BOUSFIELD, E.L.*; HENDRYCKS, E.A.; Royal Ontario Museum, Toronto; Canadian Museum of Nature, Ottawa: Functional morphology and phylogeny within the littoral marine amphipod family Hyalidae

Amphipod family Hyalidae, the most primitive of 10 families within superfamily Talitroidea, encompasses about 50 mostly newly described species in the North Pacific Basin and about 110 species in 12 genera worldwide. Ecologically and behaviourally the genera may be grouped into (1) primitive “swimmers and clingers”, and (2) more advanced intertidal “jumpers” or “saltators”. The family may be para-ancestral to the more familiar beach fleas and sandhoppers (family Talitridae) that keep ocean beaches relatively free of wave-cast algal debris. Hyalids are here shown to retain vestiges of hydrodynamic (streamlining) morphological and behavioural adaptations that characterized the primitive amphipod crustacean. Amphipods are unique among malacostracans (larger crustaceans) in their “hull design” and propulsion mechanism that facili- tates rapid and sustained swimming in a forward direction only. Other malacostracans, like lobsters and shrimps, are “hull-designed” to swim rapidly backwards in “escape reaction” (e.g., to predatory fishes). The study explores the evolutionary significance of these hydrodynamic differences.