Geographic and habitat-specific morphological variation of Littoraria (Littorinopsis) Angulifera (Lamarck, 1822)

Recent, detailed examination of the morphology of the Littorinidae inhabiti ng Indo-West Pacific mangrove forests led Reid (1986) to identify 20 specie s of Littoraria, all of which had previously been assigned to only three sp ecies within the pantropical "Littorina scabra." No similar study has been done on the neotropical Littoraria angulifera (Lamarck), which occurs in ma ngrove forests on both sides of the Atlantic Ocean. We quantified variabili ty in shell and genital morphology of L. angulifera throughout its range in the tropical Atlantic using material from both museum collections and new, field collections. We tested two hypotheses regarding variation in shell s hape and sculpture, and frequency of color morphs in populations of L. angu lifera: (1) observed variation is associated with the five major current re gimes that could restrict its dispersal throughout the tropical Atlantic; o r (2) observed variation is associated with habitat characteristics that ca n influence shell thermal properties. Strong geographical variation in shel l shape and sculptural characteristics suggested initial support for the di spersal hypothesis. Absence of geographical variation in genital morphology , however, led to the rejection of the dispersal hypothesis. Parallel assoc iations of habitat with geography suggests that L, angulifera is a single s pecies throughout the tropical Atlantic, and observed variability results p rimarily from responses to local environmental conditions. However, this co nclusion can be tested only with additional genetic analysis of disparate p opulations of L. angulifera.