This animal is not the most agile swimmer in the sea. It’s called Nautilus, and it is closely related to cuttlefish and snails. But it swims backwards and often bumps into things.

Thankfully, it has a thick shell, and can retreat into it to avoid predators. And it also dives down deep into the sea during the day when it’s not feeding. The longer it spends inside its shell, though, the harder it is to get oxygen, and levels can get dangerously low if it has to wait for a long time without any new water flowing by. While we might try to hold our breath at those depths, Nautilus holds its heart. Nautilus slows its metabolism down, and it can hold its blood in its enlarged vena cava, spacing out its heart beat to once every one or two minutes.

Sea turtles, also fantastic divers, have a similar mechanism of energy conservation. The deeper they go, and colder the waters get around them, the slower their heart beats, going down to two or three times a minute and slowing their energy use to one tenth of what they would normally use on the shore.

Photographs graciously provided by Adrian Reich of the Wessel lab at Brown University. Thanks to Brad Seibel, our favorite mollusc exercize physiologist, for his help fact-checking. More about Nautilus metabolism can be found here.

The slug pictured above, Elysia chlorotica, is a symbiont thief.

Elysia chlorotica eats the alga Vaucheria litorea but does not digest it. The slug cuts open algal filaments and sucks out the contents, transferring the living chloroplasts to its own tissue. Chloroplasts are organisms that have lived symbiotically within plant cells for many millions of years. They harness energy from the sun, which they give to the plant or alga cell they live within. Most animals digest the chloroplasts entirely when they eat plants, but not Elysia. By keeping the chloroplasts intact and transferring them to its own tissue, Elysia allows them to continue photosynthesizing, producing energy for the slug. The slug can then live for months without eating as long as sunlight is available, and can maintain the same chloroplasts for its entire adult life. This is an extremely unique relationship between an animal and plant symbionts.

Many other animals form associations with photosynthetic organisms. Corals such as the one depicted below have a symbiosis with multiple single-celled organisms called zooxanthellae. This is a multiple-level symbiosis because corals house the entire chloroplast-containing zooxanthellae cells within their tissue. This is different from Elysia chlorotica, who has cut out the middleman — instead of incorporating entire  cells, it only retains the chloroplasts.

The upper photograph (of Elysia chowing down) was taken by Nicholas E. Curtis and Ray Martinez. The second photograph is courtesy of Mary S. Tyler, and was the cover of PNAS when this paper was published. The lower picture is the coral Porites as photographed by Casey Dunn. You can watch two amazing videos of the slugs in action, here and here, both of which were included in the PNAS paper.

This is the fourth of four contributions from undergraduates in Casey Dunn’s Bio0041 Invertebrate Zoology class. This episode is inspired by the fascinating behavior of the flamingo tongue snail, Cyphoma gibbosum, which is described in further detail in Casey Dunn’s earlier post.

Video, music, and narration by Chris Vamos. This podcast is licensed under a Creative Commons Attribution-Noncommercial-No Deriviatives 3.0 United States License.

The marine snail Cyphoma gibbosum browses on the polyps of soft corals (top). It appears to have a brightly spotted shell, but when disturbed the spots begin to move (middle) and then retract within the white shell, along with the rest of the animal (bottom). This is possible because the spots are not part of the shell at all. They are patterns on the thin mantle tissue that extends out of the shell opening and up around the snail’s back. Photos by Casey Dunn.

We are pleased to present Episode 1 of CreatureCast, by Sophia Tintori. In this first video, Alison Sweeney talks about work that has been done in the Morse lab on Squid iridescence. Audio production and animations are by Sophia, who normally studies siphonophores in the Dunn lab. Music by  Lucky Dragons (here, and slowed down versions of this and this) and Sophia on the musical saw.

This video is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.

(Episode 1 was replaced with a new slightly different cut on August 18, 2009. It is now higher resolution and includes a couple different musical tracks.)