FILTER-FEEDING PATTERN AND LOCAL DISTRIBUTION OF THE BRACHIOPOD, DISCINISCA STRIGATA

¹ Department of Zoology, University of Washington, Seattle 5, Washington

1. Ecological observations on the brachiopod, Discinisca strigata, suggest that this species is zoned in shallow water in the northern Gulf of California. It occurs singly rather than in great clumps, and on the basis of a size-frequency distribution appears to be an annual.

2. Examination of the filter-feeding apparatus and its operation shows, despite an exceptional orientation of the lophophore, that there are a number of points in common with other brachiopods. The lateral lophophoral cilia beat in a frontal to abfrontal direction, and the current system through the animal is efficient.

3. The position of the inhalant aperture, relative direction of coiling of the left brachium, and orientation of the spire, although differing from those in other adult spirolophes, do not diminish the efficiency of operation. D. strigata, though showing a mixture of inhalant (80%) and exhalant (20%) filtering systems, is able to maintain its filtering efficiency, due to the disposition of filaments within the organism.