Morphology of the mouthparts and digestive system in two species of Uristidae Hurley, 1963 (Amphipoda: Lysianassoidea)

Abstract

ABSTRACT In amphipods, the morphology of the mouthparts and digestive system is known to vary according to lifestyle and feeding habits. Since mouthparts are widely used in amphipod taxonomy and the digestive system was also suggested as a source of taxonomic information, it is essential to be able to distinguish between the evolutionary conserved characters of the feeding and digestive apparatus and those influenced by dietary preferences. The opposite side of the same problem is whether the morphology of oral appendages and digestive organs can provide a useful indication of the feeding mode. The present study examined the mouthparts and the digestive apparatus of two common species of Uristidae, Anonyx nugax (Phipps, 1774) and Tmetonyx cicada (Fabricius, 1780), using light and scanning electron microscopy to assess morphological modifications that can reflect the feeding habits and to reveal characters that can be useful for taxonomy. The results show that the mouthparts of A. nugax are modified for shearing and the stomach with reduced lateralia and primary filter are adapted for processing soft muscular tissues suggesting that this species is an obligate scavenger. The morphology of T. cicada is more consistent with the lifestyle of an omnivore and opportunistic scavenger: the mouthparts are adapted both for shearing and grinding and the stomach has functional lateralia and a well-developed secondary filter. The study discusses the characters of potential taxonomic value such as the crater-like structures on the molar and setation on the inner plates of maxillae and maxillipeds.