FILTER-FEEDING PATTERN AND LOCAL DISTRIBUTION OF THE BRACHIOPOD, DISCINISCA STRIGATA ROBERT T. PAINE Department of Zoology, University f Washington, Seattle 5, Washington The recent surge of interest in the functional morphology of living brachiopods has been led mainly by paleontologists, motivated by an intent to increase the reliability of their interpretations of fossil structures. Research has been focused on the mechanics of feeding, since the morphology of the filtering organ, the lophophore, and, where present, its supports, is basic to understanding the phylum's systematics. Orton (1914) contributed the first paper in this series and has been followed by Richards (1952), Atkins (1956-1961; see Rudwick, 1962, for complete citations), Chuang (1956). Williams (1956, 1960), Rudwick (1960a, 1960b, 1962), Rowell (1961), and Williams and Wright (1961). These works suggest that, with the possible exception of Discinisca (Rowell, 1961), all Recent brachiopods show a fair degree of convergence in the characteristics of their feeding and the fleshy portions of their lophophores. On the other hand, the functioning of "fossil" feeding mechanisms has not been agreed upon. This paper describes the filtering mechanism of the inarticulate brachiopod, Discinisca strigata Broderip, which, because of its uniqueness, will permit some features common to all known brachiopod filtering mechanisms to be evaluated. MATERIAL Large numbers of D. strigata were discovered living in the tidal zone near Puertecitos, Baja California, Mexico (approximately 30 17' N.; 114 40' W.). Field observations were made from 29 March to 1 April, 1962, principally at a station 2-3 km. north of Puertecitos, and were facilitated by an estimated 20-foot tidal range. Living specimens were successfully transported back to the Scripps Institution of Oceanography where details of the feeding process were worked out. ECOLOGICAL OBSERVATIONS At the principal station an extensive sand beach is interrupted at regular intervals by patches of cobbles and small boulders extending down to the low-water mark. D. strigata lives under the flatter of these rocks, conspicuously associated with the sponge, Hyuicniacidon adrcissifonnies Dickinson, the gastro-pods, Acanthina angelica Oldroyd, Ncrita funiciilata Menke, and Monda fcr-rnginosa Reeve, and the bivalves, Barbatia rccrcana (Orbigny) and Isognoinon cliciiiuitzianits (Orbigny). Whether suitable habitats in other areas can be recognized by the presence of these species is not yet known. The brachiopods often had settled in small crevices in the rocks, and occurred in microenvironments probably characterized by reduced current scour. The size distribution of the 597
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