Creature Feature: Red Siphonophore

Siphonophores (pronounced “sigh-fawn-oh-fours”) are colonial creatures made up of specialized segments that work together as one. Scientists have described some 175 siphonophore species. Most follow a similar body plan—a gas-filled float provides buoyancy, swimming bells propel the colony, and a central stem bears specialized parts for feeding, defense, and reproduction. Most siphonophores live far from the seafloor and call the endless expanse of the ocean’s midwater zone their home.  

Because their delicate bodies can break apart at the slightest touch, siphonophores are hard to study. Thankfully, MBARI’s remotely operated vehicles (ROVs) give scientists the opportunity to get a close-up look at deep-sea siphonophores without damaging them. Our skilled pilots carefully maneuver the ROV to record stunning video of these delicate drifters. These observations complement specimens we gingerly collect with samplers on the ROV.

MBARI researchers and collaborators described the red siphonophore (Marrus claudanielis) in 2005 from specimens collected by ROVs off California and New Jersey. With observations off both coasts of North America, this species is likely widely distributed, but has simply eluded scientists in the past. Although the deep sea is the largest environment on Earth, we’ve only explored a miniscule fraction of these midnight waters. Who knows what other fascinating discoveries linger in the darkness waiting to be found?

The red siphonophore’s name recognizes its striking scarlet coloration, but its scientific name—Marrus claudanielis—honors the husband-and-wife team Claude and Danièle Carré for their contributions to our understanding of siphonophore biology.

The red siphonophore (Marrus claudanielis) lives in the midwater—the vast expanse of open water 200 meters (660 feet) below the surface and 200 meters above the seafloor—and never comes in contact with hard surfaces. Like other siphonophores, it’s hard to collect and study in the lab, but even observations in the field prove tricky for MBARI scientists. This species is sensitive to light and if we’re not careful, the lights on the ROV cause the siphonophore to shed its body parts.

Video captured by MBARI’s ROVs is critical to building our understanding of deep-sea siphonophores, but we also need to collect samples to formally describe a new species. We use a detritus sampler to carefully collect a specimen for closer examination in the lab to document its anatomy and genetics. 

While exploring the depths of Astoria Canyon off the coast of Oregon in 2009, MBARI’s ROV Doc Ricketts spotted the orange lantern siphonophore (Marrus orthocanna), a close cousin of the red siphonophore (Marrus claudanielis). While the two species look similar in appearance, the orange lantern siphonophore is typically more orange in color, has hook-shaped canals along its length, and grows longer than the red siphonophore.

MBARI’s ROVs are shedding new light on the residents of the midwater, including those that live in the midnight zone—the inky depths below 1,000 meters (3,300 feet) that scientists call the bathypelagic zone. This red siphonophore (Marrus claudanielis) was observed by MBARI’s ROV Doc Ricketts at a depth of approximately 1,500 meters (4,900 feet).

Scientists classify siphonophores into three groups—physonect siphonophores have swimming bells and a gas-filled float; cystonect siphonophores have a float, but no swimming bells; and calycophoran siphonophores have swimming bells, but no float. The red  (Marrus claudanielis) is a physonect siphonophore. 

A small, gas-filled float called a pneumatophore provides buoyancy for a red siphonophore (Marrus claudanielis).

Just behind the gas-filled pneumatophore are swimming bells called nectophores. Just like the muscular bell of a jelly, these expand and contract to propel a red siphonophore (Marrus claudanielis) through the water. When threatened, the red siphonophore can jettison its swimming bells, which glow with bioluminescence to confuse predators while the siphonophore makes its escape.  

A central stem called a siphosome runs the length of a red siphonophore (Marrus claudanielis) and connects each individual in the colony to one another. Feeding polyps (gastrozooids) extend fine tentacles to capture food. Frilly bracts are loaded with stinging cells to defend the siphonophore from predators. Clusters of gonophores aid in spawning and reproduction.