"The shape [of the fossilized brain] matches that of a comparable sized modern malacostracan
," the researchers said.
Similarly, for malacostracan
species, the analysis revealed the existence of two main groupings, one consisting of the three Patagonian zones plus Central Chile, and the other comprising Northern and North-Central Chile (Fig.
Therefore, the additional engrailed stripes in the pleon of Cherax rather argue in favor of Lauterbach's (1975) hypothesis of a loss of posterior segments in the ancestral lineage of malacostracans. The restriction of these additional stripes to the neural region and the entire lack of limb anlagen furthermore support the suggestion that these segments are vestiges of the limbless abdomen postulated by Lauterbach (1986) and Fryer (1992) for the crustacean stem species.
The other malacostracan groups, unified as the Eumalacostraca (sensu Grobben, 1892), have only six pleomeres, all equipped with limbs.
Against this background, I conclude that the composite nature of the terminal (sixth) ganglion and the pattern of its formation by fusion during embryogenesis is part of the malacostracan ground plan.
In addition, some authors report that the embryos of several malacostracan species contain terminal mesodermal somites that might be related to a vestigial seventh pleonic segment and that also fuse with the sixth pleonic somites (e.g., Manton, 1928a; Shiino, 1942).
It has long been suggested that when malacostracan crustaceans flick the lateral flagella of their antennules, they increase the penetration of ambient water into the spaces between the aesthetascs, thus bringing odor-carrying water closer to the surfaces of those aesthetascs (e.g., Snow, 1973; Schmitt and Ache, 1979; Atema, 1985; Moore et al, 1991; Gleeson et al., 1993; Koehl, 1995, 1996; Pravin and Reidenbach, 2013; Waldrop et al , 2014).
Malacostracan crustaceans flick the lateral flagella of their antennules through the water in the Re range at which the leakiness of an array of hairs is very sensitive to velocity.
Comparison of crab antennules to those of other malacostracan crustaceans