Euconulus fulvus (Müller, 1774) Brown Hive

    Figured here are digital color images (middle and right columns) of two specimens of E. fulvus from Bennington Co., VT, each in apertural and in apical view. The "typical" shell in the top row is 2.55 mm in height (H) and 2.85 mm in diameter (D) using the method of Pilsbry (1939: xi). The shell in the  bottom row right is 3.2 mm in H, 3.4 mm in D, and is unusually tall. The shell in the  top row is considered by a panel of experts to be more typical, thus it was used for the species comparisons on page one of this feature.

   Pilsbry (1946: 236; fig. 117C, 117D) showed line drawings (left column) of two E. fulvus shells: one from Herkimer Co., NY (H 2.4 mm, D 3.1 mm; top row); the other, from Buckfield, ME, (3.4 mm in both H and D; bottom row). Although only differing by about a half whorl in growth, the two exhibit a stark difference in apertural view. The H/D ratio is 0.78 vs. 1.0, the ratio of body whorl to H (BW/H) as measured at the columellar axis: 1.6/2.4 (0. 66) vs. 1.9/3.4 (0.56), and the ratio of aperture (maximum  on an axis parallel to the columella) to H (A/H): 1.1/2.4 (0.46) vs. 1.3/3.4 (0.37) respectively. These morphometric differences are attributable to variation in the process of whorl "translation" producing a smaller spire angle, a more convex (vs. trochoid) profile, and a relatively smaller aperture in the larger shell.

    A similar pattern is seen in the in the Bennington Co. E. fulvus shells, which also differ by about a half whorl: H/D .89 vs. 0.94, BW/H 1.45/2.55 (0.57) vs. 1.8/3.2 (0.52), A/H 1.33/2.55 (0.42) vs. 1.2/2.2 (0.36) respectively. Is this a paradigmatic process in this species? Evidence indicates that it is, and it appears to be a generic characteristic, at least for the North American species (see previous page). In all instances observed by me, the very juvenile shells that characteristically dominate populations observed in the field have wider spire angles than larger shells. It is likely that this "slimming-down" process continues throughout ontogeny, even affecting giant specimens such as the two 3.4 mm "atypical" ones discussed here.

Pilsbry, H. A., 1939. Land Mollusca of North America (north of Mexico) vol. 1 part 1. Academy of Natural Sciences, Philadelphia. xvii + pp 1-573 + ix. Dec. 6.

Pilsbry, H. A., 1946. Land Mollusca of North America (north of Mexico) vol. 2 part 1. Academy of Natural Sciences, Philadelphia. vii + pp 1- 520. Dec. 6.

Euconulus fulvus (Müller, 1774) Brown Hive