Kasaoka City Horseshoe Crab (kabutogani) Museum (hakubutsukan) is the only horseshoe crab museum in the world. The museum opened March 16, 1990 with the purpose of protecting and promoting the breeding of this "living fossil." This museum holds the world's foremost collection of information on the evolution of this creature that has outlived the dinosaurs that appeared on the earth when it evolved to its present figure 200 million years ago. In the park around the horseshoe crab-shaped building are large replicas of seven species of dinosaurs that also lived in the Mesozoic Era.
1. Family Tree
If the history of the world
were equated to the span of one year, one day would equal 12,600,000 years,
and one second would equal 146 years. By that analogy, the horseshoe crab
would have appeared in November. Humans would have arrived on December
31 at 6:17 p.m.
2. Horseshoe Crab Aquarium
The young North American
horseshoe crab sheds its shell from 16 to 17 times before it grows into
an adult. In the horseshoe crab aquarium, visitors may observe the horseshoe
crab's growth as well as its mating processes. These American horseshoe
crabs that are exhibited, shed their shells from 5 to 11 times. Adult Japanese
horseshoe crabs mate in monogomous pairs for several years while North
American horseshoe crabs mate with different partners. The average lifespan
for the horseshoe crab is 25 years, and they mate beginning after shedding
their shells from 16 to 17 times, with the female in front of the male.
The Japanese male horseshoe crab attaches himself with two pairs of his
six pairs of legs to the female and they remain in this position, eating
and laying eggs while still physically joined. American-male horseshoe
crabs have one pair of legs with which to attach to the female.
3. Living fossil and Families
There are from 200 to 300 other living fossils that
still exist on earth today. But because there numbers are decreasing, those
that remain are even more valuable and must be protected from extinction.
In addition to the horseshoe crab, the sea lily, nautilus and Coelacanths
fish are among 14 species of living fossils that are on display at the
museum.
4. Evolution
Horseshoe crab fossils have been found in Europe and
North America. The trilobite, a fossil dating to the Paleozoic Era, is
the ancestor of the horseshoe crab. The sea scorpion is the ancestor of
the spider and the scorpion, also descencdants of the trilobites.
5. Path of Transcontinental Migration
The horseshoe crab evolved on the Laurasian Continent
during the Paleozoic Era. The horseshoe crab reached Asia parallel to the
Thetis Sea, when the Atlantic Ocean was formed near the end the Mesozoic
Era. These are ancestors of the Japanese, Maruo, Minami horseshoe crab.
6. Species Distribution
There are four distinct species of horseshoe crabs
living on earth now. One lives on the beaches of the East Coast of
the USA. Three others live in Japan and on the southeastern shore of the
Asian continent.
7. Horseshoe Crab's Body
(1) Shell(carapace)
The front half of the horseshoe crab's shell is a
semi-circular sphere and the rear is a hexagon to which its tail is attached.
The horseshoe crab has five eyes, two on the top of its front shell which
are compound eyes, containing about 400 tiny pupils. The front pair of
eyes, which most closely resemble human eyes, look like a single eye at
the front of the shell. There are six pairs of legs on the underside (ventral)
of the body surrounding the mouth. The Japanese male horseshoe crab has
six pairs of prickly spines that extend from the rear shell and the female
has three pairs. On the underside of its rear shell, the horseshoe crab
has a gill for breathing that resembles an uchiwa style Japanese paper
fan.
(2) Internal Anatomy Heart
heart, veins,
stomach, bowels, liver
* Blood vessel
Blood has corpuscles
and plasma. Blood is greenish color and contains copper.
8. Life Cycle
(1.)Birth
Eggs are 3 millimeters in
diameter when laid. They reach 6.5 millimeters before hatching.
(2.) Growth
Only grows when it sheds
its shell. It casts off the shell covering its legs and gills in addition
to its upper shell. The horseshoe crab grows to 1.3 times its previous
size when it casts off its shell.
9. Horseshoe Crab in Kasaoka
(1.) The coast of Kasaoka
was set aside by the Japanese government as a protected area for the horseshoe
crab.
(2.) Kasaoka is the leader in taking
steps to protect this living fossil.
(3.) Land Reclamation initiatives
destroyed the protected area when the water of the Oehama area was filled
in (close up) between 1960 and 1970.
(4.) In 1972, a protected area
for the horseshoe crab was declared in Kanaura Bay.
10. Habitat
The horseshoe crab lives in shallow water near the
seashore. In winter, they live some distance from shore. They are most
active and mobile in summer when the water temperature is 18 degrees Celsius.
In summer during high tide, female horseshoe crabs lay eggs in the sand
while still attached to the male. The eggs hatch after forty days but the
newly-hatched offspring continue to live in shallow tunnels where they
were hatched until the following summer ,when they go into the sea.
11. Medical Applications
The horseshoe crab's blood has been made into a variety
of medicines that are in use today, including one that may increase the
life expectancy of AIDS patients. It also has been used to check the potency
and effectiveness of other injections.
12. Threats to Horseshoe Crab's Survival
1. Close proximity of habitat to human populations.
2. Water pollution
3. Waves caused by larger and faster ferries and other
boats have caused a decrease in the horseshoe crab population in Kanaura
Bay and protected area.
Questions About The Horseshoe Crab:
Q. How long does a horseshoe crab live?
A. An average of 25 years
Q. Is it related to the crabs, shrimp, lobsters and
shellfish?
A. No. Unlike the shrimp and crab, it has no antennae.
In fact, it is more closely related to the spider and scorpion, also descendants
of the trilobites. The spider has a breathing gill similar to the horseshoe
crab's.
Q.Where do the mothers lay their eggs?
A. In summer, at high tide, they lay them in
tunnels under the sand.
Q. How many eggs does a horseshoe crab lay?
A. At one time, several hundred can be layed in different
nests. Over a lifetime, about 100,000, but the number of offspring that
survive is unknown.