A COMPARATIVE-STUDY ON THE TUBES AND FEEDING-BEHAVIOR OF 8 SPECIES OFCOROPHIOID AMPHIPODA AND THEIR BEARING ON PHYLOGENETIC-RELATIONSHIPS WITHIN THE COROPHIOIDEA

Observations are presented on mouthpart functional morphology, and on feeding, grooming and defaecatory behaviour of eight species of coroph ioid Amphipoda, viz. Corophium bonnellii, Lembos websteri, Aora gracil is, A. spinicornis, Gammaropsis nitida, Ericthonius punctatus, Jassa f alcata and J. marmorata. These data are considered in relation to tube structure and amphipod posture in relation to the tube. All these spe cies occupy double-ended cylindrical tubes made from 'amphipod silk' s ecreted by the third and fourth peraeopods, incorporating sediment and other debris to varying degrees. Uniquely among this set of species, however, E. punctatus has a tube that is architecturally distinct. It tapers along its length and has a distinctive oblique main entrance at its widest end. This end is used preferentially. The other species st udied use either opening with equal facility. Such a feature is adapti ve in facilitating deployment of the antennae and shielding the head o f E. punctatus. Two groupings of species are proposed: group A which f eed inside their tube using pleopod-induced through-tube currents, and group B which feed outside or at the entrance to their tube using ext ernal water currents. Group A includes C. bonnellii, L. websteri and t he Aora spp. Group B includes E. punctatus and the Jassa spp. Gammarop sis nitida exhibits traits from both groups, adding weight to its perc eived status as a genus representative of the stem corophioid. The isc hyrocerid habit of externalizing food-gathering may be regarded as the first step along an evolutionary line leading to the rod-building pod ocerid types and ultimately towards the caprellids. All species examin ed show a degree of flexibility in their feeding habits which helps to explain the success of this taxon, which has radiated into a great di versify of aquatic biotopes.