Dendrochirus biocellatus
Dendrochirus zebra
Pterois antennata 
Pterois radiata
Pterois volitansFive species of lionfish inhabit the waters around Kwajalein. None are especially rare, but some have nocturnal habits that keep them from being seen very often during the day. Lionfish, also sometimes called turkeyfish or zebrafish, are generally red to black in color and have well-developed pectoral fins that expand out in fans or elongate tendrils. All are predators upon living prey, usually small fish or crustaceans. Most of their relatives in the scorpionfish family are ambush predators, waiting for prey to come within reach before striking; the lions, however, are also capable of stalking their prey. All are armed with powerfully venomous dorsal, anal and pelvic spines used for defense rather than offense. People who have been stung (including both proprietors of this web site) can attest to the potency of the venom. The venom is kept in a pair of grooves on each spine, and both venom groove and spine are covered with a thin sheet of tissue. When the spine penetrates skin, the tissue tears, releasing venom into the wound. One of my encounters with a species of lionfish from Hawaii put three punctures in my right thumb. Over the next half hour to an hour, rather intense pain worked its way up my arm to my shoulder area, after which it gradually subsided. Fortunately, the primary symptom from a lionfish sting is pain; more serious symptoms are rare and, according to one of the references below, alleged fatalities are uncomfirmed. Some references suggest placing the injury in water as hot as you can stand to help kill the pain; however, the Dangerous Marine Animals reference below says NOT to use hot water, apply a bandage or dig into the wound. I will say, however, that the pain can be excruciating, and hot water does lessen it--but I do not know why it is not now recommended. It may not be good for the wound in the longer term.
Dendrochirus biocellatus
Dendrochirus zebra
Pterois antennata
Pterois radiata
Pterois volitans
Beegbauer, M., R.F. Myers, and M. Kirschner. 2009. Dangerous Marine Animals. A&C Black Publishers. London. 384pp.
Thomas, C. and S. Scott. 1997. All Stings Considered. University of Hawaii Press. 231pp.