File:American malacological bulletin (1987) (18153031602).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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204 AMER. MALAC. BULL. 5(2) (1987) 400
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percent of maximum body weight represented by the weight of all spawn produced during life, or as total calories spawned expressed as a percent of total calories ingested. Reproduc- tive effort measured as weight was 135% for animals on ad libitum ration and about half that if provided with only three- quarters of the ad libitum amount. Expressed as calories, RE was 10.69 for ad lib ration and 7.25 for 75% ration. Because animals found in the field never achieved the size of A. juliana reared in the laboratory with an ad libitum food supply, Sarver concluded that the food regime of this animal is restrictive and that RE in the field must vary in time and space. It thus appears that there are no generalizations to be drawn relating reproductive energetics to developmental mode that can ap- ply throughout the Opisthobranchia, and RE is not a useful predictor of developmental mode. The absence of a correlation between egg size (thus hatching size) and settlement size and the lack of usefulness of reproductive effort in predicting developmental mode in- dicate that there are flaws in the original assumptions of the pie arguments, at least in application to most opisthobranchs. In addition to the absence of consistency in reproductive ef- fort across or within developmental modes, it appears that another basic problem lies in the prediction that benthic juveniles resulting from all modes should be about the same size, at least within restricted taxa or ecological types (for ex- ample sponge feeders). We showed above that settling lar- val shell sizes differed among opisthobranchs with the same and different developmental modes, and we next examine the assumption that different modes of reproduction produce similarly sized benthic juveniles (i.e. shortly after meta- morphosis). Here shell measurement is discarded except for groups like cephalaspideans where it could be a good meas- ure of juvenile size. Examing juvenile size rather than shell size seems particularly important for the nudibranchs where the two different shell types have such different relationships with egg diameters (Fig. 9), and because all nudibranchs (which are the source of most data) and most sacoglossans shed their larval shells at metamorphosis, making shell measurements poor approximations of the size of newly metamorphosed juveniles. The data presented in figure 13 reveal some rather sur- prising and, to us, not intuitive conclusions. First, as previous- ly shown, planktotrophic larvae all arise from small eggs, with essentially no overlap with the other two modes of develop- ment. Secondly, although lecithotrophic larvae arise from larger eggs, there is a limit to size of the juvenile that results from pelagic development that is common to both pelagic modes; the limiting size is a juvenile about 500 nm long. Third, while there is a broad overlap of egg sizes between pelagic- lecithotrophic and direct developers, only some direct developers "escape" the juvenile size limitation of -500 /im to produce very large juveniles, some of them up to a millimeter long. Most of the distribution of juvenile sizes among direct developers can be explained by the two pat-

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