SEM OBSERVATION OF THE NAUPLIUS OF MONSTRILLA HAMATAPEX, NEW SPECIES,FROM JAPAN AND AN EXAMPLE OF UPGRADED DESCRIPTIVE STANDARDS FOR MONSTRILLOID COPEPODS

The first description since 1901 of the free nauplius of a monstrilloi d copepod is presented, based on scanning electron microscopy. First-i nstar larvae were hatched from eggs borne by a female Monstrilla hamat apex, new species, from inshore plankton in Tanabe Bay, Honshu, Japan. The naupliar appendages are less oligomerous and bear more setae than previously reported. Their apomorphies relative to a copepod naupliar ''Bauplan'' are identified by comparison to first instar nauplii of o ther copepod orders. The new species, based on the egg-bearing female and another female from Ago Bay, Honshu, is distinguished from M. helg olandica Claus, 1863, and some literature records of the latter, a sup posedly widespread species, are brought into question. A nomenclature is devised for female monstrilloid antennular setae, and a list is pro vided of potentially diagnostic features that never or rarely have bee n used until now in adult monstrilloid taxonomy.