EMBRYOLOGICAL DEVELOPMENT OF THE SYLLID, AUTOLYTUS FASCIATUS (BOSC) (CLASS POLYCHAETA)

¹ Department of Biology, Wilson College, Chambersburg, Pennsylvania, and Institute of Marine Biology, University of Puerto Rico, Mayaguez, Puerto Rico

1. A series of developmental stages, from undivided eggs through swimming larvae, were isolated from the brood pouches of the polychaetous worm, Autolytus fasciatus (the red-banded Autolytus), collected in Puerto Rican waters. Observations on both living stages and on fixed and stained preparations have been described and photographed.

2. The diploid chromosome number for this species was determined as 12. Fertilization occurs at metaphase I. The cleavage pattern is spiral and involves polar lobe formation. Gastrulation is by epiboly. The trochophore and later larval stages show a precocious development of active cilia as compared with other syllid larvae. Characteristic differentiations of larvae at hatching are anterior and lateral tactile bristles, anterior and ventral mucus-secreting cells, and an anterior pair and two circles of pharyngeal teeth. Larvae were compared with other syllid larvae as regards ciliation, tactile bristles, and pharyngeal teeth.

3. Insofar as the writer knows, the present study is the only one recorded in the literature on the early developmental stages of Autolytus fasciatus, and the only one on the Subfamily Autolytinae which includes a series of developmental stages from uncleaved eggs through various larval stages. Much more embryological work needs to be done on the Family Syllidae.