‘The Arrow Crab’
Stenorhynchus seticornis or ‘Arrow Crab’ guarding a cave entrance
Music, Video, and Aquarium
2010 Morphologic Studios

Take a moment to look into the compound eyes of the arrow crab (Stenorhynchus seticornis)… If NASA is looking for a robot capable of navigating rocky planetary terrain, the arrow crab would be a perfect organism to model it after. In the video we look down the sharp, pointed rostrum (’nose’) of an arrow crab as it appears bobbing in space. In reality, its spindly, spider-like legs are holding it anchored like a sentinel, guarding the opening of a small cave.

Arrow crabs are an abundant species on Floridian reefs, living perched near cracks and crevices in coral heads where they can retreat if threatened. Their pointed rostrum, triangular body, and protruding eyes gives this crab the appearance of a predatory lizard fish that can dash away at a moment’s notice. Instead, the arrow crab is rather slow moving, relying on the fact that the paucity of meat inside the spiny, twig-like exoskeleton of the arrow crab makes it unappetizing to a would-be-predator. This unique anatomical configuration likely explains their abundance in the wild.

Like other decapod crustaceans, the arrow crab has 10 legs (8 walking legs, and 2 pincers or ‘chelipeds’ properly). However, if you look carefully, you’ll notice that this particular crab is missing the last leg on the right side of its body. Fortunately, crustaceans are capable of regrowing amputated legs. Only a few hours after it was filmed, this arrow crab molted, and as if by magic, regenerated its tenth limb.

‘The Fire Coral’ Pt. 1
A feeding Balanus sp. barnacle encrusted by Millepora alcicornis
Music, Video, and Aquarium
2010 Morphologic Studios

Millepora alcicornis, or fire coral, is not actually a true coral, but a hydrocoral.  Hydrocorals are colonies of hydroids that secrete a shared limestone skeleton, making them more closely related to jellyfish than true corals. Here in Florida, fire coral is extremely abundant on our reefs where they serve as the underwater equivalent of a sunburn to unsuspecting divers. Skin contact with fire coral will result in immediate burning pain, followed by an itchy welt that can last for several days. 

Fire coral is frequently found encrusting over neighboring corals, starting from the bottom and slowly killing the coral until the colony is completely encased in living limestone.  Because fire coral contains symbiotic zooxanthellae (like most tropical stony corals), they are capable of fast growth rates that help build a coral reef. Upon close inspection of fire coral, the stinging polyps can be seen as needle-like projections.  At even closer magnification, grape-like bunches of stinging nematocysts can been seen protruding along the polyps’ length.  These polyps are retractable, and when an edible food particle is captured, it can be drawn back towards one of the many mouths that dot the surface of the colony. In the video we see a colony of barnacle shells (Balanus sp.) that have been encrusted by fire coral.  Unlike the corals though, the barnacle can continue to live beneath the veneer of fire coral.

Barnacles are most commonly found living in the inter-tidal zone where they live periodic lifestyles of low tide rest and high tide activity. When immersed in water, the barnacle feeds with legs specialized for feeding called cirri. The cirri are covered with comb-like filaments that rake the water for passing plankton.  If a particle is caught in the cirri, it is drawn back to the animal’s mouth and eaten.  When barnacle larvae settle out of the floating plankton themselves, they permanently affix themselves to a life-long location. Barnacles have a special ‘cement gland’ under their bodies that produces an impressive proteinaceous adhesive that holds the animal firmly, in spite of the heaviest of waves.  A series of calcareous plates (commonly six) form a turret that protects their soft bodily tissues from predators. Despite their simple appearance, barnacles are in fact crustaceans, like shrimp, crabs, and lobsters.

‘The Sun Coral’
The feeding of a Tubastrea coccinea coral cluster
Music, Video, and Aquarium
2010 Morphologic Studios

This week’s video features a colony of Tubastrea coccinea coral polyp clones feeding on passing zooplankton. The film is sped up 10 times to emphasize the feeding abilities and coordination between the sticky tentacles and the polyps’ mouths.

Tubastrea coccinea or ‘Sun Corals’, have an unusual background story, being the only invasive stony coral to become established in the Caribbean basin. Native to the tropical Indo-Pacific Oceans, they were first noted living on ships’ hulls in Puerto Rico and Curacao (Southern Caribbean) in the mid 1940’s. Over the ensuing decades, they eventually spread elsewhere throughout the entire Caribbean and Gulf of Mexico on the prevailing water currents. It is believed that these sun corals may have originally entered our region as larval stow-aways in the ballast water of intercontinental ships that passed through the Panama Canal.

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‘Lima scabra’
The tentacles and mantle of a Lima scabra file clam filter feeding
Music, Video, and Aquarium
2010 Morphologic Studios

Lima scabra is a common resident on Floridian and Caribbean reefs where it can be found wedged in crevices, with only its long tentacles extending out into the water column. Usually these tentacles are crimson red (as seen in the specimen above), although they are occasionally white in color. Lima scabra can grow to about 3.5 (9cm) inches long.

