This project was initiated the previous year under a LSF funding. Its purpose was to provide a detailed descriptive, experimental and molecular study of aplacophoran embryology and larval development in the context of the current macro-evolutionary and developmental issuses. Research was to focus on the aplacophoran chaetoderm Chaetoderma nitidulum which is readily available at Kristineberg Marine Research Station. Aspects of aplacophoran development to be examined were the following: 1. Basic embryology and larval development. 2. Specification of the dorsal-ventral organizer and mesoderm. 3. Development of the larval and adult musculature systems and larval sensory organs. 4. Expression pattern of the engrailed gene and protein.
aplacophoran, Chaetoderma nitidulum, embryology, larval
The primary achievement of this project was the spawning of adult Chaetoderma nitidulum and subsequent culturing of their embryos and larvae to periclymma stages. Attempts made to spawn the adults at the Kristineberg Marine Research Station were unsucessful, although the animals were abundant and appeared to be ripe. At the end of our stay, Dr. Claus Nielsen took a number of adults back to his home institution in Denmark. A few weeks later these adults spawned on their own accord. Fixations of larvae were made for scanning electron microscopy and immunohistochemistry. The results of this work are to be included in the latest edition of Dr. Nielsen´s book, Animal Evolution. As was the case the previous year, the primary difficulty was inducing the apparently ripe animals to spawn in the laboratory. Increasingly, it appears that the reproductive season is simply later in the year than we had previously suspected. Preliminary observations from other labs suggest that Chaetoderma nitidulum has a mid-winter peak in its reproductive season and we planned our research accordingly. Unfortunately, this does not appaer to be the case. Our own experience over the last two years in Kristineberg suggests that the peak reproductive season is actually late winter to early spring or else it is highly variable from year to year. Because of the difficulties encountered in trying to spawn the adults, we were unable ti initiate many of the experimental studies we had hoped to perform. Instead, work was continued on the development of radialized and twinned larvae of the limpet Patella vulgata, a project which had been initiated the previous year in Kristineberg. These larvae had been created experimentally by interfering with the specification of a developmental organizer involved in the patterning of the adult body plan. Based on research and analysis performed in Kristineberg and elsewhere, we propose that this organizer may be a feature conserved for all Bilaterian animals.