File:American malacological bulletin (1987) (17968682440).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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24 AMER. MALAC. BULL. 5(1) (1987) RESULTS MICROSCOPIC ANALYSIS OF GUT CONTENTS Many chloroplasts were visible in guts of Pisidium amnicum and Sphaerium corneum, but none was observed in P. casertanum or P. conventus. Based on gut contents ex- amination, P. amnicum and S. corneum appear to feed upon suspended phytoplankton. Observations of animals fixed immediately upon field collection showed that the large stomach was usually empty, and the relatively short intestine was, at most, only partly filled, and in many cases was nearly empty. Passage of par- ticles through the stomach and midgut must be therefore fairly quick. The length of the digestive tract from mouth to anus is twice the shell length in Pisidium and almost 3 times that in Sphaerium. Such a difference is due mainly to the length of the coil at the end of the hindgut. Material in the hindgut includes particles ingested but not utilized and undigested remains of food particles, as most digestion and absorption presumably takes place in the stomach and digestive diver- ticula respectively (Owen, 1974; Morton, 1983). Intestinal contents in Pisidium spp. consisted mainly of extremely small, non-mineral particles and rarely, a few mineral particles (Fig. 1 a,b). There were relatively large par- ticles (5 to 25 jtm) in the hindgut of Sphaerium corneum, while in P. amnicum particles were less than 5 /xm (Holopainen, 1985). FEEDING BEHAVIOR Observations were made on P. conventus (2 mm shell length) in thin "antfarm" aquaria. Animals can burrow quickly, moving over 1 cm (5 body lengths) within 5 minutes. Animals established a feeding position, lying dorsal surface downwards at the distal end of a long, blind burrow (Fig. 2). Water movement in the burrow was traced by observation of small particles suspended in burrow water. Water moved unidirectionally from the blind end of the burrow to the open- ing at the sediment surface. We did not observe any particle collection by the foot. Animals were often quiescent. In one case we were able to estimate the pumping rate of a P. casertanum 3 mm long that pumped actively for some hours. The velocity of bur- row water was approximately .006 cm x sec"1, and the cross- sectional area of the burrow was approximately .03 cm2, so that pumping rate was estimated at 0.6 ml x hr"1. Pisidium casertanum is capable of suspension feeding upon very dense suspensions. A dense suspension of in- terstitial bacteria (2 x 109 cells x ml"1) was visibly cleared from suspension by 6 animals within 2 hours. Fecal pellets were observed on the bottom of the vial, indicating that the suspen- sion had been ingested. Under laboratory conditions, P. casertanum and P. conventus swallowed sedimentary particles when offered dense slurries, although most material collected by the foot was rejected as pseudofeces. The most active fecal pellet Pf WATER SEDIMENT
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Fig. 2. Typical feeding pseudofeces; fe: feces. position of Pisidium casertanum and P. conventus. Arrows indicate the water currents caused by ciliary action, pf: This figure is partly adapted from Meier-Brook (1969) and Holopainen (1985).

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