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Free Content Thumbing Doesn't Always Make the Genus: Revision of Microjassa Stebbing (Crustacea: Amphipoda: Ischyroceridae)

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Thumb production is a male secondary sexual character of the propodus of the second gnathopods in many species of ischyrocerid amphipods. Historically, it has been considered to be a synapomorphy for the ischyrocerid genera Jassa Leach and Microjassa Stebbing. This is indeed the case for Jassa, but thumb production differs fundamentally in Microjassa and is not a synapomorphy for the genus. Instead the species of Microjassa are bound by characters of the antennae and coxae. The genus is revised to comprise the type species M. cumbrensis Stebbing and Robertson. M. litotes J. L. Barnard, M. macrocoxa Shoemaker, and the new species M. floridensis, M. tetradonta, M. bahamensis, M. bousfieldi, M. barnardi, and M. boreopacifica. Microjassa claustris J. L. Barnard and M. chinipa J. L. Barnard are transferred to a new genus, Neoischyrocerus, along with Jassa lilipuna J. L. Barnard. Jassa socia Myers is transferred to the genus Ischyrocerus Krøyer. A consequence of this revision is that most prior species identifications for the genus Microjassa cannot be considered valid, particularly where species overlap in range. Most species in the genus are difficult to recognize when large males are lacking. Wherever possible characters that are not subject to sexual selection are given in the keys and descriptions to aid species identification.

Document Type: Research Article

Publication date: September 1, 1995

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