Polychaete body fossils are rare, and are almost invariably compressed and too poorly preserved for meaningful comparison with extant forms. We here describe Kenostrychus clementsi gen. et sp. nov. from the Silurian Herefordshire Konservat-LagerstÌtte of England, in which three-dimensional external morphology is preserved with a ¢delity unprecedented among fossil polychaetes. The fossils, which are preserved in calcite, were serially ground and photographed at 30 mm intervals to produce computergenerated reconstructions of the original external surface. The new genus has a generalized polychaete morphology with large biramous parapodia, unspecialized anterior segments and a small prostomium with median and lateral antennae and ventral prostomial palps. Cirriform branchiae arise from the ventral surface of each notopodium, and may be homologous with the inter-ramal branchiae of the extant nephtyids. Through cladistic analysis, Kenostrychus is interpreted as a member of a stem group of either the Phyllodocida or the Aciculata (Phyllodocida + Eunicida). Direct comparison with other fossil forms is di¤cult, but hints that inter-ramal respiratory structures may be primitive within the Phyllodocida and/ or the Aciculata.

19The entorhinal cortex plays a vital role in our spatial awareness. Much focus has been placed on the spatial 20 activity of its individual neurons, which fire in a grid-like pattern across an environment 1 . On a population 21 level, however, neurons in the entorhinal cortex also display coherent rhythmic activity known as local field 22 potential. These local field oscillations have been shown to correlate with behavioural states but it remains 23 unclear how these oscillations relate to spatial behaviour and the spatial firing pattern of individual neurons. 24 To investigate this, we recorded entorhinal cortical neurons in the human brain during spatial memory tasks 25 performed in virtual environments. We observed a spatial modulation of the phase of action potentials relative 26 to the local field potentials. In addition, the spike phase modulation displayed correlation with the movement 27 of the avatar, displayed discrete phase tuning at the cellular level, rotated phase between electrodes, and 28 expressed spatially coherent phase maps that scaled with the virtual environment. Using surrogate data, we 29 demonstrated that spike phase coherence is dependent on the spatial phase dynamics of gamma oscillations. 30 We argue that the spatial coordination of spike generation with gamma rhythm underlies the emergence of 31 grid cell activity in the entorhinal cortex. These results shed a new light on the intricate interlacing between 32 the spiking activity of neurons and local field oscillations in the brain. 33 1 The medial entorhinal cortex (EC) is found in the medial temporal lobe of the mammalian brain and plays a 34 critical role in spatial awareness in rodents 1 as well as in humans [2][3][4] . The activity of grid cells and border cells 35 in the EC, together with place cells and head direction cells in the hippocampus and subiculum, respectively, 36 constitute key components of the allocentric navigation system enabling individuals to localize themselves 37 relative to the environment. The spatially periodic activity, a hallmark of grid cells 1 and displayed by about 38 50% in the human brain 4 , is hypothesized to support spatial navigation as an internal coordinate system. 39 In addition to their spatial tuning, EC neurons generate a broad frequency range of local field potentials 40 (LFPs) with two prominent harmonic components: theta and gamma 5 . Theta and gamma are predominant 41 in the rodent and human hippocampus and EC during active exploratory behaviour and REM-sleep 2,6 42 and hippocampal theta tend to phase-couple with slow gamma (30-50 Hz) from EC 7,8 . Theta-spike and 43 theta-gamma phase coherence are instrumental for memory encoding 9,10 . Although grid cells represent the 44 allocentric coordinate system for spatial navigation in a number of mammalian species 1,11,12 , the role of 45 oscillations in the generation of this spatially periodic activity is unknown. 46A grid of 16 extracellular microelectrodes ( Fig. 3a) was implanted in the EC of two human subjects...

The ∼430-My-old Herefordshire, United Kingdom, Lagerstätte has yielded a diversity of remarkably preserved invertebrates, many of which provide fundamental insights into the evolutionary history and ecology of particular taxa. Here we report a new arthropod with 10 tiny arthropods tethered to its tergites by long individual threads. The head of the host, which is covered by a shield that projects anteriorly, bears a long stout uniramous antenna and a chelate limb followed by two biramous appendages. The trunk comprises 11 segments, all bearing limbs and covered by tergites with long slender lateral spines. A short telson bears long parallel cerci. Our phylogenetic analysis resolves the new arthropod as a stem-group mandibulate. The evidence suggests that the tethered individuals are juveniles and the association represents a complex brooding behavior. Alternative possibilities-that the tethered individuals represent a different epizoic or parasitic arthropod-appear less likely.arthropod | Silurian | brood care | juvenile | Herefordshire Lagerstätte