Figure 1. Neural characters and systems discussed mapped onto a in Neurobiology of the Anomura: Paguroidea, Galatheoidea and Hippoidea

Figure 1. Neural characters and systems discussed mapped onto a partial phylogeny of Reptantia (based on Morrison et al., 2001, and Schram, 2001). Filled boxes: character present; hatched boxes: character modified; open boxes: character lost. AT – anterior telson muscle and motoneuron; FAC – fast, anterior, contralateral flexor motoneurons; hMoG – homologue of MoG (Sillar and Heitler, 1985); MG – medial giant interneuron pair; LG – lateral giant interneurons; MG – medial giant interneurons; "MG" – modified MG system (Heitler and Fraser, 1986, 1987); MoG – motor giant flexor motoneuron; nonG – non-giant (as opposed to LGs, or MGs) interneuron system for swimming by repetitive tailflipping; RSM – return stroke muscle and motoneurons; TUSR – telson-uropod stretch receptor (nonspiking: graded potentials transmitted; spiking: receptor potential converted to action potentials). VTF – ventral telson flexor muscle. 1. It is debated whether homologues of macruran MG and LG neurons have been retained in brachyuran thoracic nerve cord. Retention of MG homologues could be expected for their direct connections to leg promotor motoneurons, which in crayfish cause the legs to extend forward, thus contributing to the rearward trajectory of the MGtriggered tailflips (Heitler and Fraser, 1989). The LG neurons have no known output to thoracic leg musculature in macrurans and are presumed absent from Brachyura. If LG homologues are present, then their losses from the thalassinid and anomuran lineages occurred independently. 2. The stereotyped movements of sand crabs' (Hippoidea) digging legs differ between legs 2/3 and leg 4, corresponding, respectively, to backward walking and forward walking movements in other species (Faulkes and Paul, 1998). 3. Rhythmic movements of the legs and "tail" co-occur in Hippoidea, whereas their homologues (walking and tailflipping) in walking species are mutually excusive (Faulkes and Paul, 1997a). 4. Right and left legs of each segment alternate at onset of digging, then switch to bilateral synchrony (Faulkes and Paul, 1997b). 5. Rhythmic digging movements of the fourth legs are coordinated with uropod strokes (homologue of nonG flexions) rather than with the anterior legs (Faulkes and Paul, 1997a). Not included are the changes from the ancestral macruran condition in aminergic systems and agonistic behaviours of M. quadrispina (Antonsen and Paul, 1997, 2001).