Validation and redescription of Cymbasoma germanicum (Timm) (Crustacea: copepoda: monstrilloida) from Helgoland with comments on Cymbasoma rigidum Thompson

Reexamination of a monstrilloid copepod collected in 1892 at Helgoland, Germany and deposited in the Zoological Museum (Berlin) offered the opportunity of (1) providing a complementary redescription of Cymbasoma germanicum (Timm) from its type locality, and (2) reviewing the taxonomical status of Cymbasoma rigidum Thompson 1888, and its presumed cosmopolitan distribution. Cymbasoma germanicum can be distinguished from the different morphotypes related to the nominal species C. rigidum by a combination of characters, including a large inner lobe of the fifth leg, an innermost fifth leg seta almost as long as the other two, the relative length of the antennules, and the presence of long elements 2v and 2d on the second antennular segment. The main distinguishing character is the presence of two knob-like processes on the posterior margin of the genital somite. Based on differences in several characters but mainly on the taxonomically important structure of the fifth legs, at least three distinct morphological patterns were detected among the main historical records of C. rigidum. This variability, the uncertainty of the identity of the original specimen, and the geographic amplitude of the records of C. rigidum suggest that the nominal species represents a taxonomic complex with several undescribed taxa.