Posted: Sep 12 2006
Crepidula plana, depressa and atrasolea, Telling depressa and atrasolea apart
Crepidula plana Say 1822
Crepidula depressa Say 1822
Crepidula atrasolea Collin, 2000
The Eastern White Slipper Shell is probably one of the most common shells found along the North American Atlantic and Gulf coasts. Because it lives clinging to almost any object it is often observed in dead shells, each one of which may house well over a dozen slippers. Until 2000 the Eastern White Slipper Shell was pretty much universally identified as C. plana. Life was easy. If it was a flat, white slipper shell, it was C. plana. Then, in 2000, along came Dr. Rachel Collin and her Phylogeny of the Crepidula plana (Gastropaoda: Calyptraeidae) cryptic species complex in North America, Can. J. Zool. 78: 1500-1514 (2000), and it went from easy to complex (and in Florida, very complex). Dr. Collin did some pretty extensive research and concluded one was really three. Not only did this range include both C. plana and C. depressa, but there was also an as yet undescribed species she named C. atrasolea. Dr. Collin then went on to make life difficult for us collectors by essentially saying, except for two characters visible to the naked eye, these three species are essentially indistinguishable. One character is the body pigmentation on the foot and mantle and the other is slight differences in the shape of the protoconch. Unfortunately, most collectors never see the animal and, as Dr. Collin acknowledges, the protoconch is usually eroded. The saving grace for us Florida collectors is that she also concluded that C. plana’s range is limited to the NE Atlantic coast only as far south as Georgia. So, if we find a live White Slipper Shell in Florida, we can easily distinguish (ha, ha) as to whether it is C. depressa or C. atrasolea. The body pigmentation on the foot, neck and mantle of C. atrasolea is “diffuse to intense sooty black.” C. depressa’s body pigmentation is “translusent white” with “some white spots in the mantle and neck.” No problem, just collect all your Florida White Slipper Shells live, identify them immediately, and be sure not to mix them up during cleaning and preparation for storage - because they regularly occur together. If you are confronted with a cleaned, dead White Slipper Shell from Florida and the protoconch is present, then you may be able to make an identification if its condition is good enough. The protoconch of C. atrasolea is composed of half a whorl and C. depressa’s is composed of one whorl. Rachel has reviewed this presentation of her findings and commented, "I just read your posting and it's great. I couldn't agree more with everything."
Makes me wonder how the two species are able to coexist in the same environment. It's rather rare one species usually outcompete the other species. Then you throw in a few other slipper snails species thou those are usually one species on rocks, another on outside of living shells. Maybe those of us who collects beached dead shells should just call those we collected eastern white slippershell.