60 THE ESSES NATURALIST
Colacium epiphyticum Fritsch
in the River Lee
By JOHN H. BELCHER and ERICA M. F. SWALE
Most species of Colacium, a colonial organism related to Euglena, are
found attached to planktonic Crustacea and rotifers, but in 1949
Fritsch2 described a species from Cheshire which was epiphytic on other
algae, naming it Colacium epiphyticum. Dr. Hilda Canter found a similar
though larger, form in a pond in Clissold Park, London.
In February, 1956, a large number of colonies of an alga apparently
identical with that described by Fritsch arose in a culture of material taken
from the River Lee Navigation Canal near Waltham Abbey, Essex.
The colonies consisted of from three to seven individuals, which were
borne on branched mucilage stalks. Individuals were very uniform in size,
about 28μ long. The numerous discoid chloroplasts were parietal in position
and a red eye spot was present in some of the cells. Some individuals under-
went metabolic (or cell) movements.
One such colony was mounted as a hanging drop culture, using the algal
culture medium no. 10 of Chu3, and placed in continuous illumination from
a fluorescent tube. Under these conditions the colony increased in size to
more than 40 individuals, attached to a common branched mucilage stalk.
Some of the cells became motile and swam about the drop for several hours
before again becoming sessile and giving rise to new colonies, the growth of
which was not followed beyond the two-celled stage. Each individual possessed
an eye spot and a thick spiral flagellum, and was much more oblong in shape
than sessile individuals, resembling the motile individuals of Colacium calvum
Stein, but with an obtusely pointed posterior end.
In September, 1956, two living individuals were found in freshly collected
material from further up the river, at Dobb's Weir. They consisted of two
individuals each and were attached to filaments of Thorea ramosissima Boryl.
They exhibited marked metabolic movements.
Apparently this is the first record of a motile stage and of metaboly in this
species.
References
1. belcher, j. h., & swale, erica m. f. (in preparation). Further uncommon
freshwater Rhodophyta from Britain.
2. Fritsch, f. E. (1949). Contributions to our knowledge of British Algae.
Hydrobiologia 1, 115 - 125.
3. peingsheim, e. g. (1946). Pure Cultures of Algae, p. 34. Cambridge
University Press.