“Jurassic Shark 3: Seavenge” (* out of four) was a jarringly awful horror thriller about a group of people (Jada Sanchez, Tim Hatch, Jamie Morgan, and others) who are stranded out in the middle of the ocean and are preyed upon by a 50-ton megalodon shark who wants to devour them all one-by-one. Umpteenth killer-shark movie may be the worst yet which is really saying something but terrible acting and some hideous special effects turn this into a real laugh riot. It’s movies like this that make you realize “Jaws 3 and 4” really weren’t as bad as we thought at the time.