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Geometric morphometric analysis discriminates native and non-native species of Caprellidae in western North America

  • Eva I. Riedlecker (a1) (a2), Gail V. Ashton (a1) and Gregory M. Ruiz (a1)


Characteristics of the second gnathopod are traditionally used to distinguish between species of caprellid amphipods. However, these distinctions are often subjective and can be variable within a species. Geometric morphometrics were used to quantitatively assess shape variation of the second gnathopod propodus of three species of caprellids in North America, including the non-native Caprella mutica. Gnathopod shapes of C. mutica specimens from different latitudes revealed distinct morphologies; the factors responsible for the shape variations are unknown. Allometric change of propodus shape was observed in C. mutica. Larger individuals showed a wide array of possible propodus morphologies. Despite this variability, there were clear differences between large specimens of C. mutica and two species native to North America: C. alaskana and C. kennerlyi. The use of geometric morphometrics and the thin-plate spline method can serve to both complement descriptions using traditional keys and aid in identification of non-native species in novel geographical regions.


Corresponding author

Correspondence should be addressed to: Gail V. Ashton, Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD 21037, US email:


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