Freshwater bryozoan  (Lophopus crystallinus)

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).

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).

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).

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).

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).

This bryozoan is a priority species under the UK Biodiversity Action Plan; the Species Action Plan aims to maintain all populations of the freshwater bryozoan 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).

Information authenticated by Dr Beth Okamura and Samantha Hill of Reading University:
http://www.ams.reading.ac.uk/zoology/okamura