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The nervous system of the actinotroch larva of Phoronis muelleri (Phoronida)

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Summary

The nervous system of the actinotroch larva of Phoronis muelleri has been investigated with the transmission electron microscope (TEM). Attempts have been made to localize all of the major nerves and to reveal the cytoarchitecture of the apical ganglion. The nervous system is intraepithelial in position and consists of an apical ganglion, located on the epistome, with at least four different cell types, including monopolar sensory cells and mono- or multipolar neuron-like cells. From the anterior part of the apical ganglion three median nerves extend to the edge of the epistome; two of these nerves connect to nerves which follow the edge of the epistome all the way to the junction of the epistome and the mesosome. From the posterior part of the ganglion extend two lateral nerves which continue along the tentacular ring. Each tentacle has three nerves located on the frontal side which connect to the nerve ring along the tentacles. Along the posterior ciliary band is a minor nerve ring. In addition, a nerve net is found on the epistome, mesosome, and metasome, but no longitudinal nerves were observed between the posterior ciliary band and the apical ganglion. All nerve cells were found in the apical ganglion and none was observed along the nerves. Sensory cells (probably mechanoreceptors) are located in two rows on each tentacle; sensory organs such as eyes and statocysts were not observed.

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Abbreviations

ac :

accessory centricle

aen :

anterior epistome edge nerve

af :

abfrontal cells

bl :

basal lamina

bl.c :

blastocoel coelomocyte

ci :

cilium

co :

collar

cp :

cell process

cr :

ciliary root

ec 1 :

epistome edge cell type 1

mne :

mouth nerve ring

mo :

mouth

mp :

metasomal pouch

ms :

mesosome

mt :

metasome

mu :

muscle

n :

nerve process

ne :

nerve

np :

neuropil

nu :

nucleus

pc 1 :

posterior ciliary band cell type 1

ec 2 :

epistome edge cell type 2

ec 3 :

epistome edge cell type 3

epi :

epidermis

es :

epistome

ese :

epistome edge

fc :

frontal cell

gc 1 :

type 1 ganglion cells

gc 2 :

type 2 ganglion cells

gc 3 :

type 3 ganglion cells

ge :

gut epithelium

ij :

intermediate junction

laf :

lateroabfrontal cell

lc :

lateral cell

lfc :

laterofrontal cell

lgc :

lateral ganglion cell

me :

metacoel epithelium

lne :

longitudinal median epistome nerves

pc 2 :

posterior ciliary band cell type 2

pc :

procoel

pe :

procoel epithelium

pen :

posterior epistome edge nerve

pr :

posterior ciliary band

p.rec :

proximal recess of procoel epithelium

prne :

nerve ring along posterior ciliary band

sj :

septate junction

sne :

secondary nerve along the tentacular ring

t :

tentacle

tr :

tentacular ring

trne :

horseshoe-shaped nerve along the tentacular ring

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Hay-Schmidt, A. The nervous system of the actinotroch larva of Phoronis muelleri (Phoronida). Zoomorphology 108, 333–351 (1989). https://doi.org/10.1007/BF00312274

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Keywords

  • Nervous System
  • Transmission Electron Microscope
  • Developmental Biology
  • Nerve Cell
  • Anterior Part