Stinging Truths, Part 1: A guide to injuries caused by invertebrates

In previous articles in Dive Training (May 1995 and June 1995) we looked at injuries from vertebrate marine animals that can injure humans, most...

In previous articles in Dive Training (May 1995 and June 1995) we looked at injuries from vertebrate marine animals that can injure humans, most commonly by bites or envenomations from spines. The other enormous group of animals that can sting the unfortunate diver is invertebrates (without a bony cartilaginous infrastructure).

Although uncommon, injuries resulting from close encounters with marine life do occur. Divers know to avoid sea animals with teeth that bite or that have painfully sharp spines, but some seemingly benign creatures can also inflict damage. Often mistaken for harmless plants or nonliving gelatinous masses—sort of the marine equivalent of jello—are the marine invertebrates, an enormous group in the marine environment, far outweighing in both species and mass all the fish in the sea. They present unique medical concerns.

In this first article in a series on marine invertebrate injuries, we will examine allergic reactions and problems caused by the seemingly docile group of animals you might never imagine could harm anyone—sponges—as well as stinging threats from better-known invertebrates, including jellyfish.

Allergic Reactions

An allergic reaction can be a serious sequel to an injury from a marine invertebrate. Like any other allergic reaction, in the previously sensitized individual, the aquatic protein from many marine invertebrates can stimulate an allergic response, which can rapidly become life-threatening (anaphylaxis) by precisely the same mechanism as with a bee sting.

The signs and symptoms of anaphylaxis may occur within minutes of a sting and include low blood pressure, difficulty in breathing, tongue and lip swelling, tightening in the throat, seizures, abnormal heart rhythms, itching, a raised red skin rash, nausea, vomiting, diarrhea, abdominal pain, and fainting. Most severe allergic reactions occur within 15-30 minutes of a sting, and nearly all occur within six hours. Death results from profoundly low blood pressure and severe swelling in the airway that prevents breathing.


Decisive treatment should be instituted at the first indication of an allergic reaction. Begin with administration of aqueous epinephrine 1:1,000 just under the skin in the upper arm (using an Ana-Kit) or lateral thigh (using an EpiPen or EpiPen Jr.) region. Aerosolized aqueous epinephrine (such as Primatene) is not adequate to abort severe anaphylaxis.

If the allergic reaction is limited to itching and a skin rash, and the victim has no difficulty breathing, no facial swelling, and does not appear to be in distress, an oral antihistamine may be used as the initial therapy. A mild reaction may be managed with diphenhydramine HCl (Benadryl), 50-75 mg. The dose for children is 1 mg per kg of body weight. Nonsedating antihistamines, such as terfenadine (Seldane), 60 mg, or cimetidine (Tagamet), 300 mg, are sometimes useful. If the reaction is severe or prolonged, or if the victim is regularly medicated with corticosteroids, administer prednisone, 50-60 mg for adults and 1 mg per kg for children.


There are approximately 4,000 species of sponges (phylum Porifera;

predominately class Desmospongiae), which are composed of horny but elastic skeletons of “spongin,” some forms of which we use as bath sponges. Embedded in the connective tissue matrices are slender pointed bodies (called spicules) of silicon dioxide (silica) or calcium carbonate, by which some sponges can be definitively identified.

In general, sponges are stationary animals that attach to the sea floor or coral beds and may be colonized by other sponges, mollusks (snails, clams, squid), coelenterates (corals, sea anemones, jellyfish), annelids (marine worms), crustaceans (lobster, shrimp, crabs), echinoderms (starfish, sea urchins), various fish, and algae. Some of these secondary coelenterate inhabitants are responsible for the skin irritation and local destructive skin reaction termed “sponge diver’s disease.”

In recognition of a medicinal property, the ancient Greeks burned sea sponges and inhaled the vapors as a preventative against goiter. Sponges harbor various biodynamic substances with possible antitumor, antibacterial, growth-stimulating, antihypertensive, neuropharmacological, psychopharmacological, and antifungal properties. A number of sponges produce toxins that may be direct skin irritants.

Clinical aspects. Contact with some sponges induces two general syndromes, with minor variations. The first is an itch-generating skin irritation similar to a plant-induced allergy, which can sometimes seem like a mild allergic reaction. A typical offender is the friable Hawaiian or West Indian fire sponge (Tedania ignis), a brilliant yellow-vermilion-orange organism with a “bread crumb” appearance found off the Hawaiian Islands and the Florida Keys. This sponge grows in branches extending from a larger base, which are easily broken off.

