Sea Slugs of Guam (Part IV)

The first nudibranch appears to be Phidiana salaamica, though the species is known only from Tanzania and Japan; it is possible that they were accidentally transported to Guam on the hulls or in the ballasts of ships.  Pleurobranchs, such as this Pleurobranchus albiguttatus, are also known as "side-gilled slugs" and are mostly nocturnal carnivores.  These Phyllaplysia sp. are members of the "sea hare" family, and are masterfully camouflaged to the only species of grass on which they live; in the daytime they are buried deep at the base of the grass, and only come out at night.  This unidentified dorid looks like a member of the Dendrodoris genus; while most nudibranchs have tooth plates know as "radulae", dendrodorids secrete digestive enzymes on sponges and ingesting the digested tissues.  One of the more charismatic nudibranchs, Risbecia tryoni is know to exhibit regular "mantle-flapping", as seen in this video; the purpose of this behavior is unknown, though it may aid in sensing chemical cues in the water.  This unidentified discodorid is well-camouflaged as a sponge, the main source of food for this group of nudibranchs.  Another pleurobranch, this Berthellina sp., has recently ingested a small snail, which can be seen through the body of the slug.  The fantastical coloring and shape of Halgerda tesselata actually makes them hard to find; however, once an observer discovers them, they become one of the most commonly seen nudibranchs on Guam.  In this video you can see two H. tesselata mating through the genital openings on the right sides of their bodies.  

Stomatopods (Mantis Shrimps)

Mantis shrimp, from the order Stomatopoda,  are not actually shrimp, which belong to the order Decapoda.  Mantis shrimp are generally divided into two basic groups:  those that spear their prey with powerful strikes of a spear-like foreclaw and those that smash prey with a blunted foreclaw.  In this video, the two Lysiosquillina species are spearers and the Odontodactylus, or "peacock mantis shrimp", is a smasher.  The striking claw of a mantis shrimp is so powerful that the friction caused by the claw pushing through the water generates so much heat that the water actually boils.

However, rather than the claws, the most "striking" feature of mantis shrimp may be the eyes.  On independently mobile stalks, they can achieve nearly 360-degree vision.  By virtue of the arrangement of optical cells in the eyes, mantis shrimp can perceive depth with just one eye.  While the human eye has only two types of photoreceptors, mantis shrimp have eight, meaning they can see color a much greater range of color than we can, into the infrared and ultraviolet realms of the light spectrum.  They also have eye cells specialized for detecting polarized light, and it has been shown that mantis shrimp have means of communicating with others of their species through color signals which can only be detected by seeing polarized light.  This ScienceBlogs post has more details.

But I CAN't tell the story of the mantis shrimp in a more entertaining fashion than The Oatmeal!  Click the image below to check out this amazing infographic:  

Spotted Porcelain Crab: Neopetrolisthes maculatus

The spotted porcelain crab is commensal on sea anemones, meaning that the crab benefits from the anemone (protected by the stinging tentacles) while the anemone is neither helped nor harmed by the presence of the crab.

Unlike true crabs, porcelain crabs (family Porcellanidae) have long antennae, a greatly-reduced fourth pair of legs which remain hidden beneath the carapace, and feed by filtering planktonic nutrients from the water with fanlike mouth parts called setae.  (Ref: Humann & DeLoach 2010).

In this video you can see the elaborate filter-feeding setae in action.  Spot patterns range from fine red spots to large polygonal red spots on a white background.  Spotted porcelain crabs are found throughout the Indo-Pacific and Japan.  These video clips were filmed in the Philippines, and I have only very rarely seen them in Guam.