The nauplius eye and frontal organs in Malacostraca (Crustacea).
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The nauplius eye and frontal organs in the Malacostraca have been investigated. The present work is a direct continuation of the author's investigation of the same organs in decapod malacostracans (Elofsson, 1963). The results obtained confirm the recognition of a nauplius eye sensu iatu and a nauplius eye sensu strictu. The former is a combination of the latter and the dorsal frontal organ. It occurs together with the ventral frontal organ in the Decapoda and the Stomatopoda. The nauplius eye s. s. and the dorsal frontal organ, though separated, occur in the Anaspidacea. The nauplius eye s. s. and the ventral frontal organ, separated as is always the case in the Malacostraca, occur in the Euphausiacea. The Mysidacea have only the ventral frontal organ, The remaining orders of the Malacostraca investigated have none of these organs. The results obtained are discussed in morphological and phylogenetic terms. The morphological problems are the homologies and criteria of the organs. The criteria established in 1963 are confirmed. The results obtained lead to interesting phylogenetic considerations. A rearrangement of supposed relationships among the Malacostraca is proposed; the metaphor of the phylogenetic tree, however, should be used with great caution.