famous workers such as Gunnar Thorson, Marie Lebour and others. The common European Periwinkle (Littorina littorea) will serve here as an ideal example of the pelagic type of development. The female spawns two to twelve hours after copulation by the male. About 200 single egg capsules are shed during the night. During the entire breeding season of six months, the total number of egg capsules per female is estimated at about 5000, and a half dozen copulations are necessary to ensure fertilization of all the eggs. The helmet-shaped capsules are shed freely and float about in the water. Each contains from one to nine eggs. The free-swimming young, called veligers, hatch on the sixth day and remain afloat for two weeks or more, depending upon temperature conditions, then sink to the bottom and begin an adult snail’s life of crawling. They reach maturity on the second or third year and may live for five to ten years.
In contrast to this mode of spawning, the Left-handed Whelk of Florida (Busycon contrarium) lays its horny strings of egg capsules during a relatively short period of a few weeks. On the west coast of Florida egg-laying usually takes place in the spring. The female digs down well below the surface of the sand and attaches the first few capsules to a buried rock or broken shell. As the process of extrusion of the egg capsules continues, the female moves toward the surface until its siphon can protrude into the water to allow easy respiration. As more capsules are made, the string may loop out into the water above the hidden adult. From five to fifteen cases may be formed each day, and a completed two-foot-long string may have nearly a hundred capsules. Within each case there may be two to twenty-five eggs which in a few weeks will develop to quarter-inch-long young. These miniature replicas of the adults eat their way out of the case at a special “door” and commence crawling and feeding immediately. The Left-handed Whelk begins spawning at a relatively early age, commonly when no larger than three inches. In such cases the capsules are only a half inch in diameter, while larger females may produce capsules about the size of a half dollar.
