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Wednesday, Feb. 8, 2006


Mud shrimp

* Japanese name: Ana-jako
* Scientific name: Upogebia major
* Description: Mud shrimps are 10-cm-long decapod crustaceans, which means they have 10 legs and a hard outer shell. They also have two pairs of antennae, of which one pair is very long. The animal is whitish in color, with large dark-brown patches on the back and antennae. The body is quite flat. The front legs are much larger than the others.
* Where to find them: Mud shrimps are hard to find because they spend a lot of their time deep in their holes in mud. However, if you look closely in muddy sediment on the coasts of Japan, on parts of the shore that are periodically drained by the retreating tide, you might see a mud shrimp's hole, with its long antennae peeping out. They are among the deepest-burrowing animals on the coast. The bigger the shrimp, the deeper the burrow.
* Food: Mud shrimps eat organic matter in the mud that washes about on the shallow sea floor where they live. The sediment contains lots of bits of plants and animals, but also, these days, lots of nasty chemicals. The shrimps eat everything up, and in polluted areas they pay the price. Pollutants affect various aspects of shrimp life including reproduction, embryonic development and larval growth. Males can also develop female characteristics as a result of pollution.
* Special features: Females start laying their eggs in their holes from December, and continue until May. Eggs start hatching in March, and when they do so, the depth of the burrow makes all the difference to their chances of survival. Predators have difficulty reaching down into deep holes, and extremes of temperature and pressure caused by tidal changes have less effect. Larvae grow rapidly, but take a long time to mature compared with other shrimp species. In other words, mud shrimps invest more energy in growing big and strong than they do in sexually maturing as quickly as possible. Hence survival as an adult is more important to them than reproducing quickly. If they build a nice deep burrow, shrimps may live for several years after maturation.


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