Monday, March 21, 2016

The Spiny River Snail

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

It seemed like months since I've worked with a snail that was "snail-sized", that is, an inch or more in size. The Spiny River Snail of Tennessee, Io fluvialis (Say, 1825), has a satisfying heft to it. It is endemic to the Tennessee River and its tributaries, particularly clear, fast-flowing, well-aerated rivers. The species name fluvialis indicates this. I prefer species names that are descriptive, rather than those that are named for someone, though biologists do like to honor special friends of theirs with species names.

Older collections of this species include members from all up and down the Tennessee Valley system, but after 1932 large portions of the rivers were dammed up by TVA and later projects, and became stagnant. Specimens are now found in comparatively few locations.

As befits a fast-water snail, it has a chunky, substantial shell. The spines probably have two functions: firstly, to help prevent rolling, and secondly, to discourage predators.

A few shells in our collection are as long as 6 cm (2.4 in.), but most are 3-4 cm or smaller. This first image shows two nice-looking specimens that were probably collected in the 1950's. If I knew who R.H.T. was I'd have a better idea of the time period.

The labels show a few misspellings. The donor to the Delaware MNH was Thelma Crow; "Crowe" is incorrect, but I have seen it on many of the labels for lots donated by her. The volunteer who entered the data for one group of Mrs. Crow's shells messed up, most likely by hearing the name but not seeing it. Then, Mrs. Crow herself doesn't know how to spell "label", as we see on the older label that came with these shells. Finally, to resolve the town's name, Rogerville or Rogersville, I consult an atlas to find that Rogersville is correct, as seen on the label by the mysterious "R.H.T.".

This image shows specimens collected in the Clinch River in Virginia. Clinchport is about 20 miles upstream of the VA-TN boundary. These shells show some of the range of variation of spine length, from quite pronounced to nearly not there. Variations such as these led early authors to describe at least ten species in the genus Io, but all are now considered the same species. I don't know why this genus was named Io; the name refers to a mortal woman who was seduced by Zeus in Greek mythology.

The old label that came with this lot states "Io etc.": it was in a box that contained more than one species. Other lots in the collection taken from the same box contain a copy of this label. This illustrates one aspect of museum collections research, that as much as possible, we try to trace the source of a specimen in location and in time. In this case, we have a location, within a mile or so along the Clinch River, but when these were collected is unknown and is only delimited by the date on which Mr. Parker gave or sold his collection to the museum, in the 1970s.

These images inside the aperture of the larger shell above show traces of its history. If we know enough about the numbering schemes of collectors we can infer who owned this shell along the way. The designation below, which I deciper as "[2092 C.M.]" probably refers to the collector. A later owner inked on the opposite side "11552", and this was probably Mr. Parker. I don't know if the brackets are his, or if they were added when someone at DMNH wrote the newest number, 131405. Our standard practice is not to bracket old numbers, but to put a single horizontal line through them, so they can still be read, but are clearly obsolete.

If a researcher wants more data on this shell or lot than we have recorded in our database, it is often possible to go to the donor's notebook, which the museum frequently has in its library.

This image shows the rather overcrowded box of 15 shells that the specimens above reside in. I share the proclivity to try to save space, but the museum's cabinets are less than half full, so we don't really need to be this anal about it. I may yet decide to replace this #4 box with a #5 box, which is 1.5 inches longer.

I tried out a small size plastic box, which is 3x3.5x1 inch, but it would only hold half the shells. Their spiny shape makes them take up a lot of room. The next size plastic box is much taller, so the #5 paper box is more appropriate.

This final image shows a lot of 13 shells of a subspecies recognized by some. The original label from U. Michigan's Museum of Zoology has "f. brevis" after the species name and author. This is a "form" name, which here indicates the shells are a little shorter for their width than is usual for this species.

These shells were collected 5.5 miles downstream of Kyles Ford, TN in late summer, 1924, so there were no mainstem dams on the Clinch River yet. To date, the portion of the Clinch near and below Kyles Ford is not yet dammed up, and a new dam that would stagnify the area is not planned, so perhaps this subspecies is still to be found there.

These labels show the chain of ownership: collected for Michigan by Wm. Clench and P.S. Remington; and Michigan probably split a portion of a larger lot for the benefit of the Kansas U. museum, which later sent DMNH their lot; we have no record that this is a further split. However, considering that one of our lots contains 100 of these shells in two 3"x6"x2" plastic boxes, it may be that Kansas U. retained half or more of the shells they got from Michigan.

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