Additions to and Distributional Annotations on the Kansas Gastropod Fauna

Abstract

Campeloma decisum (Say) Numerous living adults were secured from Shoal Creek, south of Galena, Cherokee County, between the dates of 21:X:1962 and 22:VI: 1962. This is a mud-brurowing, dioecious and viviparous species which is distrubuted throughout the entire length of Shoal Creek but usually associated with the silty mud that accumulates about the roots of Dianthera americana. We found it in no other type of habitat. Since there are relatively few reports on the biology of Campeloma some data are included here. Parthenogenesis has been demonstrated or intimated in this and other species of the genus by the studies of van Cleave and Altringer (1937) (no males in 1500 C. rufum), Mattox (1938) (no males in 700 C. rufum) and Chamberlain (1958) (no males in over 800 C. decisum). On the othet hand, Baker (1928) found males in Wisconsin populations of C. decisum but in the very low ratio of 1:99. In 470 specimens, from various Missouri and Kansas localities in Shoal Creek, about two females to every male, verified by dissection, were observed. Of 30 specimens, sampled at random, 11 were males and 19 were females. All of the females contained embryos in various stages of development, the number per adult being roughly a function of size (Table 1). The smallest embryos are located in the upper part of the uterus, averaging about 1.0 X 1.0 mm in size and having one and onehalf whorls. The young snails progressively increase in size as they move towards the birth pore, averaging 3.5 x 3.3 mm and two and threefourths whorls near the middle of the uterine length and 5.0 X 4.4 mm with three and one-fourth whorls near its ventral end. These figures are based upon 277 embryos and compare very closely with observations made by Baker (1928) on 264 embryos. Baker also found four sinistral embryos but I found none. The average number of embryos for the Kansas-Missouri specimens is 9.23, a figure near the 9.4 found by Baker (1928) in Wisconsin.