Colony of Colorful Sea Whips (Ellisella ceratophyta)

Colony of Colorful Sea Whips (Ellisella ceratophyta), Bunaken Island, Indonesia

by B. N. Sullivan

Despite its appearance, this is not a plant.  It is a colony of Sea Whips -- a type of soft coral.  This colorful species, Ellisella ceratophyta, occurs in many locations throughout the Indo-Pacific region.  I photographed this example at Indonesia's Bunaken Island.

Sea Whips are Octocorals.  That is, their polyps have eight tentacles.  Like most Octocorals, they feed at night by extending their feathery tentacles to catch tiny bits of nutrients from the surrounding water.  The colony pictured here was photographed in the daytime, so its polyps are completely retracted, giving the branches a smooth appearance.

To facilitate feeding, colonies of Sea Whips tend to establish themselves in places where there is a mild to moderate current. When the tentacles of the coral polyps are extended, they are able to catch particulates and tiny plankton carried along by the current.

 

The Channel Clinging Crab (Mithrax spinosissimus)

Channel Clinging Crab (Mithrax spinosissimus)

by B. N. Sullivan

We were on a night dive in the Turks and Caicos Islands when we came across this crab.  It is a Channel Clinging Crab (Mithrax spinosissimus), the largest species of Caribbean reef crab.

How big is he?  We estimated that this crab's carapace measured about 15 cm (6 inches) across.  If you could measure across its spread-legged footprint, however, it would easily be over to 30 cm (12 inches).

We were scanning around with our lights across a sandy area off the coast of West Caicos, when we saw this crab gallumphing along, hunting for his dinner.  I had been shooting macro photos earlier that day, but for some reason I did the night dive with a wide angle (15mm) lens on my camera.  As it turned out, that lens allowed me to get these wide angle close-up shots of this crab.

We located this crab out on the sand flat, at a depth of about 15 meters (50 feet).  I maneuvered around in the dark to position myself to intercept its path. I settled on the sand just a meter or so in front of the critter, while Jerry shone a small beam of light on it from above so that I could set up the shot.  I waited, and when the big crab was right in front of me, I snapped the shutter release.  The result is the first photo on this page.  By chance, I managed to capture him just as he began to raise one of those claws in defense!

Of course, as soon as the camera's strobe blasted the poor crab with bright light, he decided to leave in a hurry.  He 'turned on a dime' and retreated quickly, but not before I was able to capture an image of the posterior of his carapace and those wonderful, bristly, spidery walking legs!

Channel Clinging Crab (Mithrax spinosissimus), posterior view

We know this species by the common name Channel Clinging Crab, but it turns out that it has several other common names, including Reef Spider Crab, and Spiny Spider Crab, among others.  The crab's scientific name is Mithrax spinosissimus, and that designation stays the same, independent of the common name, which varies from place to place.  This crab belongs to the Majidae family and is a 'true crab' (as opposed to, say, a hermit crab).

Majidae tend to have long slender legs -- just like this example -- which is why the common names of many species in this family include the word 'spider'.  Majids also tend to have little hairs or bristle-like structures on their carapaces.  Bits of material -- algae, sponge, and so on -- attach to those hairs and act as part of the crab's camouflage.

Note that the walking legs of this species also are rather hairy, and are covered with 'stuff' while the business end of the crab -- those impressive claws -- are smooth.

Like so many reef creatures, this species forages mainly at night.  During the day, they hunker in the reefs, under ledges, and in cavelets.  Because of their size, they can't wiggle into small cervices like so many smaller species can do.  Still, they can be difficult to spot during the day, since their decorated carapaces blend so well with their surroundings.

These crabs inhabit a range from the sub-tropical western Atlantic to the Caribbean. They can be found in reef areas along the coasts of southern Florida, through the Bahamas and the Turks and Caicos Islands, and throughout much of the Caribbean.

Happy Holidays from The Right Blue!

Christmas Tree worm (Spirobranchus giganteus) and Pillar Coral (Dendrogyra cylindrus), with polyps extended

by B. N. Sullivan

We chose this image for our holiday post because we thought it looked festive. We hope you agree.

