“Crustacea”: Comparative aspects of larval development

Abstract

Talking about crustacean development is already a difficult task due to the uncertainties of the term “Crustacea” itself. In recent years, numerous studies have pointed out that “Crustacea” is a paraphyletic assemblage, especially with respect to hexapods, while other authors still vote for a sister group relationship of Crustacea and Hexapoda (Tetraconata or Pancrustacea concept; e.g., Richter 2002; Cook et al. 2005; Carapelli et al. 2007; Regier et al. 2010; Giribet and Edgecombe 2012). Thus, currently the term “Crustacea” is in a kind of limbo and with this the term “crustacean” is, too. Morphologically, Crustacea sensu lato (sensu Stein et al. 2008, amend Haug et al. 2010a) is a well-characterised monophyletic group based on a stable set of apomorphies of the feeding apparatus. The group includes all forms generally recognised as crustaceans (including a number of half-a-billion-year-old fossils), but also appears to include myriapods and insects (Zhang et al. 2007; Haug et al. 2010a, p. 345). Thus, Crustacea sensu lato is monophyletic, but most people appear not to easily accept if one refers to insects and myriapods as crustaceans. Herein and in the entire treatise, the term “crustacean” refers to any representative of Crustacea sensu lato which is not a hexapod or a myriapod. With this, “crustacean” does not refer to a natural group but to a kind of morphotype or, better, a specific set of different morphotypes. Although this is a “soft” characterisation, it appears to be the most useful one in the current context.