Other culprits include Fibula nolitangere, the “poison bun sponge,” and Microciona prolifera, the red moss sponge found in the northeastern United States. F. nolitangere is found in deeper water and grows in clusters, with holes (oscula) large enough to admit a diver’s fingers. It is brown and bready in texture and may crumble in the hands.

Within a few hours after skin contact, the reactions are characterized by itching and burning, which may progress to swelling of local joints and soft tissues, blistering, and stiffness, particularly if small pieces of broken sponge are retained in the skin near the joints. The skin may become mottled or purplish.

Most sponge-induced irritations occur on the hands, because the victim has handled sponges without proper gloves. When the sponge is penetrated, torn, or crumbled, the skin is exposed to the toxic substance(s). Without specific treatment, mild reactions will subside within three to seven days. With large skin surface area involvement, the victim may complain of fever, chills, fatigue, dizziness, nausea, muscle cramps, and itching. Blisters induced by contact with Microciona prolifera may become infected.

The second syndrome resulting from contact with a sponge is a skin irritation that follows the penetration of small spicules of silica or calcium carbonate into the skin. Most sponges have spicules; “toxic” sponges may possess surface toxins that enter microtraumatic lesions caused by the spicules.

In severe cases, extensive surface peeling of the skin may follow in 10 days to two months. No medical intervention can retard this process.

Treatment. Because it is usually impossible to distinguish clinically between the allergic and spicule-induced reactions, it is safest to treat for both. The skin should be gently dried. Spicules should be removed, if possible, using adhesive tape or a facial peel. As soon as possible, apply diluted (5 percent) acetic acid (vinegar) soaks for 10-30 minutes three to four times a day to all affected areas. Isopropyl (rubbing) alcohol (40-70 percent) is a reasonable second choice.

Although topical steroid lotions (such as hydrocortisone) or ointments may help to relieve the secondary inflammation, they are of no value as an initial decontaminant. If they precede the vinegar soak, they may even worsen the initial reaction. Delayed primary therapy or inadequate decontamination may result in the persistence of blisters that may become infected and require months to heal.

Following the initial decontamination, a mild moisturizing cream or steroid preparation may be applied to the skin. If the allergic component is severe, particularly if weeping, crusting, and blistering occur, a doctor may prescribe orally administered corticosteroids, such as prednisone. Severe itching can usually be controlled with an antihistamine drug.

As mentioned previously, sponge diver’s disease is not due to any toxin produced by the sponge, but rather is a stinging syndrome related to contact with the tentacles of the small coelenterate anemone Sagartia rosea (family Sagartiidae) or anemones from the genus Actinia (family Actiniidae), which attach to the base of the sponge. Treatment should include that for coelenterate (e.g., jellyfish) stings.

Prevention. All divers and net handlers should wear proper gloves. Sponges should not be broken, crumbled, or crushed with bare hands. Dried sponges may remain toxic.


Our sub-sea tour of medical problems continues by looking at those slimy, undulating globs that can sometimes deliver a powerful wallop—the jellyfish. But jellyfish are only one member of the coelenterates, an enormous group comprising approximately 10,000 species, at least 100 of which are dangerous to humans. Coelenterates that possess the venom-charged stinging cells called nematocysts are cnidaria (nettle); those without nematocysts are acnidaria.

For practical purposes, the cnidaria can be divided into three main groups: hydrozoans (e.g., Portuguese man-of-war); scyphozoans (e.g., true jellyfish); and anthozoans (e.g., soft corals, stony corals, and anemones). Gorgonians (order Gorgonacea, class Anthozoa, subclass Alcyonaria) can secrete mucinous substances that have toxic effects in experimental animals.

Morphology, venom, and venom apparatus. Coelenterates are predators that feed upon other fish, crustaceans, and mollusks. They are radially symmetrical animals of simple structure (95 percent water) and exist in two predominant life forms: either as sedentary, asexual polyps (hydroids) or free-swimming and sexual medusae.

Generally, the polyp is a sac-like creature attached to the substrate at the caudal (aboral) end, with a single orifice or mouth at the upper end surrounded by stinging tentacles (dactylozooids). This form predominates in the hydrozoans (jellyfish) and anthozoans (corals and sea anemones). The medusa is a bell-shaped creature with a floating gelatinous

umbrella from which hang an elongated tubular mouth and marginal nematocyst-bearing tentacles. This form predominates in the scyphozoans (jellyfish lacking a true polyp) and is also found in the hydrozoans.

