2004-05-14 / Community

Drawing On Science by Steve Yaeger

Drawing On Science by Steve Yaeger

Steve Yaeger is a retired high school science teacher (Beach Channel HS) who, between his art and photography, still keeps up with the sciences. He is a member of the Rockaway Museum Executive Board and Education Committee, Rockaway Music and Arts Council Executive Board, Rockaway Artists Alliance, and the Brooklyn Watercolor Society.

At this time of year those of us living near the ocean are treated to an animal adventure. This adventure has been going on for millions of years: the spawning of the ever-popular, some say scary and others say ugly, horseshoe crab. OK, so it’s not as adventurous as surfing, but it is older and quite interesting.

Horseshoe crabs (also known as helmet crab for their shape and king crab for their size) are not crabs at all. The only thing that crabs and horseshoe crabs have in common is that they are both classified as Arthropods, (meaning ‘jointed leg’). The Arthropods is a large group of animals called a phylum (say, "fy-lum’). It is divided into three smaller subphyla (‘phyla’ = plural for phylum). One subphylum includes Insects and Crustaceans, and the other includes Arachnids (say, ‘a-rack-nids’) and Merostomates (say, ‘mero-stow-mates,’ which means ‘legs attached to the mouth’). The third one includes extinct trilobites (say, ‘try-lo-bites’). Crabs and lobsters are Crustaceans, spiders and scorpions are Arachnids, and horseshoe crabs are Merostomates. Since Merostomates and Arachnids belong to the same subphylum, it makes horseshoe crabs related to your friendly neighborhood spiders rather than to crabs. Horseshoes, then, are not crabs. If you are not utterly confused by this time you should find the rest of this article quite interesting.

Scientists call horseshoe crabs Limulus polyphemus (say, ‘lim-u-lus polly-fee-mus’). Horseshoe crabs often frighten kids, as well as some adults, but they are really one of the most fascinating, harmless, and important creatures living today. The horseshoe has lived for some 350 million years. Their shape has remained just about the same all this time. They are found in large numbers on the North American Coast from Maine to Mexico. They are also found living in Asiatic waters from Japan to India.

The next time you find a horseshoe take some time to examine it—carefully. All arthropods, are covered by a hinged, non-living exoskeleton (‘exo’ = outside), which must be molted as the animal grows larger. The body is divided into three parts: the large, half-moon-shaped carapace (say, ‘cara-pace’) hinged to the smaller, abdominal carapace, and a triangular, spike-like tail.

They live in water a few fathoms deep where they slowly make their way through the bottom mud where they feed on worms, mollusks, and bottom algae. On the dorsal (the back or top) surface of the carapace are two large eyes. These are compound eyes. The compound eyes are for finding mates. Now—are you ready for this—there are five additional eyes on the carapace: between the side and middle ridges there are two pairs of smaller eyes.

Then there is another eye located just below the surface of the exoskeleton. These five eyes are sensitive to visible and ultraviolet light. The ventral or underside of the horseshoe crab shows the business end of the animal. You can easily see the small pincers. These small claws are used to get food rather than for pinching anyone. Then there are five pairs of walking legs surrounding the mouth. Note the brush-like spines at the base of the first four pair of legs. These are used for tearing and moving food toward the mouth. You have teeth to tear your food. The fifth pair of legs has brushes, which are used to clean the gills and to sweep away mud as the animal walks on the muddy bottom of the ocean.

Examine the abdomen noting the flap-like structures. The first pair covers two tiny openings used in reproduction. The other four pairs cover the book-gills. They are called book-gills because they look like pages in a book. Attached to the rear of the abdomen is the tail. The tail is neither used to stab nor to sting people. It is used only to right the animal if it somehow ends up on its back, and to steer the animal as it makes its way along the bottom mud. Also, the tail also has light sensors along the top and sides. They help the animal’s brain tell whether it’s light or dark.

When mating the male, which is smaller than the female and not as strong (sorry fellows—the girl is the boss in horseshoe land), climbs onto its mate’s abdominal carapace. Then it uses its hook-like first pair of walking legs to attach itself to the female. The female then drags the poor guy up onto the intertidal zone where she scoops out a small depression in the sand and deposits about two to three hundred eggs. The male then fertilizes the eggs. After spawning the pair separates, and the eggs are covered with sand. The small horseshoes have to protect and feed themselves when they hatch because mom and dad are long gone.

Early on I wrote that the horseshoe crab is important. This animal plays a very important, little-known role in the medical world. It seems that the blood of horseshoes, which is green in color due to the hemocyanin (say, ‘he-mo-sigh-a-nin’) in it, reacts to chemicals released by some bad and good bacteria by quickly clotting. It was found that the single type of blood cell or amebocyte (say, ‘a-me-bow-site’), which plays a role in clotting, is the reason why clotting occurs when the bacteria’s chemicals come in contact with the blood.

The sterilized chemical that results is called Limulus Amebocyte Lysate or LAL (Say this to your parents at dinner-time and they’ll think you’re a genius.) The medical industries, then, use horseshoe crab blood to make sure that their products are free of bad chemicals. So the next time your doctor treats you with some medication, thank the horseshoe crab. Oh, and one other thing. The horseshoe’s ability to neutralize the bacteria’s poisons serves it well in the ocean environment, which is loaded with bacteria. Unlike you and I the horseshoe lacks an immune system—it cannot produce protect itself from bacterial infections, but it does have a number of chemicals that attach to and kill bacteria, viruses, and fungus.

This makes the horseshoe crab practically disease free. So kids, the next time you see a stranded horseshoe crab, don’t kick it, throw it, or kill it. Why not take time to examine it and then place it so that it can get back home. Remember, its blood may one day help you or someone you know.

Questions? E-mail: Drawingonsc ience@aol.com.

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