In the Leech Library: Behind the scenes at the American Museum of Natural History

This is the second story in a four-part, weekly series on taxonomy and speciation. It's meant to help you as you participate in Armchair Taxonomist — a challenge from the Encyclopedia of Life to bring scientific descriptions of animals, plants, and other living things out from behind paywalls and onto the Internet. Participants can earn cool prizes, so be sure to check it out!

On the sixth floor of New York's American Museum of Natural History — far away from the throngs of tourists and packs of schoolkids — there is a cold, white room, filled with white, metal cabinets.

The cabinets are full of dead things; leeches, sea anemones, lobsters ... any kind of invertebrate you can imagine. Even a giant squid. All of them have been carefully preserved. Each soaks in its own, luxuriant ethanol bath. Here they sit, some for a hundred years or more, waiting for scientists to pull them out into the light.

It's a bit like the final scene of Raiders of the Lost Ark, but for slimy, crawly, spineless things. There are collections like this all over the world, containing every species of animal, plant, and microscopic organism. Together, they serve as a record of Earth's biodiversity, a library of life. In them, you'll find more than just random specimens. Some of the individuals are special. Called "type specimens", they serve as ambassadors for their species, real-world models that define what each species is. For instance, the leech species Myxobdella maculata is both a group of leeches and exactly one leech — A leech that I got to meet on a behind-the-scenes tour with invertebrate curators Estefania Rodriguez and Mark Siddall.

Estafania Rodriguez stands in the invertebrate collections room at the American Museum of Natural History. Behind her, you can see a row of expanding cabinets used to store many different invertebrate species. These are like the library stacks, where average specimens are organized by phylum, class, order, family, genus, and species.

The specimens stored in these cabinets are meant to demonstrate diversity, the broad range of what different animals within a single species can look like. "We've got a huge collection of lobsters," Mark Siddall said. "I had a guy come in and wanted to measure all the different antenna lengths of lobsters from a huge variation across space and time to see if that's something that changes."

Across a narrow aisle are the rows of immobile cabinets that house type specimens — individual animals that serve as the definition of what an entire species ought to be like. These are the "sacred" specimens. For each species, there is only one official model animal — the holotype — in the entire world.

When scientists find a new animal, they use holotypes to figure out which species it belongs to — or whether it might represent something entirely new that we haven't seen before. It's a simple game of deciding whether a new specimen is more like one holotype or another.

"They look horrible when they are dead," said Estafania Rodriguez, holding a small jar containing a type specimen of a sea anemone from the Arctic. In another jar, she had a type specimen of an Antarctic anemone. One of her current projects involves figuring out how closely related these two species are. There's a possibility that they might be a single, bi-polar anemone.

Color doesn't preserve well in alcohol, so even the most rainbow-hued small invertebrate can end up looking like a brown lump. Because of that, some of the information about each specimen is lost — preserved in words and drawings, rather than flesh. But this is still the best way to do it. "They loose much more information if they dry out," Siddall said. Preserving the body, even in a less-attractive state, allows scientists to come back and study both internal and external anatomy.

The museum has had collections like this since it was founded in 1869. But, over the years, the methods for storing the specimens have changed. Rodriguez pointed out these jars, sealed with white gaskets. Until recently, the jars used a red rubber gasket. Unfortunately, it turned out that the red gasket dissolved into the alcohol, damaging the specimens. It also turned brittle, allowing alcohol to evaporate. And, if that wasn't enough, the dissolved red gasket was also toxic. "You live, you learn," Siddall said.

In fact, the collections room, itself, was an innovation in specimen storage, Siddall said. It's only about a decade old and is designed to reduce the risk of fiery destruction — a big deal when you're talking about a room full of ethanol. The ceiling was covered in fire-resistant foam and dotted with sprinklers. It's also engineered to support the weight of hundreds of alcohol-filled jars.

Of course, that brings up an important question. Fire, floods, theft — these are all things that can happen. What do you do if you lose a holotype?

In this photo, Mark Siddall shows me a brown blob of preserved leech at the bottom of a vial. The drawer next to him is full of not only holotypes, but also backup specimens, called paratypes. Collected in the same place, at the same time, as the holotype, paratypes help scientists understand diversity within a species. And, in the event of the holotype's demise, they can step in and take its place. When that happens, the paratype becomes known as a neotype.

A holotype and its paratypes are usually stored in different places. That's a safety precaution, but there are other reasons for doing it, as well, including making sure that the natural heritage of other countries doesn't all end up in boxes in New York and London. Here, Siddall holds a leech paratype that he collected in Madagascar in 2002. "The holotype went to Madagascar where it belongs," he said.

This is the holotype of the species Myxobdella maculata. It was found in 1914, in what was then the Belgian Congo. Scientists Herbert Lang and James Chapin went into the Congo basin in 1909. They meant to stay a year. There were there for six years. When they finally returned, they brought with them hundreds of thousands of specimens, including 100,000 invertebrates alone. Neither of them were invertebrate specialists, however. So this leech and many others like it sat in the collections, unnamed and unnoticed until 1939 when zoologist John Percy Moore pulled it out, identified it as a species, and gave it a name.

And there's nothing particularly weird about that story. Even today, the invertebrate collections contain unidentified material. People like Siddall, who specialize in one animal, will come back from expeditions with animals they aren't familiar with. Those sit in the collection, waiting for specialists to come along and examine them more closely.

It's also worth noting that all the type specimens — whether holotype or paratype — come with more than just a name. Every label tells a history; who found the specimen, when did they find it, where was it found, and who described it and gave it a name. Some even have latitude and longitudinal coordinates. That information helps scientists match the right research papers to the right type specimen. It also helps them make comparisons across time and space. If somebody finds a Myxobdella maculata in the Democratic Republic of the Congo today, they can set it side-by-side with the holotype and see whether evolution has been at work on the species.

"With mollusks, especially, we get people who want to donate us their shell collections," Siddall said. "And that's very nice and very generous. But if I don't know where it's from, when it's from and all of that information, then the specimen is of almost no scientific value."

At the very end of my tour, Estefania Rodriguez pointed out a large container, about the size and shape of a trash dumpster, sitting ominously at the end of the aisle. "There's a giant squid in that tank," she said.

Unfortunately, I didn't get a chance to see inside. Like all the other specimens, the squid is floating in ethanol. But because it's a giant squid, it's really an awful lot of ethanol. "Because of the vapor pressure inside, opening it requires four people and a fire department," Siddall said. "And when you lift the lid, it's like a big calamari martini."

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