Structure and function of the nervous system in nectophores of the siphonophore Nanomia bijuga

Abstract

i) Although Nanomia’s bell-shaped nectophores are specialized for locomotion, their cellular elements and complex nerve structures suggest they have multiple subsidiary functions.ii) The main nerve complex is a nerve ring at the base of the bell, an adjacent columnar-shaped matrix plus two associated nerve projections. An upper nerve tract may provide a sensory input while a lower nerve tract connects with the rest of the colony apparently via a cluster of nerve cells at the stem.iii) The structure of the extensively innervated “flask cells” located around the bell margin suggests a secretory function.iv) The numerous nematocytes present on exposed ridges of the nectophore appear to have an entangling rather than a penetrating role.v) Movements of the velum, produced by contraction of the Claus’ muscle system during backwards swimming, can be elicited by electrical stimulation of the surface epithelium even when the major nerve tracts serving the nerve ring have been destroyed (confirming Mackie, 1964).vi) Epithelial impulses generated by electrical stimulation elicit slow potentials and action potentials in the velum musculature. The slow potentials arise at different sites around the velum and give rise to action potentials in contracting Claus’ muscle fibres.vii) A synaptic rather than an electrotonic model can more readily account for the time course of the slow potentials.viii) During backward swimming radial muscle fibres in the endoderm contract isometrically providing the Claus’ fibres with a firm foundation.

Two swimming modes in Trachymedusae; bell kinematics and the role of giant axons

“…In Nanomia bijuga , for example, the ability to adjust the timing of the contractions of its multiple swimming bells gives it great flexibility in forward movement ( Mackie, 1964 ; Costello et al, 2015 ). In addition, it is able to redirect its jets and escape swim backwards ( Mackie, 1964 ; Norekian and Meech, 2020 ). Forward and backward swimming utilize two different motor pathways – dual swimming par excellence but not considered here.…”

A peripheral subepithelial network for chemotactile processing in the predatory sea slug Pleurobranchaea californica

“…Rat monoclonal antityrosinated alpha-tubulin antibody used in this study was raised against yeast tubulin and has been successfully used before on species of ctenophores and hydrozoans to label neural elements [ 8 , 9 ]. The specificity of immunostaining was tested by omitting either primary or secondary antibody, for which cases no labeling was detected.…”

The distribution and evolutionary dynamics of dopaminergic neurons in molluscs

“…As reported by Wehland et al (1983) this rat monoclonal antibody “reacts specifically with the tyrosylated form of brain alpha-tubulin from different species” (Wehland and Willingham, 1983; Wehland et al, 1983). We have also successfully used this specific anti-α-tubulin antibody before on several species of ctenophores (Norekian and Moroz, 2016; 2020b) and hydrozoans (Norekian and Meech, 2020; Norekian and Moroz, 2020a) to label their nervous system. We also tested the specificity of immunostaining by omitting either the primary or the secondary antibody from the procedure.…”