, Volume 128, Issue 4, pp 275–283 | Cite as

Ultrastructure of spermiogenesis in Cristatella mucedo Cuvier (Bryozoa: Phylactolaemata: Cristatellidae)

  • Jørgen Lützen
  • Åse JespersenEmail author
  • Claus Nielsen
Original Paper


In Cristatella mucedo spermiogenesis occurs in a morula consisting of a large number of spermatids connected with a central cytophore. The mature sperm cell is filiform and consists of a head, a midpiece and a tail region, the latter two separated by a deep circular constriction. The comparatively short head contains a drop-shaped, bilaterally symmetrical and pointed nucleus capped by a minute acrosome. The single centriole is placed in a deep posterior invagination of the nucleus followed by the axoneme with the typical 9 + 2 pattern. The elongated midpiece is 0.9–1.1 μm thick and contains several helices of mitochondria surrounding the axoneme. The tail is thicker (1.3 μm) and richer in cytoplasm with many compact accumulations of an electron-dense substance lying peripherally and another less dense material wrapped around the axoneme. The course of the spermiogenesis and the fine structure of the sperm are very similar to that of Plumatella fungosa. Comparison with other species shows that the same sperm type is recognizable in four of the five families of Phylactolaemata and, provided it occurs also in the fifth family, the Stephanellidae, is a synapomorphy of the entire class.


Sperm-ultrastructure Phylactolaemata Bryozoa Cristatella mucedo 



The study was supported by a grant (2007-01-0111) from the Carlsberg Foundation. We are very grateful to Mr. Michiel van der Waaij, Groningen, The Netherlands, for his generous help offered in collecting all the material for the present study. We are further indebted to Ms. Lennie Rotvit, Copenhagen, for providing excellent technical assistance.


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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Jørgen Lützen
    • 1
  • Åse Jespersen
    • 1
    Email author
  • Claus Nielsen
    • 2
  1. 1.Department of Comparative ZoologyBiological InstituteCopenhagenDenmark
  2. 2.The State Natural History MuseumCopenhagenDenmark

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