The feeding structures and mechanisms of the brachiopod species Terebratulina septentrionalis from the Bay of Fundy, eastern Canada and Terebratalia transversa from the west coast of Canada were examined, in vivo, with an endoscope linked to a video recording system. A diet consisting of various-sized, light-reflective particles and natural seston was given to both species. Our observations demonstrate that the lateral arms are the sites where most particle rejection occurs and the median coil is the site where particle acceptance occurs. Low particle retention may be attributed to the way particles move on the outer filaments. The combined effect of localized currents produces the large-scale flow through the lophophore. The lophophore's delicate hydrodynamics are easily disturbed by attempts to observe them. Only by relatively non-invasive techniques such as endoscopy can we accurately record normal feeding behaviour. Additional key words: lophophorate, Terebratulina septentrionalis, Terebratalia transversa The lophophore, the main organ of feeding and respiration in brachiopods, is a ciliated tentacular organ that acts as a ciliary pump, producing currents that flow through the mantle cavity. The two articulate species investigated in this study have plectolophous lophophores (Fig. 1), a complex type consisting of two lateral arms that lie on either side of a median coil. Two series of ciliated filaments fringe both the lateral arms and the median coil. At the base of these filaments is a ciliated food groove (brachial groove) covered by the flexible brachial lip. Particles captured on the ciliated filaments enter the brachial groove and are transported to the mouth for ingestion (Rudwick 1970). In plectolophous species, water enters through the lateral commissure and exits through the anterior part of the gape (Atkins 1959; Rudwick 1962; Savage 1972; James et al. 1992). One aspect of brachiopod physiology that has generated increasing interest is the mechanism of feeding, especially particle acceptance and rejection (Strathmann 1973, 1982; Gilmour 1978, 1981; Jorgensen 1981; Rhodes & Thompson 1992, 1993). Although many studies have addressed feeding processes (reviewed by James et al. 1992), there is still disagreement on the role of ciliary action on the inner and outer filaments (Strathmann 1973; Gilmour 1978; a Author for correspondence. E-mail: bmacdon@unbsj.ca LaBarbera 1981), as well as on the selectivity of brachiopod feeding (McCammon 1969; Rudwick 1970; Gilmour 1981; Thayer 1986). Previous studies have described the function of the lophophore from dissected structures, or surgically altered and narcotized animals, or from observations on intact animals yielding limited views (summarized in James et al. 1992). These invasive techniques could have altered the hydrodynamics within the lophophore and mantle cavity. Also, stress associated with surgery could have stimulated excess mucus production and caused the lophophore to function abnormally. In contrast, our study, using recently developed techniques in video endoscopy (Ward et al. 1991), allowed direct in vivo observations of feeding structures and mechanisms with minimal disturbance to the animals. No surgery was performed so that the animals remained intact. Our technique enabled us to observe, at a magnification of 150X, areas such as the inside of the median coil, that are impossible to view using conventional methods. The resulting video recordings allowed for post-observational analysis of events. The aim of this study was to investigate and describe lophophore activity in the articulate brachiopods Terebratulina septentrionalis (COUTHOUY 1838) and Terebratalia transversa (SOWERBY 1846) with respect to feeding, and to clarify some of the ways these brachiopods accept and reject particles. We report on parThis content downloaded from 157.55.39.231 on Wed, 05 Oct 2016 04:36:24 UTC All use subject to http://about.jstor.org/terms Endoscopy of feeding in plectolophous brachiopods < current inside coil < current outside coil