Fine structure of the brain in Amphinomida (Annelida)

Abstract Amphinomida, some also known as fireworms, are not only notorious for their painful sting but painfully difficult phylogenetic placement. Current understanding of the annelid tree life suggests a close affinity with Sipuncula, unsegmented and sessile peanut worms. This sister‐group relationship is hard to explain from morphological perspective. Here, we present results our histological ultrastructural study central nervous system in two distantly related amphinomids: Euphrosine foliosa (Euphrosinidae) Eurythoe complanta (Amphinomidae). We provide detailed information, aiming set up groundwork future comparative studies gain insight into evolution systems. compare observations among species discuss implications annelids general more specifically sipunculan affinity. The Amphinomida differs both other errantian Sipuncula shows no clear synapomorphies that would argue or against current