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Budd et al. challenge the identity of neural traces reported for the Cambrian lobopodian Cardiodictyon catenulum. Their argumentation is unsupported, as are objections with reference to living Onychophora that misinterpret established genomic, genetic, developmental, and neuroanatomical evidence. Instead, phylogenetic data corroborate the finding that the ancestral panarthropod head and brain is unsegmented, as in C. catenulum. 

For more than a century, the origin and evolution of the arthropod head and brain have eluded a unifying rationale reconciling divergent morphologies and phylogenetic relationships. Here, clarification is provided by the fossilized nervous system of the lower Cambrian lobopodian Cardiodictyon catenulum, which reveals an unsegmented head and brain comprising three cephalic domains, distinct from the metameric ventral nervous system serving its appendicular trunk. Each domain aligns with one of three components of the foregut and with a pair of head appendages.Morphological correspondences with stemgroup arthropods and alignments of homologous gene expression patterns with those of extant panarthropods demonstrate that cephalic domains of C. catenulum predate the evolution of the euarthropod head yet correspond to neuromeres defining brains of living chelicerates and mandibulates. 

In one species of shore crab (Brachyura, Varunidae), a center that supports long-term visual habituation and that matches the reniform body's morphology has been claimed as a homolog of the insect mushroom body despite lacking traits that define it as such. The discovery in a related species of shore crab of a mushroom body possessing those defining traits renders that interpretation unsound. Two phenotypically distinct, coexisting centers cannot both be homologs of the insect mushroom body. The present commentary outlines the history of research leading to misidentification of the reniform body as a mushroom body. One conclusion is that if both centers support learning and memory, this would be viewed as a novel and fascinating attribute of the pancrustacean brain 

Just one superorder of insects is known to possess a neuronal network that mediates extremely rapid reactions in flight in response to changes in optic flow. Research on the identity and functional organization of this network has over the course of almost half a century focused exclusively on the order Diptera, a member of the approximately 300-million-year-old clade Holometabola defined by its mode of development. However, it has been broadly claimed that the pivotal neuropil containing the network, the lobula plate, originated in the Cambrian before the divergence of Hexapoda and Crustacea from a mandibulate ancestor. This essay defines the traits that designate the lobula plate and argues against a homologue in Crustacea. It proposes that the origin of the lobula plate is relatively recent and may relate to the origin of flight 

Brain centers possessing a suite of neuroanatomical characters that define mushroom bodies of dicondylic insects have been identified in mantis shrimps, which are basal malacostracan crustaceans. Recent studies of the caridean shrimp Lebbeus groenlandicus further demonstrate the existence of mushroom bodies in Malacostraca. Nevertheless, received opinion promulgates the hypothesis that domed centers called hemiellipsoid bodies typifying reptantian crustaceans, such as lobsters and crayfish, represent the malacostracan cerebral ground pattern. Here, we provide evidence from the marine hermit crab Pagurus hirsutiusculus that refutes this view. P. hirsutiusculus, which is a member of the infraorder Anomura, reveals a chimeric morphology that incorporates features of a domed hemiellipsoid body and a columnar mushroom body. These attributes indicate that a mushroom body morphology is the ancestral ground pattern, from which the domed hemiellipsoid body derives and that the “standard” reptantian hemiellipsoid bodies that typify Astacidea and Achelata are extreme examples of divergence from this ground pattern. This interpretation is underpinned by comparing the lateral protocerebrum of Pagurus with that of the crayfish Procambarus clarkii and Orconectes immunis, members of the reptantian infraorder Astacidea.