Some observations on the internal morphology of Hansen's nauplius Y (Crustacea)

• The internal morphology of the crustacean larval form that Hansen (1899) called nauplius y has revealed a remarkably advanced early nauplius. The nervous system is well developed and differentiated. It is connected with the anlagen of the compound eyes. A presumed filamentous base of the SPX-organ connects with these. The nauplius eye is present in a three-partite form with two retinula cells in each cup. The alimentary canal consists of the ectodermal oesophagus with an inner layer of longitudinal muscles and an outer circular layer, and of the endodermal midgut with cells having microvillous borders against the lumen. There is no proctodeum or anus present. There is a well-developed muscular system. The head contains a large gland with a paired ventral outlet. A new dorsocaudal organ of doubtful function is described.The morphological facts presented in this investigation indicate that the nauplius y, as knowledge stands today, is close to the Cirripedia.

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NATURVETENSKAP  -- Biologi -- Zoologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Zoology (hsv//eng)

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