Retrieved July 27, 2008. ↑ Ruppert, Edward E.; Fox, Richard S, & Barnes, Robert D. (2004), Invertebrate zoology : a functional evolutionary approach (7th ed.), Belmont, CA: Thomson-Brooks/Cole, ISBN 978-0-03-025982-1 , p. 788ff. – see particularly p. 804 ↑ Weber, M; Wey-Fabrizius Alexandra, R; Podsiadlowski, L; Witek, A; Schill Ralph, O; Sugár, L; Herlyn, H; Hankeln, T (January 2013).