Carcinization in the Anomura - fact or fiction? I. Evidence from adult morphology

Abstract

Carcinization, or the process of becoming a crab, has been, and continues to be, a focal point of anomuran evolutionary hypotheses. Traditional examples of carcinization in the Anomura are most celebrated among hermit crabs but certainly are not limited to this group. Carcinization, if it has occurred, has done so independently in all major anomuran taxa. In this critique, the traditional examples of carcinization in the Anomura are reviewed and more modern variations on the theme assessed. Potential pathways of carcinization are examined from perspectives of adult morphology in the Paguroidea, Galatheoidea, Hippoidea and Lomoidea, with emphasis on the Paguroidea. Specific attention is given to the theoretical transformation of a hermit crab-like body form into a “king crab”- like lithodid crab. Resulting coercive evidence indicates: (1) that while the evolution of a crab-like body form certainly occurs, the traditional applications, based on inadequate and often inaccurate data, are flawed; and (2) that lithodid crabs did not arise from a hermit crab predecessor through the process of carcinization.

Comparative brain architecture of the European shore crab Carcinus maenas (Brachyura) and the common hermit crab Pagurus bernhardus (Anomura) with notes on other marine hermit crabs

“…We suggest that the extensive fusion of synaptic brain areas in C. maenas may be linked to the process of "carcinization", as was suggested for the fusion of the ventral ganglia to a ventral ganglionic mass in brachyurans (Stevcic 1971). The term "carcinization" was first introduced by Borradaile (1916), who hypothesized a multiple convergent transition from non-crab to crab-like body plans in decapod crustaceans (see reviews McLaughlin and Lemaitre 1997;McLaughlin et al 2004). Stevcic (1971), who synonymously used the term "brachyurization", suggested an increased coordination of movements and a more complex behavior mainly in amphibious and terrestrial crustaceans, as a result of the higher integrative properties of the condensed central nervous system.…”

Crab or lobster? Mental principles underlying the categorization of crustaceans by biology experts and non-experts

“…However, not all members of the Brachyura are fully carcinized and do not therefore match the typological concept of a crab (Scholtz, 2014). Additionally, crabs in the typological sense are not only found within the Brachyura, but also in several other decapod crustacean groups that underwent carcinization convergently (see McLaughlin and Lemaitre, 1997;Morrison et al, 2002;Reimann et al, 2011;Tsang et al, 2011;Anker and Paulay, 2013;Bracken-Grissom et al, 2013;Guinot et al, 2013;Keiler et al, 2013). Therefore, in the case of crabs, classification based on phylogenetic relationships strongly contradicts the more intuitive grouping by external morphological similarities (see Scholtz, 2014).…”

The evolution of a key character, or how to evolve a slipper lobster

“…A particularly 'hot' topic has been the process of 'carcinisation', or the evolution of the 'crab' morphotype, respectively, the evolution of a crab-like habitus (e.g. McLaughlin and Lemaitre, 1997;McLaughlin et al, 2004;Hiller et al, 2010;Tsang et al, 2011;Scholtz, 2014). In evolutionary terms, any form of crab has evolved from an ancestral macruran or "lobster" morphotype.…”