MORPHOLOGY OF THE ANTENNARY GLAND EXIT DUCT IN ECOLOGICAL AND PHYLOGENETIC SERIES OF TALITROID-AMPHIPODA (CRUSTACEA)

The form of the proximal segments of antenna two peduncle and of the a ntennary gland exit duct on peduncle article two has been examined in 16 species of amphipod crustaceans (including 14 species of Talitridae ). Gammarus duebeni (Gammaridae), regarded as exemplifying the norm fo r aquatic amphipods, has a very distinctive fluted exit duct emanating from a pronounced gland cone. The talitroid Hyale nilssoni was regard ed as a typical representative of the hyalid-like ancestors of the Tal itridae. It also has a gland cone, but the exit duct of the antennary gland is a thin-walled, collapsible cone. The two proximal articles of antenna two peduncle are much reduced in Talitridae. Only the second may retain a degree of mobility. No gland cone remains. The structure of the urinary exit duct in seven species of simplidactylate landhoppe rs (Bousfield's Gp IVa) was very similar to the hyalid condition. Beac hfleas (Gp II) have strengthened, often sculpted ducts, whilst sandhop pers (Gp III) have no protruding exit duct at all. Only one species of Gp IVb (cuspidactylate) landhopper (Tasmanorchestia sp.) was investig ated and it has an exit duct similar in form to that of the beachfleas (Gp II). Neorchestia plicibranchiata (a Gp IVa species), however, alr eady known to be an anomalous species, has unusually elongate urinary ducts (for a Gp IVa species). These observations lend support to the n otion that the landhoppers are a polyphyletic grouping and that the sa ndhoppers are a very isolated ecomorphological grouping within the fam ily.