Planting is starting to pick up now that water allocations are known. One of the first pest problems one is going to find in recently flooded rice fields is tadpole shrimp (TPS). Most of the time, when muddy water or uprooted plants are observed, it means the TPS are large and probably already done quite a bit of damage. Young TPS are hard to detect; because of their size they might not cause mudding of the water. However, look carefully to see if you can spot them. Small TPS, when their shell is about half the size of a rice seed, can injure rice roots as they emerge from the seed; they have a hard time chewing on the coleoptile that emerges first from the seed. Larger TPS, when their shell is about the size of a rice seed, are capable of feeding on the coleoptile and roots, and can dislodge seedlings easily. 

Look carefully, there are other bugs that can be confused with small TPS, such as small beetles and clam shrimp. Small TPS look just like fully grown TPS. The very first TPS instars do not look quite like TPS, but those are really hard to spot, and do not feed on rice seedlings anyway. Here's a few images.

TPS eggs

TPS first instars next to eggs

Second or third TPS instar

Small TPS

TPS mandibles

TPS mandibles