. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. DISPERSAL AND GENETIC EXCHANGE 305 gastropod larvae have a more general response. Thus the intertidal snail Nassarius obsoletus, primarily a deposit-feeder, delays settlement in the absence of an appro- priate sediment (Scheltema, 1956, 1961), and Kiseleva (1966, 1967) has shown that the prosobranchs Rissoa splendida and Bittiitin reticulatum settle preferentially on the alga Cystoseira. In some species settlement may be simply a tactile response to a surface, apparently the case with the architectonicid Philippia krcbsii. *
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. DISPERSAL AND GENETIC EXCHANGE 305 gastropod larvae have a more general response. Thus the intertidal snail Nassarius obsoletus, primarily a deposit-feeder, delays settlement in the absence of an appro- priate sediment (Scheltema, 1956, 1961), and Kiseleva (1966, 1967) has shown that the prosobranchs Rissoa splendida and Bittiitin reticulatum settle preferentially on the alga Cystoseira. In some species settlement may be simply a tactile response to a surface, apparently the case with the architectonicid Philippia krcbsii. * >: • y^4' / *. ,'; r^' "**£ " *° •' » . o. 6Q FIGURE 11. Geographical distribution of the larvae of Smaragdia riridis (Linne) : filled black circles = larvae of Smaragdia riridis; small open circles = plankton stations where Smaragdia riridis was not found. Stippled areas show approximate regions where post-larval Smaragdia riridis is found; eastern and western Atlantic subspecies are respectively designated Smaragdia riridis riridis (Linne) and Smaragdia viridis riridcmaris (Alaury). Distributional data are compiled from the collections of the Museum of Comparative Zoology and the Phila- delphia Academy of Natural Sciences. Arrows show direction of surface currents. The larval development of many phytoplanktotrophic gastropod veligers can be divided for convenience into two periods (Scheltema, 1967). The first of these— one of rapid growth and morphological development—may be termed the "develop- mental ; Its end is marked by the inflection point on the cumulative growth curve and the completion of external morphological development (Schel- tema, 1967, page 260, Fig. 4). Larvae are ready to settle at this time. Estimates of the duration of pelagic larval development based on tin- differences in size be-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colorati
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
