Homework: Invertebrates

1. Name of organism (Classification kingdom, phylum, class, order, family, genus, species)

Picture found in: NOAA: Horseshoe Crab
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Cheilcerata
Class: Merostomata
Subclass: Xiphosura
Order: Xiphosurida
Family: Limulidae
Genus: Limulus
Species: polyphemus

2. Habitat (where in the ocean does it live)
Horseshoe crabs can tolerate a wide range of temperatures and have distinct physiological processes that enable them to survive in areas of low oxygen environments. Adult horseshoe crabs have been found burrowed into muds and intertidal flats at low tide. They can move out of the water during spawning and survive extended periods of time out of the water as long as their book gills are kept moist. Since horseshoe crabs go through inshore and offshore migrations, they are particularly affected by environmental degradations in both estuarine and oceanic habitats.

3. Food source
Adult horseshoe crabs feed primarily on marine worms and shellfish, including razor clams and soft-shelled clams, and since they lack jaws, horseshoe crabs use the spiny bases of their legs to crush and grind their food and to push it into their mouths.

4. Description of life cycle (egg to death)
After fertilization, the eggs begin to develop into trilobite larvae. By day five, miniature legs are visible inside the translucent egg. On day six, the larvae molt for the first time. On day seven, the outer membrane of the egg ruptures and the inner membrane swells to replace it. By the end of the second week, the larvae will molt twice for its preparation of hatching. (The rate of which the egg hatches is determined by the tides and warmth of the sun which ranges from a two week period ~ three or four weeks or even months.) Upon hatching, their digestive system is not yet functional; instead, they swim around for about a week absorbing the yolk sac as their digestive systems mature. Around day 21, the larvae settle from the water column and onto the soft sediments; there, they shed their shells, their bodies expand, a telson grows, and chitin hardens the new carapace. Horseshoe crabs molt an average of three or four times a year, where sub-adults (horseshoe crabs that are five to seven years old) appear to molt annually, until they reach until they reach sexual maturity (males = 16 ; females = 17). Their lifespan is currently unknown, but some scientist think that they may live up to 20 years or more. As for the unlucky ones, they may get eaten during their larvae form or even by birds when they are struggling to get to their upright position.

5. How does it move (if it moves)
Horseshoe crabs move by the use of their seven pairs of leg-like appendages found under their shell, which are used for gathering and eating food as well.

6. Unique characteristics
-One of the oldest living life forms
-Resemble trilobites (during their larvae stage)
-Their blood is of value to medical science which is harvested by biomedical labs and used to test the sterility of surgical instruments before surgery

7. Role in the ecosystem
A horseshoe crab is virtually a "walking hotel," with several numbers of creatures living attached to its shell: mollusks, bryozoans, sponges, flatworms, diatoms, fungi, and bacteria. Horseshoe crabs also play a big role in terms of bird migratory patterns where recent bird count shave shown alarming decreases in numbers due to horseshoe crab over-harvesting.