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One of the great mysteries of neurobiology is how memories are stored.  We have a few tantalizing clues, but the precise biological mechanism for how memories are created and where they are stored in cells is still unknown.  All of your lost loves and childhood dreams, your family’s birthdays and preferences, your own name and darkest secret…nobody knows where they are in your head.  And, um, we still don’t know…however, thanks to research on sea snails, we have some new clues.

Scientists have long believed that memories are stored within the structure and connective patterns between the synapses which connect neurons.  The new experiment suggests that this may prove to be a misconception.

Scientists trained a particular sort of sea snail (which have “small” brains with only 20,000 neurons) to respond in certain unusual ways to electrical shocks.  Then the team removed ribonucleic acid (RNA), from nerve tissue of the trained snails and injected it into the circulatory system of untrained snails.  Other “control” snails which were untampered with responded to electrical shocks naturally, however the snails which were treated with RNA from snails taught to curl their tails for prolonged periods immediately demonstrated this unusual behavior.

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The findings suggest that our conjecture about where memories are stored may be quite wrong…or at least disturbingly incomplete.  The snail research indicates that, at some fundamental level, memories are stored in the nuclei of neurons.  Now scientists will try to replicate the results in other animals to test this hypothesis.  Everything in this sort of research ends of being more complicated and interlinked than initially thought, so don’t forget about those synapses just yet.  We are still at the beginning of this tantalizing scientific quest.

The Common Limpet (Patella vulgata)

Limpets are gastropods with simple cone-shaped shells.  The majority of limpets are herbivores which live by grazing up films of algae by means of radula—an organ which is a tongue covered in rows of teeth.  The most salient feature of limpets is their incredible tenacity. They cling to rocks and other haed surfaces with incredible tenacity—to such an extent that they have become synonymous with tenacity and obduracy.  Brute force will not compel a limpet to stop clamping to a favored surface and the animal will allow itself to be destroyed before giving up its grip.

There are a number of limpet-like gastropods but the true limpets are named Patellogastropoda.  The majority are tiny—less than 8 cm (3 inches) although a few larger species are known.  Some limpets have a “home scar” on their favorite rock—a niche which fits them carefully and where they are perfectly camouflaged.  Such limpets tend to be territorial and will fight for the grazing rights to algae near their scar.

Although limpets are most familiar to people at the tidal line (where rockbound limpets survive above the low tide line by adhering to rocks and tightly maintaining moisture) the creatures exist in numerous different marine ecosystems, including the depths of the sea, coral reefs, whale skeltons, seagrass forests, black smokers, and cold seeps.  The deepwater limpets are probably detritivores.  Limpets begin sexual life as males, but when they mature to a couple of years old they turn female. Young limpets undergo a brief larval stage before clamping down on a hard surface and stating to graze or forage.

A limpet shell pillbox

Clione or “sea angels” swimming in a Tokyo aquarium (Photo by REUTERS/Kimimasa Mayama)

In terms of taxonomical diversity the gastropods are second most diverse class of animals on Earth (outnumbered only by the teeming class Insecta of the other great invertebrate phylum Arthropoda).  This means that there are some deeply strange arthropods out there. While we traditionally think of gastropods as snails and slugs there are odd subcategories of these creatures, like the subject of today’s post, sea angels (of the clade Gymnosomata).

A “Sea Angel” (Clione limacina)

Sea angels consist of six different families of pelagic marine opisthobranch gastropod molluscs.  Gastropods are named for their famous foot (the name means “stomach-foot”–a misnomer since gastropods all have true stomachs elsewhere) however the name is even more inappropriate for sea angels.  In these free-smimming predators, the gastropod foot, so familiar to us as seen on snails, has evolved into a pair of delicate wings for swimming through the water. Sea angels are very small: the largest species only reach 5 cm (2 inches) in length and most varieties are much more miniscule.  They prey on other tiny creatures swimming among the plankton—particularly other smaller slower species of gelatinous mollusks.

A hunting sea angel (photo by Alexander Semenov)

Adult sea angels lack any sort of shell—which they discard when they metamorphose into adulthood.  Their feeding apparatuses can be strangely complicated—pseudoarms and tentacles which recall their cousins the cephalopods. Sea angels are numerous in the oceans but some scientists are concerned that the acidification of the world’s oceans will cause substantial problems for the tiny translucent gastropods.

Sea Angel (Platybrachium antarcticum)

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