Crustacean or Arachnid?

Have you encountered a horseshoe crab? Few months back, I sighted one while we walked along Cockle Cove beach (Chatham, MA) and was wondering what it was!  It had a hard shell like a crab but has a tail, by appearance it formed like a ray but with hard externals. It was dead though as we found it partly buried on the sand. We found few more shells around in different sizes. The next day while on trail at Hamblen Park (Welfleet, MA), we found more on grassy wetlands. It was lifeless though, but bigger and still complete I thought at first it was alive. My sister said it’s not edible but never dangerous. I have never seen this animal in the Philippines.

Here are few interesting facts about the specie, I learned it’s not alien in Philippine waters and just one of many significant critters in marine world.

  1. Horseshoe crabs are actually not true crabs at all, being more closely related to arachnids (a group that includes spiders and scorpions) than to crustaceans (a group that includes true crabs, lobsters, and shrimp).
  2. Often called “living fossils,” horseshoe crab ancestors can traced back through the geologic record to around 445 million years ago, 200 million years before dinosaurs existed.
  3. There are four species of horseshoe crabs that exists today, viz.
    a.) Atlantic horseshoe crab (Limulus polyphemus) lives around the Gulf and eastern Atlantic coasts of the United States.
    b.) Mangrove horseshoe crab (Carcinoscorpius rotundicauda) and the Coastal horseshoe crab (Tachypleus gigas) have similar ranges. They live in parts of the Indian and Pacific Oceans.
    c.) Chinese horseshoe crab (Tachypleus tridentatus). This species is found in parts of the eastern Pacific Ocean.
  4. This animal is harmless in reality, although some people viewed them as dangerous due to its spike-like tail. The horseshoe crab’s tail is used primarily to flip the animal upright if it is overturned.
  5. Horseshoe crabs are known for their large nesting aggregations or groups on beaches, the male fertilizes the eggs as the female lays them in a nest in the sand.  Most of this nesting activity takes place during high tides around the time of a new or full moon.
  6. The young and adult horseshoe crabs spend most of their time on the sandy bottoms of intertidal flats or zones above the low tide mark and feed on various invertebrates.
  7. Horseshoe crabs are an important part of the ecology of coastal communities. Their eggs are the major food sourceof migrating birds and these birds evolve to time their migration to coincide during spawning activity.  Many fish species have been observed feeding on horseshoe crab eggs in Florida. Adult horseshoes serve as prey for sea turtles, alligators, horse conchs and sharks.
  8. Horseshoe crabs are also extremely important to the biomedical industry because their unique, copper-based blue blood contains a substance called “Limulus Amebocyte Lysate”(LAL) that are chemically used to determine the presence of toxins. This compound coagulates in the presence of small amounts of bacterial toxins and is used to test for sterility of medical equipment and virtually all injectable drugs.
  9. Horseshoe crabs are marine animals, which means they live in salt water. The eggs are laid on the sand, when hatched the juvenile stay on shallow water where they are protected, like estuaries until they reached two years old. After two years, the now-adult horseshoe crabs can move into deeper water. Adults are found at depths ranging from 100 feet deep to more than 600 feet deep.
  1. They can and do swim, but for the most part they simply walk along the bottom since this is where their food is located.Its main diet consists of worms as well as mollusks, which are animals with a soft body, no spine, and a hard protective shell. Clams are the most common mollusk in the horseshoe crab’s diet.

There are three species of horseshoe crabs that can be found in the country; the Mangrove, Coastal and Chinese but unfortunately haven’t encountered any yet so far. I could only wish I will see one in the sandy bottom in the depths. Actually, they are endangered species in the Philippines and I think the remaining resources needs to be protected and managed.  They are very important in biodiversity conservation and plays an important role in the marine ecosystem.

NB.  Above facts were resourced from