The photo, taken during a night dive off  Providenciales in the Turks and Caicos Islands, shows a stand of Pillar Coral (Dendrogyra cylindrus) with its polyps extended for feeding.  Nestled cozily in the coral is a kind of Polychaete worm called the Christmas Tree worm (Spirobranchus giganteus).  The worm burrows into coral and secretes a calcareous tube in which it lives.  Only its pair of feathery 'Christmas Tree' shaped crowns are visible outside its tube. The feathery tentacles on the crowns trap tiny tidbits of food, and also are used for respiration.

The Christmas Tree worm can retract its crowns into its tube for protection.  When the crowns retract, a structure called the operculum closes snugly over the tube like a lid or a little trap door.  Christmas Tree worms come in lots of colors: red, orange, yellow, blue, and white. We also have seen a version that is striped!

We hope all of our readers are enjoying the holiday season, and we wish you all a very happy, healthy, and prosperous New Year.

Hold that pose, little crab!

Yellowline Arrow Crab, getting situated on a sponge

A Yellowline Arrow Crab strikes a pose

by B. N. Sullivan

This series of photos depicts a Yellowline Arrow Crab (Stenorhyncus seticornis), a common Caribbean species.  With its distinctive pointy-headed spidery shape, bulging eyes, yellow knees and tiny purple claws, it is an interesting photo subject.  As we approached this individual, it skittered onto a bright orange sponge -- also quite photogenic.

But crabs are not always the best photo models.

In this instance, the crab first struggled to get situated on the sponge, as if it wasn't quite sure how to arrange all of those gangly legs.  A few moments later it was settled in place, and I snapped its portrait.

I began to move around a bit, hoping to catch it from a slightly different angle, but my crabby friend would have none of it.  Without a by-your-leave, the crab simply left the scene.

It was time to look around for another subject.

"I'm outa here...!" - Yellowline Arrow Crab

I took these photos of the Yellowline Arrow Crab during a night dive at Little Cayman Island.

A Beautful, Fragile Bryozoan Colony

Macro photo of a Lace Bryozoan (Reteporelina denticulata)

by B. N. Sullivan

This beautiful marine organism is a colony of Lace Bryozoa (Reteporelina denticulata).  Despite their appearance, Bryozoans are neither a coral nor a plant.  Taxonomically, the Bryozoa form a phylum all their own.  Most of the more than 4,000 species of Bryozoans live in the sea.

The name Bryozoa translates to "moss animal."  The individual animals that make up the colony are microscopic.  This species builds lacy calcareous structures of interconnected branches, made from the mineralized exoskeletons of thousands of tiny individuals.  The macro photo at the top of this page gives a good idea of how intricate and intertwined the branches can be.  It takes the colony of organisms a very long time to build these lovely structures.

The colonies are pretty, yet they are quite brittle and therefore very fragile.  If you come across a Bryozoan colony while diving, be careful not to touch it or bump it. The delicate structures will almost surely break if handled.

Almost all Bryozoans are sessile -- that is, the colonies are attached to some hard substrate like rock or hard coral.  The photo below shows a colony of Reteporelina denticulata growing on a hard coral (Porites lobata).  Once in awhile, a diver may come across a small Bryozoan colony that appears to be growing out of packed sand or mud, but closer inspection will almost certainly reveal that it is in fact attached to a rock or lump of coral rubble that is buried.

The Bryozoan species pictured here is rarely seen at depths of less than about 10 meters, but we have seen them on rocks below 40 meters.  In our experience, larger colonies are found at deeper depths -- perhaps because they are less likely to be disturbed and damaged by surge.

I photographed the Lace Bryozoan colonies shown here off the coast of Puako, Hawaii at depths between 20 and 30 meters.  The colonies pictured here are quite large for the species -- approximately four inches (10 cm) across.

Lace Bryozoan colony growing on coral in Hawaii

Droopy Gorgonian Sea Plume - Needs Water??

