Strophia nana Maynard, 1889

Original Description

"11. STROPHIA NANA Novo.

Dwarf Strophia.

Plate II, 11, A, B, & c, shell; D, section.

DESCRIPTION.

                SP. CH. Size, exceedingly small. Shell, moderately heavy. Striations, present. Tentacles, short, about one fourth as long as the eye peduncles. Whirls, 11. Teeth, long. Examined 2,000 specimens.

                Form of shell, an elongated cone, with the first whirl the largest; the next three are successively a trifle smaller, then the shell slopes rapidly to a point, making an angle of about 60 degrees. The striations are 18 on the upper whirl, prominent, and excepting on the first whirl, where they are narrower above and enlarged in the middle, are largest at the top, and gradually become narrower, attaining the minimum near the suture, where both they and the shell are depressed below the di­ameter; from this point to the suture the striations become suddenly enlarged and widened as much as at the beginning above, and are slightly inclined to the left. The striations are not arranged in lines, and are slightly inclined from right to left; the interspaces are a trifle wider than the prominences which are roof-shaped, with the ridge somewhat rounded, and the surface is smooth. The striations are absent on the two or three lowest whirls. The sutures between the whirls are not very deep.

                Aperture, large and open, but does not measure any more within than at the entrance. Lower tooth, not very prominent, is .10 long and .02 high, and the upper which is situated just above it, is not at all prominent, being a mere elevation, but more within the cavity is higher, and makes a complete turn around the column.

                Margin, not produced forward quite as far as the diameter of the shell, and is inclined slightly backward; it is not thickened, and the outer portion is produced into a thin, but not prominent, edge that is not rolled downward. The frontal bar is quite prominent and interrupts the striations. Animal, not large; eye peduncles, .20 long; tentacles, .05. Jaw, smooth.

                Color of shell, externally, dull ashy. The frontal bar, teeth, and margin, internally, are bluish white, but within the aperture this color gradually deepens into pale purplish brown which pervades the whole interior.  Color of animal, pale brown, with the minute granulations on the anterior portion of body and head, black.

DIMENSIONS.

                Size of types, .62 by .25 and .60 by .18. Largest specimen, .64 by .26; smallest, .53 by .20. Greatest diameter, .28; smallest, .18. Long­est specimen, .64; shortest, .53.

OBSERVATIONS.

                The type as described and figured on Plate II, 11, A, is the most prevalent, but a more cylindrical form is very common, ib., B, in which there is but very little difference either in diameter or width between the second, third, and fourth whirls, the first being wider, but not much larger in diameter. The specimen figured has the striations far from prominent, but this one is almost, if not wholly, unique in this respect. The remaining form is shorter than the type, but has about the same proportions. The depressed line above the suture and the inclined en­largment of the base of the striations are some of the singular features of this most remarkable Strophia, and remind one of a similar structure in the genus Chondropoma. The peculiar ashy colors may be partly due  to minute, dark, apparently eroded dots, with which the shells are cov­ered. Striations vary from 16 to 20; whirls, 10 or 11.

                Known from all other species, by the presence of striations, exceed­ingly small size, elongated form, and long teeth.

DISTRIBUTION AND HABITS.

                The island of Little Cayman is only ten miles long with an average width of two miles, and is thus a mere spot in the waters of the Caribbe­an Sea, and the Dwarf Strophias occur in a space which is only five or six yards wide by twenty long, on this little key, and as they were rigidly confined to this narrow area, which on a good sized chart of the West Indies, would be more than covered by the point of a fine cambric nee­dle, I consider that this species has the most restricted range of any animal with which I am acquainted. This spot is on the west end of Little Cayman, on the eastern most of the two paths that cross the key, near their junction.

                In habit, this species is social, and I found many of them clinging to a kind of heath-like plant which was about eighteen inches high, and which had small gray leaves of nearly the same color as the shells, and which on being crushed, gave out a strong odor. Here these Strophias were exposed to the burning rays of a nearly vertical sun, and the heat in which they lived during the day, was intense. Some, perhaps one third of them, had retreated beneath stones, a situation in which it is rare to find a Strophia, the only other species that I have found in a sim­ilar situation, being S. incana from Key West, which retreated from the cold of winter, and one other species occurring in the pine woods on the island of New Providence, to be mentioned later.

                It is evident that in this species, we have a Strophia dwarfed to an exteme degree, from feeding on the pungent leaves of the plant described, and isolated as it is by surrounding areas of rough, jagged rocks, the process of diminution has gone as far as it can go and allow the animal to live as a Strophia, with the ordinary habits of Strophia. The ground as strewed with thousands of dead shells, showing that mortality among them was great, and the, perhaps, recently acquired habits of seeking the shelter of rocks is one to which they are driven in order to preserve the species from utter extermination, but it is doubtful whether they 11 even keep their generic characters under this new mode of existence, for further remarks upon this very interesting subject consult General conclusions.  (Maynard, 1889: 27-29).

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