Phenotypic Reversion to Ancestral Form and Habit in a Marine Snail

Abstract

IN separating the polyphyletic Vermetidae (s.l.) into its separate lineages, Morton¹ noted the extreme anatomical similarity between Vermicularia and the coiled turritellids: “It is in fact little more than a turritellid which has taken on a sessile posture embedded in a hard substratum and proceeded to uncoil its shell whorls” (page 80 of ref. 1). Vermicularia is a ciliary suspension feeder, a common condition among sessile gastropods². Only a few free living forms feed in this manner and one of these is Turritella. T. communis burrows into mud and may remain indefinitely in its favoured position. (Apex down and inclined at a high angle to the horizontal. The habits of Turritella are described in refs. 3 and 4.) The juvenile, regularly coiled Vermicularia lives in the same manner; its later attachment and uncoiling is a response to the availability of firm objects providing a substrate for rapid upgrowth.