Gorgonian Sea Plume (Pseudopterogorgia sp)

by B. N. Sullivan

We were swimming along the pretty reefs off the coast of West Caicos in the Turks and Caicos Islands, looking for things to photograph.  I spotted this Gorgonian Sea Plume at the edge of a patch reef.  The first thing I noticed was that it was quite tall -- with a height  of about two meters.  But the thing that really struck me was how droopy its branchlets looked. The spontaneous thought that popped into my head was that it looked like a large house plant that someone forgot to water!

That was a silly thought, of course, and it made me chuckle to myself at the time.  But when we were reviewing the photos I had taken on that dive, Jerry looked at this one and immediately said, "Hmm, needs water."  I told him I had thought the same thing when we were out there on the reef, and we both had a laugh about that.  So, from the start, our title for this photo has been "Needs Water."

Cerianthids: Marine animals that look like flowers

Cerianthid "tube anemone" - Hawaii

by B. N. Sullivan

The creatures pictured here look like anemones, but they are not true anemones.  They are Cerianthids, commonly referred to as ‘tube anemones’, which are taxonomically quite distinct from true anemones.

Cerianthids and true anemones do belong to the same phylum, Cnidaria, and the same class, Anthozoa, but tube anemones belong to the subclass Ceriantipatharia, a taxon that also includes the so-called ‘black corals’ (Antipatharia).

Dark-colored Cerianthid, Hawaii

One of the visible features that distinguishes Cerianthid tube anemones from true anemones is the morphology of their tentacles.  Cerianthids have shorter tentacles in their centers, and longer tentacles around the margin.  The color of the shorter tentacles usually is different from that of the longer tentacles, making them look a lot like flowers (at least to me).

Side view of a Cerianthid, showing its tube

Cerianthids dwell inside a rubbery tube (thus the name tube anemone) which is built from mucus secreted by the animal.  The tube is embedded in mud or packed sand. When not feeding, or when disturbed, the animal retracts inside its tube for protection.

These creatures can be difficult to photograph for several reasons.  Most Cerianthids are relatively small; their crowns of tentacles are perhaps 5 cm (2 in) across, so it’s necessary to get very close to them in order to photograph them.  If the photographer accidentally touches one of the tentacles, piff! the critter retracts.  And although Cerianthids happily feed in gentle currents, any nearby turbulence — like that created by the photographer as he or she moves about — causes the critter to quickly go into hiding.

These tend to be deep-dwelling creatures — all of the examples in this post were photographed at depths greater than 40 meters (130 ft).  They are accustomed to low levels of ambient light at those depths, so Cerianthids do not take kindly to blasts of artificial light from a camera strobe.  At best, one or two shots of an individual is all that a photographer can hope for before all that is left to photograph is the tube!

Cerianthid retracted into its tube

All of the Cerianthid tube anemones pictured in this post were photographed off the west coast of Hawaii’s Big Island.  This post was adapted from an article I wrote several years ago for ScienceBlogs.com.

Scarlet Hermit Crab from the Cayman Islands

Scarlet Hermit Crab (Paguristes cadenati), Cayman Islands

by B. N. Sullivan

Many small crustaceans look quite similar to one another, but it's hard to misidentify this little hermit crab.  A denizen of reefs in the Caribbean Sea, the brilliant coloring of the Scarlet Hermit Crab (Paguristes cadenati) sets it apart from other hermit crab species of that region.

These little crabs (about an inch long) inhabit old gastropod shells, and for some unknown reason, the shells they choose as their portable houses usually are pretty cruddy looking.  The one in the photo on this page is covered with a layer of coralline algae so thick that it almost looked like a stone, rather than a seashell.

Like many hermit crab species, these little guys are difficult to find during daylight hours.  At dusk they emerge from their hiding places in the reef and go about foraging for their food.  We spotted this individual during a night dive at Little Cayman island.

Most often, divers see only the crab's red legs and pale eyestalks poking out of the aperture of the shell in which they live.  This individual was cruising along across some coral, so we got to see a bit of the pretty speckled markings on its back, too.

The Scarlet Hermit Crab is a member of the Diogenidae family.  Comprised of more than 400 known species, the Diogenidae are the second-largest family of marine hermit crabs.

