Carnegie Museum of Natural History

One of the Four Carnegie Museums of Pittsburgh

mollusks

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Clams

Boat dock

Is having a few hundred clams under your lake dock a good thing or a bad thing?

A reader recently asked that question of Cottage Life magazine. To get an answer, reporters got in touch with Timothy Pearce, the assistant curator and head of the Section of Mollusks at Carnegie Museum of Natural History.

“The sudden appearance of large numbers of organisms can sometimes result from the introduction of a non-native species,” Timothy said. “They’re often free from the predators and diseases that kept their numbers in check elsewhere, so they can proliferate into large populations.”

According to the article, seeing fresh water clams in a fresh water lake is not unusual.

“It’s like having dandelions,” Timothy said. “It always appears as though they’re aggregating. But that’s just because they’re in your yard.”

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Snails

Shells of tree snails from Florida and land snails from Cuba
Tree snails from Florida (top row) and land snails from Cuba (bottom row) on display at Carnegie Museum of Natural History
(Photo by Hayley Pontia)

 

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Mollusk Collection

specimen drawers from the Mollusk Collectionby Hayley Pontia

Carnegie Museum of Natural History’s collection of mollusks is home to about 3 million specimens that include more land and freshwater snails from Pennsylvania and its adjacent states than all other U.S. museums combined.

What are mollusks you ask? They are one of the most diverse groups of animals on the planet. They have a soft body with a ‘head’ and ‘tail’ region. Their bodies are most commonly covered in a hard exoskeleton, but some can even have their shells on the inside.

You may know the most common mollusks without even knowing they are mollusks: snails, clams, octopuses, scallops, oysters, and even squids are all part of this phylum. Many people are around these animals, yet know very little about them.

As assistant curator and head of mollusks at Carnegie Museum of Natural History, Tim Pearce spends a lot of time researching and understanding these specimens.  Every second Saturday, Pearce gives tours of the collection found in the basement of the museum for those interested in learning more about these unique species.

Pearce collecting snails at Carrington Point on Santa Rosa Island, California. San Miguel Island is visible in the distance. (Photo by Charles Drost.)

Hayley Pontia is the marketing assistant at Carnegie Museum of Natural History and a student at the University of Pittsburgh. Museum employees are encouraged to blog about their unique experiences of working at the museum.

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Researchers chase snails on Santa Rosa Island, California

Pearce collecting snails at Carrington Point
Pearce collecting snails at Carrington Point on Santa Rosa Island, California. San Miguel Island is visible in the distance. (Photo by Charles Drost.)

by Tim Pearce

Islands often contain peculiar species, including some that are endemic (found only there). Tim Pearce, Assistant Curator of the Section of Mollusks at Carnegie Museum of Natural History, spent five days with two other researchers surveying the land snails of Santa Rosa Island, one of the California Channel Islands. This survey is part of a larger project, funded by the National Park Service, to understand the land snails of the California Borderlands.

The researchers braved spiny vegetation and strong winds (sometimes pebbles became airborne) to find at least three new land snail records for the island among the dozen or so species they found. Several species found are endemic to the California Channel Islands. Further scrutiny of the finds will reveal whether any species are endemic to just Santa Rosa Island or possibly new to science.

Snails were often surprisingly difficult to find, which might reflect recent disturbance history of the island. The last of the large non-native mammals (goats, sheep, pigs, cattle, deer, and elk) were removed from the island in 2013. These animals can impact snail populations through trampling and more importantly by eating vegetation, changing it from forest to grassland. This study provides a baseline to inform future investigation of how snail faunas recover after disturbance.

Timothy A. Pearce, PhD, is the head of the mollusks section at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

 

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Snail eating snails: two species become one

Two land snails Land snail
by Timothy Pearce

The land snail family Haplotrematidae is widespread in North America. They are omnivorous, eating other snails as well as plants. Western North America hosts most (16 of 18) species of this family that occur in the
United States and Canada. Some species are found under sword ferns where they might gain protection by mimicking fern fiddleheads (see figure of Haplotrema vancouverense beside a fiddlehead).

Two related species, Ancotrema hybridum and Ancotrema sportella, are sometimes difficult to separate. Their beautiful shell sculpture includes ridges radiating outward like bicycle spokes, and finer spiral grooves cutting across the tops of the ridges, looking like beads (see figure of Ancotrema with beaded sculpture). The beaded sculpture extends to the end of growth in A. sportella, but the sculpture becomes smooth on the last, largest whorl in A. hybridum. They are easy to tell apart until you find one that is smooth on only half, or a quarter, of the last whorl.

Two things made us suspect that they might really be one species. First, some shells were difficult to classify. Second, the ranges of both species coincide from northern California to Alaska.

To address whether they are two species or one, we examined 311 museum specimens. If they are two species, we expected to see a two-humped curve (bimodality) in amount of smooth sculpture on the last whorl. We expected
many specimens without smooth sculpture at the end, many specimens with smooth sculpture on the entire last whorl, and very few specimens having smooth sculpture on just half the last whorl.

Instead, we saw continuous variation, with no hint of bimodality. That result is consistent with their really being one species. Furthermore, we discovered on every shell the sculpture became smooth around whorl number 5. If shell growth stopped before whorl 5, then it resembled A. sportella. If it grew beyond whorl 5 before becoming adult, then it gained the smoother sculpture of A. hybridum.

Next, we looked for reproductive differences. When new species arise, reproductive structures are sometimes the first to change. These changes might help individuals to recognize the correct mate. We found no consistent differences in the reproductive parts.

These (and most land snails) are hermaphrodites (one individual is both male and female), so we know we were not looking at male – female differences. Also, we knew we had adults only because the upper lip dips
downward at the end of growth, so we were not comparing adult – juvenile features.

Finding continuous variation in the feature traditionally used for separating the two species, no differences in the reproductive parts, coincidental geographical ranges, and discovering that the sculpture always
diminished about whorl 5, all led us to conclude that they are one species. A. sportella was named first, so by the law of priority, that is the name we will use.

Scientists get more glory for naming new species, not sinking a name as we did here, but this taxonomic cleanup work is important, too.

For more details, please review Pearce, T.A. & Fields, M.C. 2015. Shell and genital morphology fails to separate Ancotrema hybridum (Ancey, 1888) and A. sportella (Gould, 1846) (Gastropoda: Haplotrematidae). Malacologia, 59(1): 21-32.

Tim Pearce is assistant curator of mollusks at the Carnegie Museum of Natural History. He studies ecology and systematics of land snails.