Creature Feature: Angler Siphonophore

Siphonophores are close cousins of jellies. They’re fragile creatures composed of individual, specialized parts connected to each other in a chain. Some parts pulse and steer the colony, others stun and ingest prey.

Siphonophores thrive in the midwater where there aren’t any sharp surfaces to damage their delicate bodies. MBARI’s remotely operated vehicles, or ROVs, have revealed a surprising diversity of siphonophores in Monterey Bay and we’ve learned they’re important predators in the ocean’s depths.

Fish-eating siphonophores in the genus Erenna snare small fishes in their stinging tentacles. The upper half of the colony consists of swimming bells that pulse the animal through the water. The lower half carries hundreds of pale white stinging tentacles, which the siphonophore deploys to catch small fishes.

To attract prey, an angler siphonophore (Erenna sirena) goes fishing. It wiggles gaudy, glow-in-the-dark red lures, which dangle down among the tentacles on the right half of the body in this photo.

A closer look at the tentilla—the finest branches of the tentacles—on an angler siphonophore (Erenna sirena) reveals glowing red lures. The species’ scientific name references the sirens of Greek mythology who lured sailors to their deaths.

Scientists suspect the glowing red lures of the angler siphonophore (Erenna sirena) mimic bright red copepods—an alluring morsel for a hungry midwater fish.

Each species of fish-eating siphonophore in the genus Erenna has a unique shape to its tentilla. Researchers think each form and behavior targets a specific prey. Scale bars represent one millimeter for E. laciniata, E. cornuta, and E. sirena, and five millimeters for E. richardi and E. insidiator.

In 2005, MBARI researchers came across an undescribed species of siphonophore with unusual red luminescent lures. In 2016, MBARI scientist Steve Haddock and frequent collaborator Philip Pugh officially published the scientific description for this remarkable discovery—the angler siphonophore (Erenna sirena). It’s one of more than 200 new species MBARI has discovered during more than 30 years of research in the deep sea.

The shaggy siphonophore (Erenna insidiator) was also discovered by MBARI scientists. Unlike the related angler siphonophore (Erenna sirena), its lures are far more elaborate in structure and they aren’t red. Because this animal has only been observed twice, MBARI scientists aren’t yet sure if the shaggy siphonophore’s lures are luminescent. This deep-dwelling individual was observed by MBARI’s remotely operated vehicle Doc Ricketts near the Davidson Seamount at approximately 2,800 meters (9,200 feet).

The feather boa siphonophore (Erenna richardi) is closely related to the angler siphonophore (Erenna sirena). While both use luminescent lures to attract unsuspecting fishes, the lures on a feather boa siphonophore aren’t red and its posterior portion has a distinctively feathered appearance.

The lacy siphonophore (Erenna laciniata) is similar in appearance to the angler siphonophore (Erenna sirena), but this close cousin lacks red luminescent lures, instead capturing prey with an array of delicate—and deadly—tentacles with glowing tips.

This horned siphonophore (Erenna cornuta) was observed by MBARI’s ROV Doc Ricketts during a dive off the coast of Big Sur at a depth of almost 1,400 meters (4,600 feet) in the oxygen minimum zone—a layer of oxygen-poor water deep beneath the ocean’s surface. Like the angler siphonophore (Erenna sirena), this species uses luminescent lures to snare a meal of small fishes, but its lures lack the unique crimson color.