FEEDING ACTIVITY IN ECHINASTER AND ITS INDUCTION WITH DISSOLVED NUTRIENTS

¹ Florida Presbyterian College, St. Petersburg, Florida 33733

1. Echinaster echinophorus possesses a digestive system very similar to that of Henricia. Its Tiedemann's pouches are well developed and appear to function as pump organs.

2. About one third of the specimens seen in the field are found in a feeding posture on sponges (even though the sponges do not appear to be greatly harmed). Occasionally specimens are also found with everted stomachs on sand, algae, ascidians, molluscs, and other organisms. Captive specimens will assume a feeding position on opened clams and other defenseless invertebrates, but rarely completely devour them.

3. Tracer experiments demonstrate that various dissolved amino acids, glucose, and possibly proteins are taken up continually by the exposed superficial tissues of the body. If present in suitable concentration (usually about 25 mg%) most of these substances will also be taken up into the internal digestive organs, presumably because they stimulate the animals to engage in filter-pumping.

4. Of the substances that have been studied, glucose is the most effective stimulator of the pumping process, followed by the neutral amino acids (particularly leucine and phenylalanine). The charged amino acids—arginine, lysine, and glutamic acid—are very poor stimulators, as are apparently several types of protein.

5. It is concluded that the digestive apparatus of Echinaster can function effectively in collecting nutrients from a variety of sources. It can take up dissolved nutrients released through modest external digestive activity or obtained from other natural sources, such as carrion, detritus, or organic-rich sea water. It may also be able to accumulate considerable quantities of particulate materials.