Chimeras
Island Science

Small Monsters in the Water – Chimeras

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

A chimera (from the Greek word for she-goat) is a fire breathing female creature from Greek mythology made of three different animals; a lion, a serpent and a goat. The chimera was the “daughter” of Typhon and Echidna and the “sister” of Cerberus and the Hydra. The chimera was destroyed by Bellerophon atop his steed, Pegasus, another even better known chimera. In literature, the term chimera is used to describe any mythical or fictional animal composed of parts of other animals like the griffin or Minotaur.

In genetics a chimera is a single organism (usually an animal but can be a plant) composed of two or more different populations of genetically different cells that come from two different zygotes involved in sexual reproduction. In other words they form when two embryos fuse together in the womb or seed and the result is a mix of tissues. This occurs in humans and is more common in vitro fertilization. It can even result in a person having two different blood types or both types of sexual organs and this condition is not as rare as originally beloved. Almost all marmosets are chimeras, specifically germline chimeras, as a result of being born as fraternal twins and sharing DNA with their sibling (http://en.wikipedia.org/wiki/Chimera_(genetics) accessed August 12, 2012).

Anglerfish exhibit probably the strangest case of “parasitic chimerism” as a “natural” part of their life stages. This is one of those “truth is stranger than fiction” stories. Male Ceratioid Anglerfish (deep sea fish also called Sea Devils) start searching for a female anglerfish from the moment they are born. They find the females using super developed olfactory glands and latch on to the much larger females. Then these little males (sometimes can be more than one) release an enzyme that begins to digest the skin and scales of both themselves and the female down to the blood vessel level until they fuse into a hermaphroditic individual. This is crazy isn’t it?  This process is a little similar to our hermaphroditic slipper shells bivalves that we discussed a few years ago. Well, there is a method to this madness. Once they are fused to the female; the males develop into sexual maturity becoming essentially one giant set of testicles (I know, I am trying to be good and leave out the obvious commentary) that supplies a constant amount of sperm that fertilizes the Borg-like females’ so that more offspring can be produced. Why this is not a Ridley Scott movie I don’t know.

ChimerasToday’s subject is probably closer to the former than the latter and is called a mantis shrimp which is a large invertebrate crustacean with praying mantis-like front claws. They are neither shrimp nor mantids. This week one of our youngest visitors (who’s almost three) found a HUGE mantis shrimp in the intertidal area up on the beach (see the picture with a ruler juxtaposed for size). From “A Practical Guide to the Marine Animals of Northeastern North America” by Leland W. Pollock, we learned as a team that the mantis shrimp’s Latin name is Squilla empusa. They are in the Superorder Hoplocarida, Order Stomatopoda, Family Squillidae, and they are often known by their order name Stomatopods (which is from Greek “stoma” mouth + “-podos” for foot)   These relatively large invertebrate critters (ours was between 8.5 and 10 inches long depending on where you measured it) are dorso-ventrally flattened (like a cross between a crawfish and a lobster or a creature who wants to win at limbo-ing). They are yellowish green with pink tinges and bright green eyes.

Crustaceans are in the Phylum Arthropoda which includes three subphylum: the Uniramia which includes the centipedes, millipedes, and insects; the Chelicerata which includes spiders, ticks, mites, sea spiders, and horseshoe crabs; and the one we are most interested in today, the Crustacea which includes most marine arthropods.

S. empusa are nocturnal and live in U shaped burrows emerging to feed on crustaceans and fish. They like to dig their burrows in deep mud and they may have multiple openings to the surface spread two or three feet apart. I’ve been told by my junior rangers that the Maria Mitchell Aquarium on Washington Street has one of these living in a U shaped PVC tunnel that has been cut in half so you can see it “under the sand”. This species of mantis shrimp are mud and sand dwellers, they are aggressive and are relatively common from the Cape Cod region down to Gulf of Mexico and off the coast of Brazil and in the Mediterranean Sea. Most other species of mantis shrimp are tropical or subtropical. Adult S. empusa can grow to a length of 8-10 inches or 30 cm. long, making our specimen full grown and most likely past the point of needing to molt. Their long flattened bodies are segmented and tend to be translucent to light. Their body is divided into 2 main parts, a cephalothorax (head fused with the thorax), and an abdomen that ends with a telson. The abdomen is broad and fully developed, fanning out towards the end. It is divided into 5 clear segments that are outlined by a dark greenish bluish color or sometimes yellow (these colors help them recognize other mantis shrimp). Attached to the abdomen’s middle line are several pairs of pleopods or swimmerets used for swimming, which also have special filaments and gills for respiration. The last pair of appendages is the uropods found at the sides of the tail or telson. Their telson is covered by 6 sharp spikes and is highly flexible and is normally used to fend off enemies and other mantis shrimp.