The stinging organelles, or nematocysts (cnidocytes), are located on the outer surfaces of the tentacles or near the mouth and are triggered by contact with the victim’s body surface. The nematocyst is contained within an outer capsule called the cnidoblast, to which is attached a single-pointed “trigger,” or cnidocil. The nematocyst is filled with fluid (venom) and contains a hollow, sharply pointed, and coiled thread tube (nema). This tube may attain lengths of 200–400 microns and is sufficiently hardy to penetrate a latex surgical glove. The tube is lined with spines, which assist it in penetrating the victim.

When the cnidocil is stimulated, either by physical contact or by a chemical-stimulation mechanism, it causes the opening of a “trap door” (operculum) in the cnidoblast, and the venom-containing thread tube is thrust out. The sharp tip of the thread tube enters the victim’s skin and envenomation occurs.

The velocity of ejection is estimated to reach 2 meters per second, which corresponds to an acceleration of 40,000 times the force of gravity, with an estimated skin striking force of 2-5 pounds per square inch. A human encounter with a large Portuguese man-of-war could conceivably trigger the release of several million stinging cells. The thread penetrates the skin, where the viscous venom diffuses into the general circulation. The agitated victim runs and assists the venom’s distribution by the muscle-pump mechanism.

Coelenterate venoms are thick mixtures of proteins, carbohydrates, and other nonprotein components. To date, they have been very difficult to analyze. Although they are destroyed by heat in the laboratory, this does not seem to apply in the clinical setting.

In this first part of our series on invertebrates, we will look at the first group of coelenterates: hydrozoa. The hydrozoans range in configuration from the feather hydroids and sedentary millepora hydroid coral to the free-floating siphonophore Physalia (Portuguese man-of-war).


Hydroids are the most numerous of the hydrozoans. The feather hydroids of the order Leptomedusae, typified by Lytocarpus philippinus (“fire weed” or “fire fern”), are feather- or plumelike animals that sting the victim who brushes against or handles them. Following a storm, the branches may be fragmented and dispersed through the water, so that merely diving or swimming in the vicinity causes itching and burning and may induce a visible skin irritation.

Clinical aspects. Contact with the nematocysts of a feather hydroid induces a mild reaction, which consists of instantaneous burning, itching, and red raised skin rash. If the exposure is brief, the skin rash may not be noticeable or consists of a faint cluster of dots.

A second variety of sting consists of a delayed reaction with onset four to 12 hours after contact. In turbulent waters or in a strong current, fragments may be washed into a diver’s mask or regulator mouthpiece, causing a burning sensation in the eyes or mouth. Severe reactions, involving large areas of skin surface, are rarely reported. Allergic reactions clearly occur.

Treatment. If the victim is still on the dive boat or has come out of the water onto the beach, the skin may be rinsed with seawater and gently dried without abrasive activity. The application of fresh water and brisk rubbing are strictly prohibited, as these will encourage any nematocysts remaining on the skin to discharge and thus worsen the envenomation.

Acetic acid 5 percent (vinegar) or rubbing alcohol 40-70 percent have been traditionally recommended for application to the skin for 15-30 minutes to relieve the skin reaction. Insulated and dry cold packs may be helpful. (Alternate topical agents wll be addressed in a larger discussion on therapy for coelenterate stings in a future article.) After pain relief is achieved, a mild steroid cream (hydrocortisone 1 percent) or moisturizing lotion may be applied.


The stony, hydroid, and coral-like millepora (e.g., M. alcicornis), or fire corals, are not true corals. They are widely distributed in shallow tropical waters and are found attached to the bottom in depths of up to 1,000 meters. Often, they may be mistaken for seaweed in their attachment to pilings, rocks, shells, or coral. Although smaller segments resemble little Christmas trees or bushes 3-4 inches high, they may attain heights of 6 feet or more. Their colors range from white to yellow-green, with pale yellow most common.

Fire coral is structured upon a razor-sharp lime carbonate exoskeleton, which is an important component in the development of coral reefs. The outcroppings assume upright, clavate, bladelike, or branching calcareous growth structures that form encrustations over coral and objects such as sunken vessels.