Find the lobster in this photo

Sculptured Slipper Lobster (Parribacus antarcticus), Hawaii

by B. N. Sullivan

What you are looking at in the photo above is the ceiling of an underwater cavelet in Hawaii.  The bright red stuff is an encrusting sponge.  Most of the rest of the surface is covered by various kinds of algae.  The purplish blob in the center of all that red is not a clump of algae; it is a slipper lobster wearing a clever disguise.

This is the Sculptured Slipper Lobster (Parribacus antarcticus),  a member of the Scyllaridae family.  It is said to be the most common slipper lobster species found in Hawaiian waters, but if you polled a sample of divers there you would find that relatively few have seen these critters.  Part of the reason is that their camouflage makes them easy to miss, and their flattish profile also helps them to blend into the background.  In addition, they are rather small -- maybe five or six inches long at most.

The individual in the photos here was snuggled into a crevice in a cavelet we visited during a night dive at Puako, Hawaii.  We had been inside this cavelet many times during the day and often found pretty nudibranchs on the walls and roof surface.  Expecting that we might see some of those at night as well, we shined our lights all around as we entered.  We didn't find any nudibranchs that night, but as it happened, our bubbles hit the spot on the ceiling where this little slipper lobster was hanging out.  Annoyed, it skittered across the surface to escape the bubbles.  We hadn't noticed it until it moved, even though the beams from our lights had swept the area several times.

Below is another photo of the same creature.  Note the snazzy fringe along the edge of its carapace.  In case you are still scratching your head about what you are seeing, the little lobster is facing left in the photo below.  If you look very carefully you may be able to distinguish its widely spaced eyes from the rest of the mottling.

Sculptured Slipper Lobster (Parribacus antarcticus), Hawaii

A Queen Conch snail, giving us the eye

Eyes and proboscis of a Queen Conch (Strombus gigas)

by B. N. Sullivan

Conch shells, like all seashells, are created by secretions from the mantle of the snail that lives inside. This happens gradually, over the snail's lifetime.  Most people have seen empty Conch shells, yet few have seen the snails that are the natural inhabitants of those large, heavy shells.  Fewer still realize that those critters have wonderful stalked eyes.

All of the snails in the family Strombidae, to which Conchs belong, have these stalked eyes.  If you come across a live Conch shell while diving, you can see the snail's eyes for yourself if you are patient.  If you pick up the shell and turn it over, the animal inside will retract into the shell almost immediately.  Set the shell down with the glossy aperture exposed and just wait.  Eventually -- say, in five or ten minutes -- the snail will extend its eyes to look around.  If you are lucky, you also may get to see its proboscis (tubular mouth), as in the photo above.

The snail in an upended Conch shell has the ability to right itself, but to do so takes quite a bit of effort on the part of the critter.  So, if you do handle one or set it aperture side up to try and catch a glimpse of the eyes, please do return it to its natural aperture-down position before you leave it.  The photo below shows the snail's eye peeking out of the shell as it moves along the sand in its normal position.

The creature in the photos on this page is a Queen Conch (Strombus gigas), a species common to the Caribbean. I photographed this one during a night dive off the north coast of Cayman Brac.

An eye peeks out as a Queen Conch snail crawls along the sand

Moon Jelly (Aurelia aurita)

Moon Jelly (Aurelia aurita)

by B. N. Sullivan

This week we commemorate the 45th anniversary of the first moon landing  (by Apollo 11 on July 20, 1969) with a photo of a Scyphozoan known as the Moon Jelly.  Jellies of the genus Aurelia are common in coastal waters worldwide, including the Arctic.

In the photo you can see the four oral arms suspended from the body of the jelly, arranged around the critter's mouth.  Along the edge of the bell of the Moon Jelly are tiny hair-like tentacles -- not really visible in this photo.  Both the tentacles and the oral arms bear nematocysts, the stinging cells used for defense and to immobilize prey.  Moon Jellies "prey" on zooplankton.

I photographed this Moon Jelly (A. aurita)  in the Aegean Sea, just a few meters from the shore near Vouliagmeni, Greece.  This one was about a foot (30 cm) in diameter, although some nearly half again as large have been recorded.

