Immunolocalization of SIFamide-like neuropeptides in the adult and developing central nervous system of the amphipod Parhyale hawaiensis (Malacostraca, Peracarida, Amphipoda)

Immunohistochemical analyses on the distribution of neuropeptides in the pancrustacean brain in the past have focussed mostly on representatives of the decapod (“ten-legged”) pancrustaceans whereas other taxa are understudied in this respect. The current report examines the post-embryogenic and adult brain and ventral nerve cord of the amphipod pancrustacean Parhyale hawaiensis (Dana. 1853; Peracarida, Amphipoda, Hyalide), a subtropical species with a body size of 1.5 cm and a direct post-embryonic development using immunohistochemistry to label the neuropeptide SIFamide and synaptic proteins (synapsins). We found strong SIFamide-like labelling in proto-, deuto- and tritocerebrum, especially in the lamina, the lateral protocerebrum, lateral assessory lobe, the central body, olfactory lobe, medial antenna 1 neuropil and antenna 2 neuropil. Out of a total of 28 ± 5 (N = 12) SIFamide-positive neurons in the central brain of adult P. hawaiensis, we found three individually identifiable somata which were consistently present within the brain of adult and subadult animals. Additionally, the subesophageal and two adjacent thoracic ganglia were analysed in only adult animals and also showed a strong SIFamide-like immunoreactivity. We compare our findings to other pancrustaceans including hexapods and discuss them in an evolutionary context.