Notes on the reproductive cycles of several Golfingia species (Sipuncula)

Extract

In an earlier paper (Gibbs, 1973) it was shown that in populations of Golfingia elongata (Keferstein) in the Plymouth area, a significant proportion of individuals possess fewer retractor muscles than is typical for the species. These individuals have three or two retractors instead of the normal four (= subgenus Golfingia) but otherwise are typical G. elongata in all characters. A morphologically similar species G. rimicola Gibbs is also common in the area and this species differs in possessing only two retractor muscles (= subgenus Phascoloides). One possible reason for the presence of aberrant individuals with an intermediate number of retractor muscles is hybridization; if the spawning seasons of the two species overlap in time, then cross-fertilization could be a feasible explanation for this anomaly.