Contributions to Zoology, 85 (4) – 2016Jonas Keiler; Stefan Richter; Christian S Wirkner: Revealing their innermost secrets: an evolutionary perspective on the disparity of the organ systems in anomuran crabs (Crustacea: Decapoda: Anomura)

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The anterior shift and compaction of the pleonal ganglia in Lomis is coherent with a crab-like habitus

As well as the pleonal muscles, the pleonal ganglia in Lomis also underwent changes in morphology in the course of carcinization. In the ground pattern of Australopoda, pleonal ganglia pn2-pn6 were probably arranged segmentally, one per segment, and at roughly the same distances from each other, a condition seen in Kiwa and galatheoid squat lobsters (see Keiler et al., 2015a). Pleonal ganglia play an important role in controlling the caridoid escape reaction and other rapid pleonal movements (e.g. Paul, 1989, 2003; Faulkes, 2008). Decapods which exhibit a high level of pleonal activity all possess segmentally arranged pleonal ganglia (see e.g. Bouvier, 1889; Jackson, 1913; Siller and Heitler, 1985; Paul, 2004). The pleonal ganglia in Lomis are proportionally smaller than in Aegla and Kiwa and situated much more anteriorly in the rear cephalothorax, a shift which possibly occurred in response to the loss of the caridoid escape reaction and to the hidden lifestyle. This transformation in the pleonal ganglia may thus also have been (indirectly) affected by carcinization, a theory corroborated by findings in other crab-like taxa (see Keiler et al., 2015a, b). A comprehensive review covering the similar morphological transformations in the independently evolved crab-like habitus, associated coherences and their relevance for convergent evolution is in preparation (Keiler et al., in prep.).