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Biol Bull 136: 405-433. (June 1969)
© 1969 Marine Biological Laboratory
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OBSERVATIONS ON THE NUTRITION OF SEVEN SPECIES OF RHYNCHOCOELAN WORMS

J. B. JENNINGS 1 and RAY GIBSON 1

1 Department of Zoology, The University of Leeds, England, U.K.

1. A comparative study has been made of the food, feeding mechanisms, gut structure, digestive physiology and food reserves of representative species from three of the four orders of Rhynchocoela (Anopla: Palaeonemertini and Heteronemertini; Enopla: Hoplonemertini).

2. Polychaete or oligochaete annelids form the staple diet in the Anopla and one species of Enopla. Amphiporus lactifloreus (Enopla) is exceptional in that it feeds exclusively on the amphipod crustacean Gammarus locusta.

3. Living prey are captured by means of the proboscis, but inert or dead foods, when taken, are ingested directly without proboscis eversion.

4. In the Hoplonemertini the proboscis is armed with stylets and toxic secretions which kill the prey before ingestion, and a forerunner of this system is seen in the Palaeonemertini where minute epithelial barbs perforate the prey's integument to allow entry of paralyzing substances. In the Heteronemertini, though, the prey is swallowed alive and killed by acid secretions in the foregut.

5. In the Hoplonemertini the gut has an additional portion, the stomach, and in Amphiporus lactifloreus this is everted within the prey which is then ingested in fragments.

6. The basic digestive physiology is similar in both Anopla and Enopla, with extracellular acidic proteolysis being followed by phagocytosis and completion of digestion intracellularly by proteases, carbohydrases and lipases acting in concert. Intracellular digestion is in two phases, firstly acidic and then alkaline, and acid and alkaline phosphatases are associated with the appropriate phase.

7. The endopeptidase responsible for extracellular digestion is produced in the Anopla by gastrodermal gland cells but in the Enopla this function has been taken over by the columnar cells of the gastrodermis. Functional gland cells still occur in the Enopla but their role has not been determined.

8. The food reserves consist mainly of fat, stored in the gastrodermis in all species and, occasionally, in the parenchyma.

9. These findings are discussed in relation to previous work on nutrition in the remaining order of the Rhynchocoela (Enopla: Bdellonemertini).




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