Thursday, September 08, 2016

The Noble Hornsnail

kw: species summaries, natural history, natural science, museums, research, photographs

The image above shows all the specimens held by the Delaware Museum of Natural History for the species Pleurocera nobilis (I. Lea, 1845). From the lot-by-lot pictures below, you can see that two lots were originally identified as P. moniliferum (Lea, 1862). That species is now considered a synonym of P. nobilis. This species is found throughout the Tennessee River watershed, but particularly in and near that stretch of the Tennessee River running a hundred miles on both sides of the Tennessee-Alabama border, and into its tributaries.

When Isaac Lea named the species moniliferum, he was referring to a necklace, monile in Latin. With a length of at most 3 cm, this is hardly an impressive river snail. But compared to the rest of the genus Pleurocera it is larger and a little prettier.

Pleurocera means "ribbed horn", referring to the rib or ribs running along the whorls. In this species the rib is rather subtle. This lot of two shells was collected in or near the Holston River in Tennessee north of Knoxville, possibly quite far north, as that river is 160 miles long.

I took pictures for earlier posts on various backgrounds. Someone had said perhaps a standard gray would work, but I found that anything other than black or white tends to make the specimens harder to see. Today I used an enameled black surface, a background for one of the inspection microscopes. It worked pretty well but is rather reflective, so I guess it is time to spring for some black velveteen. I put paperclips under the specimens so I could orient them appropriately.
This lot and the next show how we occasionally run across misspellings and other errors on labels from collectors. "Bridgepark" actually refers to Bridgeport, a small Alabama city on the Tennessee River just south of the state border.

These were collected in 1877, as handwritten on the museum label, which was learned from Richardson's notes. He did not put collector or collecting information on his own labels, but fortunately had notes about many of the specimens he sold to the museum.

Being from a quieter part of the river system than the first lot, or the one that follows, these shells are a little larger and cleaner, not quite so banged up near the tip of the spire. If you'd spent a few weeks looking at other species in this genus, as I have, you would realize that when Isaac Lea named this species nobilis, he really meant it. Most of the pleurocerids are horn-shaped, but are usually rather small, and seldom undamaged. These seem "noble" by comparison.

This lot of three is also from the Holston River, though the original collector misspelled the river name. John D Parker, who gave these to the museum, didn't add his own label, so the volunteer on duty the day this was cataloged just used the spelling from the collector's label.

I included this fourth lot because when I saw it I thought, "It looks just like P. nobilis." These were found near Knoxville, probably at or near the confluence of the Holston and Tennessee rivers. Here is where habitat notes, so rarely made by a collector, might have helped us distinguish what species it really is.

Also, I could find no reference to a Pleurocera species named nodulatum, nor any variation such as nodatum, authored by Say or anyone else, and I don't know who identified it for Richardson or the person he might have obtained it from. There is nothing about that in Richardson's notes. But rather than re-classify it just now, I've put a note in the database that it may be P. nobilis, and to ask the next specialist in pleurocerids who visits to take a look at it.

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