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

Abstract

The first description since 1901 of the free nauplius of a monstrilloid copepod is presented, based on scanning electron microscopy. First-instar larvae were hatched from eggs borne by a female Monstrilla hamatapex, 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 other copepod orders. The new species, based on the egg-bearing female and another female from Ago Bay, Honshu, is distinguished from M. helgolandica Claus, 1863, and some literature records of the latter, a supposedly widespread species, are brought into question. A nomenclature is devised for female monstrilloid antennular setae, and a list is provided of potentially diagnostic features that never or rarely have been used until now in adult monstrilloid taxonomy.