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Ultrastructure of the protonephridia in Pycnophyes kielensis (Kinorhyncha, Homalorhagida)

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Summary

Pycnophyes kielensis possesses one pair of protonephridia. The single excretory organ of a female consists of 25 cells: 22 terminal cells, 2 canal cells, and 1 nephroporus cell. Generally, all cells exhibit two cilia, the only exception being the nephroporus cell, which contains a diplosome instead. The slashed peripheral cytoplasmic walls of the 22 terminal cells altogether constitute one compound filter and a common filtration area. The protonephridia discharge via cuticularized cavities and six cuticularized tubes. Two accessory cells with modified cilia penetrate the nephroporus cell. These cells are considered to be receptor cells. The protonephridium of the first juvenile stage of P. kielensis is built up of only 5 cells: 3 terminal cells, 1 canal cell, and 1 nephroporus cell. It opens to the outside via 1 cuticularized tube. The protonephridia within both the Kinorhyncha and the Bilateria are discussed. Presumably excretory organs with compound filters developed independently within Bilateria.

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Abbreviations

bb :

basal body

c :

canal cell

ca :

cuticularized cavity

ci :

cilium

cu :

cuticle

d :

dictyosome

de :

desmosome

di :

diplosome

dl :

dorsal longitudinal muscle

dv :

dorsoventral muscle

ecm :

extracellular matrix

ep :

epidermal cell

ex :

excretory organ

fc :

filter cleft

fi :

filter

fm :

fastening muscle cell

he :

hemidesmosome

i :

intestine

if :

intercellular fluid

m :

mitochondrium

mv :

microvilli

n :

nephroporus cell

nu :

nucleus

r :

ciliary rootlet

re :

accessory cell (presumable receptor cell)

sj :

septate junction

t :

terminal cell

tu :

cuticularized tube

v :

vesicle

w :

peripheral cytoplasmic wall

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Authors and Affiliations

  1. II. Zoologisches Institut und Museum, Berliner Strasse 28, D-3400, Göttingen, Federal Republic of Germany

    Birger Neuhaus

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  1. Birger Neuhaus
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Neuhaus, B. Ultrastructure of the protonephridia in Pycnophyes kielensis (Kinorhyncha, Homalorhagida). Zoomorphology 108, 245–253 (1988). https://doi.org/10.1007/BF00312224

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  • DOI: https://doi.org/10.1007/BF00312224

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