Blue Snowflake Coral (Sarcothelia edmonsoni), a Hawaiian endemic

Blue Snowflake Coral (Sarcothelia edmonsoni), a Hawaiian endemic Octocoral

by B. N. Sullivan

The underwater landscape in Hawaii is not known for the presence of soft corals. There are hard, stony corals aplenty on Hawaiian reefs, but the sea plumes, colorful Nephtheid soft corals, and sea fans found on most other tropical reefs around the world are largely absent in Hawaii.

The pretty blue Octocoral pictured above is one of relatively few soft coral species that live in Hawaiian waters.  Some soft corals in Hawaii are not seen by divers because they grow at depths beyond sport diving range.  Others, like this one, are overlooked more often than not.

It is easy for a diver to swim right past a patch of Blue Snowflake coral without noticing it.  The species is what we think of as a "low-rise" coral.  The colonies form mats on the surfaces of rocks and dead coral.  From a distance, the colonies look kind of "mossy."  You have to get in close to observe the tiny flower-like polyps, but once you spot those, there is no doubt that you are looking at an Octocoral.

Blue Snowflake Coral is a Hawaiian endemic, i.e., it occurs naturally only in Hawaiian waters.  Its scientific name is Sarcothelia edmonsoni, but it was formerly classified as Anthelia edmonsoni.  (If you are searching for information about the species, you may have to look up both names).  It is a member of the Xeniidae family.

Sarcothelia edmonsoni is the primary food source for another creature endemic to Hawaii, the sea slug Marionia hawaiiensis* (formerly known as Tritonia hawaiiensis).  It makes sense -- doesn't it? -- that an endemic critter would have another endemic species as its main prey.

I photographed this example of Sarcothelia edmonsoni along the South Kona coast of Hawaii's Big Island, near the edge of Honaunau Bay.

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*I don't have a photo of Marionia hawaiiensis, so click here to see the creature on Cory Pittman and Pauline Fiene's site, Sea Slugs of Hawaii.

Sea Plumes in the Caribbean

A Caribbean Sea Plume (Pseudopterogorgia sp.)

by B. N. Sullivan

In earlier posts (such as this one about the Red Sea) I have noted that underwater scenery varies a lot from one region to the next.  Fauna characteristic of a given area can provide instantly recognizable clues to the location of a photo.  For the Caribbean and adjacent tropical waters, one of those clues is the presence of Sea Plumes like the one in the photo above.

Sea Plumes can be found on patch reefs and along dropoffs throughout the Caribbean, as well as some areas of the south Florida coast, the Keys, and in the Bahamas [which are technically in the Atlantic, not the Caribbean].  They are a type of Gorgonian soft coral, in the same taxonomic Order as Sea Fans and Sea Whips.

The polyps of Sea Plumes tend to be arranged in rows along their branchlets.  The colony has a furry or fuzzy appearance when the polyps are extended, as in the photo above.  When the polyps are retracted the branchlets have a smooth, stick-like appearance.  Sea Plumes like to establish themselves in areas where there is some tidal current or other flow that facilitates feeding.  To feed, the polyps catch plankton and other nutrients that pass over them.

Sea Plumes come in an assortment of colors -- mostly greens and browns, but also purple.  The color depends on the presence or absence of zooxanthellae in their tissues.

Some species grow more than a meter tall.  The one in the photo above, which I photographed at Cayman Brac, was about a half meter tall and its branches spread nearly a meter wide.

A Splash of 'Velvia' Color on a Sipadan Reef

by B. N. Sullivan

In the days before digital photography, we shot all of our photos as transparencies (slides).  From about 1990 onward, my preferred film for use underwater was Fuji Velvia (ISO 50).  We jokingly referred to it as "Disneychrome" because it rendered such dazzling colors.  Also, it was developed using the E-6 process, available just about everywhere including on many live-aboard dive boats.  No more having to send the Kodachrome off for processing and waiting, waiting, waiting for the results.

