3 Answers

According to most online sources, the gluteus maximus or buttock muscle is the biggest of the 639 named muscles in the human body.

The longest muscle in the human body is the sartorius. This narrow muscle of the thigh passes obliquely across the front of the thigh and helps rotate the leg to the position assumed in sitting cross-legged.

The strongest muscle depends on how you measure strength. A good case could be made for the heart!

Information from ehow.com:

In terms of absolute force, the strongest muscle in the body is the masseter, the prime mover of the jaw for chewing. It can create force of 55 lbs. on the incisors or 200 lbs. on the molars.

The hardest-working muscle in the body is the heart. It pumps 2 oz. blood at every heartbeat, at least 2,500 gallons daily.

The muscle that can pull with the greatest force is the soleus, underneath the calf muscle. It is this muscle that keeps us from falling backward while standing up, and it is essential to running, walking and dancing.

The largest muscle in the body is also one of the strongest--the gluteus maximus. This large muscle in the buttocks keeps us standing upright and fights against gravity when we walk up stairs.

The most flexible muscle is the tongue, which can take many shapes and also is always moving, even in sleep.

The most active of muscles is the eye muscles. Muscles of the eye are constantly moving. In an hour's worth of reading, they can move 10,000 times. Unlike the heart, however, eye muscles can get fatigued easily.

Wikia.

I don't have any crustaceans in my body at the moment but the biggest one I ever had in my body was a Lobster .  I love Lobster! .