Foregut morphology of amphipoda (crustacea). An example of its relevance for systematics

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Abstract
Amphipods exhibit a remarkable morphological diversity of their foreguts. In certain amphipod groups the foregut morphology is derived from a reconstructible basic pattern and is related to the preferred food. In this contribution for the first time the foregut morphology is used in amphipod systematics. The highly specialized foreguts of stilipedids and stegocephalids show numerous characters diverging from the basic foregut construction: the foreguts of both groups appear to be inflated dorsally and cover the anterior region of midguts and midgut caeca. Only the lateralia, lateral invaginations posterior to the entrance of the esophagus into the stomach chamber, and the ventral foregut region are strongly chitinized. The dorsal cuticle is thin with small folds posteriorly which give extra elasticity. The lateralia are narrow and bear three units of setae. However, the examined pardaliscid species does not display such features, but retains the basic construction of amphipod foreguts. Supported by the synapomorphic characters found in the foregut morphology the family Stilipedidae, earlier included in the Pardaliscoidea, is transferred into the superfamily Stegocephaloidea.