Are marine invertebrates dangerous to humans?

Since many marine invertebrates do not have a shell and are soft-bodied, many of them have developed a variety of ways to protect themselves from predators.  These defenses can cause harm to humans and are generally in the form of stings from tentacles or spines that release a toxin into the body.  Generally the wounds from marine invertebrates are not life threatening and can be treated and will heal just fine.