SHELL REPAIR FREQUENCIES IN WHELKS AND MOON SNAILS FROM DELAWARE AND SOUTHERN NEW-JERSEY

More than 1,500 specimens combined from the extant moon snails Euspira heros (Say) and Neverita duplicata (Say), and the whelks Busycon cari ca (Gmelin) and Busycotypus canaliculatus (Linnaeus) from southern New Jersey tidal flats were examined for breakage-induced shell repair. A dditionally, 500 specimens of E. heros and N. duplicata and Busycon sc alarispira (Conrad) from the Miocene Kirkwood Formation collected from northern Delaware were examined. On each specimen, body whorl diamete r (WD) and apertural lip thickness (ALT) at three positions, namely, a nterior-most, mid-length, and posterior-most location on the lip, were measured and number of scars per final whorl counted. Although mean n umber of repairs per specimen differed among the five species, average s were comparable for Recent moon snails (1.1 for N. duplicata and 1.0 for E. heros) and whelks (5.3 for B. carica and 5.2 for B. canalicula tus). Mean repairs/specimen were appreciably lower for Miocene naticid s (0.4) and the melongenid (0.7). Repair frequencies/shell ranged from zero to 12 for Recent whelk species and Recent N. duplicata, zero to seven for the Recent E. heros, and zero to four for Miocene moon snail s and whelks. Only four and three percent of shells of B. canaliculatu s and B. carica lack repairs, whereas 48% and 57% of Recent E. heros a nd N. duplicata, respectively, lack repairs. The majority of shells in every size class of Miocene whelks and moon snails lacked repairs, sa ve for the largest size class of B. scalarispira. Repair frequencies a ccumulated at a greater rate (regression line slope) and are more stro ngly correlated (higher r value) with WD and ALT for thicker lipped Re cent whelks than either thinner lipped moon snails or Miocene whelks. Presence of an umbilical plug in N. duplicata renders posteriorly loca ted breaks on the apertural lip repairable, unlike the plug-lacking E. heros. Greater rate of scar accumulation with increasing shell size a mong Recent naticids reflects increase in breakage-localizing shell th ickness since the Miocene. Greater mean repair frequencies in Recent w helks relative to Recent moon snails is attributed to the additive eff ect of sublethal predation on whelks plus prey-induced apertural lip f racture during valve-wedging by feeding whelks. The substantially lowe r frequency of repair/shell in B. scalarispira versus B. carica and B. canaliculatus suggests that the habit of shell-wedging of prey had no t yet evolved, or was ineffectually practiced by Miocene whelks.