Sponge-inhabiting barnacles of the Americas: A new species of Acasta (Cirripedia, Archaeobalanidae), first record from the eastern Pacific, includingdiscussion of the evolution of cirral morphology

Acasta newmani n. sp. from the Gulf of California, Mexico is described. Thi s is the first report of Acasta from the eastern Pacific. Hypotheses are di scussed concerning the correlation of cirral morphology with feeding method s and host specificity. The similarities between A. newmani and Acasta cyat hus Darwin, 1854 indicate that they are examples of the common pattern of t rans-isthmian sibling taxa in the Caribbean and eastern tropical Pacific. A key to the seven sponge-inhabiting barnacle species of the Americas is pre sented with citations noting their host sponge species and known ranges in the Americas. The range of Membranobalanus nebrias (Zullo & Beach, 1973) is extended from the Galapagos Islands to the Gulf of California.