Variations in the Number of Intestinal Loops in Scaphopoda (Mollusca)

Abstract. The intestinal loops of two species of the genus Bathoxiphus (Entalinidae) and of Cadulus aberrans (Gadilidae) have been reconstructed from serial sections. The results are compared to the 'textbook scaphopod' Antalis dentalis having the hindgut coiled in three loops. Bathoxiphus ensiculus has four or five intestinal loops, B. sp. S 153 four, and C. aberrans two. The buccal pouch contents included Foraminifera in all species, with agglomerates of sediment being found only in Bathoxiphus and Antalis. The mean ratio of intestinal length to body length ranges from 1.05 in B. ensiculus , over 0.98 in the four-looped B. sp. S 153, to 0.7 in A. dentalis and 0.6 in the twice-looped C. aberrans. The correlation of intestinal length with diet—additional deposit-feeding in Bathoxiphus and highly specialized 'carnivory' in C. aberrans —is probable. Despite the differences in feeding ecology, the elongated hindgut of both deep-sea species of Bathoxiphus resembles the adaptations of some bivalves to poorly nutritious deep-sea sediments.