Sensory and glandular equipment of the trunk limbs of the Chydoridae and Macrothricidae (Crustacea: Anomopoda)

Abstract

Each of the five pairs of trunk limbs of theChydoridae and Macrothricidae contains one or severalcuticular pores, some of which connect to glands whichsecrete to the filter chamber. They are situated in afixed or a variable position, usually on the endite ofthe limb.Limbs 2 to 5 are also equipped with small sensoryorgans which may be apically perforated or not.Relatively large, perforated sensilla, often with aspecies- or genus-specific morphology occur on theendites of P3, P4 and sometimes on P5; unperforatedpapilliform and batilliform sensilla occur in variouspositions on P2, P3, and P4. In the Macrothrixlaticornis-group, three of the six setae of theposterior row of the endite of P3, which arefiltratory in other species groups, are modified intorod-like structures resembling the esthetascs of thefirst antenna.We conclude that the filter chamber in the familiesstudied here combines a sensory and a glandularfunction with the filtratory one. These functions,typical of a mouth, are localised behind themasticatory apparatus in vertebrates. In theseCladocera, however, they are physically situated infront of the mandibles.