Comparative morphology of the feeding appendages of four mesozooplankton species in the Sundays River estuary

ENGLISH ABSTRACT: The morphology of feeding appendages of the coexisting estuarine copepods, Pseudodiaptomud hessei and Acartia longipatella, and mysids, Rhopalophthalmus terranatalis and Mesopodopsis wooldridgei, were examined and compared as an aid in elucidating dietary differences. The robust mandibles of P. hessei copepodids compared to the more pointed and slender teeth with no molar region, of A. longipatela suggest that the latter species relies on more fragile food particles. Mandible edge indices indicate, however, omnivorous feeding by both species. No clear dietary differences could be deduced from the dimensions of the second maxillae of these copepods. Mandible edge indices calculated for the mysid species suggest a more herbivorous feeding mode in M. wooldridgei and a more carnivorous one in R. terranafalis, supporting previous studies on their diets. No interspecific differences between the mysid size classes were evident from edge indices. Significant increments in setae and setule lengths and spacing with increasing mysid size class were evident, reflecting differences in food particle sizes utilized. The morphological differences in the feeding apparatus could reflect differences in the diets between species and indicate differences in food particle sizes utilized by the various developmental stages within species. These differences in diet should reduce inter- and intraspecific competition. ************* AFRIKAANSE OPSOMMING: Die modologie van die voedingsapparaat van die kopepoda-spesies, Pseudodiaptomus hessei en Acartia longipatella en mysidacea-spesies, Rhopalophthalmus terranatalis en Mesopodopsis wooldridgei is ondersoek en vergelyk as 'n hulpmiddel om verskille in dieet toe te lig. Die robuste kake van P. hessei in vergelyking met die meer gepunte en delikate tande, sonder enige maaltand-gedeelte, van A. longipatella, dui op die verbruik van meer delikate voedseldeeltjies deur laasgenoemde. Kaak-indekse dui egter op 'n omnivoriese voedingswyse deur beide spesies. Dieet verskille tussen die twee kopepoda-spesies word nie deur afmetings van die sekondêre maksilla geillustreer nie. Kaak-indekse vir die mysidacea-spesies dui op 'n meer herbivoriese voedingswyse vir M. wooldridgrei in vergelyking met 'n meer karnivoriese voedingswyse in R. terranatalis, wat steun verleen aan vorige studies. Geen interspesifieke verskille tussen die kaak-indekse van die mysidacea grootte-klasse is gevind nie. Betekenisvolle toenames in die lengtes en spasi ring van setae en sekondêre setae is gevind met ‘n toename in mysidacea grootte-klasse, wat d