Preliminary Survey of the Relationship Between the Feeding Habit and the Structure of the Mouth-Parts of Marine Copepods

The feeding of 6 copepods (Calanus finmarchicus, Acartia tonsa, Centropages hamatus, C . typicus, Labidocera aestiua, and Tortanus discaudatus) was examined with 3 different foods-a ) diatoms ( Thalassiosira flt~uiatilis) alone, b ) diatoms plus Artemia nauplii, and c ) Artemia alone-and compared with the structure of their mouth-parts. Calanus finmarchicus is predominantly an herbivore, but in absence of plant food can definitely capture small motile animals. Acartia tonsa is a typical omnivore which can eat either plant or animal food efficiently. Centropages hamatus and C . typicus are also omnivorous, but both prefer an animal diet. Although Labidocera aestiua is predatory, some setae used for filtering food are found at the base of the second maxillae. Finally, Tortanus discaudatus is a typical predatory copepod. There is close relationship between the structure of the mouth-parts and the feeding habits of these species. In herbivorous species (Calanus finmarchicus), the 2nd antennae, mandibular palps, 1st maxillae, and maxillipeds are well developed to produce a pair of "feeding swirls." The 2nd maxillae are also formed as efficient filtering nets. The cutting edges of the mandibles are provided with grinding teeth. In predatory species ( Tortanus discaudatus), the mouth-parts have few setae and are on the whole much simpler. The 1st maxillae, 2nd maxillae, and mavillipeds are modified as prehensile appendages. The cutting edges of the mandibles have very sharp teeth. In on~nivores, these appendages generally have a structure intermediate between those of the two previous types; the 2nd maxillae are used partly for filtering and are partly prehensile. The teeth are heavier than those of the herbivores, but they are not as stout as for predators. ISTRODUCTIO;\2nd antennae. the mandibles. the 1st maxilThe usual method for determining the lae, the 2nd maxillae, and maxillipeds) when feeding (Esterly 1916; Cannon 1928; food preferences of copepods has hitherto Lowndes 1935). There is a correlation bebeen a direct examination of the gut. Thus, tween the distance between the setules of Lebour (1922) and Marshall (1924) rethe 2nd maxillae and the size of the food ported that various species feed on both organisms filtered (Ussing 1938; Marshall phytoplankton and zooplankton, some feedand Orr 1956). The movements of the ing predominantly on diatoms, others conmouth-parts of Cyclops (Fryer 1957b) and sistently preying on animals. The feeding mechanisms of living copepods have also the anatomy of the cutting edge of the mandible of several marine copepods (Beklemibeen studied. Lebour (1925) observed the shev 1959) have also been examined. Howfeeding of Anomalocera pattersoni in a ever, there have been few demonstrations plunger jar and found that it even attacked of the food taken by direct measurements a larval fish. Many fresh-water cyclopoid of depletion of the available diet in the copepods are also carnivores (Fryer 1957a ) . medium. Recently, the omnivorous nature of Acartia clausi and A , latisetosa has been extensively The authors are indebted to Dr Mary Sears for her helpful criticism and careful investigated (Petipa 1959a, b ) . reading of the manuscript. We are grateful Copepods use 5 pairs of appendages (the to Dr Bostwick H. Ketchum for his valuable suggestions and encouragement. Thanks lcontribution No. 1278 from the Woods Hole are also due to the other members of Oceanographic Institution. The present investigation was made possible by grants from the Nastaff of the Woods Hole Oceanographic Intional Science Foundation, G-13010 and G-17508. stitution for their assistance.