Current knowledge and research perspectives of the shell formation process in the genus Arcella (Arcellinida: Amoebozoa)

Abstract

Arcellinida is an Amoebozoa lineage characterized by the presence of an external shell. A comprehensive cyto-morphological description of the shell structure and formation (thecagenesis) process has been generated due to publications in the time span of more than a century. Recently, few works have advanced our understanding of the thecagenesis process or discussed this rich literature; however, several aspects of the shell formation and structure are still puzzles, as remains the relationship between genes and shell formation morphogenesis. Here we present an overview of the literature about shell formation and structure, focusing on the genus Arcella, the best-studied lineage. We show that some aspects regarding shell formation are still open questions. Moreover, based on the current knowledge, we can establish new frameworks, to address such issues as the origin and evolution of the shell in Arcellinida.