EMBRYOLOGICAL DEVELOPMENT OF THE POLYCHAETOUS ANNELID, DIOPATRA CUPREA (BOSC)

¹ Marine Biological Laboratory, Woods Hole, Massachusetts

1. Larvae of Diopatra cuprea (Bosc) have been raised, following artificial fertilization, to a stage with seven sets of setae. Observations on living stages and also on fixed and stained preparations have been described and photographed.

2. Cell lineage studies have not been made, but observations indicate that the early cleavages are typical of those for spiral cleavage and that the ciliated stage (age, three hours) has a typical annelid cross and apical rosette. It, therefore, seems justifiable to conclude that the development of Diopatra cuprea follows the typical spiral pattern and mosaic development characteristic of other polychaetous annelids.

3. Peculiarities of the development of this polychaete, and possibly of closely related species, are the following: the peculiar algal-like nurse cells attached to the developing oocyte (also characteristic of Onuphis eggs) when floating free in the coelom, the amazing rapidity of development to the free-swimming stage (three hours), the four plates of cells which appear to develop from cells of the prototroch and their peculiar posterior extensions into at least four plates of yolk spheres, and the asymmetry of the maxillary plates.

4. Very little can be found in the literature on the embryology of the genus, Diopatra, and at least two authors have pointed out the possibility of error as to species in the identification of the developmental stages. Evidence is presented here which indicates that the early embryological and larval stages described by other investigators have been erroneously assigned to Diopatra cuprea.

5. If the above is correct—and it would appear that Diopatra cuprea is the only onuphid found intertidally in the Woods Hole area—one may conclude that the investigation presented by the writer is probably the only study recorded in the literature on the early developmental stages of Diopatra cuprea (Bosc). This is exclusive of Monro's description of the later (post-larval) stage which, if not belonging to D. cuprea, is undoubtedly closely related to this species.