Freshwater bryozoan (Lophopus crystallinus)

Lophopus crystallinus
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Freshwater bryozoan fact file

Freshwater bryozoan description

GenusLophopus (1)

There are 11 described species of freshwater bryozoa in the UK; this bryozoan is the only member of the family Lophopodidae to be found here (3). Bryozoans are a group of small aquatic animals that live as colonies. The colony is comprised of zooids, or individual animals, that each contain a set of internal organs and a crown of tentacles, surrounding the mouth, which is used to gather food (2). The gelatinous colonies (4) of L. crystallinus form cream-coloured globular patches that grow to about 1cm in diameter. When L. crystallinus is submerged, the horseshoe-shaped crowns of tentacles of the component zooids are visible with the use of a hand-lens (2).

Diameter: up to 1 cm (2)

Freshwater bryozoan biology

Bryozoans can reproduce either sexually, in which a free-swimming stage results, or asexually either through 'budding' or by the production of a dormant 'statoblast' stage. These statoblasts are packages of cells, in which there is stored food, surrounded by a tough layer. They can survive freezing and drying-out, and can persist for many years (5). L. crystallinus produces distinctive lemon-shaped statoblasts, which may allow the species to disperse over quite long distances (2). These statoblasts are approximately 1mm long and 0.5mm wide and range in colour from dark to light brown (2).


Freshwater bryozoan range

The freshwater bryozoan is found in various countries in Europe, but its precise status is presently unclear, although it is classified as Rare in the British Red Data Book (1). Since 1970 it has only been recorded from 5 sites in Norfolk, Oxfordshire, Humberside and Lancashire (3). Following recent work commissioned by Action for Invertebrates and further work conducted by Reading University, two sites are currently known, Barton Blow Wells in north Lincolnshire, and Chil Brook in Oxfordshire (6). Elsewhere, it also occurs in the Middle East, and America, where it is rare (4).

You can view distribution information for this species at the National Biodiversity Network Atlas.

Freshwater bryozoan habitat

This species grows on the underside of various substrate types such as plants, rock, wood, plastic, glass, and shells in freshwater lakes, ponds, ditches and rivers (2).


Freshwater bryozoan status

Classified as Rare in Great Britain (2).


Freshwater bryozoan threats

Water abstraction and eutrophication are thought to have affected this species, along with over-zealous tidying of waterways (3). Habitat loss and increased boat traffic are also likely to have played a part in the decline (4).


Freshwater bryozoan conservation

This bryozoan is a priority species under the UK Biodiversity Action Plan; the Species Action Plan aims to maintain all populations of the freshwater bryozoans and assist an increase in the species' range by 2010, perhaps using artificial substrata to aid research and monitoring (3). One of the sites that supports this species is designated a Site of Special Scientific Interest (SSSI), and therefore receives a degree of protection (4).

The UK Biodiversity Action Plan for this species is available at UK BAP.
There may be further information about this species available via the National Biodiversity Network Atlas.


Information authenticated by Dr Beth Okamura and Samantha Hill of Reading University:



Of asexual reproduction: reproduction that does not involve the formation of sex cells ('gametes'). In many species, asexual reproduction can occur by fission (or in plants 'vegetative reproduction'); part of the organism breaks away and develops into a separate individual. Some animals, including vertebrates can develop from unfertilised eggs, this process, known as parthenogenesis gives rise to offspring that are genetically identical to the parent
A group of small aquatic animals that form branching, encrusting, or gelatinous moss-like colonies. The colony is comprised of zooids, or individual animals, that each contain a set of internal organs and a crown of tentacles, surrounding the mouth, which is used to gather food.
Type of asexual reproduction (reproduction that does not involve the formation of sex cells), in which new individuals develop from the parent organism, forming a swelling similar in appearance to a bud. The 'bud' slowly separates from the parent as it grows.
A group of organisms living together, individuals in the group are not physiologically connected and may not be related, such as a colony of birds. Another meaning refers to organisms, such as bryozoans, which are composed of numerous genetically identical modules (also referred to as zooids or 'individuals'), which are produced by budding and remain physiologically connected.
Nutrient enrichment of aquatic or terrestrial ecosystems.


  1. National Biodiversity Network Species Dictionary (September, 2002)
  2. S. Hill & Dr B. Okamura (2003) Reading University. Pers. Comm.
  3. UK Biodiversity. Species Action Plan. (September, 2002):
  4. Bratton, J. H. (Ed) (1991) British Red Data Books: 2 Invertebrates other than insects. JNCC, Peterborough.
  5. Buck, D. (2003) The Environment Agency. Pers. Comm.
  6. Allaby, M. (1991) The Concise Oxford Dictionary of Zoology. Oxford University Press, Oxford.

Image credit

Lophopus crystallinus  
Lophopus crystallinus

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