From numerous minute surface-feeding pores protrude tiny nematocyst-bearing tentacles, wherein lies the stinging apparatus. M. alcicornis probably accounts for more coelenterate envenomations than any other species. Unprotected and unwary recreational scuba enthusiasts handle, kneel, or lean upon this marine stinger regularly.

Clinical aspects. Immediately following contact with fire coral, the victim suffers burning or stinging pain. Intense and painful itching and a slight rash follow within seconds, which frequently induces the victim to rub the affected area vigorously, worsening the sting. Over the course of 5-30 minutes, a raised rash develops, marked by intense redness, warmth, and itching. The rash becomes moderately swollen and reaches a maximum size in 30-60 minutes.

Untreated, the patches will flatten over 14-24 hours and will resolve entirely over three to seven days, occasionally leaving an area of dark skin coloration that may require four to eight weeks to disappear. The pain generally resolves without treatment in 30-90 minutes. In the case of multiple stings, adjacent lymph glands may become inflamed and painful.

Treatment. Rinse the victim’s skin liberally with sea water and then immediately soak it in acetic acid 5 percent (vinegar) or isopropyl alcohol 40-70 percent until pain relief is achieved. (Alternate topical agents will be discussed in an upcoming article.) Residual skin irritation is generally not very severe and can be managed in a fashion similar to that following a feather hydroid sting. If the rash becomes persistent and problematic, the physician may prescribe oral corticosteroids.


The Atlantic Portuguese man-of-war (Physalia physalis) of the phylum Coelenterata, order Siphonophora, is a pelagic (open-sea) creature that inhabits the surface of the ocean. It is constructed of a blue or pink-violet iridescent floating sail (pneumatophore), nitrogen- and carbon monoxide-filled, and up to 12 inches/30 cm in length, from which are suspended multiple nematocyst-bearing tentacles, which may measure up to 98 feet in length.

An Australian version of Physalia physalis was recently reported in northern Australian waters. The smaller Pacific bluebottle (Physalia utriculus) usually has a single fishing tentacle that attains lengths of up to 49 feet. In some species, the sail can be deflated to allow the animal to submerge in rough weather and water.

The Physaliae depend upon the winds, currents, and tides for movement, traveling as individuals or in floating colonies that resemble flotillas. They are widely distributed but seem to abound in tropical waters and in the semitropical Atlantic Ocean, particularly off the coast of Florida and in the Gulf of Mexico. Their arrival at surf’s edge can transform a halcyon vacation into a stinging nightmare. Unfortunately, both the man-of-war’s and sea nettle’s peak appearance comes in July to September, prime beach season.

As with an iceberg, the scene above water does not fully tell the story. Because the tentacles are nearly transparent, they pose a hazard to the unwary. As the animal moves in the ocean, the tentacles rhythmically contract, sampling the water for potential prey.

If tentacles strike a foreign object, the nematocysts are stimulated and discharge their contents into the victim. Each tentacle in a larger specimen may carry more than 750,000 nematocysts. To increase the intensity of the “attack,” the remainder of the tentacle shortens in such a sway as to create loops and folds, presenting a greater surface area and number of nematocysts for offensive action in what are called “stinging batteries.”

Detached moistened tentacles, often found by the thousands fragmented on the beach, carry live nematocysts capable of discharging for months. Air-dried nematocysts may retain considerable potency, even after weeks have passed. The loggerhead turtle (Caretta caretta) feeds upon Physalia. This is a gastronomic feat that is not purposefully duplicated by any cerebrating adult creature.

As does the clownfish with the sea anemone, the brightly colored fish Nomeus gronovii has a unique symbiotic relationship with the man-of-war, living freely among the tentacles. Two species of nudibranch (sea slug), Glaucus atlanticus and G. glaucilla, eat the tentacles and nematocysts of P. physalis. The nematocysts are not digested and ultimately reside in the dorsal papillae of the nudibranchcs, where they may sting upon contact. Skin irritation can also result from contact with water containing venom that has already been released from stimulated nematocysts.

Upcoming articles in this series will look at Scyphozoa and Anthozoa, as well as review the symptoms and treatment of the coelenterate syndrome.

The velocity of ejection is estimated to reach 2 meters per second, which corresponds to an acceleration of 40,000 times the force of gravity, with an estimated skin striking force of 2-5 pounds per square inch.


By Paul S. Auerbach, M.D.