Classification of the Dutch freshwater bryozoans

Verder in Nederlands

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This page describes the classification of the freshwater bryozoans likely to be found in the Netherlands and is largely derived from [Wood] and [Ryland]. Further down on this page the various classes and genera are described in more detail .
Please see the overview of all synonyms in use to find a species by its synonym (use the search function of the browser (CTRL-F)).

Of the three classes in the Bryozoa phylum two live (partially) in fresh water:

  1. The Gymnolaemata (some species)
  2. The Phylactolaemata (completely)

The Gymnolaemata class consists of the following genera, that live in fresh or brackish water:

  1. Paludicella (fresh)
  2. Victorella (brackish)

The Phylactolaemata class consists of the following genera:

  1. Cristatella
  2. Fredericella
  3. Lophopodella
  4. Lophopus
  5. Pectinatella
  6. Plumatella

According to [Wood] the following bryozoans are found in North-West Europe and therefore are likely to also live in the Netherlands.

Class Family Genus Species Described by
Gymnolaemata Ctenostomata Paludicella P. articulata Ehrenberg 1831
Gymnolaemata Ctenostomata Victorella V. pavida Savilli Kent 1870
Phylactolaemata Cristatellidae Cristatella C. mucedo Cuvier 1798
Phylactolaemata Fredericellidae Fredericella F. sultana Blumenbach 1779
Phylactolaemata Lophopodiae Lophopus L. crystallinus Pallas 1768
Phylactolaemata Lophopodiae Pectinatella P. magnifica Leidy 1851
Phylactolaemata Plumatellidae Hyalinella H. punctata Hannock 1850
Phylactolaemata Plumatellidae Plumatella P. casmiana Oka 1907
Phylactolaemata Plumatellidae Plumatella P. emarginata Allman 1844
Phylactolaemata Plumatellidae Plumatella P. fruticosa Allman 1844
Phylactolaemata Plumatellidae Plumatella P. fungosa Pallas 1768
Phylactolaemata Plumatellidae Plumatella P. geimermassardi Wood & Okamura 2004
Phylactolaemata Plumatellidae Plumatella P. repens Linnaeus 1758

Detail description of Classes

Class Gymnolaemata

For the Gymnolaemata in general:

  1. Zooids are cylindrical or compact
  2. The lophophoor is (almost) round
  3. There is no epistome
  4. The body wall consists of different tissues, without muscle tissue
  5. The body wall is sometimes calcified (not in freshwater or brackish water species)
  6. The ejection of the lophophore is dependent on body wall deformation by muscles
  7. The coelom of each zooid is separated fully from all other zooids by a septum or a double wall
  8. New zooids are produced by branching series that often lay closely together, by formation of new septa behind a growing point
  9. Cystid formation goes before polypide formation
  10. There is creation of spermatozoa in large amounts
  11. Zooids are polymorph (marine species)

Class Phylacolaemata

For the Phylacolaemata in general:

  1. The main shape of zooids is cylindrical
  2. The lophophore and therefore the tentacle plume is horse shoe shaped
  3. The tentacle plume is double, and the inner tentacles are shorter than the outer.
  4. The mouth is placed in the bend of the horseshoe shaped lopophore
  5. There is an epistome
  6. The body wall contains muscle tissue
  7. The mechanism for evocation of the lopophore is dependent on circular muscles in the body wall.
  8. There is never calcification of the body wall
  9. The coelom is continuous (in open connection) between the zooids
  10. New zooids are created by first replicating the polipid (without the lopophore).
  11. The cystids differentiate after the polypids are created
  12. There is creation of spermatozoa in large amounts
  13. There is creation of statoblasts

Order Ctenostomata

The Ctenostomata (ktenos = comb, stoma = mouth) is especially relevant for fresh water:

  1. There is a sub-order Carnosa
  2. The zooids are cylindrical to flattened
  3. The body walls are membranous to gelatinous, never calcified
  4. The lopophore opening is almost at the end of the polypid
  5. The lopophore opening is often enclosed by a collar

Sub-order Carnosa

For the Carnosa it is interesting that:

  1. The primary zooid creates a full 'dougter' by budding. Something that is different in some marine species
  2. The zooids are flattened and adherent. They do not grow out of a stolon
  3. If two colonies grow into each other then
    1. they will not grow into each other (merge)
    2. they will nog grow over each other as if the other colony was a mere obstacle
  4. If two lobes of one colony grow into each other they will merge