Thimble Jellyfish

From: Field Guide to Venomous and Medically Important Invertebrates Affecting Military Operations
"The thimble jellyfish, Linuche unguiculata, is a small (~0.78 inch or 20 mm diameter) species widely distributed in the Caribbean. They have a distinct appearance and appear dark brown internally. Thimble jellyfish often occur in swarms of several thousand specimens, but isolated individuals are occasionally seen as well. They are distributed throughout the Caribbean and where they breed throughout the summer although populations tend to peak in May. Initial contact with thimble jellyfish is generally noted by a sensation of contact followed by mild irritation. Within a few days, the stings develop into an itchy, reddened rash on exposed areas of the body. Symptoms generally self-resolve and itching can be aided with antihistamines."