Localization of ArPPLN2h‐immunoreactivity (ArPPLN2h‐ir) in the radial nerve cord, the circumoral nerve ring and marginal nerve of A. rubens. (a) Transverse section of a radial nerve cord showing ArPPLN2h‐ir in both the ectoneural and hyponeural regions. The inset of (a) shows absence of immunostaining in a radial nerve cord section incubated with ArPPLN1b antiserum pre‐absorbed with the antigen peptide (ArPPLN2h‐ag), demonstrating the specificity of immunostaining observed with the ArPPLN2 antiserum. (b) Immunostaining in a transverse section of the circumoral nerve ring; here immunostained processes can also be seen here in the peristomial membrane, an adjacent oral tube foot and in a Tiedemann's body. A high magnification image of the boxed region can be seen in (d). (c) High magnification image of the ectoneural region of the radial nerve cord showing immunostained bipolar cells in the sub‐cuticular epithelium (arrowheads) and densely packed immunostained processes (asterisks) in the underlying neuropile region. (d). Immunostained monopolar shaped cells (black arrowheads) in the hyponeural region of the circumoral nerve ring, with stained processes (white arrowhead) projecting into a fiber layer that is adjacent to the unstained collagenous tissue layer (arrow). The intensely stained ectoneural neuropile is labeled here with an asterisk. (e) The continuity of immunostaining in the ectoneural region of the radial nerve and in the basiepithelial nerve plexus of an adjacent tube foot (asterisks) can be seen here. The stained process(es) (arrowhead) of a hyponeural neuron(s) can be seen projecting over the roof of the peri‐hemal canal in close association with the transverse infra‐ambulacral muscle (arrow). (f) Immunostaining in the marginal nerve (arrow) and in axonal processes of the lateral motor nerve (arrowheads). CONR, circumoral nerve ring; CuL, cuticle layer; Ec, ectoneural region; Hy, hyponeural region; PM, peristomial membrane; RHS, radial hemal strand; TB, Tiedemann's body; TF, tube foot. Scale bars: 50 μm in (a), (f); 200 μm in (a) inset; 10 μm in (b), (d); 100 μm in (c); 20 μm in (e)