FEEDING HABITS AND PHARYNGEAL STRUCTURE IN STENOSTOMUM

¹ From the Department of Zoölogy, University of Georgia

The variations in feeding habits exhibited by different species of the genus Stenostomum are largely dependent upon adaptive modification of pharyngeal structure.

The pharynx of S. grande is well adapted to the ingestion of large masses of relatively inert food material. The heavy band of radial muscles attached at the lip region is so arranged that it is capable of causing the enormous distension of the oro-pharyngeal region thus making possible the ingestion of very large masses. The heavy ciliary coat of the anterior, pharyngeal region is adapted to aid in the backward propulsion of such large masses into the thin-walled, distensible, sophageal region of the pharynx from whence the mass may be forced through the pharyngo-enteric sphincter by the activity of the intrinsic, pharyngeal musculature.

In S. virginianum, the food of which is largely made up of small, highly motile prey, we find well-developed oral and pharyngo-enteric sphincters which allow the imprisonment of the captured organisms in the pharynx. There are several large bundles of radial fibers so disposed as to make possible a quick distension of the lips, and the sudden contraction of the powerful, radial, pharyngeal musculature enables this species to generate sufficient suction to draw its prey into the pharynx.

The pharynx of S. predatorium shows two prime structural adaptations. The radial musculature is strong enough to produce sufficient suction to draw into the mouth the tissues of another species of Stenostotmum and the special oral sphincter by its contraction is capable of pinching off from the body of the prey the mass of tissue drawn into the pharynx.

In general it may be said for all species that the extrinsic, radial musculature primarily determines the method by which the food is drawn into the pharynx and the general intrinsic musculature of the pharyngeal wall is responsible for the transmission of the food to the enteron.

We have been unable to assign any differential, functional capacity to the pharyngeal glands in spite of the fact that sizes and distribution in the three species are sharply different.