Like most bivalves, Lima scabra is a filter feeder. It siphons water in through its fleshy mantle (seen in the video), and strains any edible particulate matter before pumping the water back it out. It holds itself semi-permanently in place through the use of ‘byssus threads’. The threads are formed by a viscous protein secretion that cures instantly upon contact with seawater. These byssus threads have captured the attention of bio-engineers who seek to replicate their strong adhesive properties for industrial applications. However, if the clam comes under attack from a predator, it is capable of detaching and swimming away. They can move surprisingly quick; swimming in fast, jerky movements, propelled by the repeated snapping-together of its shell.

‘Purple Forest’
Decorator Crab (Microphrys bicornuta) on Asparagopsis taxiformis algae
Music, Video, and Aquarium
2010 Morphologic Studios

This week’s video features an aquascape comprised of the beautiful purple macro algae  Asparagopsis taxiformis. However, if you pay close attention to the left 1/3 of the screen, you’ll notice something… moving with claws… Nestled amongst the algae is a perfectly camouflaged decorator crab (Microphrys bicornuta).  Keep paying attention… at 26 seconds into the clip you’ll notice a tiny isopod crustacean float by in the current and descend helicopter-style right onto the crab’s back. The unsuspecting isopod has no idea that it has landed upon an algae covered beast. Furthermore, it appears that the crab is not aware of the unexpected visitor until the isopod begins to explore its decorated exoskeleton.  50 seconds into the clip the isopod meets its fate with a few swift snatches of the crab’s claws.  Without missing a beat, the crab continues scavenging amongst the rocks and algae.  And life on the reef goes on…

Decorator crabs are amazing creatures in that they pick up pieces of their surrounding habitat and place them on their carapace (back, exoskeleton) in order to blend into their surroundings.  Decorator crabs that live amongst sponges decorate with sponges, those that live amongst zoanthids use zoanthids, and so on. This instinctual logic is truly remarkable.  The  crab in the video has attached small pieces of the Asparagopsis upon itself, and as a result is all but indistinguishable from its surroundings.

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‘Corynactis viridis’
The feeding of a Corynactis viridis corallimorph
Music, Video, and Aquarium
2010 Morphologic Studios

This past week we finally received our long awaited Corynactis viridis from our good friend Dr. Yvan Perez at the Institut Méditerranéen d’Ecologie in Marseilles, France. I collected these polyps this past June while diving in the Mediterranean, and Dr. Perez has been culturing them in his lab in the interim. Laurent Foure, the current curator of the Noumea Aquarium in New Caledonia, also collected us several stunning morphs from a different Mediterranean location before he left for the South Pacific.

Corynactis viridis is an archetypal corallimorph species found all along the cold, rocky coastlines of Western Europe. Its distribution across the Mediterranean is much more sporadic and considerably less common. They are frequently referred to as ‘jewel anemones’, which is a misnomer, as they are not anemones despite their superficial resemblance. Typically, polyps range in size from about 3-10mm in diameter and can be found in a seemingly limitless number of color morphs. What they lack in individual size, however, they make up for in colonial dominance. It is not uncommon for colonies to completely carpet large areas, frequently rocky outcrops and vertical surfaces. As these colonies are comprised of clones, this carpet will be of uniform coloration, creating the illusion of a singular connected organism. Multiple color morphs will often be found living in close proximity, creating a technicolor patchwork of tiny individuals. Their colors are often vibrant with fluorescent accents. Unlike most of our tropical corallimorphs, C. viridis are non-photosynthetic, relying entirely on the capture of plankton by their sticky tentacles. At the end of each tentacle is a small ball known as an acrosphere; a tell-tale characteristic of all non-photosynthetic corallimorphs.

In this video a single Corynactis viridis polyp (about 8mm in diameter) is seen capturing and digesting tiny plankton as they flow past in the current. As the tentacles capture food, they retract towards the animal’s mouth, located at the center of the polyp. The mouth is likewise transformable; capable of extending, expanding, and enveloping food items. The total elapsed time was roughly 12 minutes and sped up 1200% in order to demonstrate the hydraulic muscular contractions and contortions that the polyp goes through while feeding. 470nm LED light is used to highlight the fluorescent orange ring around the outer diameter of the polyp.

‘The Christmas Tree Worm’
Spirobranchus giganteus – Amber Morph
Music, Video, and Aquarium
2010 Morphologic Studios

Christmas tree worms (Spirobranchus giganteus) are an abundant creature on Floridian reefs, making their permanent homes encased inside the limestone skeletons of live coral. Found in a seemingly endless variety of colors and measuring 2-3 cm in diameter, dozens of these worms will typically adorn massive coral heads in local waters.

Using only the perception of light and vibration, these animals will retract at lighting speed at the first sense of something ominous approaching. Fortunately the worms come equipped with a a protective double-horned operculum that seals the worm safely inside the inpenetrable coral. A sharp, calcareous spike extends forward of the tube’s opening, acting as a further deterant to a would-be predator.

The spiraled, ‘branchial crown’ serves as both breathing and feeding apparatus for the worm, and is the only part of the worm’s body that is extended into the water column. The feathery appendages, known radioles, collect plankton that drift by in the current. The radioles are lined with cilia that direct the captured food down the spiral to the worm’s mouth.