Journal of the Marine Biological Association of the United Kingdom

Research Article

Self- and cross-fertilization in Spirorbis borealis and S. pagenstecheri

J. M. Geea1 p1 and G. Brinley Williamsa2 p2

a1 Department of Zoology, University College of Swansea

a2 Marine Science Laboratories, Menai Bridge

Evidence is presented that eggs and sperm of Spirorbis borealis are shed through the nephridioducts, and that fertilization occurs externally to the body but inside the tube.

The eggs fail to develop in vitro unless sperm is present. In individuals collected in winter and maintained at 15 or 19° C, the male and female gonads mature more or less simultaneously. Among groups of individuals sperm is usually shed first and soon afterwards a large proportion may be observed to have extruded ova.

Correspondence:

p1 Present address: East African Fisheries Organization, Jinja, Uganda.

p2 Present address: The Laboratory, Citadel Hill, Plymouth, Devon.