I do not miss most aspects of film photography.  I certainly don't miss having to return to the boat or shore to change film after, say, 36 shots [you can't change film underwater!], nor do I miss having to wait until the film was developed to see if the images I captured were the ones I wanted.  But, once in awhile I get nostalgic for the incredible color saturation and fine grain that only Fuji Velvia seemed to yield.

The photo above was shot using Fuji Velvia.  The transparency was later scanned for online use.  The subject was an unusually 'fluffy' crinoid -- species unknown -- posing for us near a stand of equally fluffy-looking and very colorful Nephtheid soft corals. The location was Barracuda Point at Pulau Sipadan, Malaysia.

The 'Big Guns' on Bloody Bay Wall

Caribbean Brown Tube Sponge (Agelas conifera)

by B. N. Sullivan

Although they resemble cannons, these 'big guns' are sponges -- Caribbean Brown Tube Sponges (Agelas conifera) to be exact.  We found this particular cluster of sponges standing guard on Bloody Bay Wall on the north side of Little Cayman Island.  The two larger tubes were at least two feet long.

Here is another photo of Ageles conifera that we posted a few years ago.

Hermit Crab with Bright Blue Eyes

by B. N. Sullivan

This is the White Speckled Hermit Crab (Paguristes punticeps), a Caribbean species of the Diogenidae family.  Adults of this species grow to a length of  3 to 5 inches (about 8 to 13 cm).  These reef dwellers inhabit empty gastropod shells, tail end first, so you won't normally get to see the crab's full length.

Without the artificial light produced by the camera strobe, these crabs look dark brown with white speckles.  It's also difficult to make out those wonderful bright blue eyes without artificial light and a macro lens.  But that's why macro photography was invented, right?

Jeepers, creepers -- where'd he get those peepers?!

One of the most noticeable morphological features of this species: both of its claws (chelipeds)  are approximately equal in size.  More commonly, the claws of hermit crab species are of different sizes -- typically the left claw is larger than the right.

All of the images on this page are of the same individual, photographed during a night dive at a site known as Cumber's Caves on the north shore of Little Cayman island.

Octocoral polyps - Little flowers of the sea

Open polyps on a Nephtheid soft coral

by B. N. Sullivan

Octocorals (Octocorallia) are a subclass of corals whose polyps have eight tentacles.  The name Octocoral derives from this morphological feature [in Greek, "okto" means "eight"].

When the polyps are feeding, the feathery tentacles are spread wide to capture passing bits of nutrients.  In macro photos of Octocorals, like the one above, the open polyps look like a dense garden of little flowers.

When the coral polyps are not feeding, the tentacles retract into little balls, like an open hand closing into a fist.  To see what I mean, look at these recently posted macro photos of another soft coral with closed polyps.

The Octocoral species pictured above is a a Nephtheid soft coral.  I took the photo at Indonesia's Bunaken National Park, a lush marine preserve near the northern tip of Sulawesi Island.

Animal, Vegetable, or Mineral?

by B. N. Sullivan

Take a look at the photos below. What's your guess: animal, vegetable or mineral?

At first glance they look like some kind of vegetable, don't they? Perhaps cauliflower or broccoli come to mind?

In fact, the correct answer is "animal."  The images above are macro photos of a type of soft coral in the genus Dendronephthya.  The common name for this variety is "Broccoli Coral," and you can see why that is so.

Although this kind of coral can resemble broccoli in appearance, it definitely is not a plant.  It is a colony of animals -- the coral polyps. The polyps arrange themselves in bundles at the ends of the rubbery stalks. Each polyp has exactly eight short, feathery tentacles. In order to feed, the polyps open and close their little tentacles, grabbing tiny nutrient particles that are suspended in the water.

This feeding activity happens mostly at night.  During daylight hours, the polyps retract into tiny bundles, as you see in these photos.

The final photo, below, shows what the entire colony looks like.  All of these photos were taken in the Red Sea, but this species also can be found elsewhere in the Indo-Pacific region.

