Strophia mutata Maynard, 1894

Original Description


Changing Strophia.

FIG. 37, B, front view.


            SP. CH. Size, medium. Shell, rather thick. Striations, present. Whirls, ten. Examined 100 specimens.

            Form of shell, a pointed cylinder, with the first whirl the largest, then each successive whirl is slightly smaller than the one above it, as far as the fifth whirl, when the shell slopes gradually to a point, form­ing an angle of fifty-seven degrees. The striations are numerous, thirty on the first whirl, are small, slender, and regular, but not arranged in lines; they are slightly inclined from right to left, are not furrowed, but are smooth and rounded and a little more than one half as wide as the interspaces between them.

            Aperture, rather small, and considerably contracted at the entrance. Lower tooth, not prominent, about .04 high, and about twice as long as high; it is not elevated, and is set back about once its length. The upper tooth is represented by a mere tubercle.

            Margin produced forward nearly as far as the diameter of the shell, and is very slightly inclined to the right, a trifle beyond the diameter of the shell; it is thickened all around, hollowed out in the middle, and then projected backward into a sharp edge, which is not rolled over. The frontal bar is very thin and completely interrupts the striations.

            Color of shell, deep umber brown, with most of the striations creamy white. Brown within, becoming creamy white on the edge of the margin and frontal bar.


            Size of type, 1.15 by .40. Largest specimen, 1.14 by .50. smallest, .88 by .38. Greatest diameter, .50; smallest, .38. Longest specimen, 1.25; shortest, .88.


            Individual variation consists of gradual gradation into a smaller form, on one hand, with rather less number of striations, twenty-five on first whirl, and on the other, to a larger, thicker form with more numerous striations, thirty-seven on the first whirl, but there is no decided form among these.

            No. 1. The only inclination to assume a form is, singularly enough, one which grades directly into typical S. cinerea. In fact, at one extremity of this form we have a cylindrical shell much like typical S. c. mutata, and at the other, shells which I confess I cannot distinguish in the smallest particular from typical S. cinerea.

            The presence of this singular sub-species of S cinerea on Long Key was a great surprise to me, the more so, as on Spruce Key, an island only about a half mile to the north of Long Key, I found two distinct species, not only different from anything on either Hog Island or on New Providence, but varying widely from one another.

            Typical specimens of the Changing Strophia are very beautiful and so utterly different from S. cinerea that no one would suspect the relationship, but that, too, as stated, complete gradations occur between the two. I do not hesitate to affirm, however, that this species is of quite recent origin and that it has not had time to completely change. My reason for making this statement is mainly because I could not find any dead specimens of any forms on the ground, as is the case among old established species. This is also true in regard to the Mottled Strophia.

            How long it takes to evolve a form of Strophia with characters so widely different as those exhibited by this one, it is difficult to say, with our present knowledge of the subject. I should think, however, that these mollusks, when placed under a widely different environment from

that under which they had been living, would begin to change in two or three generations; but what the length of the life of a single indi­vidual is, and how long it is in coming to maturity is impossible to say. Judging, however, from the fact that in the winter it is so difficult to find a young Strophia with less than four whirls, that, with all my experience, I never saw a specimen with less than this number. it is probable that they grow quite rapidly, especially in summer, and probably acquire their full size in one year. Twenty years would mean much to a colony of Strophia, and would naturally produce many changes, while in a hundred years I should think that many species would grow old and become extinct.

            Be these matters, which are, after all, somewhat speculative (but not, perhaps, as much as they seem) as they may, here we have in this Strophia a fine example of the changing of one species into another, and also very clearly shows how careful we, of to-day, must be in recording all the steps of change in order that future generations may benefit by our researches.

            The typical Changing Strophia may be at once recognized by the dark color, white, and numerous striations.


            I found the Changing Strophia on March 29, 1893, clinging to shrubs along the rocky, northern shore of the western half of Long Key, an island that lies about a mile east of Hog Island. I traced the shells westward along the shore as far as the little bay on which the Marine Hospital stands and eastward to a sand beach about midway on the key. They were not found more than a few yards back from

the water's edge. As the weather had been very dry all of the shells were fixed and hybernating."

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