Growth, Trematode Parasitism, and Longevity of a Long-Lived Marine Gastropod (Ilyanassa Obsoleta)

Ilyanassa obsoleta (Say) (Mollusca: Neogastropoda) is a conspicuous biotic element of marine / estuarine habitats along the eastern North American coast. Growth among larger individuals (-18–30 mm shell height) has not been assessed. Trematode infections are common in this group and their effect on growth must be considered. Snails were individually marked, measured, and released on the Cape Henlopen sand-flat at the mouth of Delaware Bay. Shell height change (growth) and trematode parasitism were assessed in recaptured snails. Most or all growth occurred in June and July. Mean growth of uninfected snails was 1–2 mm per season. Snails that started out larger grew more slowly, but there was much individual variability. Mean growth of parasitized snails was 0–2 mm per season and independent of initial size. The maximum age of this snail is currently documented at 7 y, which is too low. Size reflects age only approximately. However, the minimum and maximum age of a snail of given size, based on maximal and minimal growth per season, can be estimated. A mid-range estimate for lifespan of unparasitized and parasitized individuals is 30–40 y.