Purple sea slug (Hypselodoris apolegma)

by B. N. Sullivan

Isn't this a pretty little critter?  It is  Hypselodoris apolegma, a nudibranch from the family Chromodorididae.  It doesn't have a standard common name, so we just call it the purple sea slug. This attractive nudibranch lives in the western tropical Pacific region.

H. apolegma feeds on sponges. It seems to prefer a dysideid sponge of the genus Euryspongia, but it may feed on other sponges as well.

Like many nudibranchs, the purple sea slug lays its eggs in a ribbon-like mass. The egg mass of H. apolegma is yellow.

The creature's striking coloration makes it an attractive subject for underwater macro photography.  I photographed this one off the northern coast of the Indonesia island of  Sulawesi, in the Celebes Sea.  This specimen was about 3 cm long (about an inch).

The species fact sheet for H. apolegma on the Australian Museum's authoritative Sea Slug Forum describes this creature's coloring as follows:

The background colour is a rich pinkish purple with a white border to the mantle. At the edge of the mantle the border is solid white but inside this is a region of varying width in which the white forms a reticulate pattern gradually merging in to the pinkish purple. The rhinophore stalks and the base of the gills is an intense purple, the rhinophore clubs and the gills are orange yellow.

Yep, that's our purple sea slug!

Visit the Hypselodoris apolegma species page on the Sea Slug Forum for more information and photos, including feeding records, mating, and the egg mass of this species.

Seeing stars in the Mediterranean Sea

by B. N. Sullivan

If you go diving or snorkeling in coastal areas of the Mediterranean region, you are very likely to see this Red Sea Star (Echinaster sepositus), which is the most common starfish species in that area.  Divers and snorkelers have a good chance to spot this sea star resting on the bottom along rocky coastlines.  Although there are records of Mediterranean Red Sea Stars found at depths of more than 200 meters, they are seen most often in relatively shallow water -- less than 10 meters.

Mediterranean Red Sea Stars are actually red-orange in color, rather than pure red.  As sea stars go, they are relatively large.  The one in the top photo on this page was about 20 cm (8 in) in diameter.  The individual in the photos below was even larger -- nearly 30 cm (12 in) across.

Like many common sea star species, Echinaster sepositus has five rays, or arms.  One time, however, we found a six-armed sea star that looked just like E. sepositus, except that it had an extra arm.  At first I was not certain that it was indeed the same species, so I took the time to photograph it carefully.  Someone who knows much more than we do about Echinoderms looked at the photos and assured us that the six-armed sea star was a less common, though well-known, morphological variant of E. sepositus.

The two macro photos below are of the unusual six-armed Mediterranean Red Sea Star.  In these macro photos you can see the characteristic surface of the sea star, which is uneven -- sort of dimpled.  In the first of the two photos below, you can see the tiny structures, called papullae, which protrude from the 'dimple' indentations on the sea star's surface. In the second photo below you can see the animal's tube feet protruding from grooves on the underside of each ray.

Both the tube feet and the papullae facilitate water exchange, and are involved in the animal's respiration and excretion.  The sea star 'breathes' by extracting oxygen from sea water.  It excretes some dissolved waste matter through the papullae and tube feet, too.

The tube feet also aid the sea star in locomotion.  The tube feet in each row move successively, in a wave, using hydraulic pressure from the animal's water vascular system.  This allows the critter to crawl along.  By a similar process, the tube feet also can be used to pass bits of food from the distal ends of the rays to the sea star's mouth, which is at the center of its underside.

If you look closely at the second macro photo below, you can see that there is a little suction cup at the tip of each tube foot.  These structures help the animal stay put after it situates itself on a rock or other hard surface.  If a sea star gets overturned, it can right itself by twisting one or more of its rays so that the tube feet can grab hold of the surface and turn itself right-side up again.  (This process can take quite awhile and consumes a lot of the critter's energy, so if you pick up a sea star to look at it, be kind enough to return it to its normal position!)

The sea star lounging in an algae bed in the photo at the top of this page was photographed in the shallows of Aedipsos Bay, on the coast of the Greek island of Evia.  The two macro images below, of the six-armed Mediterranean Red Sea Star, were photographed at Cape Greco, Cyprus.