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Sunday, October 17, 2021

Column: Planet of the mollusks

We mammals are arrogant.

The mammal clique has humans, which is like the high school clique that has the quarterback of the football team. The other animals are jealous of our brains and bipedalism. We mammals fawn over live young, while the slimy, scaly kids write emo poetry. They want to join the mammal posse.

“Do you have fur? I didn’t think so.”

But times are changing, and mammals need to watch out for Club Mollusk. The phylum Mollusca includes weirdos like snails, slugs, squid and octopi. Mollusks may look freaky, with their eyes on stalks or suction-cupped arms, but recent research has found that mollusks are smarter and better adapted than we ever expected.

A team of biologists from the Museum Victoria in Australia have discovered that octopi use tools. Veined octopi (Amphioctopus marginatus) often carry halves of coconut shells to use for shelter. The tiny octopi use their suction-cups to carry the halves underneath their bodies and walk around with the tips of their tentacles draped over the edge of the shell. When threatened, an octopus can just roll under the shell and hide. They will even close themselves up between two coconut halves to create tiny fortresses. (YouTube “coconut-carrying octopus” and you’ll see.)

Veined octopi are the first invertebrates to be observed using tools. Sure, hermit crabs carry around seashells, but those seashells are in constant use. A tool is an object that provides no benefit until used for a specific purpose.

An octopus can move pretty fast with its jet propulsion system, so it does have a chance of out-swimming predators. But odds are better with the coconut shell for shelter. The use of shells shows that octopi are capable of advanced planning.

Octopi are smart, but their sea slug cousins are willing to play dirty.

Dr. Sidney Pierce of the University of Southern Florida reported last month that a species of greenish sea slug (Elysia chlorotica) steals chloroplasts and chlorphyll-making genes from algae.

The slugs can photosynthesize.

Not to sound like a total nerd, but wowza!

Photosynthesis is a chemical reaction in plants, algae and certain bacteria that allows organisms to synthesize food from carbon dioxide using energy from the sun. Organisms that photosynthesize can produce their own food. Animals do not photosynthesize. That is a rule.

Sea slugs are rebels.

Pierce found that the seas slugs are born with genetic material that produces chlorophyll, a pigment needed for photosynthesis. Pierce used radioactive tracers to prove that the slugs were really producing the chlorophyll themselves, not just relying on stolen algae reserves. The genetic material came from algae at some point, but Pierce is still not sure how the genes transferred to slugs.

Newly born slugs can’t photosynthesize yet because they don’t have chloroplasts (the tiny organelles where photosynthesis takes place), but they can kidnap chloroplasts from algae for their own use. Chloroplasts get trapped inside cells within a slug’s gut system. The baby slugs just eat up some algae and then they can photosynthesize for the rest of their nearly yearlong lives. Pierce told sciencenews.org that he can keep slugs in aquariums happy as long as they have a light source.

As climate change continues and the polar ice caps keep melting, the world is getting wetter. We land mammals will suffer as habitats for ocean-dwelling mollusks increase. Smart, resourceful mollusks are like that geeky kid in high school who grows up to be a brilliant and gorgeous science writer.

Don’t underestimate the mollusks.

MADELINE McCURRY-SCHMIDT sometimes wishes she could hide under a coconut shell. E-mail her at memschmidt@ucdavis.edu.

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