File:American malacological bulletin (1987) (17533907294).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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108 AMER. MALAC. BULL. 5(1) (1987)
Text Appearing After Image:
ISLAND Fig. 1. Map of Ireland showing the locations of collected populations of Ancylus fluviatilis. Insert on the left is an expanded portion of the map showing the location of collection sites in southern Co. Donegal. Solid circles indicate populations collected in late 1978 and 1979, open triangles, populations collected in 1982, open circles, populations collected in 1984 and solid triangles populations collected in both 1982 and 1984. Numbers next to collection sites can be used to identify site locations listed in Table 1. the vertical surface of the cover slip during measurement. For each sample the number of individuals in each 0.1 millimeter AL size class were expressed as a percentage of the total sample size and plotted as size-frequency polygons in 1 mm intervals (after Russell-Hunter, 1953). Visual ex- amination of these polygons allowed samples to be divided into adult and juvenile size classes. As Ancylus fluviatilis is an annual species (Russell-Hunter, 1953; Geldiay, 1956; McMahon, 1980), samples taken in the late spring and early summer were characterized by the presence of two cohorts of individuals marked by distinctly different, non-overlapping distributions of AL. A cohort of larger individuals represented the adults of the previous year's generation and a cohort of smaller individuals represented recently hatched juvenile snails from the oviposition of the previous year's adults (Russell-Hunter, 1953). For Irish populations of A. fluviatilis oviposition is initiated in late April to mid-May and hatching occurs approximately two to three weeks later (McMahon, unpublished observations). Similar life cycles have been reported for British populations of this species (Russell- Hunter, 1953; Geldiay, 1956). Therefore, the mean growth rate of the adult generation in each population of A. fluviatilis was estimated by dividing the mean AL of that generation by the number of days between an approximate hatching date of 30 May and the subsequent date on which a population was sampled. Multiplying this daily growth rate figure by 30 DORSAL

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