I bet you didn’t know that mantis shrimp have the fastest punch of any animal in the world. According to the web site “Not exactly Rocket Science” (http://notexactlyrocketscience.wordpress.com/2006/08/28/mantis-shrimps-the-worlds-fastest-punch/ accessed August 11th, 2012), “Mantis shrimps are mere inches long but can throw the fastest punch of any animal. They strike with the force of a rifle bullet and can shatter aquarium glass and crab shells alike. Now with the aid of super-speed cameras, we are beginning to truly appreciate how powerful this animal is. Their secret weapons are a pair of hinged arms folded away under their head, which they can unfurl at incredible speeds. The “punch” can be delivered in two different manners depending on the species of mantis shrimp. The “spearer” species have arms ending in a fiendish barbed spike that they use to impale soft-bodied prey like fish. But the larger “smasher” species have arms ending in heavy clubs, and use them to deliver blows with the same force as a rifle bullet.” A four inch long (remembering our specimen is 10 inches long) mantis shrimp managed to break a ¼ inch glass aquarium tank and escape. Ironically, this shrimp was named Tyson. The researchers had a heck of a time finding a fast motion video or still camera that could capture the creature’s movement. Sheila Patek, a researcher at USC Berkeley, was able to finally record these species with the help of a BBC crew and their special fast motion video camera used for the television series Animal Camera. As an aside, Dr. Patek also discovered that the fastest limb movement of any animal belongs to the trapjaw ant whose mandibles close with an almost unbelievable maximum speed of 140 mph. The mantis shrimp came in second at 50 miles per hour. And this lightning like strike is through water which is much denser than air. The mantis shrimp does this using its hinged arms, which, when pulled back, are latched with a ratchet like device that compresses a cuplike (or Pringle chip shaped) spring that stores energy. These are unleashed in a punch that is much stronger and faster than simply muscles extending outward. Next week we’ll talk about biomimicry and how this naturally developed spring lock action could be used to develop superior machines.

Patek’s cameras revealed that each of the smasher’s strikes produced small flashes of light that occur because the club moves so quickly that it lowers the pressure of the water in front of it, causing it to boil. The water then releases bubbles as the water pressure normalizes within a blink of an eye, causing cavitation or turbulence that further harms their truly hapless victim. Even the thick exoskeleton of a crab is no match for this force and fish are speared expertly as if the mantis shrimp wielded a spear gun. For the S. empusa, the sharp claw is assisted by 6 spines found at the last joint which gives the claw extra slicing abilities that have been known to cut human flesh which gives these creatures some of their many nicknames such as “thumbsplitters”.

The “amazingness” (is that a word?) does not end there. Mantis shrimp have the most evolved eyes in the animal world. Stomatopods can see polarized light and even parts of the UV spectrum. They have 16 different types of photoreceptors, 12 of which are devoted to color (the human eye has 3) and 4 for UV light, allowing them to perceive a total of 100,000 different colors. The S. Empusa can see polarized light but not colors which is an adaptation to the murkier sediments it inhabits (Cronin et al. 1994). According to the University of Michigan’s Museum of Zoology Animal Diversity Web (which I highly recommend) (http://animaldiversity.ummz.umich.edu/site/accounts/information/Squilla_empusa.html accessed August 12, 2012), the Squilla empusa (which sounds a bit like a Spongebob Squarepants character) is extremely intelligent, very belligerent, a solitary animal and one of the spearing type Stomatopods. They can solve problems and figure out simple puzzles despite having no real brain. They also recognize others of their species and rivals up to a month later assisted by the colors lining the exoskeleton mentioned above. And they are extremely aggressive, more so than other similar sized crustaceans like lobsters. Their fast reflexes, which include jumping back from predators and flipping around in a somersault to run away, to punching or spearing their prey, result from a series of ganglia running along their long bodes which allow them to respond extremely quickly to a variety of stimuli. The more one learns about these creatures, the more interesting they become, although many aquarists detest these wily, hungry, aquarium-escaping creatures.

I am off to write a scary monster movie based on the mantis shrimp, maybe a cross between “When Tyson met Predator”. See you next week. Learn more about mantis shrimp at the “Lurkers Guide to Stomatopods” which, although an old site, is relatively thorough with research and links up to 2004 at http://www.blueboard.com/mantis/ accessed August 12, 2012.

References: Patek, Korff & Caldwell. 2004. Nature 428: 819-820.
Cronin, T., N. Marshall, M. Land. July-August 1994. The unique visual system of the mantis shrimp. American Scientist, v82: 356-366.